Electrochemical ammonia (NH₃) synthesis from nitrate (NO₃⁻) offers a promising greener alternative to the fossil-fuel-based Haber-Bosch process to support the increasing demand for nitrogen fertilizers while removing environmental waste. Previous studies have mainly focused on designing catalysts to promote the direct conversion (NO₃⁻ → NH₃) while suppressing the two-step pathway (NO₃⁻ → NO₂⁻ → NH₃). We hypothesize that efficient nitrate reduction is possible on simple catalysts by instead promoting the two-step reaction and using chemical reactor principles in a membrane electrode assembly, despite NO₂⁻ intermediates. Here, we use an unmodified copper catalyst and control reactivity through current density, flow rate, and electrolyte recycling. Balancing the electrolyte flow rate with current density results in ideal residence times for NO₂⁻, allowing for 91% FE_NH3 in a 5 cm² electrolyzer with a NO₃⁻ to NH₃ partial current of 1.8 A. This work shows that traditional engineering principles can substantially boost the NO₃ reduction reaction, even for simple catalysts.

The electrochemical CO₂ reduction reaction (CO₂RR) is an attractive method to produce renewable fuel and chemical feedstock using clean energy sources. Formate production represents one of the most economical target products from CO₂RR but is primarily produced using post-transition metal catalysts that require comparatively high overpotentials. Here a composition of bimetallic Cu–Pd is formulated on 2D Ti₃C₂T_x (MXene) nanosheets that are lyophilized into a highly porous 3D aerogel, resulting in formate production much more efficient than post-transition metals. Using a membrane electrode assembly (MEA), formate selectivities >90% are achieved with a current density of 150 mA cm⁻² resulting in the highest ever reported overall energy efficiency of 47% (cell potentials of −2.8 V), over 5 h of operation. A comparable Cu-Pd aerogel achieves near-unity CO production without the MXene templating. This simple strategy represents an important step toward the experimental demonstration of 3D-MXenes-based electrocatalysts for CO₂RR application and opens a new platform for the fabrication of macroscale aerogel MXene-based electrocatalysts.

Electrochemical reduction of CO₂ presents an attractive way to store renewable energy in chemical bonds in a potentially carbon-neutral way. However, the available electrolyzers suffer from intrinsic problems, like flooding and salt accumulation, that must be overcome to industrialize the technology. To mitigate flooding and salt precipitation issues, researchers have used super-hydrophobic electrodes based on either expanded polytetrafluoroethylene (ePTFE) gas-diffusion layers (GDL’s), or carbon-based GDL’s with added PTFE. While the PTFE backbone is highly resistant to flooding, the non-conductive nature of PTFE means that without additional current collection the catalyst layer itself is responsible for electron-dispersion, which penalizes system efficiency and stability. In this work, we present operando results that illustrate that the current distribution and electrical potential distribution is far from a uniform distribution in thin catalyst layers (~50 nm) deposited onto ePTFE GDL’s. We then compare the effects of thicker catalyst layers (~500 nm) and a newly developed non-invasive current collector (NICC). The NICC can maintain more uniform current distributions with 10-fold thinner catalyst layers while improving stability towards ethylene (≥ 30%) by approximately two-fold.

Oxygen-ion conducting perovskite oxides are important functional materials for solid oxide fuel cells and oxygen-permeable membranes operating at high temperatures (>500 °C). Co-doped perovskites have recently shown their potential to boost oxygen-related kinetics, but challenges remain in understanding the underlying mechanisms. This study unveils the local cation arrangement as a new key factor controlling oxygen kinetics in perovskite oxides. By single- and co-doping Nb⁵⁺ and Ta⁵⁺ into SrCoO_3-δ, dominant factors affecting oxygen kinetics, such as lattice geometry, cobalt states, and oxygen vacancies, which are confirmed by neutron and synchrotron X-ray diffraction as well as high-temperature X-ray absorption spectroscopy, are controlled. The combined experimental and theoretical study unveils that co-doping likely leads to higher cation dispersion at the B-site compared to single-doping. Consequently, a high-entropy configuration enhances oxygen ion migration in the lattice, translating to improved oxygen reduction activity.

