Ion-transfer reactions in the presence of electric fields are ubiquitous in (bio/electro)chemical systems and catalysis, yet the impact of the electric field is poorly understood. Here, we use bipolar membranes (BPMs) to isolate electric-field-driven non-faradaic water dissociation (WD: H2O -> H+ + OH-) on catalytic surfaces. We find the catalyst layer's ionic properties dictate both the transport and kinetic processes within the BPM. The role of these properties are explored via a series of membrane architectures, and catalyst poisoning experiments, and the corresponding current-voltage and impedance responses. Arrhenius analyses show that an acidic graphene-oxide (GO(x)) catalyst layer gives rise to low interfacial H2O entropy in the heterojunction, illustrated via a >100 fold increase in the Arrhenius prefactor relative to baseline TiO2 measurements. Furthermore, similar to 50% of the applied driving force goes towards reducing the apparent enthalpic activation barrier in the case of GO(x), while other metal-oxide catalysts have enthalpic barriers independent of driving force. This analysis demonstrates a new mechanistic understanding of WD, where local electric fields augment enthalpic transition-state barriers, and the local ionic environment facilitates field-driven ion transfer. Ultimately, these results present a new design space for designing ion-transfer catalytic processes, and ionic heterojunctions more broadly.

Industrial CO2 streams vary widely in composition, from pure to as low as 3%, posing challenges for purification or direct conversion. Electrochemical reduction offers a route for converting dilute CO2 streams but faces severe mass transport limitations. This study demonstrates that pulsed electrolysis effectively overcomes these limitations, enhancing CO2 electroreduction across variable feed compositions and current densities, particularly at low CO2 concentrations and high current densities. At 25% CO2 and 400 mA cm-2, pulsing improved selectivity from 25.6 to 78.6%, production rate from 13.7 to 21.0 mol m-2 h-1, and energy productivity from 0.77 to 2.59 mol kWh-1. A dynamic, multiphysics continuum model confirms a 64% increase in CO2 concentration within the catalyst layer during pulsing, resolving the transient chemical microenvironment. These findings establish pulsed electrolysis as a viable strategy for converting dilute industrial CO2 streams into valuable feedstocks, bypassing costly pre-separation.

Bipolar membranes (BPMs) create counteracting spatial gradients of pH and electrostatic potential in electrochemical systems, enabling applications in pH regulation, electrocatalysis, and separations. At the polarized junction of a BPM the water dissociation (WD, 2H2O ⇌ H3O+ + OH-) reaction can be driven, but it remains poorly understood. In this Perspective, we integrate molecular insights from bulk-water autoionization and the associated field effects with continuum descriptions of BPM electrostatics and experimental WD kinetic analyses to describe possible mechanisms of voltage-driven WD. Pristine BPM junctions highlight both the limits of primarily electric-field-driven WD and the practical challenges of junction stability at extreme reverse bias. Introducing heterogeneous catalyst layers, commonly metal oxides and graphene oxides, accelerates WD by orders of magnitude through hypothesized coupled effects in which surface acid-base functionality and high-density hydroxyl sites mediate proton-transfer steps, and catalyst mobile electronic/ionic charges redistribute the junction electric potential drop to shape the local electric fields and reactive microenvironments. Kinetic analyses suggest two regimes of heterogeneous WD mechanism, including field-driven ordering of interfacial water and a Second-Wien-Effect dissociation-barrier lowering. We conclude by defining the key unknown variables (local pH, electrostatic potential, catalyst charge state and relationships among mechanisms) and outlining experimental and multiscale modeling strategies needed for predictive WD catalysis and for controlling related ion-transfer reactions.

Industrial routes for propylene oxide and propylene glycol production involve either explosive hydrogen peroxide or corrosive chlorine-containing reagents, which produce hazardous halogenated by-products. Direct aqueous electrooxidation is a safe and sustainable alternative that uses water as an oxygen source at a catalytically competent anode. Until now, the direct aqueous route has only been demonstrated on noble metals (Pd, Pt, Au, Ag), which are unstable unless operated in halogenated electrolytes. Here we have developed a noble metal- and halogen-free catalytic system using a cobalt-based perovskite oxide with a Faradaic efficiency of 40% toward propylene oxide and propylene glycol, maintained over 24 h of operation. Kinetic analysis revealed potential-dependent rate-limiting steps involving electrochemical oxygen species generation and thermochemical oxygen transfer to propylene. This work establishes a cost-effective and safe synthetic route with earth-abundant non-noble metal-based catalysts, not only for propylene epoxidation but also for other heterogeneous oxygen-transfer reactions.

