Michael J. Aziz

Electrosynthesis offers a direct route to utilize clean electricity to create low‑emission pathways for chemical manufacturing. For direct electrosynthesis of highly active compounds such as hydrogen peroxide (H 2 O 2 ), however, the close coupling of product formation and decomposition at electrode interfaces, together with energy intensive product–electrolyte separation, leads to energy losses and limited scalability. Here, we develop an electrified supported liquid membrane platform as a scalable and practical method for H 2 O 2 production as an important model compound. In this architecture, electrons from an external power source are temporarily stored in a designed organic mediator that is subsequently autoxidized within a physically segregated supported liquid membrane domain. This structural-decoupling strategy suppresses electrode driven decomposition, simplifies product handling, and permits independent tuning of electrochemical, transport, and product formation environments within a compact, modular device constructed from inexpensive components. The platform produces metal-free aqueous H 2 O 2 at concentrations above 1 g L -1 with Faradaic efficiencies up to 80%. We further demonstrate direct, on‑site utilization of the generated oxidizing equivalents via in situ Fenton oxidation of an organic contaminant, thereby converting intermittent renewable electricity into localized water-treatment capability. More broadly, this strategy establishes an integrated and flexible reactor design framework for multiphase, electrochemically mediated synthetic processes beyond H 2 O 2 .

Widespread deployment of hydrogen energy is limited by the safety risks and energy penalties of compressed and liquefied storage, whereas alternative hydrogen carriers often require harsh operating conditions or exhibit sluggish kinetics. Here we report a redox-mediated flow cell architecture based on solid organic hydrogen carriers (SOHCs) that enables reversible hydrogen storage and release at ambient temperature and pressure. The system is driven by the rapid, reversible interconversion between hydrogen and proton-electron pairs via the hydrogen oxidation and evolution reactions, while soluble redox mediators shuttle protons and electrons between the electrode and a separate tank containing the solid carrier. This dual-mediator proton-coupled electron transfer (PCET) strategy enables rapid charging and discharging under ambient conditions while decoupling electrochemical hydrogen conversion from hydrogen storage. Using this approach, we achieve a volumetric hydrogen storage density equivalent to approximately 120 bar compressed gas without pressurized vessels. These results open a route that combines the high power density of flow cells with the high energy density of solid-phase materials and provides a scalable, safe, and efficient pathway for stationary hydrogen storage. The modularity in this approach provides a general platform in which the solid carrier, redox mediators, and flow-cell operation can be optimized independently, creating pathways to higher storage density, lower voltage hysteresis, improved kinetics, and broader materials compatibility beyond the specific substances demonstrated here, e.g., including inorganic materials exhibiting a PCET mechanism.

A living document on best practices and common pitfalls in flow battery electrolyte research and development for public discussion and peer-reviewed changes by anyone in the flow battery community.

A living document on best practices and common pitfalls in flow battery electrolyte research and development for public discussion and peer-reviewed changes by anyone in the flow battery community.

Green synthesis of hydrogen peroxide (H2O2) using renewable electricity remains a substantial challenge due to strict requirements of complex catalysts and unavoidable H2O2 decomposition in electrochemical reactors. Here we report a compact electrified phenazine autoxidation (e-PAO) platform that couples an alkaline electrolyzer and a supported liquid membrane (SLM) reactor for continuous, high-purity H2O2 production. This electrified phenazine mediation system avoids the use of precious metal catalysts and gaseous reactants in electrocatalytic and conventional thermocatalytic H 2 O2 manufacture systems. The concept of SLM is applied to integrate hydrogenation, autoxidation and extraction into a single module, efficiently shuttling electrons from the aqueous electrolyte to H2O2 product across a fixed nonaqueous medium with Faradaic efficiency up to 80%. In this SLM architecture, separating electroreduction from H2O2 formation into distinct environments mitigates the H2O2 decomposition that is widespread in other electrochemical methods. We demonstrate direct applicability to advanced oxidation via in-situ Fenton treatment of organic pollutants, highlighting the potential of the e-PAO platform for modular, on demand H2O2 generation and wastewater remediation. This strategy provides an integrated and flexible reactor-construction framework for multiphase, electrochemically mediated synthetic processes.

In the first, multi-institution study of its kind for flow batteries, several laboratories worldwide performed identical single-cell experiments. The findings show that procedural choices significantly alter commonly reported electrochemical metrics.

The use of redox-active organic molecules for aqueous electrochemical carbon dioxide capture is limited by their tendency to undergo reversible oxidation by oxygen. Here we show that a naphthoquinone derivative, when reduced in the presence of tetraalkylammonium countercations, displays enhanced stability toward oxygen while maintaining carbon dioxide binding ability. By combining structural modification with control of non-covalent interactions, we mitigate a previously observed trade-off between carbon dioxide capture performance and resistance to aerobic oxidation. In situ spectrophotometry and comparative voltammetry indicate that ion pairing stabilizes the reduced quinone both by shifting its redox potential and by promoting carbon dioxide adduct formation. Among the cations tested, tetraethylammonium provides the most favorable balance, supporting efficient capture and release cycle with 87 % Coulombic efficiency and an energy cost of 157 kilojoules per mole of carbon dioxide from a gas mixture containing carbon dioxide, oxygen, and nitrogen. These findings illustrate how molecular design combined with electrolyte engineering can improve the durability of aqueous quinone-based electrochemical carbon capture systems and may inform the development of more robust and energy-efficient approaches for sustainable carbon management. Quinone-based electrochemical systems can capture carbon dioxide but are limited by oxygen reactivity. Here, authors present a naphthoquinone and electrolyte design that improves oxygen tolerance while maintaining efficient carbon dioxide capture and concentration in aqueous flow cells.

Aqueous-nonaqueous interfacial proton coupled electron transfer (ANIPCET) represents a promising strategy for integrating aqueous electrochemistry with traditional nonaqueous chemical processes. In our previous work, we demonstrated ANIPCET applied to electrify the incumbent anthraquinone autoxidation (AO) industrial process for hydrogen peroxide (H₂O₂) synthesis. The ANIPCET-based electrochemical AO (e-AO) process achieves high Faradaic efficiency at high current densities, substantially minimizing metal contamination and electrolyte pollution. Building upon this approach, we expanded ANIPCET to aqueous-solid-nonaqueous interfacial hydrogenation reactions, where hydrogen atoms generated electrochemically in an aqueous medium are efficiently transferred across a solid mediator into a nonaqueous phase. We investigated the kinetics of the interfacial hydrogen atom adsorption and hydrogenation reaction mechanisms. This tri-phase mediated hydrogenation process provides enhanced reaction selectivity, improved mass transport, and superior process safety through the elimination of gaseous hydrogen. This aqueous-solid-nonaqueous ANIPCET strategy thus provides a sustainable and broadly applicable electrochemical pathway for diverse nonaqueous hydrogenations traditionally dependent on precious metal catalysts and hydrogen gas, paving the way for safer and more controllable synthetic methodologies.

