Adam Boies

Photocatalytic oxidation (PCO) is a promising strategy for indoor air purification and outdoor pollutant abatement, potentially offering treatment for climate- and health-relevant pollutants such as methane (CH$_4$), nitrogen oxides (NO$_\text{x}$) and volatile organic compounds (VOCs). In this work, we present experiments evaluating the PCO of CH$_4$ (2 to 10 ppm) under varying UV-C light intensities (4 to 59 W/m$^2$), using titanium dioxide (TiO$_2$) as the photocatalyst. At 2 ppm CH$_4$, TiO$_2$ achieves a maximum conversion efficiency of 24.4% and a maximum apparent quantum yield of $0.013$\% over the tested UV-C light intensities, demonstrating activity at environmentally relevant concentrations. We develop a model to interpret the experimental results and assess the potential of PCO for ventilation applications. The model is validated against our CH$_4$ data and literature results for formaldehyde (HCHO) and NO$_\text{x}$. While laboratory-scale configurations achieve high conversions (e.g., 24.4% for CH$_4$), ventilation-scale performance is predicted to be limited by thin concentration boundary layers and short residence times, with conversion efficiencies dropping to around $0.017$%. Finally, we estimate the climate impact of CH$_4$ removal in terms of CO$_2$e emission rates, demonstrating that TiO$_2$-based PCO in ventilation applications can yield a net climate benefit (i.e., a net-negative CO$_2$e emissions rate) when the modelled CO$_2$e removal rate exceeds the emissions from catalyst material production and UV operation, particularly when pre-existing UV-C irradiation is leveraged.

Photocatalytic oxidation (PCO) is a promising strategy for indoor air purification and outdoor pollutant abatement, potentially offering treatment for climate- and health-relevant pollutants such as methane (CH$_4$), nitrogen oxides (NO$_\text{x}$) and volatile organic compounds (VOCs). In this work, we present experiments evaluating the PCO of CH$_4$ (2 to 10 ppm) under varying UV-C light intensities (4 to 59 W/m$^2$), using titanium dioxide (TiO$_2$) as the photocatalyst. At 2 ppm CH$_4$, TiO$_2$ achieves a maximum conversion efficiency of 24.4% and a maximum apparent quantum yield of $0.013$\% over the tested UV-C light intensities, demonstrating activity at environmentally relevant concentrations. We develop a model to interpret the experimental results and assess the potential of PCO for ventilation applications. The model is validated against our CH$_4$ data and literature results for formaldehyde (HCHO) and NO$_\text{x}$. While laboratory-scale configurations achieve high conversions (e.g., 24.4% for CH$_4$), ventilation-scale performance is predicted to be limited by thin concentration boundary layers and short residence times, with conversion efficiencies dropping to around $0.017$%. Finally, we estimate the climate impact of CH$_4$ removal in terms of CO$_2$e emission rates, demonstrating that TiO$_2$-based PCO in ventilation applications can yield a net climate benefit (i.e., a net-negative CO$_2$e emissions rate) when the modelled CO$_2$e removal rate exceeds the emissions from catalyst material production and UV operation, particularly when pre-existing UV-C irradiation is leveraged.

Ultrafine particles (UFPs, <100 nm) pose significant risks to human health due to their prevolence in the environment and ability to enter into the respiratory system. Presently, the World Health Organization (WHO) have regulated optical particle mass (PM) based counters (measuring diameters >300 nm), which have resulted in wide adoption of PM sensors. However, these PM counters do not detect UFPs which represent the largest fraction of particle number (PN) in many indoor and outdoor environments. Condensation particle counters (CPCs) currently remain the gold standard instrumentation for PN-based instruments, yet current CPCs remain unsuitable for large-scale deployment due to their size constraints. Miniaturization efforts are fundamentally constrained by particle penetration and condensation dynamics, especially under low Reynolds number (Re) regimes where Brownian diffusion dominates. To address these challenges, we present a numerical and experimental investigation of a prototype miniaturized CPC growth chamber (CPC-GC) with a radially-sheathed airflow introduced through porous tube media. Building upon our previously reported non-dimensional computational framework documented in Balendra et al. (Citation2024), we incorporate the fluid dynamics of radial sheathing to reassess growth chamber design limits. This new framework collapses the miniaturization constraints onto aspect-ratio bounds by eliminating the need to satisfy the particle penetration criterion required in unsheathed designs. Numerical simulations demonstrate that radial sheathing strongly confines UFPs to the flow centerline, substantially reducing particle losses and improving growth uniformity. Compared with unsheated CPCs, the radially sheathed design enables up to a ×6 increase in upper limit of penetration aspect ratio, Lmax,p,sh∗ and allows operation at Reynolds numbers ×19 lower, facilitating smaller device footprints and reduced flow rates. A miniaturized radial sheathing CPC was successfully fabricated via DMLS, with additional guidelines developed for researchers and designers to manufacture via both additive and subtractive methods. Experimental validation outlined an optimal sheath ratio, R≈2–3 identified for maximizing counting efficiency, mean droplet size, and size uniformity, while accommodating manufacturing tolerances such as surface roughness and wick fiber variability. Our findings indicate that radial sheathing serves as a key enabler of broader miniaturized CPC technology, supporting both scientific exploration and practical device development with important benefits for air quality monitoring and public health.

Ultrafine particles (UFPs, &lt;100 nm) pose significant risks to human health due to their prevolence in the environment and ability to enter into the respiratory system. Presently, the World Health Organization (WHO) have regulated optical particle mass (PM) based counters (measuring diameters &gt;300 nm), which have resulted in wide adoption of PM sensors. However, these PM counters do not detect UFPs which represent the largest fraction of particle number (PN) in many indoor and outdoor environments. Condensation particle counters (CPCs) currently remain the gold standard instrumentation for PN-based instruments, yet current CPCs remain unsuitable for large-scale deployment due to their size constraints. Miniaturization efforts are fundamentally constrained by particle penetration and condensation dynamics, especially under low Reynolds number (Re) regimes where Brownian diffusion dominates. To address these challenges, we present a numerical and experimental investigation of a prototype miniaturized CPC growth chamber (CPC-GC) with a radially-sheathed airflow introduced through porous tube media. Building upon our previously reported non-dimensional computational framework documented in Balendra et al. (2024), we incorporate the fluid dynamics of radial sheathing to reassess growth chamber design limits. This new framework collapses the miniaturization constraints onto aspect-ratio bounds by eliminating the need to satisfy the particle penetration criterion required in unsheathed designs. Numerical simulations demonstrate that radial sheathing strongly confines UFPs to the flow centerline, substantially reducing particle losses and improving growth uniformity. Compared with unsheated CPCs, the radially sheathed design enables up to a ×6 increase in upper limit of penetration aspect ratio, Lmax,p,sh∗ and allows operation at Reynolds numbers ×19 lower, facilitating smaller device footprints and reduced flow rates. A miniaturized radial sheathing CPC was successfully fabricated <i>via</i> DMLS, with additional guidelines developed for researchers and designers to manufacture <i>via</i> both additive and subtractive methods. Experimental validation outlined an optimal sheath ratio, R≈2–3 identified for maximizing counting efficiency, mean droplet size, and size uniformity, while accommodating manufacturing tolerances such as surface roughness and wick fiber variability. Our findings indicate that radial sheathing serves as a key enabler of broader miniaturized CPC technology, supporting both scientific exploration and practical device development with important benefits for air quality monitoring and public health.

