Atomically dispersed metal-nitrogen-carbon (M-Nx-C) catalysts offer theoretically maximum metal utilization and high selectivity toward CO (FECO) for electrochemical CO2 reduction (eCO2R), yet sustaining a high number of accessible active sites at industrially relevant current densities (∼500 mA cm−2) remains challenging. Here, we report a surfactant-assisted dual-metal strategy to develop a hierarchically porous Fe/Ni-N-C catalyst for high-rate eCO2R to CO conversion. The coexistence of Fe-Nx and Ni-Nx active sites enables complementary catalytic behavior by balancing the low-overpotential activity of Fe-Nx with the high-overpotential performance of Ni-Nx, while surfactant-derived porosity enhances active-site accessibility and dispersion. Device-level performance was evaluated in a zero-gap membrane electrode assembly. The modified Fe/Ni-N-C catalyst (Fe:Ni∼1:2, total metal loading of 0.82 at%) achieves a partial current density toward CO of 563 mA cm−2 at a high-frequency resistance (HFR)-free cell voltage of 2.84 V under near-neutral conditions. At an industrially relevant total current density of 500 mA cm−2, it maintains FECO> 96% with an energy efficiency of 43% (non-HFR corrected). Post-electrolysis characterization of continuous 100 h and pulsed 200 h operation at 100 mA cm−2 demonstrated structural and electrochemical stability of the modified Fe/Ni-N-C catalyst. These findings establish dual-metal site engineering coupled with hierarchical porosity as a viable materials design strategy for high-rate eCO2R.

Electrode slurry coating is critical to battery manufacturing, with downstream production steps and battery performance dependent on the electrode cast quality. While commercial facilities use roll-to-roll coating to minimize processing times and ensure inter-batch consistency, these techniques are not feasible for lab-scale R&D owing to the high cost and large footprint of the infrastructure. As such, lab-scale electrodes are typically prepared manually with minimal control over quality-affecting parameters (i.e., blade speed and height), which can introduce interelectrode variability. This lack of reproducibility can cause issues with performance validation and repeatability across laboratories when developing new materials. Herein, we apply an automated casting system developed from 3D printer architecture to demonstrate how shear control during lab-scale electrode casting enables consistent replication of quality metrics such as active material loading and capacity. By accurately modulating the blade speed during casting, variance in loading across a 100 cm(2) sheet was greatly reduced. Interelectrode coefficient of variation for loading was minimized to <7% when casting at 5.00 cm s(-1) and 150 mu m, in comparison to >15% when done manually. This work highlights the importance of maintaining control over electrode casting conditions to improve inter-lab comparisons, generate reliable results, and support next-generation battery material development.

To advance sustainable energy technologies like fuel cells, metal-air batteries, and electrosynthesis of H2O2 driven by the oxygen reduction reaction (ORR) - pyrolyzed transition metal-carbon-nitrogen (TM-Nx/C) electrocatalysts derived from zeolitic imidazolate frameworks (ZIFs) are promising alternatives to platinum-group metals. Pyrolysis, an essential step in preparing ZIF-derived TM-Nx/C electrocatalysts, can induce the formation of metal-based nanoparticles, thereby reducing active-site density and catalytic efficiency. Understanding the formation of nanoparticles and mitigating them is therefore critical. Herein, we employ four strategies used during synthesis to minimize the presence of Co nanoparticles in Co-ZIF-derived ORR electrocatalysts: spatial isolation, dimensionality control, thermal exfoliation, and acid-washing. Electrochemical performance of the prepared electrocatalysts was evaluated using a rotating ring-disk electrode in 0.1 M KOH, and the materials were characterized by a variety of techniques to understand their physical and chemical properties. Besides influencing nanoparticle formation and presence, mitigation strategies also impacted catalyst surface areas, concentration of N-doped carbon defects, exposure of active sites, electrochemical surface areas, and electrocatalytic selectivity towards HO2- . Unlike spatial isolation (using dual Co2+/Zn2+ nodes) and dimensionality control (2D vs. 3D ZIFs), acid washing (with nitric acid) and exfoliation (via KCl intercalation pre-pyrolysis) effectively produced Co nanoparticle-free electrocatalysts. Optimal ORR performance metrics were linked with combining multiple mitigation strategies, such as spatial isolation and exfoliation. Correlative physical and electrochemical characterizations illustrated the complex interplay between structure, property, and performance with different nanoparticle mitigation strategies. This work offers insights into deriving sustainable nanoparticle-free ZIF-derived electrocatalysts via pyrolysis, addressing a critical need in ORR-based technologies.