In this work, we demonstrated that a pinhole-free, solid-state and electron-conductive membrane can function as an ion exchange membrane or a solid electrolyte through bipolarized Faradaic interfacial reactions. The bipolar Faradaic interface membrane (BFIM) is an insulator to ionic conduction in the bulk phase. However, as a unity, it functions as a proton exchange membrane, a hydroxide exchange membrane or a bipolar membrane (BPM) depending on the utilized electrolyte. We demonstrated that the BFIM, which exhibits simultaneous transport of electrons and hydrogen atoms, functions through bipolarized inner sphere proton coupled electron transfer (BISPCET). Pinhole-free BFIMs, as strictly crossover-free ion-exchange membranes, can facilitate crossover-sensitive applications such as isotope separation and water-sensitive nonaqueous electrosynthesis. We further demonstrated BISPCET can be a possible mechanism for catalyzing water dissociation (WD, H 2 O → H + + OH − ), the dominant overpotential consumer, in BPMs. For many of the conductive nanoparticles working as WD catalysts in BPMs, BISPCET can be the dominant mechanism for WD, bringing insights into future WD catalysts and BPM design.

Acknowledgements: The authors gratefully acknowledge the Queen's University Belfast Agility Fund+ scheme for funding research activities. All participants greatly acknowledge the RSC Researcher Collaborations Grant (C24-8470737976) for support. FRB and AHQ gratefully acknowledge support from The Royal Society International Exchanges Grant (IES\R3\213001). AHQ gratefully acknowledges the National Science Foundation Graduate Research Fellowship Program under Grant Number 1745302. Any opinion, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NSF. AHQ also acknowledges the Alfred P. Sloan Foundation's Minority PhD (MPHD) Program. ABJS acknowledges the UK Research and Innovation for her Future Leaders Fellowship no. MR/T041412/1. Fig. 1 was created using BioRender, incorporating illustrations generated with ChatGPT-4 (OpenAI) based on original photographs and descriptions from the study to produce stylised depictions of experimental activities.

Microporous electrodes (pores <2 nm in width) can confine molecules into uniquely packed, charged volumes that exhibit characteristics different from molecules from a bulk solution interacting with an electrode surface. By using surface and electrochemical characterizations, we show the confinement of organic molecules in micropores can shift their redox potentials beyond the classical Nernstian regime, with a shift as large as 252 mV. We identify an excess contribution to the electrochemical potentials of ions that leads to the thermodynamic limit for these shifts and use continuum-scale simulations from a modified Donnan model to confirm this limit and derive deviations from it. Density functional theory simulations confirm that micropore confinement can change the mechanism of charge transfer. We find trends in behavior in micropore environments for organic and metalorganic molecules in aqueous solutions based on their electrophilicity, charge, core molecules, and molecular functionalizations (i.e., side chains). Finally, using micropore confinement on the high and low potential sides of an enclosed secondary battery to increase the open circuit voltage, we demonstrate an increase in average discharge cell voltage of 39% and a corresponding increase in discharge energy density of 36% by replacing macroporous electrodes with microporous electrodes.

This paper introduces simple phenomenological rate theory from the perspective of molecular interconversions and then applies it, in the form of Transition State Theory, to processes such as atomic diffusion and thermally-activated crystal growth in condensed matter composed of very large numbers of atoms or molecules. It is shown that in classical Transition State Theory, the unimolecular rate constant is the “thermal frequency” kBT/h times a Boltzmann factor in the free energy of activation, provided the transition state is defined as a slice of 3N-dimensional configuration space of thickness equal to the thermal deBroglie wavelength, where N is the number of atoms in the system. Equivalently, the unimolecular rate constant is the product of a normal mode frequency and a Boltzmann factor in the free energy of activation, provided the free energy is evaluated for a 3N-1 dimensional hypersurface that is perpendicular to the direction of normal mode motion along the reaction coordinate. Various other expressions for the unimolecular rate constant are derived for various other definitions of the transition state. The apparent activation enthalpy and the pre-exponential factor in the Van’t Hoff-Arrhenius equation for the temperature-dependence of the unimolecular rate constant are interpreted in terms of 3N-dimensional thermodynamic properties of the system and the thermal frequency, as well as in terms of 3N-1 dimensional thermodynamic properties of the system and a normal mode frequency. The relationship between the back reaction and the forward reaction is developed, providing an expression for the net rate as a function of thermodynamic driving force. Examples are presented for which the ratio of net rate constant to the unbiased forward rate constant saturates or increases exponentially with increasing thermodynamic driving force. This approach was developed for teaching a graduate course in materials science called “Kinetics of Condensed Phase Processes” in the late 20th century.

Understanding ion transport processes in polymeric ion exchange layers is an important direction for the development of bipolar membranes, particularly as the applications of these composite materials expand into concentrated and compositionally complex electrolytes. This work shows that the presence of salt (e.g. KCl) as an impurity in strong acid/base causes erosion of the transmembrane potential (the open circuit voltage, OCV) beyond what is predicted by the Nernst equation, and that this OCV erosion is related to increased salt crossover current under reverse bias polarization. We interrogate these phenomena through a combined approach of electrochemical experiments in a four-electrode setup and 1D continuum modeling. The results reveal that ion-ion associative interactions, which we represent in the model as reactions between mobile ions and fixed charge sites within the membrane, provide mechanistic pathways for the experimentally observed salt crossover and OCV erosion.

Understanding ion transport processes in polymeric ion exchange layers is an important direction for the development of bipolar membranes, particularly as the applications of these composite materials expand into concentrated and compositionally complex electrolytes. This work shows that the presence of salt (e.g. KCl) as an impurity in strong acid/base causes erosion of the transmembrane potential (the open circuit voltage, OCV) beyond what is predicted by the Nernst equation, and that this OCV erosion is related to increased salt crossover current under reverse bias polarization. We interrogate these phenomena through a combined approach of electrochemical experiments in a four-electrode setup and 1D continuum modeling. The results reveal that ion-ion associative interactions, which we represent in the model as reactions between mobile ions and fixed charge sites within the membrane, provide mechanistic pathways for the experimentally observed salt crossover and OCV erosion.