The electrical double layer (EDL) has long been known to influence observed rates of electrocatalysis, but a complete understanding of its role has been elusive due to the complex, multicomponent interactions that dictate double layer structure. To resolve these effects, we bridge electrochemical transport theory and Marcus-Hush-Chidsey theory from the nano- to mesoscale to model the EDL structure and its effects during the electroreduction of CO2 to CO over Ag catalysts. The model exhibits strong agreement between predicted and experimental CO2 reduction rates as a function of cation identity, CO2 partial pressure, and electrolyte concentration, along with spectroscopic measurements of the microenvironment at the Ag surface (e.g., local pH and CO2 activity), all without the need for empirical fit parameters. The model reveals that small, hydrated cations (Cs+ and K+) pack tightly in the EDL and enable large electric fields, which polarize water molecules in the Stern layer. This polarization reduces the energy for water reorganization and, in turn, the transition state barrier for reductive CO2 adsorption. These findings implicate solvent reorganization as a principal phenomenon that governs the impact of EDL structure on catalysis, emphasizing the need for multiscale understanding in the study of complex catalytic interfaces.

Electrochemical nitrate reduction (ENR) is an appealing method for remediating nitrate contamination in wastewater and producing ammonia using renewable electricity. However, a mechanistic understanding of coupled mass transfer and electrocatalysis at the electrode-electrolyte interface, which dictates ENR efficiency, is limited. In this study, we develop an experimentally-validated multiphysics model of the Stern, diffuse, and diffusion layers near the surface of a polycrystalline titanium catalyst to investigate the effect of the electric double layer on ENR. The developed model couples the generalized-modified-Nernst-Planck equation with Frumkin-Butler-Volmer kinetics and numerical optimization to quantify the effect of applied potential and bulk electrolyte concentration on the ammonia formation rate. Our results reveal how dynamic driving forces at the polarized interface give rise to experimentally observed trends in ENR. Guided by this insight, we show that a more negative potential-of-zero-charge increases the limiting current density for ammonia synthesis by enabling faster migration of nitrate towards the cathode surface. The results motivate the development of multi-scale models that link transport phenomena with molecular-scale modelling to design and tailor interfaces for efficient ENR.

Water electrolysis provides a means of producing H2 gas without carbon emissions. However, H2 production through water electrolysis is more costly compared to methods using fossil fuels. A key element to the cost of water electrolysis is the need to purify the water fed to the electrolyzer. Impure feeds can lead to corroding electrodes (e.g. chloride oxidation) and fouling of commonly-used monopolar membranes (i.e., cation and anion exchange membranes). Bipolar Membranes (BPMs), consisting of a cation and anion exchange membranes with a water dissociation catalyst at the interface, pose unique advantages. Because each layer can be tuned independently, BPMs enable higher control of co-ion transport and impurities, unlike monopolar membranes. However, challenges arise in rationally-designing BPMs for impure water electrolysis due to a lack of fundamental understanding of the coupled interactions between water, mobile ions, and fixed charge groups. In this study, we develop a continuum model to systematically investigate the use of BPMs for water electrolysis with impure feedstocks (e.g. seawater). The model defines the flux of each species using a modified Nernst-Planck-Poisson framework while explicitly considering non-ideal contributions to chemical potential from ion-ion, ion-membrane, swelling, electrostatic, steric, and solvation interactions to the electrochemical potential. The simulations quantify the effect of these interactions and membrane properties on ion transport, and how they could be modulated to mitigate the deleterious effects of impurities and co-ions. Our analysis shows that simple dilute-solution theory is not capable of predicting the effect of impurities on BPM water electrolysis and identifies the dominant interactions that dictate transport in BPMs. This study provides guidelines for modelling water electrolysis and materials design strategies for water electrolysis in non-ideal conditions.