Ultrafine particles (UFPs, &lt;100 nm) pose significant risks to human health due to their prevolence in the environment and ability to enter into the respiratory system. Presently, the World Health Organization (WHO) have regulated optical particle mass (PM) based counters (measuring diameters &gt;300 nm), which have resulted in wide adoption of PM sensors. However, these PM counters do not detect UFPs which represent the largest fraction of particle number (PN) in many indoor and outdoor environments. Condensation particle counters (CPCs) currently remain the gold standard instrumentation for PN-based instruments, yet current CPCs remain unsuitable for large-scale deployment due to their size constraints. Miniaturization efforts are fundamentally constrained by particle penetration and condensation dynamics, especially under low Reynolds number (Re) regimes where Brownian diffusion dominates. To address these challenges, we present a numerical and experimental investigation of a prototype miniaturized CPC growth chamber (CPC-GC) with a radially-sheathed airflow introduced through porous tube media. Building upon our previously reported non-dimensional computational framework documented in Balendra et al. (2024), we incorporate the fluid dynamics of radial sheathing to reassess growth chamber design limits. This new framework collapses the miniaturization constraints onto aspect-ratio bounds by eliminating the need to satisfy the particle penetration criterion required in unsheathed designs. Numerical simulations demonstrate that radial sheathing strongly confines UFPs to the flow centerline, substantially reducing particle losses and improving growth uniformity. Compared with unsheated CPCs, the radially sheathed design enables up to a ×6 increase in upper limit of penetration aspect ratio, Lmax,p,sh∗ and allows operation at Reynolds numbers ×19 lower, facilitating smaller device footprints and reduced flow rates. A miniaturized radial sheathing CPC was successfully fabricated <i>via</i> DMLS, with additional guidelines developed for researchers and designers to manufacture <i>via</i> both additive and subtractive methods. Experimental validation outlined an optimal sheath ratio, R≈2–3 identified for maximizing counting efficiency, mean droplet size, and size uniformity, while accommodating manufacturing tolerances such as surface roughness and wick fiber variability. Our findings indicate that radial sheathing serves as a key enabler of broader miniaturized CPC technology, supporting both scientific exploration and practical device development with important benefits for air quality monitoring and public health.

Methane (CH 4 ), is a potent greenhouse gas released from a wide range of natural and anthropogenic sources. This study explores the performance of thermal catalysis for CH 4 abatement under dilute conditions (10–500 ppm), using a fixed-bed reactor operated at a total flow rate of 100 ml min −1 . A matrix of catalysts comprising of 1 wt% Pd, Ni, and Ag metals supported on CeO 2 , TiO 2 , and Al 2 O 3 was synthesized and evaluated under identical reactor conditions to enable comparative assessment of catalyst performance for CH 4 oxidation. In particular, 1 wt% Pd/CeO 2 presented the highest activity across all concentrations, achieving complete conversion ( > 95 %) below 500 ∘ C at 500 ppm down to 10 ppm of CH 4 , for the flow rate considered in this study. It also demonstrated low onset temperatures (180 ∘ C–200 ∘ C) at 10 ppm and comparatively low apparent activation energies (45 kJ mol −1 ), indicating high catalytic activity and energy efficiency ( 1.8 × 10 − 3 kWh g −1 CO 2 e at GWP 20 ) due to reduced heating requirements to initiate methane conversion. In contrast, Ag- and Ni-based catalysts, particularly when supported on Al 2 O 3 , demonstrated promising activity at higher temperatures, over 80% conversion at 800 ∘ C and onset temperatures at 400 ∘ C–580 ∘ C for 10 ppm, for 100 ml min −1 considered in this study. Activation energies ranging from 10–80 kJ mol −1 and 75–110 kJ mol −1 at 10–500 ppm have been calculated for Ag/Al 2 O 3 and Ni/Al 2 O 3 , respectively. While Pd/CeO 2 achieves superior CH 4 conversion, its high life-cycle emissions reduce its relative climate advantage, yielding net CO 2 e emission rates (−0.0166 gCO 2 e s −1 at 500 ppm and GWP 20 ) comparable to Ag/TiO 2 (−0.0164 gCO 2 e s −1 ) and Ni/CeO 2 (−0.0145 gCO 2 e s −1 ), assuming specific catalyst area and operating time. These results demonstrate that catalysts with lower catalytic activity can achieve comparable net climate benefit when energy demand and embodied emissions are included, highlighting the importance of life-cycle metrics and material impact for scalable, low-concentration CH 4 mitigation strategies.

Methane (CH4) is a potent greenhouse gas with a global warming potential approximately 80 times greater than that of carbon dioxide over a 20-year time horizon, making its atmospheric removal an urgent environmental priority. Photochemical oxidation (PO) represents a promising strategy for indoor air purification and outdoor pollutant abatement by enabling the degradation of climate- and health-relevant trace gases under ultraviolet irradiation. In this work, we investigate CH4 photochemical oxidation under UV-C light, with particular emphasis on the role of ozone and hydroxyl (OH) radical formation in enhancing methane conversion. Experiments were conducted using UV-C sources at 200 nm (ozone creation) and 254 nm (ozone-free) under dry and humid conditions, with and without the use of a photocatalyst, while varying gas residence time. Irradiation at 200 nm was found to generate ozone in situ, which subsequently promotes the formation of highly reactive OH radicals in the presence of water vapor. This radical-driven chemistry significantly enhances methane oxidation, with humid conditions yielding up to a 30% increase in CH4 conversion compared to dry conditions. Following an extended catalyst screening, the addition of an optimal photocatalyst provided a modest further improvement of up to 8%, indicating a limited but measurable catalytic contribution under the investigated conditions. Increased residence time consistently resulted in higher methane conversion, underscoring the importance of flow dynamics in PO reactor optimization. These findings highlight the synergistic roles of UV-driven ozone production, OH radical chemistry, and photocatalysis in methane oxidation, and provide key insights for the design of efficient UV-based photochemical systems for air purification and greenhouse gas mitigation.