Aqueous organic redox flow batteries offer a sustainable approach to long-duration energy storage but suffer from molecular degradation. Here, we present a mixed redox-active strategy that stabilizes 2,6-dihydroxyanthraquinone (DHAQ) by enabling in situ regeneration of redox-active species under standard operating conditions. By incorporating 0.1 M of 4,4′-((9,10-anthraquinone-2,6-diyl)dioxy)dibutyrate (DBEAQ) into a 0.1 M DHAQ electrolyte, the fade rate is reduced from 4.7% to 0.9% per day, a 62% decrease relative to the 2.35%/day expected from a noninteracting mixture. Increasing DBEAQ concentration to 0.2 M further lowers fade to 0.43% per day, representing a 73% reduction relative to the expected value of 1.57%. Electrochemical and NMR data show that regeneration occurs via chemical oxidation of anthrone to a dimer, followed by electrochemical reoxidation to DHAQ. This approach is not limited to DBEAQ, suggesting broad applicability to other anthraquinones. The underlying regeneration mechanism offers a general framework for improving electrolyte stability in organic redox flow batteries.

We introduce a simplified, tubing-free static cell design that eliminates external reservoirs, enabling straightforward evaluation of extremely low capacity fade rates for flow battery electrolytes. These static cells demonstrate reduced standard deviations in measured overall fade rates in percent per day across experiments for a molecule with an extremely low fade rate, ((9,10-dioxo-9,10-dihydroanthracene-2,6-diyl) bis-(oxy)) bis (propane-3,1-diyl)) bis (phosphonic acid)—2,6-DPPEAQ—when compared to traditional flow cells. We demonstrate the importance of temperature control, showing how its absence exacerbates variability in fade rate measurements on the order of the measured fade rate. These developments permit us, through regression analysis of constant current, constant-voltage cycling at varied current densities at pH 14, to present the first decoupled quantification of time- and cycling rate-based fade rates. We report a slight decrease in the overall capacity fade rate with increased cycling rate for 2,6-DPPEAQ and an effect of cycling rate for 4,4′\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$'$$\end{document}-(9,10-anthraquinone-2,6-diyl) dioxy) dibutyrate—2,6-DBEAQ—that is statistically indistinguishable from zero. This article introduces static cells with temperature control as a method for improving the precision of evaluating capacity fade rates of molecules for redox flow batteries. Using the small volumes required for these cells compared to flow cells, these cells demonstrated, for the first time, the capability to decouple time- and cycling rate-based contributions to capacity fade. Because of influences due to variability in cycling protocols, temperature, flow battery composition, and inherent noise in measurements, there is uncertainty in the stability of various redox-active molecules for aqueous organic redox flow batteries. Additionally, relating stability of a molecule to time has remained as a limitation to studying these materials because it cannot capture nonlinearity due to multiple steps in decomposition from complex degradation pathways of organic redox-active molecules.

Aqueous organic redox flow batteries (AORFBs) represent a promising technology for large-scale energy storage due to their ability to decouple power and energy, potential low cost, and reliance on sustainably sourced molecules. Despite advancements, such as the introduction of inexpensive, abundant active materials and selective ion-exchange membranes, AORFBs require further development to achieve viability for grid-scale applications. Limited understanding of interactions between organic molecules and porous electrode fibers remains a key challenge. Porous carbonaceous electrodes— available as felts, cloths, and papers—play a critical role in energy storage systems like fuel cells and AORFBs. However, commercial carbon electrodes often exhibit heterogeneous performance(1), complicating efforts to distinguish structural effects from electrochemical effects. Integrating 3D-printed architected electrodes with electrochemical confocal fluorescence microscopy(2) enables direct visualization of interactions between fibers and electrochemical species. This approach reveals how porous electrode geometry influences AORFB performance. Architected electrodes isolate geometric contributions to diffusion and mass transport limitations of reduced species(3). A combination of physics-based modeling and experimental approaches allows for a detailed investigation of flow and electrochemical behavior. We derived 3D state-of-charge (SOC) maps from imaging to quantify reduced species concentrations within each voxel. Notably, both experiment and model reveal tails of electrolyte in the flow direction and mass transport limitations emerge near the outlet. This experimentally validated model facilitates the customization of electrodes for specific energy storage applications, paving the way for performance-based design and the development of next-generation electrodes that significantly outperform current commercial options. A. A. Wong, S. M. Rubinstein and M. J. Aziz, Cell Reports Physical Science , 2 , 100388 (2021). A.M. Graf, T. Cochard, K. Amini, M.S. Emanuel, S.M. Rubinstein, and M. J. Aziz. "Quantitative Local State of Charge Mapping by Operando Electrochemical Fluorescence Microscopy in Porous Electrodes" Energy Advances 3 , 2468 (2024). D. M. Barber et al., “Print-and-plate architected electrodes for electrochemical transformations under flow,” ChemRxiv(2024). This content is a preprint and has not been peer-reviewed. https://doi.org/10.26434/chemrxiv-2024-2hxnb Figure 1

Aqueous redox flow batteries with organic molecules offer a potentially cost-effective solution for long-discharge-duration electrical energy storage, addressing renewable energy intermittency. However, their commercialization is hindered by the chemical instability of redox-active organic molecules. Although structural modifications can improve stability, they often increase molecular weight and synthesis costs, creating trade-offs between stability, solubility, manufacturing cost, and redox potential. 2,6-Dihydroxyanthraquinone (DHAQ), a well-studied negolyte, suffers from a high fade rate due to degradation into the redox-inactive species 2,6-dihydroxyanthrone and 2,6-dihydroxyanthrol, which can further oxidize into dimers ((DHA)₂⁴⁻) that are irreversibly lost. These degradation pathways deplete active material and limit battery life. Previously, we explored the possibility of regenerating degraded species through oxidation by exposing them to oxygen or utilizing electrochemical regeneration via deep discharging at lower voltages. These methods demonstrated the potential for achieving a nearly complete regeneration cycle of DHAQ but are constrained by challenges such as electrolyte imbalances and energy requirements, presenting opportunities for alternative strategies.[1] We investigated a mixed redox-active electrolyte strategy to mitigate DHAQ degradation, eliminating the need for sacrificial oxidants or energy-intensive regeneration protocols. This approach was validated using 4,4′-((9,10-anthraquinone-2,6-diyl)dioxy)dibutyrate (2,6-DBEAQ)[2] as a representative redox-active compound. A mixture of 0.2 M DBEAQ and 0.1 M DHAQ exhibited a significantly reduced fade rate of 0.43% per day, outperforming the weighted average fade rate of the individual components (1.56% per day, based on 4.7% per day for DHAQ and &lt;0.01% per day for DBEAQ). Through electrochemical and NMR analyses, we elucidated the underlying mechanisms. Notably, contrary to conventional understanding, our results show that decomposed species of DHAQ can be converted back into redox-active monomers during cycling in the presence of a secondary redox-active species. Further validation was conducted with additional anthraquinone derivatives, including N-TSAQ[3], 2,6-DPPEAQ[4], and D2PEAQ[5], all of which exhibited similar recovery behavior. These results highlight the versatility and scalability of the mixed redox-active electrolyte strategy across a range of organic molecules. Beyond mitigating degradation, the introduction of a secondary redox-active species also enhances the overall energy density of the battery system, contributing to improved performance and cost-effectiveness. In summary, the mixed redox-active electrolyte strategy effectively reduces the fade rate of DHAQ by sustainably regenerating degraded molecules. This approach improves energy density, stabilizes long-term battery performance, and demonstrates versatility across various anthraquinone derivatives, offering a robust solution to enhance the reliability of organic redox flow batteries for energy storage applications. Bahari, M., et al., 200-Fold Lifetime Extension of 2,6- Dihydroxyanthraquinone Electrolyte during Flow Battery Operation. ACS Applied Materials &amp; Interfaces, 2024. 16 (39): p. 52144-52152. Kwabi, D.G., et al., Alkaline Quinone Flow Battery with Long Lifetime at pH 12. Joule, 2018. 2 (9): p. 1907-1908. Wu, M., et al., Highly Stable, Low Redox Potential Quinone for Aqueous Flow Batteries**. Batteries &amp; Supercaps, 2022. 5 (6): p. e202200009. Ji, Y., et al., A Phosphonate-Functionalized Quinone Redox Flow Battery at Near-Neutral pH with Record Capacity Retention Rate. Advanced Energy Materials, 2019. 9 (12): p. 1900039. Emily F. Kerr, Z.T., Thomas Y. George, Shijian Jin, Eric M. Fell, Kiana Amini, Yan Jing, Min Wu, Roy G. Gordon, Michael J. Aziz High Energy Density Aqueous Flow Battery Utilizing Extremely Stable, Branching-Induced High-Solubility Anthraquinone near Neutral pH. ACS Energy Letters 2023. 8 (1): p. 600-607. Figure 1