The highly efficient and stable electrolysis needs the rational control of the catalytically active interface during the reactions. Here we report a new operando surface restructuring pathway activated by pairing catalyst and electrolyte ions. Using SrCoO_3-δ-based perovskites as model catalysts, we unveil the critical role of matching the catalyst properties with the electrolyte conditions in modulating catalyst ion leaching and steering surface restructuring processes toward efficient oxygen evolution reaction catalysis in both pH-neutral and alkaline electrolytes. Our results regarding multiple perovskites show that the catalyst ion leaching is controlled by catalyst ion solubility and anions of the electrolyte. Only when the electrolyte cations are smaller than catalyst's leaching cations, the formation of an outer amorphous shell can be triggered via backfilling electrolyte cations into the cationic vacancy at the catalyst surface under electrochemical polarization. Consequently, the current density of reconstructed SrCoO_3-δ is increased by 21 folds compared to the pristine SrCoO_3-δ at 1.75 V vs reversible hydrogen electrode and outperforms the benchmark IrO₂ by 2.1 folds and most state-of-the-art electrocatalysts in the pH-neutral electrolyte. Our work could be a starting point to rationally control the electrocatalyst surface restructuring via matching the compositional chemistry of the catalyst with the electrolyte properties.

To explore the effects of solvent-ionomer interactions in catalyst inks on the structure and performance of Cu catalyst layers (CLs) for CO₂ electrolysis, we used a “like for like” rationale to select acetone and methanol as dispersion solvents with a distinct affinity for the ionomer backbone or sulfonated ionic heads, respectively, of the perfluorinated sulfonic acid (PFSA) ionomer Aquivion. First, we characterized the morphology and wettability of Aquivion films drop-cast from acetone- and methanol-based inks on flat Cu foils and glassy carbons. On a flat surface, the ionomer films cast from the Aquivion and acetone mixture were more continuous and hydrophobic than films cast from methanol-based inks. Our study’s second stage compared the performance of Cu nanoparticle CLs prepared with acetone and methanol on gas diffusion electrodes (GDEs) in a flow cell electrolyzer. The effects of the ionomer-solvent interaction led to a more uniform and flooding-tolerant GDE when acetone was the dispersion solvent (acetone-CL) than when we used methanol (methanol-CL). As a result, acetone-CL yielded a higher selectivity for CO₂ electrolysis to C₂₊ products at high current density, up to 25% greater than methanol-CL at 500 mA cm^-2. Ethylene was the primary product for both CLs, with a Faradaic efficiency for ethylene of 47.4 ± 4.0% on the acetone-CL and that of 37.6 ± 5.5% on the methanol-CL at a current density of 300 mA cm^-2. We attribute the enhanced C₂₊ selectivity of the acetone-CL to this electrode’s better resistance to electrolyte flooding, with zero seepage observed at tested current densities. Our findings reveal the critical role of solvent-ionomer interaction in determining the film structure and hydrophobicity, providing new insights into the CL design for enhanced multicarbon production in high current densities in CO₂ electrolysis processes.

The electrochemical reduction of carbon dioxide (CO₂) to value-added chemicals is a promising strategy to mitigate climate change. Metalloporphyrins have been used as a promising class of stable and tunable catalysts for the electrochemical reduction reaction of CO₂ (CO₂RR) but have been primarily restricted to single-carbon reduction products. Here, we utilize functionalized earth-abundant manganese tetraphenylporphyrin-based (Mn-TPP) molecular electrocatalysts that have been immobilized via electrografting onto a glassy carbon electrode (GCE) to convert CO₂ with overall 94 % Faradaic efficiencies, with 62 % being converted to acetate. Tuning of Mn-TPP with electron-withdrawing sulfonate groups (Mn-TPPS) introduced mechanistic changes arising from the electrostatic interaction between the sulfonate groups and water molecules, resulting in better surface coverage, which facilitated higher conversion rates than the non-functionalized Mn-TPP. For Mn-TPP only carbon monoxide and formate were detected as CO₂ reduction products. Density-functional theory (DFT) calculations confirm that the additional sulfonate groups could alter the C−C coupling pathway from *CO→*COH→*COH-CO to *CO→*CO-CO→*COH-CO, reducing the free energy barrier of C−C coupling in the case of Mn-TPPS. This opens a new approach to designing metalloporphyrin catalysts for two carbon products in CO₂RR.