Aerosol particles play a central role in atmospheric processes, influencing air quality, human health, and climate. To fully understand these impacts, it is essential to quantify not only the physical properties such as concentration or size but also their chemical composition. Offline chemical analysis of aerosol samples or online mass spectrometry are generally complicated or expensive. Another efficient method is to determine the partitioning between the volatile and non-volatile fractions. This information provides insight into the chemical composition of an air mass and allows to infer information about aerosol sources, chemical aging, and transformation processes in the atmosphere (e.g. Weinzierl et al. (2006); Wehner et al. (2005, 2009); Ehn et al. (2007)).A catalytic stripper (CS) is commonly used to separate the volatile and semi-volatile fraction from the solid aerosol particles, which allows for precise measurement of the non-volatile fraction and the total aerosol load (Swanson and Kittelson, 2010). Compared to a thermal denuder, it has the advantage that volatile substances undergo catalytic transformation and cannot recondense into particles after treatment. The CS has successfully been used in many automotive applications such as Particle Measurement Program (PMP) compliant studies (Giechaskiel et al., 2020; Swanson and Kittelson, 2010). However, not many atmospheric aerosol studies apply this simple distinction between volatile and solid particles, which plays an important factor for the investigation of air quality, human health and climate impact of aerosols.Here we present the application of a CS for measurements of non-volatile aerosol particles at the Aerosol Observatory of the University of Vienna which is on track to become a National Facility for aerosol in-situ observations within the pan-European Aerosol, Clouds, and Trace Gas Research Infrastructure ACTRIS. This study includes the characterization of the CS with respect to particle penetration and removal efficiency of volatile and semi-volatile components. For particle penetration silver particles were generated with the Silver Particle Generator (SPG) and treated by the Sintering Stage S8000 to obtain thermally stable silver spheres in the size range between 2nm and 100nm. The characterization of the removal efficiency of volatile and semi-volatile particles is done with tetracontane, which is a well-established method in many regulations for the testing of volatile particle removal (VPR) systems in the automotive section (e.g. Euro-7). The aim of this study is to present initial results from continuous measurements of the non-volatile aerosol fraction over several weeks at the Aerosol Observatory in Vienna, demonstrating their potential for source identification and chemical characterization, and highlighting the importance of non-volatile particle measurements. Weinzierl et. al. (2009). Tellus B: Chem. Phys. Meteorol., 61(1), 96.Wehner et al. (2005), Geophys. Res. Lett., 32, L17810.Ehn et al. (2007), Atmos. Chem. Phys., 7.Wehner et al. (2009), J. Geophys. Res., 114.Swanson and Kittelson (2010). J. Aerosol Sci. 41 (12):1113.Giechaskiel et al. (2020). Vehicles 2 (2):342.

High Resolution Image Download MS PowerPoint Slide Brake wear particles (BWP) are a significant source of urban air pollution, yet the toxicity linked to their chemical composition remains poorly understood. While studies have examined either chemical composition or toxicity, comprehensive investigations combining both remain limited. Here, we conducted an in-depth physicochemical characterization of airborne, size-separated BWP from two brake pad types and comprehensively assessed their in vitro toxicity using human lung epithelial cells (A549). Iron, primarily in the form of iron oxide, was the most abundant element in the wear particles (33–50% by mass), with evidence pointing to the brake disc as the main source. A surprisingly high resemblance in elemental composition at the nano- and microscale was observed. This, along with an absence of clear differences in metal profiles or toxicological responses between size fractions, suggests that brake wear microparticles may form through compaction of vapor-condensed nanoparticles on the friction surfaces, followed by their release through mechanical shearing. Acellular and cellular assays showed the concentration-dependent ability of all studied particles to induce reactive oxygen species production, antioxidant depletion, and oxidative stress-mediated DNA damage. The nonasbestos organic pad, with more than 50-fold higher copper levels than the low-metallic pad, induced stronger DNA damage and acellular antioxidant depletion, suggesting copper as a potential source for the enhanced toxicity.

Brake wear particles (BWP) are a significant source of urban air pollution, yet the toxicity linked to their chemical composition remains poorly understood. While studies have examined either chemical composition or toxicity, comprehensive investigations combining both remain limited. Here, we conducted an in-depth physicochemical characterization of airborne, size-separated BWP from two brake pad types and comprehensively assessed their in vitro toxicity using human lung epithelial cells (A549). Iron, primarily in the form of iron oxide, was the most abundant element in the wear particles (33-50% by mass), with evidence pointing to the brake disc as the main source. A surprisingly high resemblance in elemental composition at the nano- and microscale was observed. This, along with an absence of clear differences in metal profiles or toxicological responses between size fractions, suggests that brake wear microparticles may form through compaction of vapor-condensed nanoparticles on the friction surfaces, followed by their release through mechanical shearing. Acellular and cellular assays showed the concentration-dependent ability of all studied particles to induce reactive oxygen species production, antioxidant depletion, and oxidative stress-mediated DNA damage. The nonasbestos organic pad, with more than 50-fold higher copper levels than the low-metallic pad, induced stronger DNA damage and acellular antioxidant depletion, suggesting copper as a potential source for the enhanced toxicity.

Une technique de mesure précise et rapide du volume et de la densité des nanoparticules en phase aérosol est proposée. Elle repose sur la condensation d'un revêtement liquide sur chacune des nanoparticules grâce au développement une chambre de grossissement unique. Apres validation sur des particules sphériques en polystyrène, des particules aux morphologies et chimies complexes telles que des poudres et des agrégats ont été mesurées. Cette approche propose une alternative aux méthodes de mesure d'ensemble ex situ et ouvre une nouvelle voie dans la métrologie appliquée aux nanotechnologies.

Un étalonnage précis des instruments de mesure des aérosols requiert une source d'aérosols stable et bien définie produisant des particules sphériques solides, inertes, insolubles et thermiquement stables. Les particules d'argent peuvent satisfaire à l'ensemble de ces critères lorsque l'aérosol est généré et traité de manière appropriée. Nous présentons ici une approche de haute qualité, fondée sur une configuration remarquablement simple, permettant de produire des particules sphériques d'argent compactes et thermiquement stables jusqu'à 100 nm pour l'étalonnage des compteurs de particules par condensation (CPC), des analyseurs de mobilité différentielle (DMA) et des facteurs de réduction de concentration des particules (PCRF).

, depending on the tyre sampled. These particles were round, consistent with a gas-to-particle conversion and were produced at rubber temperatures between 37 and 44 °C. TREADS is the first low-cost, bench-top and portable system able to produce nano-TPs and is designed to be reproducible and user-friendly, allowing for hour-long generation of nano-TPs free from any environmental or road surface contamination.