Organic redox reactants offer tunable structures through chemical synthesis, thereby unlocking a vast space of physical and chemical properties for the design redox flow batteries beyond the incumbent all-vanadium chemistry. Evaluating the stability of these redox reactants under conditions of electrochemical cycling between oxidized and reduced states is of paramount importance for choosing materials for long-lifetime. Organic redox reactants in flow batteries are subject to myriad state-of-charge (SOC) dependent chemical reactions that can result in structural changes and the loss of redox activity under cycling conditions, and these reactions may be superimposed on top of crossover though the membrane, complicating the matter of understanding the cause of capacity fade. The volumetrically unbalanced compositionally symmetric cell (hereafter referred to as symmetric cell) method was devised to isolate the contribution of chemical decomposition to capacity fade. 1 In principle the symmetric cell minimizes concentration gradients across the membrane, which would otherwise drive crossover. However, under conditions when the time-averaged SOC of capacity limiting side (CLS) and non-capacity limiting side (NCLS) deviate from 50%, net crossover may occur and influence the measured capacity. 2 We tested symmetric cells of anthraquinone disulfonic acid (AQDS) with Nafion membranes of varied thickness and manufacture (NR211, NR212, N115, and N117, ranging 25–183 μm). Membranes were tested both as-received and pretreated with a common procedure of soaking in water at elevated temperature and then dilute hydrogen peroxide. 3 We found no significant difference in capacity fade rates of symmetric cells with any of the membranes as-received, indicating a negligible influence of crossover. However, we observed increased capacity fade with increased crossover flux through pre-treated membranes. Supported by zero-dimensional modeling and operando UV-vis spectrophotometry, we propose a mechanism for net crossover in AQDS symmetric cells based on a higher time-averaged concentration of quinhydrone dimers in the NCLS than in the CLS, driving net crossover of AQDS reactants out of the CLS. Further, we illustrate other hypothetical scenarios of net crossover using the zero-dimensional model. Overall, many membrane-electrolyte systems used in symmetric cell studies have sufficiently low crossover flux as to avoid the influence of crossover on capacity fade, but under conditions of higher crossover flux, complex interactions of crossover and chemical reactions may result in diverse capacity fade trajectories, the mechanisms of which may be untangled with appropriate measurements and modeling. [1] Goulet, M.-A.; Aziz, M. J. Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods. Journal of The Electrochemical Society 2018 , 165, A1466–A1477 [2] Nolte, O.; Volodin, I. A.; Stolze, C.; Hager, M. D.; Schubert, U. S. Trust is good, control is better: A review on monitoring and characterization techniques for flow battery electrolytes. Materials Horizons 2021 , 8(7) , 1866-1925 [3] Lin, K.; Chen, Q.; Gerhardt, M. R.; Tong, L.; Kim, S. B.; Eisenach, L.; Valle, A. W.; Hardee, D.; Gordon, R. G.; Aziz, M. J.; Marshak, M. P. Alkaline Quinone Flow Battery. Science 2015 , 349, 1529–1532

Buses are the primary mode of public transportation in Dhaka, the capital of Bangladesh, offering affordable fares and broad accessibility across varying distances. However, the efficiency and reliability of bus travel in the city are frequently undermined by unofficial stops, overcrowding, and chronic traffic congestion, all of which contribute to extended travel times, passenger discomfort, and heightened safety concerns. As of 2024, Dhaka operates 366 bus routes, serviced by 6,551 buses and 2,325 minibuses, creating significant operational and management challenges for city authorities. This research focuses on the analysis of Route No. A-314, specifically the “Gabtoli to Staff Quarter via Badda” route, as a case study to highlight and address these challenges. The study employs a combination of primary and secondary data to provide a thorough understanding of the current bus management system. Primary data were collected through structured questionnaire surveys distributed to 385 passengers and 38 drivers, each containing 14 and 10 questions, respectively, aimed at assessing the daily experiences of passengers and drivers. The surveys gathered information on various aspects of bus operations, including frequency, punctuality, and the behavior of drivers and conductors (driver’s assistant-cum-fare collector), as well as passenger safety and satisfaction. Secondary data, such as accident reports and ridership statistics, were sourced from relevant transport authorities to further enrich the analysis. The study’s findings identified key patterns and challenges, including inefficiencies in route management, poor road infrastructure, and a lack of standardized services, all of which negatively affect both passenger comfort and operational safety. Passenger feedback highlighted the inadequacies in the current system, including the need for more frequent and reliable services, better driver training, and improved vehicle maintenance. The study underscores the urgent need for comprehensive reforms to enhance the overall efficiency, comfort, and safety of Dhaka’s bus transport system. These insights provide valuable guidance not only for Bangladesh’s road transport authorities but also for other regions facing similar urban public transport challenges.