A novel magnetic 2D/2D heterogeneous structure MXene@NiFe-LDH@Fe₃O₄ was prepared for immobilization of laccase. In this work, two-dimensional MXene nanosheets with abundant surface functional groups were heterogeneously assembled with layered double hydroxide (LDH) by in situ co-precipitation method, and magnetic nanoparticle Fe₃O₄ with excellent biocompatibility and rapid separation of materials and substrates was introduced subsequently, and then silane coupling agent was coated on the surface of MXene@NiFe-LDH@Fe₃O₄. The functionalized MXene@NiFe-LDH@Fe₃O₄ was employed as a carrier to immobilize laccase from Trametes-Versicolor. The enzyme loading of the nanocomposite material is as high as 167.9 mg/g. Compared with free enzymes, the immobilized laccase showed a notable improvement in stability in a wider range of pHs (2.0–8.0), temperatures (25–60 °C), and organic solvent concentration (1–5 M). The reusability study suggested that after 7 cycles of repeated catalysis, the degradation efficiency could reach 55.5% for 2,4-dichlorophenol, 92.1% for bisphenol A and70.9% for pyrocatechol. The results provide a new carrier preparation strategy for the efficient immobilization of laccase.

Electrochemical conversion of gaseous CO₂ to value-added products and fuels is a promising approach to achieve net-zero CO₂ emission energy systems. Significant efforts have been achieved in the design and synthesis of highly active and selective electrocatalysts for this reaction and their reaction mechanism. To perform an efficient conversion and desired product selectivity in practical applications, we need an active, cost-effective, stable, and scalable electrolyzer design. Membrane-electrode assemblies (MEAs) can be an efficient solution to address the key challenges in the aqueous gas diffusion electrodes (GDE), e.g., ohmic resistances and complex reactor design. This review presents a critical overview of recent advances in experimental design and simulation of MEAs for CO₂ reduction reaction, including the shortcomings and remedial strategies. In the last section, the remaining challenges and future research opportunities are suggested to support the advancement of CO₂ electrochemical technologies.

The electrochemical reduction of CO2 (CO2RR) on silver catalysts has been demonstrated under elevated current density, longer reaction times, and intermittent operation. Maintaining performance requires that CO2 can access the entire geometric catalyst area, thus maximizing catalyst utilization. Here we probe the time-dependent factors impacting geometric catalyst utilization for CO2RR in a zero-gap membrane electrode assembly. We use three flow fields (serpentine, parallel, and interdigitated) as tools to disambiguate cell behavior. Cathode pressure drop is found to play the most critical role in maintaining catalyst utilization at all time scales by encouraging in-plane CO2 transport throughout the gas-diffusion layer (GDL) and around salt and water blockages. The serpentine flow channel with the highest pressure drop is then the most failure-resistant, achieving a CO partial current density of 205 mA/cm2 at 2.76 V. These findings are confirmed through selectivity measurements over time, double-layer capacitance measurements to estimate GDL flooding, and transport modeling of the spatial CO2 concentration.