Atmospheric pollution from particulate matter, volatile organic compounds and greenhouse gases is a critical environmental and public health issue, leading to respiratory diseases and climate change. A potential mitigation strategy involves utilising ventilation systems, which process large volumes of indoor and outdoor air and remove particulate pollutants through filtration. However, the integration of catalytic technologies with filters in ventilation systems remains underexplored, despite their potential to simultaneously remove particulate matter and gases, as seen in flue gas treatment and automotive exhaust systems. In this study, we develop a predictive, long-wave model for V-shaped filters, with and without separators. The model, validated against experimental and numerical data, provides a framework for enhancing flow rates by increasing fibre diameter and porosity while reducing aspect ratio and filter thickness. These changes lead to increased permeability, which lowers energy requirements. However, they also reduce the pollutant removal efficiency, highlighting the trade-off between flow, filtration performance and operational costs. Leveraging the long-wave model alongside experimental results, we estimate the maximum potential removal rate ( 4 . 5 × 1 0 − 3 GtPM 2.5 , 6 . 4 × 1 0 − 3 GtNO x , 2 . 0 × 1 0 − 2 GtCH 4 per year; 1 . 6 × 1 0 0 GtCO 2 e per year, 20-year GWP for CH 4 ) and minimum cost ($ 3 . 4 × 1 0 3 per tNO x , $ 1 . 1 × 1 0 3 per tCH 4 ; $ 1 . 3 × 1 0 1 per tCO 2 e) if a billion V-shaped filters integrated with catalytic enhancements were deployed in operation. These findings highlight the feasibility of catalytic filters as a scalable, high-efficiency solution for improving air quality and mitigating atmospheric pollution.

Abstract Converting natural gas into hydrogen and solid carbon materials using methane pyrolysis presents a promising opportunity to produce sustainable fuels and materials. The production of hydrogen and bulk carbon nanotubes (CNTs) via methane pyrolysis has been demonstrated independently, but concurrent production from the same reactor has remained elusive. Here we present a multi-pass floating catalyst chemical vapour deposition (FCCVD) reactor that converts methane into hydrogen and CNT aerogel. Whereas previous FCCVD CNT production consumed hydrogen, the multi-pass reactor recycles the carrier gas to eliminate the need for a hydrogen input. This results in a net output of 85 vol% hydrogen alongside CNT aerogel and a 446-fold increase in molar process efficiency. Furthermore, the demonstrated use of biogas to produce CNT aerogel enables a potential net sequestration of CO 2 from the atmosphere. The results of this study have been extrapolated to a pilot-scale reactor, using data gathered at a commercial facility, to consider the challenges and opportunities associated with scale-up.

Aerosol science relies on multiple classification techniques that separate particles based on distinct physical properties such as mass, mobility, and aerodynamic diameter. Instruments like the differential mobility analyser (DMA), aerosol aerodynamic classifier (AAC), and centrifugal particle mass analyser (CPMA) enable these separations. By combining two of these measurement methods in tandem, it becomes possible to infer additional particle characteristics, such as effective density, which are crucial for understanding aerosol morphology. In this work, we investigate how morphological diversity within a particle population and classification-induced asymmetries influence the retrieval of average aerosol properties in tandem measurements. Numerical simulations reveal that instruments such as the AAC and, to a lesser extent, the CPMA select particles asymmetrically about the mean of a mass–mobility distribution, leading to systematic shifts in the inferred effective density. Experimental measurements of soot aerosols confirm these predictions, showing that the order of classifiers in tandem setups alters the retrieved mass–mobility parameters, in some cases producing physically unrealistic exponents. These findings highlight that classification-induced biases, if unaccounted for, can lead to misinterpretation of ensemble-averaged morphology, particularly for morphologically diverse aerosols. We emphasise the need for careful selection of classifier pairings and correction strategies when comparing mass–mobility relationships across different instruments, studies, or laboratories.

Methane pyrolysis for hydrogen production is critical for decarbonization efforts, provided that the co-produced solid carbon can be separated affordably and valorized at scale. Studies demonstrate the potential of molten metal alloy catalysts operating in bubble column reactors, achieving industrial-relevant productivities (10⁻⁵ to 10⁻⁶ mol/s/cm³). Key catalytic mechanisms involve surface segregation and surface charge distribution, with electronic effects significantly influencing C–H and C–O bond activation rates. For instance, copper-indium alloys are shown to catalyze the formation of multi-walled carbon nanotubes (CNTs) from nanodroplets, with subsequent heat treatment enabling effective catalyst removal. Another approach, utilizing floating-catalyst gas-phase reactors with iron and sulfur precursors and gas recycling, has demonstrated net hydrogen production (84.5 vol% H₂) alongside CNTs. Significant advances in post-processing have led to CNT fibers with tensile strengths exceeding 8 GPa and recent reports of electrical conductivity surpassing copper and aluminum, making them competitive with high-end carbon fibers. Reactor productivity has increased 100-fold, though further optimization of catalyst selectivity and residence time is needed to prevent undesirable radial growth and ensure high-quality product. For industrial-scale application, a non-catalytic methane pyrolysis process aims for cost parity with steam methane reforming (SMR) coupled with carbon capture, utilization, and storage (CCUS). While initial Gen 1 reactors demonstrated hydrogen and carbon yields, achieving consistent commercial-grade carbon black requires improved reactor temperature and retention time control. New Gen 2 reactor architectures are being developed to increase hydrogen capacity and ensure consistent carbon quality. Overall, the economic viability and scalability of methane pyrolysis are contingent on developing robust carbon valorization pathways, with new markets beyond traditional carbon black, such as in construction materials, advanced conductors, and aerospace composites, being essential for accommodating the substantial volumes of carbon produced. Considerations for the long-term fate of carbon and the reduction of upstream fugitive methane emissions are also critical for the overall environmental impact. Welcome from the Chair Molten metal catalyzed carbon nanotube production Pyrolysis of Methane to Bulk CNT Materials: Manufacturing Carbons that Are Useful for Manufacturing EKONA: Our Journey to Develop Low-Cost, Clean Hydrogen from Methane Pyrolysis Discussion

Tyre additives such as p-phenylenediamines (PPDs) and benzothiazoles (BTs) are ubiquitous in the environment. They have been frequently detected in urban air and have been detected in the human body. However, few studies have examined the toxicological effects in human cells. In this study we perform cytotoxicity, oxidative stress and DNA damage assays on A549 human alveolar lung cells with N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine-quinone (6PPD-Q), diphenyl-p-phenylenediamine (DPPD), 1,3-benzothiazole (BTZ) and 2-mercaptobenzothiazole (MBT). It was found that all additives were able to cause glutathione (GSH) depletion and induce DNA strand breaks after 24 h exposure in a concentration-dependent manner. The presence of N-acetyl-L-cysteine (NAC), a GSH precursor, mitigated both GSH depletion and DNA damage from 6PPD. Although the tested concentrations of tyre additives exceeded typical levels reported for ambient air, these additives have been detected in wastewater, road runoff and road dust. Therefore, human exposure can occur through multiple routes, including inhalation, ingestion, and dermal absorption, ultimately reaching alveolar cells either directly via the lungs or indirectly through the bloodstream.