Aqueous redox flow batteries using organic molecules offer a sustainable solution for long-duration energy storage, but their commercialization is challenged by capacity fade from molecular degradation. Here, we introduce a mixed-electrolyte strategy that enhances the stability of 2,6-dihydroxyanthraquinone (DHAQ) by enabling continuous in situ regeneration of redox-active species under standard operating conditions. By incorporating 0.1 M 4,4′-((9,10-anthraquinone-2,6-diyl)dioxy)dibutyrate (DBEAQ) into a 0.1 M DHAQ electrolyte, the capacity fade rate is reduced from 4.7% to 0.9% per day, representing a 62% decrease with respect to the value of 2.35%/day expected from the rule of mixtures for a non-interacting mixture. Increasing the DBEAQ concentration to 0.2 M further decreases the fade rate to 0.43% per day, representing a 73% reduction relative to the expected value of 1.57%. Electrochemical and NMR analyses reveal that regeneration occurs via a two-step process: chemical oxidation of anthrone to its dimer, followed by electrochemical oxidation of the dimer back to DHAQ. This regeneration pathway is made possible by the mixed-electrolyte system, which shifts the concentration balance between DHA and dimer toward dimer formation, as DBEAQ acts as an oxidant due to its more positive redox potential. We demonstrate that this mixed-electrolyte strategy is not limited to DBEAQ, highlighting its broader applicability across the anthraquinone species. Moreover, the underlying regeneration mechanism may be extended to other anthraquinone derivatives that degrade through similar pathways, offering a promising framework to enhance electrolyte longevity and stability in organic redox flow batteries.

Dinas Sosial Kabupaten Boyolali memiliki tanggung jawab besar dalam mengelola dan mendistribusikan bantuan sosial kepada masyarakat yang membutuhkan. Namun, proses pencatatan barang masuk dan keluar yang masih dilakukan secara manual menimbulkan berbagai kendala seperti ketidakefisienan dan risiko kesalahan data. Penelitian ini bertujuan untuk mengembangkan tampilan user interface yang user-friendly menggunakan framework Bootstrap berbasis web untuk memudahkan pengelolaan barang bantuan sosial. Metode yang digunakan adalah prototype dengan tahapan analisis kebutuhan, desain, implementasi, evaluasi, perbaikan, dan pemeliharaan. Pengembangan sistem memanfaatkan framework Laravel, Bootstrap, dan database MySQL. Sistem yang dikembangkan mencakup dua modul utama yaitu modul pendataan barang persediaan bantuan sosial dan modul pelaporan barang ke Kementerian. Hasil pengujian menggunakan blackbox testing menunjukkan tingkat kemudahan penggunaan sistem dengan persentase sangat mudah sebesar 22% dan mudah 78%. Implementasi sistem ini telah memungkinkan Dinas Sosial Kabupaten Boyolali mengelola barang masuk dan keluar dengan lebih baik, membuat pencatatan menjadi lebih efisien, dan mempercepat proses pembuatan laporan dari harian hingga tahunan. Sistem ini juga menyediakan keamanan data yang terlindungi dari akses yang tidak sah.

A widely utilized organophosphate pesticide for crop pest control, profenofos and diazinon, have been categorized as moderately toxic by the World Health Organization (WHO).Hence, the identification of profenofos and diazinon residues holds importance for ensuring food safety.This study focuses on the alternative profenofos and diazinon detection method utilizing optical sensors, offering a label-free and real-time measurement scheme.The sensor utilizes zinc oxide (ZnO) with a microflowers structure (ZnO MFs) as the sensing material, chosen for its enlarged surface area, which enhances sensitivity to alterations in the surrounding medium.Synthesized via the solution route method, the ZnO MFs exhibit dimensions of 5.47 0.84 m in length, 1.30 0.26 m in width, and an aspect ratio of 4.35 1.02.Profenofos and diazinon concentrations ranging from 1 to 10,000 ppm are used as targeted analytes for sensor testing.The findings demonstrate distinct responses of the optical sensor, with a detection limit (LoD) of 1 ppm.The sensing parameter, Absolute Optical Change (AOC), exhibits its highest value at 1 ppm for profenofos and 100 ppm for diazinon, indicating an optimal sensitivity.In conclusion, optical sensors using ZnO MFs as sensing material offer a good potential to be used as an alternative method for pesticide detection, with further improvement in LoD and sensitivity aspects needed.

Microporous electrodes (pores &lt;2 nm in width) can confine molecules into uniquely packed, charged volumes that exhibit characteristics different from molecules from a bulk solution interacting with an electrode surface. By using surface and electrochemical characterizations, we show the confinement of organic molecules in micropores can shift their redox potentials beyond the classical Nernstian regime, with a shift as large as 252 mV. We identify an excess contribution to the electrochemical potentials of ions that leads to the thermodynamic limit for these shifts and use continuum-scale simulations from a modified Donnan model to confirm this limit and derive deviations from it. Density functional theory simulations confirm that micropore confinement can change the mechanism of charge transfer. We find trends in behavior in micropore environments for organic and metalorganic molecules in aqueous solutions based on their electrophilicity, charge, core molecules, and molecular functionalizations (i.e. side chains). Finally, using micropore confinement on the high and low potential sides of an enclosed secondary battery to increase the open circuit voltage, we demonstrate an increase in average discharge cell voltage of 39% and a corresponding increase in discharge energy density of 36% by replacing macroporous electrodes with microporous electrodes.

Reduction and oxidation are cornerstone transformations in organic synthesis. While reagents have traditionally been used to effect organic redox reactions, recent advances in electrochemical methodology have offered an attractive alternative approach. In principle, the electrification of these processes could minimize stoichiometric waste, supply arbitrarily tunable potentials, and leverage sustainable energy. However, the practical realization of these advantages is hampered by the need to use organic solvents, which originates from the insolubility of typical substrates in water. As a result, many electrosynthetic reactions require superstoichiometric organic supporting electrolytes, operate under constant current conditions with limited potential control at each electrode, and function under high Ohmic resistance and therefore low efficiencies. Here, we demonstrate a biphasic aqueous-organic approach to electrosynthesis enables the efficient, metal-free, and selective reduction of nitrogen centers. This hybrid format combines the highly optimized performance of aqueous electrochemical platforms with the synthetic versatility of organic media. By integrating reaction and separation into a single process, we minimize byproduct formation, bypass chromatographic purification, and recycle the metal-free redox mediator – either in sequential batch experiments or in continuous flow – with minimal loss (&lt;1% per cycle). Mechanistic experiments demonstrate that reduction proceeds through hydrogen atom transfer in a thin zone near the phase boundary, with the overall process achieving near-perfect Faradaic efficiency and high current density. The concept of biphasic electrosynthesis readily generalizes to other redox transformations, offering more sustainable and more ideal options for both discovery and manufacturing