The ability for bipolar membranes (BPMs) to interconvert voltage and pH makes them attractive materials for use in energy conversion and storage. Reverse-biased BPMs, which use electrical voltage to dissociate water into acid and base, have become increasingly well studied. However, forward-biased BPMs (FB-BPMs), in which voltage is extracted from pH gradients through recombination, require further study. Here physics-based modeling elucidates how the complex coupling of transport and kinetics dictates the performance of FB-BPMs in electrochemical devices. Simulations reveal that the open-circuit potential of FB-BPMs is dictated by the balance of ion recombination and crossover, where recombination of buffering counter-ions attenuates the open-circuit potential. Counter-ion mass-transport limitations and uptake of ionic impurities limit achievable current densities by reducing the applied pH gradient or the available fixed-charge sites that mediate recombination. The model highlights the importance of selective ion management in mitigating energy losses and provides insight into the rational material design of FB-BPMs for energy applications. Forward-biased bipolar membranes (FB-BPMs), which recover potential from pH gradients through ion–ion recombination, show promise for application in sustainable devices. The authors use physics-based modeling to elucidate how ion-specific phenomena dictate performance, reveal how selective ion management can mitigate energy losses and provide insights into the rational design of next-generation FB-BPMs.

Integrated solar fuels devices for CO2 reduction (CO2R) are a promising technology class towards achieving net-negative carbon emissions. Designing integrated CO2R solar fuels devices requires careful co-design of electrochemical and photovoltaic components as well as consideration of the diurnal and seasonal effects of solar irradiance, temperature, and other meteorological factors expected for ‘on-sun’ deployment. Using a photovoltaic-electrochemical (PV-EC) platform, we developed a temperature and potential-dependent diurnal and annual model using experimental CO2R performance of Cu-based electrocatalysts, local meteorological data from the National Solar Radiation Database (NSRD), and modeled performance of commercial c-Si PVs. We simulated diurnal product outputs with and without the effects of ambient temperature to determine gaseous product temperature sensitivity. From these outputs, we observed seasonal variation in gaseous product generation, with up to two-fold increases in ethylene productivity between the Winter and Summer, analyzed the consequences of dynamic cloud coverage, and identified periods where device cooling/heating mechanisms could be implemented to maximize ethylene generation. Finally, we modeled the annual ethylene generation for a scaled 1 MW solar farm at three different locations (Beijing, CN; Sydney, AUS; Barstow, CA) to determine the consequences of local meteorological climates on PV-EC CO2R product output, recording a maximum ethylene output of 18.5 tonne/yr at Barstow. Overall, this model presents a critical tool for streamlining the translation of experimental solar-driven electrochemical research to real-world implementation.

THE BIGGER PICTURE Challenges and opportunities: center dot The low cost and short time frame in which parts can be manufactured through 3D printing lowers the barrier to improved electrochemical cell design, which, in turn, facilitates faster and more in-depth investigation of electrochemical systems. center dot We stress the importance and accessibility of engaging in a technological feedback loop between modeling, printing, and experimenting to inform the understanding of reaction mechanisms and the optimization of electrochemical reactor performance. center dot The development of new resin technologies expands the scope of accessible chemistries with 3D- printed electrochemical cells, although there is still room for innovation in 3D-printing techniques and materials design. SUMMARY With a recent surge in electrochemical technologies, the number of electrochemical cell designs for applications ranging from biosensors to high-current electrolyzers has grown massively. While electrode and electrocatalyst materials have been the traditional focus of electrochemistry research, the expanded experimental and computational study of dynamic conditions within electrochemical cells has revealed the importance of co-designing the cell's components. Additive manufacturing via 3D printing has historically been used to prototype parts before getting them machined out of materials with more favorable properties. However, developments in printer accuracy, filament and resin robustness, and printer accessibility in recent years have broadened the scope of the potential applications of additive manufacturing. In this perspective, we provide insight into the acceleration of reactor design and implementation for electrochemistry and catalysis facilitated by advances in vat photopolymerization.