Methane (CH4), is a potent greenhouse gas released from a wide range of natural and anthropogenic sources. This study explores the performance of thermal catalysis for CH4 abatement under dilute conditions (10–500 ppm), representative of real-world environments. A matrix of catalysts comprising of 1 wt% Pd, Ni, and Ag metals supported on CeO2, TiO2, and Al2O3 was synthesized and screened for CH4 oxidation activity. Pd/CeO2 exhibited the highest activity across all concentrations, achieving complete conversion (&gt;95%) below 500°C at 500 ppm down to 10 ppm of CH4. However, Ag- and Ni-based catalysts, particularly when supported on Al2O3, demonstrated promising activity at higher temperatures, over 80% conversion at 800°C for all CH4 concentrations examined, offering potential cheaper alternatives to Pd. A life-cycle climate-impact assessment further contextualised the catalysts potential for CH4 abatement, accounting for CO2 production, CH4 removal, heating and material emissions. While Pd catalysts showed the highest CH4 conversion, some Ag and Ni catalysts delivered similar net CO2e emission rates when life- cycle costs were included. The results highlight the balance between catalyst cost, activity, and net climate benefit, emphasizing the importance of material selection for scalable, low-concentration CH4 mitigation.

For an evolving aerosol solely undergoing coagulation, an asymptotic form of a self-preserving distribution (SPD), uncorrelated with the initial state, is achieved after sufficient time. To better understand the existence of this state, we hypothesize that non-equilibrium theory can be applied to the SPD formation that has almost entirely been studied via kinetic relations. This study is the first known work to investigate the thermodynamic principles underlying aerosol coagulation, based on the existing definition of colloidal entropy and the self-similar state observed in grain growth. We use molecular dynamics models along with definitions of entropy for an aerosol undergoing collisions and coalescence that includes kinetic entropy, surface entropy and configurational entropy. We find that aerosols have high surface and configurational entropy changes, but note that the SPD can persist in scenarios characterized by non-coalescing particles (minimal surface entropy change) and homogenous mixing (no configurational entropy change). Thus, kinetic entropy alone is the dominant thermodynamic driver of SPD formation. A scaled entropy production (σN,scaled) is introduced and shown to remain constant once an aerosol has achieved an SPD. Applying non-equilibrium flux and force approaches, we find a linear flux-force relationship when the coagulation starts with a polydisperse aerosol and σN,scaled approaches a minimum value at SPD. Conversely, aerosols evolving from an initial monodisperse distribution to the polydisperse SPD exhibit a non-linear flux-force relationship and σN,scaled approaches a maximum value at SPD.

This talk discusses the high rate production of catalyst nanoparticles from plasma processes where the charged species and high reactivity provide a means for synthesizing and controlling aerosol chemistry and dynamics. The talk focuses on two processes, namely spark discharge and corona discharge reactors to produce catalyst materials at high concentrations (&gt;10 8 part/cm 3 ) while controlling chemistry and size. The spark discharge generator (SDG) has long been used to generate aerosols of metallic particles at high number concentrations but more recently it has found renewed interest in the nanomaterials community as a route for continuous NP production from bulk metal, bypassing the issues of preparing and delivering organometallic precursors. By charging a capacitor to a high voltage and inducing a spark (i.e. an electrical discharge) within the thin gap between two active electrodes, the instantaneous high current heats up the surface of the active electrode (&gt;20,000 K), causing surface ablation. The rapid cooling results in the formation of small primary particles, while the high number concentration results in fast coagulation and the formation of agglomerates. The SDG enables precise control of Pt aggregate diameters through selection of carrier gas type, adjustment of flow rates, inter-electrode gap distance, input current, and breakdown voltage. Interestingly, primary particle diameters remained constant (2–3 nm) across varying generation parameters, as confirmed by mass-mobility measurements and transmission electron microscopy (TEM) studies. Similar results were observed with iridium and its oxides, leading to the proposal of a novel particle formation mechanism. In this model, nucleated particles are transported by an expanding shock wave, resulting in cooling times substantially shorter than coalescence times, thus forming fractal-like agglomerates with consistent primary particle sizes. SPG Pt particles demonstrated exceptional catalytic activity. A filter-like catalyst containing an order of magnitude less Pt than commercial monolithic catalysts achieved comparable CO oxidation light-off temperatures (T50). Fixed-bed catalyst tests further substantiated this high activity, with merely 1.4 mg of Pt reducing T50 from 201°C to 107°C. Furthermore, this study established a robust correlation between CO light-off performance and a combination of Pt mass loading and geometric mean diameter of spark-generated Pt aggregates, marking the statistically verified relationship between particle mean diameter and catalytic activity in this context for the first time. In further studies, the SDG is employed to produce bimetallic NPs containing iron and another metallic element (Mo, W, Re, Cu). Size-controlled nanoparticles were used for the synthesis of SWCNTs via substrate chemical vapour deposition and their effects on the nanotube diameter (dt) and electrical type of the SWCNTs were examined. SWCNTs with a narrow dt distribution (1.4±0.2nm) could be synthesized from Fe or Co nanoparticles under optimal synthesis conditions. However, for SWCNTs smaller than 1.8nm in diameter, the dependency of tube diameter on catalyst size weakens. To further facilitate the structure-controlled synthesis of SWCNTs by tuning catalyst composition, four Fe-containing bimetallic NPs were synthesized and tested. Fe/W was found to be a promising candidate for catalysing the growth of ultra-small SWCNTs (dt &lt; 1.2 nm); Fe/Re for better thermal stability and the growth of semi-conducting SWCNTs (80%); and Fe/Cu for the growth of metallic SWCNTs (87%) with a narrow dt distribution (1.24±0.1nm). This study also discusses the advantages and challenges of synthesizing catalysts via aerosol processes and proposes future research opportunities accordingly. Further, this presentation reports the development a novel aerosol synthesis route induced by corona discharge at ambient conditions to harness the effect of unipolar charge in suppressing coagulation and producing nanoparticles with a more monodisperse particle size distribution (PSD). The produced aerosol has a tunable size within 3- 10 nm and the PSD was found to be distinctively narrower (geometric standard deviation GSD = 1.15−1.38) than the default self-preserving PSDs (GSD= 1.46−1.48). A formation mechanism driven by positive ions was proposed and investigated with an aerosol dynamics model, which revealed that a unipolar charge fraction as small as 0.1% could significantly narrow the PSD. The mechanism was confirmed by measurements of the mobility spectra in the range of 0.8- 5 nm at the early stage of particle formation. This is also the first known experimental measurement of cluster formation from ferrocene which leads to aerosol generation, providing new insights into the relationship between process parameters and aerosol growth dynamics.