Abstract Flow cell electrodes are typically composed of porous carbon materials, such as papers, felts, and cloths. However, their random architecture hinders the fundamental characterization of electrode structure‐performance relationships during in situ operation of porous electrochemical flow systems. This work describes a “print‐and‐plate” method that combines direct ink writing of micro‐periodic lattices with a two‐step metal plating process that converts them into highly conductive (sheet resistance 40 mΩ sq −1 ) electrodes. Their operando performance is assessed in an anthraquinone disulfonic acid half‐cell using widefield electrochemical fluorescence microscopy, where output current and fluorescence intensity are in excellent agreement. The pressure drop associated with flow through three electrode designs is determined via simulations from which the most efficient design is identified and manufactured via print‐and‐plate. Confocal fluorescence microscopy is then used to create a 3D map of the state of charge (SOC) inside this print‐and‐plate electrode. The experimental state of the charge map is in good agreement with computational predictions. The rapid design, simulation, and fabrication of print‐and‐plate electrodes enable fundamental investigations of how architected porosity affects electrochemical performance under flow.

Electrochemical production of highly concentrated acid and base with a high current efficiency allows decoupled reactions outside of the electrochemcial cell for carbon dioxide capture and management.

Current hydrogen peroxide (H 2 O 2 ) production is dominantly made through thermocatalytic anthraquinone autoxidation (t-AO) method at industrial scale. Incumbent anthraquinone hydrogenation involves pressurized hydrogen input and requires palladium-based catalysts that can over-reduce anthraquinone to non-reactive molecules. A considerable amount of energy is associated with the distillation and transportation of H 2 O 2 , which could be avoided with decentralized electrochemical H 2 O 2 production methods. We developed an interfacial hydrogen atom transfer reaction between an aqueous and a nonaqueous phase to realize an electrochemical AO process (e-AO), avoiding undesired over-reduction side-reactions. The ambient aqueous electrochemical process enables us to produce H 2 O 2 with a Faradaic efficiency about 80% under high current densities (&gt; 200 mA cm −2 ). The system can be free of hydrogen gas and noble metal. The H 2 O 2 produced this way can be at high concentration (&gt; 10%) and free of electrolyte. This method can facilitate the electrification and decentralization of H 2 O 2 production and reduce the major waste associated with the decomposition of anthraquinone molecules. The electrochemically obtained non-aqueous peroxide can also be directly used in organic synthesis of other high-value chemicals. Figure 1

Bipolar membranes (BPMs), consisting of an anion exchange polymer membrane layer, a cation exchange polymer membrane layer, with a catalytic interfacial layer in between, enable electrolysis cells with large difference of pH between adjacent chambers. This pH gradient is a working principle of a number of devices for energy and sustainability: acid/base batteries store and release energy by building and depleting a pH difference; BPM electrodialysis reactors capture CO 2 in alkaline electrolytes and release CO 2 by acidifying; CO 2 and H 2 O electrolysis devices may employ pH-decoupled electrodes to avoid precious metal electrocatalysts while maintaining low electrode overpotentials. For all of these devices the most efficient operation - in terms of extracting maximum voltage from a battery or driving electrolysis with minimum overpotentials - is achieved when the BPM selectively transports H + and OH - ions in the cation and anion exchange layers respectively. But in practical devices, salt impurities may be present in the electrolytes, or supporting salt may be intentionally added to improve electrolyte conductivity. In this work, we explore how ion exchange processes in bipolar membranes in impure electrolytes affect the ion composition at the bipolar junction - the interfacial layer where the two membrane layers meet. We propose that the ion composition at this interface determines the voltage measured across the membrane at open-circuit, as well as the polarization behavior of the membrane under applied current. We investigate the proposed mechanism using a model system comprising electrolytes with KOH, HCl, and KCl at various relative concentrations with a commercially available BPM (Fumasep FBM). We combine analysis of polarization experiments in a four-electrode setup with a 1D continuum model of water dissociation and multi-ion transport. We report that increased relative salt concentration in the electrolytes erodes the open-circuit voltage across the membrane, yielding voltages significantly lower than expected based on the measured pH difference, indicating that H + and OH - ions within the BPM exchange with ions from the added salt to occupy membrane fixed charges at the bipolar junction. This phenomenon penalizes the energy efficiency of BPM acid/base batteries. Additionally, we find that during polarization, impure electrolytes exhibit salt crossover at low current density and that the magnitude of this crossover depends on the relative concentration of the salt versus H + and OH - ions. We utilize the 1D continuum model to visualize concentration profiles of ions in the BPM at both open-circuit and applied current conditions. This work illustrates the importance of electrolyte species on interfacial BPM phenomena and provides guidance both for designing new BPM materials and for choosing electrolytes and operating conditions in electrochemical cells. Figure 1

Climate change caused by the accumulation of anthropogenic CO 2 emissions motivates the development and deployment of cost-effective, scalable, modular, and energetically efficient techniques to capture CO 2 from point or diffuse sources. Electrochemically-driven CO 2 capture processes utilizing redox-active organics in aqueous flow chemistry and operating at ambient temperature and pressure show promise for nonflammability, continuous-flow engineering, and the possibility of being driven at high current density by inexpensive, clean electricity. [1-2] We show that the deprotonated hydroquinone-CO 2 adducts, whose insolubility limits the utility of the quinone-hydroquinone redox couple, become soluble when alkylammonium cations are introduced. Consequently, we introduce alkylammonium groups to anthraquinone via covalent bonds, making the resulting bis[3-(trimethylammonio)propyl]-anthraquinones (BTMAPAQs) soluble. [3] We report the first aqueous quinone flow electrochemistry induced CO 2 capture/release process, which occurs at ambient temperature and pressure. We show that the electrochemically reduced BTMAPAQs are both Lewis bases and Brønsted bases, thus capturing CO 2 via both a pH-swing and a nucleophilicity-swing mechanism. Among the 1,4-, 1,5-, and 1,8-BTMAPAQ isomers, 1,5-BTMAPAQ reaches the theoretical capture capacity of two CO 2 molecules per quinone from 1-bar CO 2 -N 2 mixtures for which the CO 2 partial pressure is as low as 0.05 bar, or the applied current density is as high as 100 mA/cm 2 , or the organic concentration is as high as 0.4 M. The energetic cost ranges from 48 to 140 kJ/molCO 2 . In a crude simulated flue gas composed of 3% O 2 , 10% CO 2 , and 87% N 2 with a flow rate of ~12 mL/min, 1,5-BTMAPAQ electrolyte reversibly captured and released 50% of the theoretical capacity during an exposure of over 4 hours. It outperforms its isomeric counterparts 1,4-, and 1,8-BTMAPAQ in capture capacity and O 2 tolerance, demonstrating a substituent position effect on the reactivity of isomers with CO 2 and O 2 . The results provide fundamental insight into CO 2 capture with aqueous quinone flow electrochemistry. The oxygen tolerance of reduced quinones may be significantly advanced through molecular engineering by introducing steric and/or electronic effects, intra-molecular interactions, elevating or lowering the oxidation potentials of reduced quinones. [1] Jin, S.; Wu, M.; Gordon, R. G.; Aziz, M. J.; Kwabi, D. G. pH swing cycle for CO 2 capture electrochemically driven through proton-coupled electron transfer, Energy Environ. Sci. , 2020 , 13 , 3706-3722. [2] Jin, S.; Wu, M.; Jing, Y.; Gordon, R. G.; Aziz, M. J. Low energy carbon capture via electrochemically induced pH swing with electrochemical rebalancing, Nature Communications , 2022 , 13 , 2140. [3] Jing, Y.; Amin, K.; Xi, D.; Jin, S.; Alfaraidi, A.; Kerr, E.F.; Gordon, R.G.; Aziz, M.J, Electrochemically induced CO 2 capture enabled by aqueous quinone flow chemistry, ChemRxiv , 2023 , DOIs:10.26434/chemrxiv-2023-nfg6z-v2; 10.26434/chemrxiv-2023-nfg6z.