Bipolar membranes in electrochemical CO 2 conversion cells enable different reaction environments in the CO 2 -reduction and oxygen-evolution compartments. Under ideal conditions, water-splitting in the bipolar membrane allows for platinum-group-metal-free anode materials and high CO 2 utilizations. In practice, however, even minor unwanted ion crossover limits stability to short time periods. Here we report the vital role of managing ionic species to improve CO 2 conversion efficiency while preventing acidification of the anodic compartment. Through transport modelling, we identify that an anion-exchange ionomer in the catalyst layer improves local bicarbonate availability and increasing the proton transference number in the bipolar membranes increases CO 2 regeneration and limits K + concentration in the cathode region. Through experiments, we show that a uniform local distribution of bicarbonate ions increases the accessibility of reverted CO 2 to the catalyst surface, improving Faradaic efficiency and limiting current densities by twofold. Using these insights, we demonstrate a fully PGM-free bipolar membrane electrode assembly CO 2 conversion system exhibiting < 1% CO 2 /cation crossover rates and 80–90% CO 2 -to-CO utilization efficiency over 150 h operation at 100 mA cm − 2 without anolyte replenishment.

Liquid-alkaline water electrolyzers (LAWEs) use electricity to drive the conversion of water to H2 and O2 gas. These devices benefit from the use of low-cost nickel electrodes and metal-oxide separators, but suffer from lower current densities and higher cell voltages than proton-exchange-membrane water electrolyzers. Identifying the inefficiencies that result in this poor performance is key to mitigating losses and optimizing LAWEs. Here, we report an experimentally-validated 1-D continuum model of a LAWE that elucidates the gradients within the cell, simulates H2 crossover, and projects the energy improvements made possible by modulating the properties of the electrodes and separator. The model captures the Nernstian polarization losses and the distribution of gas- and liquid-phases within the electrodes, enabling quantification of energy losses associated with kinetic, ohmic, and bubble-induced (mass-transport) resistances. Simulations demonstrate that LAWE can achieve energy intensities of 50 kWh kg-1 of H2 at 1 A cm-2 using improved electrode and separator properties.

Electrochemical CO2 reduction (CO2R) using renewable electricity is a key pathway toward synthesizing fuels and chemicals. In this study, multi-physics modeling is used to interpret experimental data obtained for CO2R to CO using Ag catalysts in a membrane electrode assembly. The one-dimensional model is validated using measured CO2 crossover and product formation rates. The kinetics of CO formation are described by Marcus–Hush–Chidsey kinetics, which enables accurate prediction of the experimental data by accounting for the reorganization of the solvent during CO2R. The results show how the performance is dictated by competing phenomena including ion formation and transport, CO2 solubility, and water management. The model shows that increasing the ion-exchange capacity of the membrane and surface area of the catalyst increases CO formation rates by >100 mA cm–2 without negatively impacting CO2 utilization. Here we provide insights into how to manage the trade-off between productivity and CO2 utilization in CO2 electrolyzers. The design of CO2 electrolyzers is complicated by coupled transport and reaction phenomena. Here the authors develop a continuum model incorporating physical phenomena across multiple scales to predict the activity and selectivity of CO2 electrolysis, along with the loss of CO2 due to crossover in membrane electrode assemblies.

Bipolar membranes (BPMs) enable control of ion concentrations and fluxes in electrochemical cells suitable for a wide range of applications. Here we present the multi-scale physics of BPMs in an electrochemical engineering context and articulate design principles to drive the development of advanced BPMs. The chemistry, structure, and physics of BPMs are illustrated and related to the thermodynamics, transport phenomena, and chemical kinetics that dictate ion and species fluxes and selectivity. These interactions give rise to emergent structure–property–performance relationships that yield design criteria for BPMs that achieve high permselectivity, durability, and voltaic efficiency. The resulting performance trade-offs for BPMs are presented in the context of emerging applications in energy conversion or storage, and environmental remediation. By connecting the fundamental physical phenomena in BPMs to device-level performance and engineering, we aim to facilitate the development of next-generation BPMs for sustainable electrochemical processes. Bipolar ion-exchange membranes are a class of charged polymers that enable precise control of ionic fluxes and local pH, making them potentially valuable for many energy and environmental applications. This Review focuses on the fundamental physics underpinning their operation across multiple scales, from nanomorphology to integration within devices such as in bipolar-membrane electrodialysis (BPM-ED).