Work over the past decade has shown benefits of using carbon nanotubes (CNTs) as conductive additives to lithium-ion battery electrodes. CNTs often serve as the electron conduction pathways in battery cathode materials (e.g. NMC, LFP, NCA) which often have dielectric constants &lt;20. Commercially, most cathode materials and an emerging number of anodes (e.g. Si or TNO) require 1-5% conductive carbon additives, which take the form(s) of carbon black (e.g. Super P), graphite, CNTs or graphene. CNTs are often chosen as a conductive additive to provide long-range conductivity through thick electrodes, but may have limitations in short-range electron transport at the interface with the Li-active material. In this study we examine the impact of CNTs on battery performance with a focus on commercially-relevant thick electrodes with area densities &gt;2 mA/cm 2 . Impacts of CNT length, number density, wall number and mass fraction are compared to electrochemical performance of anode (Si and Nb) and cathode (LCO and NMC) materials. Comparisons are also made between conversion materials (Si and Fe x Al y O z ) and intercalation crystals (LTO, LCO and NMC). First cycle efficiency, energy density and rate performance are compared for the materials in half cell and full cell configurations. Our work over the last ten years has found a distinct benefit of covalent binding between CNTs and the active materials, particularly for conversion anode materials. We find that for Iron Silicide (FeSi) conversion materials, the specific capacity is &gt;200% greater when CNTs are covalently bound compared to mixtures of CNTs after 300 cycles. The developed electrodes retain a gravimetric capacity of 1150 mAh/g over 300 cycles at 1A/g as well as a 43% capacity retention at a rate of 5 C. Further, Si-blended electrodes with graphite delivered a 539 mAh/g with high electrode density (∼1.6 g/cm3) and areal capacity (∼3.5 mAh/cm2) with stable cycling performance. Likewise, lithium-titanate (LTO) battery anodes employing ultra-long carbon nanotubes (ULCNTs), grown in a floating catalyst chemical vapor deposition (FCCVD) reactor as their conductive additive, were manufactured and investigated to study effects of CNT incorporation upon their electrical conductivity, rate performance and cycle life. The CNT fibres were electrochemically exfoliated in a salt solution, rinsed of salt, then mechanically ground, blended, and dispersed using high power probe sonication. By comparing equivalent anodes (same carbon mass) produced with carbon black and CNT agglomerates (2 to 20 µm diameters), CNT anodes possessed the greater electrical conductivity by a factor of x20. The superior electronic conductivity of UCNTs show extension of the battery's cyclability rate performance in Li-LTO half-cells. Finally, the work compares CNTs grown from FexAlyOz cores grown in high rate plasma processes. New aerosol-based methods were used for the first time on a battery material to characterize aggregate and primary particle morphologies, while showing good agreement with observations from TEM measurements. As an anode for lithium ion batteries, a reversible capacity of 870 mA h g^−1 based on metal oxide mass was observed and the material showed good recovery from high rate cycling. The high rate of material synthesis (∼10 s residence time) enables this plasma hierarchical material synthesis platform to be optimized as a means for energetic material production for the global energy storage material supply chain. Collectively, this work show benefits and drawbacks of using CNTs. Directly growing CNTs from the surface of active materials results in better performance when normalized by a active material basis. However, unwanted CNT growth (&gt;5% by mass) can be challenging to suppress in some material systems. Thus, ultimate large-scale manufacturing of battery electrodes will be a balance of ease of manufacturing by “drop in” processes (e.g. CNT powders) with better performance (e.g. covalently bound CNTs).

Atmospheric pollution from particulate matter, volatile organic compounds and greenhouse gases is a critical environmental and public health issue, leading to respiratory diseases and climate change. A potential mitigation strategy involves utilising ventilation systems, which process large volumes of indoor and outdoor air and remove particulate pollutants through filtration. However, the integration of catalytic technologies with filters in ventilation systems remains underexplored, despite their potential to simultaneously remove particulate matter and gases, as seen in flue gas treatment and automotive exhaust systems. In this study, we develop a predictive, long-wave model for V-shaped filters, with and without separators. The model, validated against experimental and numerical data, provides a framework for enhancing flow rates by increasing fibre diameter and porosity while reducing aspect ratio and filter thickness. These changes lead to increased permeability, which lowers energy requirements. However, they also reduce the pollutant removal efficiency, highlighting the trade-off between flow, filtration performance and operational costs. Leveraging the long-wave model alongside experimental results, we estimate the maximum potential removal rate ($4.5\times10^{-3}$ GtPM$_{2.5}$, $6.4\times10^{-3}$ GtNO$_{\text{x}}$, $2.0\times10^{-2}$ GtCH$_{4}$ per year; $1.6\times10^{0}$ GtCO$_{2}$e per year, 20-year GWP for CH$_4$) and minimum cost (\$$3.4\times10^{3}$ per tNO$_{\text{x}}$, \$$1.1\times10^{3}$ per tCH$_{4}$; \$$1.3\times10^{1}$ per tCO$_{2}$e) if a billion V-shaped filters integrated with catalytic enhancements were deployed in operation. These findings highlight the feasibility of catalytic filters as a scalable, high-efficiency solution for improving air quality and mitigating atmospheric pollution.

This study assesses a facile method to produce stable, inorganic aerosols (NaCl, NaI, KCl, LiCl) for calibrating condensation particle counters (CPCs) expanding the functionality of the Silver Particle Generator (SPG), a commercially available evaporation-condensation-based particle generator. The impact of the temperature on the particle size distributions generated is examined and the aerosol stability evaluated. Different salts are compared to evaluate their impact on the counting efficiency in CPCs. The SPG was able to generate aerosols efficiently while controlling particle sizes. The results showed that both operating temperature and particle composition had a significant impact on particle generation. Particle concentrations were observed to exceed 106 cm−3 at temperatures below 400 °C. The geometric mean diameter remained stable day-to-day, with less than 6% variation for two evaluated settings at 13 and 57 nm, respectively. The assessment of the counting efficiency for three different CPCs revealed that the salt composition has a significant impact on the 50% detection threshold diameter (d50) of a 23 nm CPC, which ranged from 8.5 to 32.7 nm. An evaluation of the counting efficiency of two 2.5 nm CPCs, based on butanol and water, showed a reduced influence of particle composition, particularly for the butanol-based model. Additionally, the water-based CPC showed an increased d50 diameter for the generated silver particles compared to the inorganic salts.