Capture of CO 2 from point sources or directly from the atmosphere can provide an important contribution to climate-change mitigation efforts in the coming decades. Electrochemically driven CO 2 capture utilizing proton-coupled redox organics (PCROs) in aqueous solution has great potential because of the process's low energy use, the nonflammability and high ionic conductivity of the medium, and the ability to be powered by cheap, clean electricity at high current density. However, all PCROs reported previously for this application are, in their reduced form, reversibly chemically oxidized by oxygen, resulting in impractically low efficiency. In this work, we attempt to better understand this sensitivity by studying the oxidation mechanism using electrochemical techniques and by measuring the oxidation rate of various reported and newly developed PCROs. This guides us in the development of new PCROs for electrochemical CO 2 capture with decreased reactivity with oxygen, and we experimentally demonstrate their performance in electrochemical flow CO 2 capture system.

Aqueous organic redox flow batteries (AORFBs) have emerged as potentially disruptive technologies for the storage of electrical energy from intermittent renewable sources. With the goal of cost-effective, safe, and scalable stationary long duration energy storage systems, AORFBs could become preferred over Li-ion batteries for grid-scale stationary storage due to their inherent non-flammability, lack of materials scarcity fluctuations, and intrinsic decoupling of energy and power capacities. Our group has demonstrated that calendar life, rather than cycle life, limits molecular lifetimes in AORFBs due to various molecular instabilities that lead to side reactions, thus inhibiting performance [1]. To accurately determine molecular fade rates, we utilize potentiostatic cycling to avoid artifacts caused by drifts in internal resistance and employ volumetrically unbalanced compositionally symmetric cell configurations to distinguish molecular fade from membrane crossover or cell unbalancing. Redox-active organic molecule stability has improved to the point that the most stable chemistries degrade at less than 1% per year [2]. With further lifetime increases, the measurement of lower capacity fade rates necessitates higher precision coulometry methods and thermally accelerated degradation protocols to determine which stabilizing approaches are most effective without waiting for multi-month cycling tests to quantify capacity fade. We developed a high-throughput setup for cycling AORFBs at elevated temperatures, providing a new dimension in the flow battery characterization space to explore [3,4]. Capacity fade rates of previously published redox-active organic molecules, as functions of temperature, were evaluated in the high-throughput setup. Demonstrated Arrhenius-like behavior in the temporal capacity fade rates of multiple AORFB electrolytes provided the ability to extrapolate fade rates to lower operating temperatures. Complemented by open source zero-dimensional modelling that incorporates redox-active material degradation [5], we explored temporal capacity evolution in symmetric cells driven by different capacity fade mechanisms such as active species degradation, self-discharge [6], and membrane crossover. Collectively, these results highlight the relevance of electrochemical techniques to understand molecular degradation and expedite the screening process of candidate molecules for long lifetime AORFBs, which may enable massive grid penetration of intermittent renewable energy. References [1] M.-A. Goulet and M. J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods,” Journal of The Electrochemical Society , 165 , A1466 (2018). [2] M. Wu, Y. Jing, A. A. Wong, E. M. Fell, S. Jin, Z. Tang, R. G. Gordon, M. J. Aziz, “Extremely Stable Anthraquinone Negolytes Synthesized from Common Precursors,” Chem , 6 , 1432 (2020). [3] E. M. Fell and M. J. Aziz, “High-Throughput Electrochemical Characterization of Aqueous Organic Redox Flow Battery Active Material,” Journal of The Electrochemical Society , 170 , 100507 (2023). [4] E. M. Fell, T. Y. George, Y. Jing, R. G. Gordon, M. J. Aziz, “Leveraging Temperature-Dependent (Electro)Chemical Kinetics for High-Throughput Flow Battery Characterization,” Journal of The Electrochemical Society , 171 , 040501 (2024). [5] E. M. Fell, J. A. Fell, M. J. Aziz, “RFBzero: A Python package for zero-dimensional simulation of redox flow battery cycling,” Journal of Open Source Software , in review (2024). Software available at https://pypi.org/project/rfbzero/ [6] E. M. Fell, D. De Porcellinis, Y. Jing, V. Gutierrez-Venegas, T. Y. George, R. G. Gordon, S. Granados-Focil, M. J. Aziz, “Long-Term Stability of Ferri-/Ferrocyanide as an Electroactive Component for Redox Flow Battery Applications: On the Origin of Apparent Capacity Fade,” Journal of The Electrochemical Society , 170 , 070525 (2023).