Carbon dioxide (CO₂) electrolysis is a promising route to utilise captured CO₂ as a building block to produce valuable feedstocks and fuels such as carbon monoxide and ethylene. Very recently, CO₂ electrolysis has been proposed as an alternative process to replace the amine recovery unit of the commercially available amine-based CO₂ capture process. This process would replace the most energy-intensive unit operation in amine scrubbing while providing a route for CO₂ conversion. The key enabler for such process integration is to develop an efficient integrated electrolyser that can convert CO₂ and recover the amine simultaneously. Herein, this review provides an overview of the fundamentals and recent progress in advancing integrated CO₂ conversion in amine-based capture media. This review first discusses the mechanisms for both CO₂ absorption in the capture medium and electrochemical conversion of the absorbed CO₂. We then summarise recent advances in improving the efficiency of integrated electrolysis via innovating electrodes, tailoring the local reaction environment, optimising operation conditions (e.g., temperatures and pressures), and modifying cell configurations. This review is concluded with future research directions for understanding and developing integrated CO₂ electrolysers.

Regulating the rational wettability on gas-diffusion electrodes (GDEs) plays a pivotal role to improve the efficiency of CO₂RR via fine-tuning the reaction zone and boosting the formation of triple-phase interfaces. Herein, we present a wettability regulation strategy that modulates the triple-phase reaction zone in the catalyst layer of GDEs. This strategy was employed on a flow-through hollow fiber GDE coated with a Bi-embedded catalyst layer. Compared to other ex-situ methods (e.g., adding wetting agents) affecting the bulk of electrocatalysts or catalyst layer, we create distinctive hydrophilic-hydrophobic regions within the catalyst layer. Catalyst layer with hydrophilic-hydrophobic regions outperforms the fully hydrophilic one by facilitating the species transport, boosting triple-phase interface formation, and maximizing the active sites. This regulation strategy showed stable wettability during CO₂RR cathodic conditions, evidenced by the direct measurement of penetration depth. The electrode with the regulated wettability exhibited over 80% catalyst utilization and 4 times higher formate partial current density (~150 mA cm⁻² with FE_formate> 90%) compared to the untreated electrode, outperforming other GDEs employed for CO₂RR to formate in the same concentrations of bicarbonate. The finding of this versatile microenvironment regulation strategy can be extended to GDEs used for other gas-phase reactions.

Electrochemical carbon dioxide (CO₂) reduction (ECR) is a promising technology to produce valuable fuels and feedstocks from CO₂. Despite large efforts to develop ECR catalysts, the investigation of the catalytic performance and electrochemical behavior of complex metal oxides, especially perovskite oxides, is rarely reported. Here, the inorganic perovskite oxide Ag-doped (La_0.8Sr_0.2)_0.95Ag_0.05MnO_3–δ (LSA0.05M) is reported as an efficient electrocatalyst for ECR to CO for the first time, which exhibits a Faradaic efficiency (FE) of 84.3%, a remarkable mass activity of 75 A g⁻¹ (normalized to the mass of Ag), and stability of 130 h at a moderate overpotential of 0.79 V. The LSA0.05M catalyst experiences structure reconstruction during ECR, creating the in operando-formed interface between the perovskite and the evolved Ag phase. The evolved Ag is uniformly distributed with a small particle size on the perovskite surface. Theoretical calculations indicate the reconstruction of LSA0.05M during ECR and reveal that the perovskite–Ag interface provides adsorption sites for CO₂ and accelerates the desorption of the *CO intermediate to enhance ECR. This study presents a novel high-performance perovskite catalyst for ECR and may inspire the future design of electrocatalysts via the in operando formation of metal–metal oxide interfaces.

The electrochemical reduction of carbon dioxide (CO₂) to value-added materials has received considerable attention. Both bulk transition-metal catalysts and molecular catalysts affixed to conductive noncatalytic solid supports represent a promising approach toward the electroreduction of CO₂. Here, we report a combined silver (Ag) and pyridine catalyst through a one-pot and irreversible electrografting process, which demonstrates the enhanced CO₂conversion versus individual counterparts. We find that by tailoring the pyridine carbon chain length, a 200 mV shift in the onset potential is obtainable compared to the bare silver electrode. A 10-fold activity enhancement at -0.7 V vs reversible hydrogen electrode (RHE) is then observed with demonstratable higher partial current densities for CO, indicating that a cocatalytic effect is attainable through the integration of the two different catalytic structures. We extended the performance to a flow cell operating at 150 mA/cm², demonstrating the approach's potential for substantial adaptation with various transition metals as supports and electrografted molecular cocatalysts.