Current estimates of the climate impacts of aviation condensation trails (contrails) are highly uncertain, primarily due to limited observational data and inconsistencies among different contrail models. However, contrails are thought to contribute substantially to the overall climate impacts of aviation, even at the lower end of the estimated uncertainty. One potential mitigation strategy is to reduce ice-forming emissions through advancements in fuel and engine technology. However, our current understanding of the sensitivities of contrail formation and radiative forcing to engine design variables and fuel properties is limited. Initial studies show that the early plume microphysics modeling (EPM) in contrail models such as the Aircraft Plume Chemistry, Emissions, and Microphysics Model (APCEMM) do not sufficiently capture the role of various emission species.&amp;#160;These limitations include lack of representation of ice formation through homogeneous freezing of volatile aerosols, the effect of chemi-ions on aerosol coagulation, and a simplified treatment of nvPM and their activation.To address these gaps, we aim to improve the existing EPM by including first principle-based modeling, supported by experimental results. In particular, the physics of condensation at the single-particle level is key to determining the transition towards ice crystals. This study investigates the role of nvPM activation via sulfates and organics, as well as the role of pore condensation and freezing, in contrail formation.&amp;#160; The presence of sulfuric precursors can promote the activation of initially hydrophobic soot particles. Such particles have complex fractal shapes that include regions with high surface energy associated with open nano-and micro-pores, favoring the nucleation of critical water droplets. First results have shown that liquid fills the gaps between the primary particles of soot aggregates to form pendular rings which can develop even in a low saturation environment (Sr

The growth kinetics of carbon nanotubes (CNTs) and precursor pyrolysis mechanisms within floating catalyst chemical vapor deposition (FCCVD) reactors have remained opaque despite significant interest in the catalytic mechanisms, CNT growth, and aerogel formation. This study utilizes in situ characterization of reactants and CNTs to determine CNT growth kinetics. By modulating precursors, we avoid the formation of a CNT aerogel within the reactor, which enables direct sampling at independent axial locations of single and agglomerated CNTs and catalyst nanoparticles. Electron microscopy of the in situ sampled aerosols enables measurement of the length of the nanotubes within them and the extent of nanotube agglomeration. Concurrent real-time individual CNT and catalyst mass measurements via a centrifugal particle mass analyzer details the evolution of individual and bundled CNT masses. The number density of CNT-containing particles increases >10-fold as flow travels through a zone of rising temperature. CNT lengths range from 0.1 to 54 μm, and CNTs of length >10 μm account for over half of the total mass produced. A conservative measure of the CNT mean growth rate of 250 μm/s is the highest growth rate observed in literature. A comparison of experimentally determined CNT growth rates reveals that the exceptionally high rates achieved in FCCVD reactors is due to the uniquely high reactor temperatures (>1500 K). The rate of CNT mass production within the reactor does not vary monotonically with temperature, which suggests that other factors, such as changing activity of catalyst, determine the overall CNT mass production rate.

Abstract Assembling 1D nanoparticles (nanowires (NW) or nanotubes) as networks enables bridging multiple scales to form macroscopic materials such as fibers, sheets and electrodes. This can be done directly in the gas phase from 1D nanoparticle aerosols grown by floating catalyst chemical vapor deposition (FCCVD). In FCCVD nanowires/nanotubes grow to high aspect ratios (10 2 –10 6 ) floating in a gas stream and can agglomerate to form an aerogel. This work studies the agglomeration of Si nanowires by scanning electron microscopy of samples taken from the gas downstream of the reaction zone, and through simulations with a Brownian collision algorithm to form agglomerate models. In the experimental analysis of over 312 samples no individualized NWs are found, only agglomerates. This is consistent with the fast binary collision rates of 0.24 s estimated. The agglomerates show “fractal” scaling, with a fractional dimension D f of 1.8 and agglomerate size increasing with the number of nanowires to the power of 1/D f , consistent with a diffusion limited cluster aggregation process. Formation of a nanowire aerogel involves percolation of agglomerates, therefore occurring at much lower volume fraction than for individualized particles considering excluded volume theory. Compared to FCCVD carbon nanotubes of higher aspect ratio, these SiNWs require longer residence time for gelation.

Systematic synthesis of titanium niobium oxides unveils TiNb 2 O 7 's superior cycling and rate performance, attributed to efficient Nb redox utilization, offering advancements in high-power Li-ion battery anodes.

High Resolution Image Download MS PowerPoint Slide Tires are a ubiquitous part of on-road transport systems serving as the critical connecting component at the interface of the motive power and road surface. While tires are essential to automobile function, the wear of tires as a source of particulate air pollution is still poorly understood. The variety of reported emissions found in the secondary literature motivated us to summarize all known mass-based tire wear emission factors for light-duty vehicles in primary research. When excluding road wear and resuspension, mean emissions of 1.1 mg/km/vehicle (median 0.2 mg/km/vehicle) were found for tire wear PM 10 and mean emissions of 2.7 mg/km/vehicle (median 1.1 mg/km/vehicle) when including studies with resuspended tire wear. Notably, these factors are substantially lower than broadly cited and accepted factors in the secondary literature with mean emissions of 6.5 mg/km/vehicle (median 6.1 mg/km/vehicle). As revealed by our analysis, secondary literature reports emission factors systematically higher than those of the primary sources on which they are based. This divergence is due to misunderstandings and misquotations that have been prevalent since the year 1995. Currently accepted mass-based emission factors for directly emitted airborne tire wear particles need revision, including those from the United States Environmental Protection Agency and the European Environment Agency.

In floating catalyst chemical vapor deposition (FCCVD), high-aspect-ratio carbon nanotubes (CNTs) are produced in the gas phase at high number concentrations and undergo collision and agglomeration, eventually giving rise to a macroscale aerogel, enabling functional material forms such as fibers or mats to be obtained directly from the synthesis process. The self-assembly behavior between high-aspect-ratio CNTs dictates the resulting morphology at the nanoscale and subsequently the bulk properties of the CNT product. Reorientation between CNTs after collision is a critical step that results in bundle formation and precedes aerogel formation. However, it has been challenging to study the phenomenon with existing methods as it spans multiple time and length scales. In this study, a physics-based semi-analytical model was developed to study the gas-phase reorientation dynamics of high-aspect-ratio CNTs and their bundles, with ±10% accuracy compared with mesoscale molecular dynamics simulations, but at <0.1% the computational cost. It was revealed that the reorientation time scale is dictated by the interplay among the van der Waals potential, drag, and the geometric configuration of CNTs upon collision. This then allows the time scale of reorientation (i.e., bundle formation) to be compared with other gas-phase dynamics in a typical FCCVD reactor and offers new insights into the self-assembly behavior of 1D nanoparticles in the gas phase.