Bipolar membranes (BPMs) enable isolated acidic/alkaline regions in electrochemical devices, facilitating optimized catalytic environments for water electrolysis, CO2 reduction, and electrodialysis. For economic feasibility, BPMs must achieve stable, high current density operation with low overpotentials. We report a graphene oxide (GrOx) catalyzed, asymmetric BPM capable of electrodialysis at 1 A cm-2 with overpotentials < 250 mV. Experiments and continuum modeling demonstrate that the low overpotentials for water dissociation are achieved by deprotonation at GrOx catalyst sites located within the high electric field BPM junction region. The asymmetric nature of the BPM allows it to overcome water transport limitations due to its thin anion exchange layer, while maintaining near unity Faradaic efficiency for acid and base generation. Additionally, the asymmetric BPM exhibits voltage stability exceeding 1100 hours at 80 mA cm-2 and 100 hours at 500 mA cm-2 and its freestanding architecture implemented in an electrodialysis cell stack demonstrates its real-world applicability.

Bipolar membranes (BPMs) provide a platform for the interconversion between electric and chemical potential gradients and the precise control over local ion concentrations and fluxes, making BPMs attractive materials for many electrochemical processes. In reverse bias charge carriers must be generated via heterolytic water dissociation (WD, 2H2O → OH- + H3O+), and which must be accomplished at high rates and low overpotentials to realize scalable BPM applications. It is hypothesized that WD is driven by a combination of electric field and catalytic effects within the bipolar junction. However, the extent to which each contributes to observed rates, and the possible interplay between the two, is yet to be resolved. Here, we explore the interfacial physics within the BPM to understand the kinetics and mechanisms of water dissociation on TiO2 and graphene oxide (GO) derivative catalysts. Using a membrane-potential-sensing testbed we isolate the WD polarization signature in a BPM water electrolyzer. We find that neat-GO exhibits an anomalous exponential current response as a function of WD overpotential, contrary to the linear polarization response of TiO2 (and other metal oxides, reported previously). Similarly, the rates were independent of GO loading, contrasting the typical U-shaped loading dependence on WD performance using metal oxide catalysts. We hypothesize the unique behavior of GO can be linked to the double layer profile within the bipolar junction, which can be screened and localized to the catalyst/AEL interface via the acidic carboxylate moieties on the GO surface. We validate this framework by controlling the degree of hydroxyl/carboxylation on the graphene-oxide surface, and thus the electric double layer profile, to control the polarization response. Using temperature-dependent measurements at varying potentials and a simple Arrhenius-type equation we decouple the apparent enthalpic and entropic driving forces for WD within a confined and polarized heterojunction. Broadly, this work advances our understanding of the interplay between catalyst surface chemistry and electric double layer formation under confinement, and how this effect can be leveraged in (electro)chemical transformations. Figure 1. A large electric field within the catalyst layer increases the WD rate within the BPM Figure 1

Carbon dioxide (CO2) must be removed from the atmosphere to mitigate the negative effects of climate change. However, the most scalable methods for removing CO2 from the air require heat from fossil-fuel combustion to produce pure CO2 and continuously regenerate the sorbent. Bipolar-membrane electrodialysis (BPM-ED) is a promising technology that uses renewable electricity to dissociate water into acid and base to regenerate bicarbonate-based CO2 capture solutions, such as those used in chemical loops of direct-air-capture (DAC) processes, and also in direct-ocean capture (DOC) to promote atmospheric CO2 drawdown via decarbonization of the shallow ocean. However, a lack of understanding of the mechanisms of reactive carbon species transport in BPMs has precluded industrial-scale deployment of BPM-ED. In this study, we develop an experimentally-validated 1D model for the electrochemical regeneration of CO2 from bicarbonate-based carbon capture solutions and seawater using BPM-ED. Our experimental and computational results demonstrate that out-of-equilibrium buffer reactions within the BPM drive the formation of CO2 at the BPM/electrolyte interface with energy-intensities of less than 150 kJ mol-1. However, high rates of bubble formation increase the energy intensity of CO2 recovery at current densities >100 mA cm−2. Sensitivity analyses show that optimizing the BPM and bubble removal could enable CO2 recovery from bicarbonate solutions at energy intensities <100 kJ mol−1 and current densities >100 mA cm−2. These results provide design principles for industrial-scale CO2 recovery using BPM-ED.

Continuum modeling elucidates non-equilibrium behavior in bipolar membranes (BPMs) used for carbon capture. The model resolves contributions to applied voltage, identifying CO 2 bubble removal and water dissociation catalysis as the dominant energy losses.

We demonstrate pOH imaging with confocal microscopy to probe the microenvironment of an operating CO 2 reduction gas diffusion electrode. We find that the micrometer-scale morphology plays an important role in defining the CO 2 reduction performance.