Aqueous Organic Redox Flow Batteries (AORFBs) have shown growing potential as a stationary energy storage technology used to alleviate the issue of intermittency i for renewable energy sources. For systems with charge/discharge duration of 10 or more hours, the capital cost of a flow battery asymptotically approaches the cost of the electroactive material. ii While the field has made many new materials iii and developed proper protocols for evaluating their decomposition iv , uncertainty in the fade rates of extremely stable iii materials remains comparable to the fade rates themselves v , frustrating the evaluation of prospects of the material for commercialization. Additionally, evaluation of new materials in flow cells requires a significant amount of material synthesis, whereas evaluation methods requiring less material could accelerate the development of AORFBs. vi To reduce noise in measurements by removing pumping, splashing, and bubbling of solutions that occurs in flow cells, and to reduce the amount of required active material, we use static cells composed solely of porous electrodes sandwiched about a membrane, gaskets, and graphitic current collectors with no flow. With reduced material consumption, increased cycling rate, and less noise in capacity measurements, we more rapidly and more accurately determine the capacity fade rates for extremely stable materials for AORFBs (Figure 1) and test the limits for cycle-denominated fade rates. In addition, we discuss relevant reporting statistics for making fair comparisons between extremely stable materials. To evaluate overpotentials in the system due to kinetics, mass transfer, and Ohmic resistance, we model the system using Newman’s porous electrode model vii to ensure the use of proper cycling protocols to access all of the capacity of the system. Figure 1: (left) An example of potentiostatic cycling of 0.1 M 2,6-DPPEAQ at pH 14 in a volumetrically unbalanced compositionally symmetric static cell with an applied voltage square wave of amplitude 0.20 V across the cell, held until the current drops to 1 mA/cm 2 . After cycling for a day while the electrolyte equilibrates, a capacity fade rate is evaluated from the slope of the natural log of discharge capacity vs time. (right) A whisker and box plot for capacity fade measurements from several potentiostatic symmetric cell cycling experiments in a flow cell from Ref [5], static cells with no attention to temperature fluctuations, and static cells where temperature fluctuations are kept within 1 degree Celsius. [i] J. Rugolo and M. J. Aziz, “Electricity storage for intermittent renewable sources.” Energy Environ. Sci ., 2012, 5 , 7151 [ii] F. R. Brushett, M. J. Aziz, and K. E. Rodby. ACS Energy Lett . 2020, 5 , 879−884 [iii] David G. Kwabi, Yunlong Ji, and Michael J. Aziz, “Electrolyte Lifetime in Aqueous Organic Redox Flow Batteries: A Critical Review.” Chemical Reviews 2020 120 (14), 6467-6489 [iv]M.A. Goulet and M. J. Aziz, “Flow Battery Molecular Reactant Stability Determined by Symmetric Cell Cycling Methods”. J. Electrochem. Soc , 165 (7) A1466-A1477 (2018) [v] Eric M. Fell and Michael J. Aziz, “High-Throughput Electrochemical Characterization of Aqueous Organic Redox Flow Battery Active Material.” 2023 J. Electrochem. Soc. 170 100507 [vi] Cao, Y., Aspuru-Guzik, A. “Accelerating discovery in organic redox flow batteries.” Nat Comput Sci 4 , 89–91 (2024) [vii] J. Newman and C. W. Tobias, J. Electrochem. Soc., 1962, 109, 1183 Figure 1

Aqueous redox flow batteries (ARFBs) constitute a promising technology for cost-effective and scalable storage of intermittent renewable energy from sources like wind and solar. For long discharge-duration storage (&gt; 8 h), these batteries offer a unique advantage by decoupling energy storage from power generation, providing a level of design versatility and scalability that traditional rechargeable batteries can hardly match. Typically, the negolyte and posolyte of ARFBs exhibiting long-term operation have roughly the same pH. In contrast, pH-decoupling aqueous redox flow batteries (ARFBs) utilize different pH values in the negolyte and the posolyte, enabling the cell to achieve higher cell voltages and support a broader range of redox pair combinations. Managing the crossover of acid and base, along with an economical and straightforward method to recover their crossover, is critical for long-term operation of pH-decoupling ARFBs. We have previously investigated the crossover of acid and base in multichamber pH-decoupling ARFBs and developed a small, but adequately-sized bipolar membrane (BPM) sub-cell for pH recovery. 1 Here, we introduce a new pH-decoupling design utilizing a conventional single-membrane ARFB architecture. This approach reduces the ohmic area-specific resistance while maintaining an acceptably low level of acid-base crossover. We explore various electrolyte pairs, ranging from solutions to semi-solids, anions to cations, acids to bases, showing that this design allows flexibility in electrolyte combinations. The setup can result in improved energy efficiency, higher areal power density, and reduced capital costs. Along with different cells, we demonstrated how proton-coupled electrochemical reactions can serve as proton pumps, enabling in-situ or ex-situ pH recovery in these pH-decoupling setups and discussed its relationship to BPM pH recovery. 1. Xi, D., Alfaraidi, A.M., Gao, J. et al. Mild pH-decoupling aqueous flow battery with practical pH recovery. Nat Energy (2024). https://doi.org/10.1038/s41560-024-01474-1 Figure 1

CO 2 reduction is an important step in carbon capture, utilization, and storage (CCUS). The utilization of a membrane electrode assembly (MEA) with a gas diffusion electrode (GDE) realizes high current density CO 2 reduction. However, most of the developed CO 2 reduction catalysts suffer from low Faradaic efficiency when using a proton exchange membrane MEA, due to low local pH surrounding catalysts. Alternatively, with an anion exchange membrane MEA, CO 2 reduction suffers from low conversion efficiency due to carbonate-bicarbonate crossover through the membrane to the anode. For continuously-running CO 2 electrolyzers, the crossover of acids and cations results in low reduction efficiency and flooding of the GDE. We have designed and characterized an asymmetric membrane that prohibits carbonate-bicarbonate crossover, yet can maintain a high local pH surrounding the catalyst. The resulting MEA can achieve high Faradaic efficiency toward CO 2 reduction using developed catalysts with near-zero CO 2 crossover. When using oxygen evolution in the anode, we further developed an ion-blockage strategy to diminish the crossover of acids or cations during long-term operation, maintaining a relatively stable and suitable environment for CO 2 reduction on GDE. The crossover management of carbonate, bicarbonate, protons and cations can lead to a long lifetime high-efficiency CO 2 electrolyzer.

Flow cell electrodes are typically composed of porous carbon materials, such as papers, felts, and cloths. However, their random architecture hinders fundamental characterization of electrode structure-performance relationships during in situ operation of porous electrochemical flow systems. Here, we report a “print-and-plate” method that uses high-resolution direct ink writing to produce periodic lattices followed by a two-step metal plating process to convert these lattices into highly conductive (sheet resistance 40 milli-Ohm per square) electrodes. We assessed their in operando performance in an anthraquinone disulfonic acid half-cell using electrochemical fluorescence microscopy, where output current and fluorescence intensity are in excellent agreement. We then compared the pressure drop of three electrode designs simulated with a high-fidelity numerical solution to the governing PDEs. The most efficient design was then fabricated via the print-and-plate method and confocal fluorescence microscopy was used to generate a 3D map of the state of charge (SOC) inside the working electrode. The experimental state of charge map is in good agreement with our simulations. By unlocking programmable architectures, print-and-plate electrodes offer new opportunities for fundamental investigations relating porous electrode microstructure to performance and direct replication of simulated structures.