Organic molecules such as 9,10-phenanthrenequinone have shown promise as active materials for cathodes in aqueous rechargeable zinc-ion batteries. However, organic molecules are commonly prone to inactivation during charge and discharge that can result in substantial capacity fade, limiting their operational lifespan. One technique to stabilize quinone active materials is covalent grafting on a conductive carbon substrate via diazonium salt reactions. Although explored for other battery chemistries (e.g., Li-ion), this study applies the chemical grafting technique to stabilize 9,10-phenanthrenequinone on carbon black for rechargeable zinc-ion battery cathodes. In one example, cathodes with 9,10-phenanthrenequinone grafted to carbon black maintained a discharge capacity of 99 mAh g-1 (67 % capacity retention) after 1000 cycles of accelerated testing (200 mA g-1), a 12 % improvement in capacity retention compared to cathodes consisting of 9,10-phenanthrenequinone simply adsorbed on carbon black. Grafting was found to restrict quinone mobility and inactivation, leading to increased battery capacity retention and operational lifespan. Such an increase in capacity retention highlights how grafting can be a useful quinone stabilization tool, which could be applied to other organic cathode designs. This work not only emphasized the impact that different carbon substrates can have on organic cathode behaviour, but also demonstrated how grafting organic materials to a carbon substrate is a simple modification that improves organic cathode performance in zinc-ion batteries.

Rechargeable zinc-ion batteries (ZIBs) are an attractive energy storage system for the growing renewable energy sector but still face technological bottlenecks such as a lack of high-capacity cathode materials with long cycling stability. Organic redox-active molecules, a class of cathode material, offer potential for high discharge capacities. However, they suffer from undesired degradation reactions over repeated charge and discharge cycling causing limited capacity retention, emphasizing there is still a need for structural modifications to enhance material stability. In this work, [N,N '-bis(2-anthraquinone)]-perylene-3,4,9,10-tetracarboxydiimide (PTCDI-DAQ) was synthesized from 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and 2-aminoanthraquinone for use as cathode material in ZIBs. The discharge capacity of PTCDI-DAQ cathodes was found to be 186 mAh/g. At 100 mA/g, PTCDI-DAQ showed a capacity retention of 76.0% by cycle 20, outperforming PTCDA that retained only 33.3%. X-ray diffraction revealed crystal structure alterations of both PTCDA and PTCDI-DAQ starting at the first discharge, which could contribute to the observed capacity degradation. This work proposes an approach towards enhancing the capacity retention of organic cathodes that will accelerate the development and commercialization of ZIBs.