We report a new strategy to improve the reactivity and durability of a membrane electrode assembly (MEA)-type electrolyzer for CO2 electrolysis to CO by modifying the silver catalyst layer with urea. Our experimental and theoretical results show that mixing urea with the silver catalyst can promote electrochemical CO2 reduction (CO2R), relieve limitations of alkali cation transport from the anolyte, and mitigate salt precipitation in the gas diffusion electrode in long-term stability tests. In a 10 mM KHCO3 anolyte, the urea-modified Ag catalyst achieved CO selectivity 1.3 times better with energy efficiency 2.8-fold better than an untreated Ag catalyst, and operated stably at 100 mA cm-2 with a faradaic efficiency for CO above 85% for 200 h. Our work provides an alternative approach to fabricating catalyst interfaces in MEAs by modifying the catalyst structure and the local reaction environment for critical electrochemical applications such as CO2 electrolysis and fuel cells.

Integrating carbon dioxide (CO2) electrolysis with CO2 capture provides exciting new opportunities for energy reductions by simultaneously removing the energy-demanding regeneration step in CO2 capture and avoiding critical issues faced by CO2 gas-fed electrolysers. However, understanding the potential energy advantages of an integrated process is not straightforward due to the interconnected processes which require knowledge of both capture and electrochemical conversion processes. Here, we identify the upper limits of the integrated process from an energy perspective by comparing the working principles and performance of integrated and sequential approaches. Our high-level energy analyses unveil that an integrated electrolyser must show similar performance to the gas-fed electrolyser to ensure an energy benefit of up to 44% versus the sequential route. However, such energy benefits diminish if future gas-fed electrolysers resolve the CO2 utilisation issue and if an integrated electrolyser shows lower conversion efficiencies than the gas-fed system.

Achieving operational stability at high current densities remains a challenge in CO2 electrolyzers due to flooding of the gas diffusion layer (GDL) that supports the electrocatalyst. We mitigated electrode flooding at high current densities using a vacuum-assisted infiltration method to embed 200-400 nm-sized polytetrafluoroethylene (PTFE) particles at the interface of the microporous layer (MPL) and carbon cloth in a commercial GDL. In CO2 electrolysis to CO over a silver nanoparticle catalyst on the GDL, the PTFE-embedded GDL not only just exhibited less than 10% of the electrolyte seepage rates observed in untreated GDLs at a current density of 300 mA·cm-2 but also expanded the electrochemical active area across the testing conditions. The PTFE-embedded GDL also maintained a Faradaic efficiency for CO2 electrolysis to CO above 80% for more than 100 h at 100 mA·cm-2, which was a 50-fold improvement in the stable operation time of the electrolyzer.

Understanding the relationship between gas diffusion electrode (GDE) structures and the performance of electrochemical CO₂ reduction reaction (CO₂RR) is crucial to developing industrial-scale technologies to convert CO₂ to valuable products. We studied how the microporous layer (MPL) on GDE's coated with silver nanoparticle catalysts affects the electrochemical CO₂ conversion to CO in a flow cell electrolyser. We demonstrate a convenient method to measure the rate of catholyte seepage through a GDE during CO₂RR experiments and used this method to show how the MPL thickness affects flooding of the GDE. We found the GDE with the thickest MPL (39BB) had the best selectivity for CO and stability at current densities above 100 mA cm⁻² as the thick MPL minimized flooding. However, at low current densities the 39BB electrode achieved a lower CO selectivity than the GDE with thinner MPL. These results suggest opportunities to improve CO₂ electrolyser performances at high current by optimisation of the MPL structure and wettability.