Few studies have considered the real-world impact of changes in traffic signal timings on air pollution and pedestrian exposure with most only drawing their conclusion from vehicle emission models alone. Here, we consider two distinct cycle timings at a junction in London, UK, model the impact using a traffic microsimulation and a NO x emissions model, and compare these results with NO x and other air pollution measurements collected during a two-week field study at the junction. Our models predict that extending the cycle time leads to a 23% decrease in NO x emissions within a 15 m radius of the junction itself. When the wind direction was such that our sensors were downwind of the junction a 21% decrease in traffic and background-adjusted NO x concentrations were seen, suggesting that the intervention was successful. However, when the sensors were upwind of the junction, we observed an increase of 23% in adjusted NO x concentrations. Similar patterns were found for the other pollutants NO 2 , lung deposited surface area, black carbon and CO 2 we measured. This indicates that meteorology was by far the greatest determinant of roadside concentrations during our two-week study period. Looking at pedestrian exposure for pedestrians waiting to cross the road, we found that their NO x exposure increased by 46% as waiting times to cross the road increased and that potential small reductions in air pollution were offset by increases in waiting times on the main road. The study demonstrates the need to go beyond assessing the impact of hyper-local traffic interventions on vehicle emissions. Real-world trials over extended periods are required to evaluate the impact of meteorology and changes to air pollution concentrations and pedestrian exposures. • Vehicle emission models not sufficient to predict impact caused by signal changes. • Important to consider effects on emissions, air pollution and pedestrian exposure. • Meteorological conditions can have larger impact than change in signal timings. • Pedestrian waiting times key component of pedestrian exposure. • Emissions modelling was combined with real-world air pollution measurements.

Surface charge is an important property of particles. It has been utilized to separate particles in microfluidic devices, where dielectrophoresis (DEP) is often the driving force. However, current DEP-based particle separations based on the charge differences work only for particles of similar sizes. They become less effective and may even fail for a mixture of particles differing in both charge and size. We demonstrate that our recently developed AC insulator-based dielectrophoresis (AC iDEP) technique can direct microparticles toward charge-dependent equilibrium positions in a ratchet microchannel. Such charge-based particle separation is controlled by the imposed AC voltage frequency and amplitude but is nearly unaffected by the size of either type of particle in the mixture except for the time required to achieve an effective separation. This AC iDEP technique may potentially be used to focus and separate submicron or even nanoparticles because of its virtually "infinite" channel length.

High Resolution Image Download MS PowerPoint Slide We report the synthesis of LiCoO 2 (LCO) cathode materials for lithium-ion batteries via aerosol spray pyrolysis, focusing on the effect of synthesis temperatures from 600 to 1000 °C on the materials’ structural and morphological features. Utilizing both nitrate and acetate metal precursors, we conducted a comprehensive analysis of material properties through X-ray diffraction (XRD), Raman spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). Our findings reveal enhanced crystallinity and significant oxide decomposition within the examined temperature range. Morphologically, nitrate-derived particles exhibited hollow, spherical shapes, whereas acetate-derived particles were irregular. Guided by high-temperature X-ray diffraction (HT-XRD) data, the formation of a layered LCO oxide structure, with distinct spinel Li 2 Co 2 O 4 and layered oxide LCO phases was shown to emerge at different annealing temperatures. Optimally annealed particles showcased well-defined layered structures, translating to high electrochemical performance. Specifically, nitrate-based particles annealed at 775 °C for 1 h demonstrated initial discharge capacities close to 179 mAh/g, while acetate-based particles, annealed at 750 °C for 3 h, achieved 136 mAh/g at a 0.1 C discharge rate. This study elucidates the influence of synthesis conditions on LCO cathode material properties, offering insights that advance high throughput processes for lithium-ion battery materials synthesis.

Abstract Methane, a potent greenhouse gas, is a significant contributor to global warming, with future increases in its abundance potentially leading to an increase of more than 1 ∘ C by 2050 beyond other greenhouse gases if left unaddressed. To remain within the crucial target of limiting global warming to 1.5 ∘ C, it is imperative to evaluate the potential of methane removal techniques. This study presents a scoping analysis of different catalytic technologies (thermal, photochemical and electrochemical) and materials to evaluate potential limitations and energy requirements. An analysis of mass transport and reaction rates is conducted for atmospheric methane conversion system configurations. For the vast majority of catalytic technologies, the reaction rates limit the conversion which motivates future efforts for catalyst development. An analysis of energy requirements for atmospheric methane conversion shows minimum energy configurations for various catalytic technologies within classic tube or parallel plate architectures that have analogs to ventilation and industrial fins. Methane concentrations ranging from 2 ppm (ambient) to 1000 ppm (sources, such as wetlands, fossil-fuel extraction sites, landfills etc) are examined. The study finds that electrocatalysis offers the most energy efficient approach (∼0.2 GJ tonne −1 CO 2 e) for new installations in turbulent ducts, with a total energy intensity <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>&lt;</mml:mo> </mml:mrow> </mml:math> 1 GJ tonne −1 CO 2 e. Photocatalytic methane removal catalysts are moderately more energy intensive (∼2 GJ tonne −1 CO 2 e), but could derive much of their energy input from ‘free’ solar energy sources. Thermal systems are shown to be excessively energy intensive ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>&gt;</mml:mo> </mml:mrow> </mml:math> 100 GJ tonne −1 ), while combining photovoltaics with electrochemical catalysts (∼1 GJ tonne −1 CO 2 e) have comparable energy intensity to photocatalytic methane removal catalysts.

High Resolution Image Download MS PowerPoint Slide Progress in electrochemical water-splitting devices as future renewable and clean energy systems requires the development of electrodes composed of efficient and earth-abundant bifunctional electrocatalysts. This study reveals a novel flexible and bifunctional electrode ( NiO@CNTR ) by hybridizing macroscopically assembled carbon nanotube ribbons ( CNTRs ) and atmospheric plasma-synthesized NiO quantum dots (QDs) with varied loadings to demonstrate bifunctional electrocatalytic activity for stable and efficient overall water-splitting (OWS) applications. Comparative studies on the effect of different electrolytes, e.g., acid and alkaline, reveal a strong preference for alkaline electrolytes for the developed NiO@CNTR electrode, suggesting its bifunctionality for both HER and OER activities. Our proposed NiO@CNTR electrode demonstrates significantly enhanced overall catalytic performance in a two-electrode alkaline electrolyzer cell configuration by assembling the same electrode materials as both the anode and the cathode, with a remarkable long-standing stability retaining ∼100% of the initial current after a 100 h long OWS run, which is attributed to the “synergistic coupling” between NiO QD catalysts and the CNTR matrix. Interestingly, the developed electrode exhibits a cell potential ( E 10 ) of only 1.81 V with significantly low NiO QD loading (83 μg/cm 2 ) compared to other catalyst loading values reported in the literature. This study demonstrates a potential class of carbon-based electrodes with single-metal-based bifunctional catalysts that opens up a cost-effective and large-scale pathway for further development of catalysts and their loading engineering suitable for alkaline-based OWS applications and green hydrogen generation.