Ammonia (NH3) is a vital fertilizer and industrial chemical predominantly produced via the energy-intensive Haber-Bosch process. The electrochemical reduction of nitrate (NO3 -) to NH3 offers an alternative that can source nitrogen from NO3 - in wastewater or industrial processes. In this work, we evaluate the impact of the local atomic environment of four molecular catalysts supported on carbon nanotubes (CNTs): copper phthalocyanine (CuPc/CNT), copper tetraphenylporphyrin (CuTPP/CNT), iron phthalocyanine (FePc/CNT), and iron tetraphenylporphyrin (FeTPP/CNT). FePc/CNT coated electrodes achieved the highest performance, exhibiting a partial current density of 61.2 mA cm-2 at -0.9 VRHE and a Faradaic efficiency of 98.9% toward NH3 at -0.6 VRHE. Notably, the phthalocyanine catalysts outperformed their porphyrin analogues, underscoring the impact of the second shell coordination environment on the activity and stability of the catalysts. Density functional theory (DFT) calculations revealed that Fe-based catalysts facilitate stronger pi-back bonding to *NO, reducing the thermodynamic barrier for NO reduction, which is typically a rate limiting step in the NO3 - reduction mechanism. In situ X-ray absorption spectroscopy (XAS) coupled with post-mortem ex situ transmission electron microscopy (TEM) and X-ray diffraction (XRD) showed that FePc/CNT retained Fe-N coordination at potentials as negative as -0.8 VRHE, whereas the metal centers of the other catalysts were reduced into metallic clusters at potentials more negative than -0.6 VRHE. We attribute the enhanced stability and selectivity of FePc/CNT to its local coordination environment. By integrating experimental and theoretical insights, this work elucidates the impact of metal identity and the local atomic environment that synergistically governs the electrocatalytic performance and stability.

Currently explored rechargeable aqueous zinc-ion battery (RAZIB) cathode materials, such as α-MnO_2, suffer from severe capacity fade when cycling at rates appropriate for grid-scale operation. Mn dissolution has been previously identified as the cause of α-MnO_2 cathode degradation during RAZIB cycling, with conflicting evidence being found in support of the proposed Jahn-Teller effect-assisted charge disproportionation reaction as the mechanism behind Mn dissolution. In order to unveil the Mn dissolution mechanism in MnO_2 cathode cells under RAZIB operation conditions, the energetic feasibility for Mn vacancy formation was probed in both charged (MnO_2) and discharged (ZnMn_2O_4) phases of α and λ polymorphs of MnO_2 using density functional theory. The formation of a Mn vacancy, and consequently the dissolution of Mn as Mn^2+_(aq), was found to be thermodynamically feasible for the α-ZnMn_2O_4 phase due to the energetically unfavourable Zn bent coordination formed during the Zn^2+ intercalation process, indicating that Mn dissolution is promoted by an unstable Zn coordination environment. The theoretical calculations were then corroborated by operando ^1H nuclear magnetic resonance experiments which captured the Mn dissolution occurring throughout the RAZIB discharge, with subsequent electrochemical deposition of the Mn atoms on the electrode during charge. The combined computational and experimental analysis reveals the critical role of defect energetics and coordination environment in driving active material dissolution, and consequently capacity fade, with the proposed mechanism also relevant for understanding cathode degradation in other intercalating ion battery chemistries.

Achieving both high catalytic activity and long-term electrochemical stability remains a central challenge for acidic oxygen evolution reaction (OER) catalysts. Using benchmark ruthenium oxide (RuO2) as a model system, we employ the Pourbaix decomposition free energy (ΔGpbx) as a quantitative stability descriptor and demonstrate that high-entropy design enables access to RuO2-based oxides with enhanced stability. Guided by this insight, we computationally identify an idealized stoichiometric high-entropy oxide, RuMnFeNiCuO2, with markedly reduced ΔGpbx. Machine-learning-assisted density functional theory calculations reveal that compositional complexity modulates Ru-O bonding characteristics and diversifies the electronic structure of surface Ru sites, enabling roughly two-thirds of them to outperform those on pristine RuO2. Proof-of-concept experiments validate these predictions using the corresponding synthesized RuMnFeNiCuOx catalyst, where x accounts for oxygen nonstoichiometry. This catalyst exhibits an overpotential of 196 mV at 10 mA cm-2 and only 2% activity loss after 1000 accelerated CV cycles, surpassing RuO2 in both activity and durability. This work establishes an entropy-enabled and ΔGpbx-guided design framework for acid-stable and high-performance OER catalysts, providing a generalizable strategy for next-generation energy conversion materials.

The electrochemical reduction of nitrate (NO3-) to ammonia (NH3) offers a sustainable route for nitrogen cycle remediation and decentralized NH3 production. In this work, we systematically investigated the impact of electronic structure and wettability in regulating the catalytic performance of molecular catalysts using functionalized iron phthalocyanines (FePc-R, R = NH2, COOH, CN, and t-Bu) supported on carbon nanotubes. The strongly hydrophilic FePc-NH2/CNT (electron-donating functional group-containing) catalyst achieved a maximum Faradaic efficiency of 94.1% at -0.6 VRHE and a partial current density of 83.9 mA cm-2 toward NH3 at -0.9 VRHE. In contrast, strongly hydrophilic FePc-COOH/CNT and weakly hydrophilic FePc-CN/CNT, containing electron-withdrawing functional groups, delivered a lower performance across all potentials. Density functional theory (DFT) calculations revealed that electron-donating functional groups elevate the Fe-center HOMO level, facilitating hydrogenation of NHx intermediates and enhancing turnover frequency. In situ X-ray absorption spectroscopy (XAS) confirmed that Fe-N4 coordination in FePc-NH2/CNT remains stable across all tested potentials, while electron-withdrawing functional group-containing catalysts (FePc-COOH/CNT and FePc-CN/CNT) exhibited Fe-Fe cluster formation at -0.8 and -0.7 VRHE, respectively. Furthermore, coupled mass transport and reaction modeling indicated that more hydrophilic surfaces reduce the diffusion layer thickness, promoting NO3- accessibility and NH3 formation. Together, these findings decoupled the synergistic role of electronic tuning and wettability control in governing both activity and stability, providing mechanistic design principles for molecular and heterogeneous catalysts in the reduction of electrochemical NO3- to NH3.

The oxygen reduction reaction (ORR) is central to many sustainable energy technologies such as fuel cells, metal-air batteries, and peroxide electrosynthesis, but the scalability of ORR-based technologies requires cost-effective, active, and selective electrocatalysts free from the costly and scarce platinum-group-metals (PGMs). Despite considerable advances, state-of-the-art PGM-free N-doped carbon (N-C) and metal-nitrogen-carbon (M-Nx/C) electrocatalysts face performance bottlenecks. Defect engineering in ceria (CeO2), a promising electrocatalyst modifier, leveraging its Ce3+/Ce4+ redox and oxygen-vacancy (Vo) capacity, offers a promising route to modulate the electronic structure of N-C and M-Nx/C electrocatalysts. However, how Vo in ceria modulate the electronic structure and the 2e-/4e- ORR selectivity of N-C and Co/N-C electrocatalysts remains underexplored. Here, we engineer Vo-rich ceria via plasma and thermal reduction, followed by embedding into zeolitic imidazolate frameworks (Zn-ZIF8 and Co/Zn-ZIF) and pyrolysis (at 900 degrees C) to derive ceria@N-C and ceria@Co/N-C electrocatalysts. The structural and physicochemical properties of the ceria variants, ceria@ZIF precursors, and developed electrocatalyst were investigated. The electrochemical properties and ORR performance were evaluated in alkaline media (0.1 M KOH). Vo-rich ceria samples exhibited enhanced onset and half-wave potentials relative to as-synthesized ceria, while modulating the 2e- and 4e- ORR selectivity differently depending on the host matrix and surrounding type of active site structure(s). In Co-free systems, Ce3+-Vo centers led to mixed 2e-/4e- pathways, while in Co-containing systems, Vo-rich ceria partially suppressed the dominant 4e- ORR of Co nanoparticles. ECSA-normalized activity confirmed that Vo-rich ceria modulates selectivity but dilutes intrinsic site activity, revealing a trade-off between activity and selectivity. This work establishes Vo defect engineering in ceria as a lever in modulating ZIF-derived ORR electrocatalysts as a strategy toward the rational design of application-ready PGM-free electrocatalysts.

The catalytic and self-sanitizing properties of copper (Cu) can be significantly enhanced by inducing nanoporosity into the structure. In this review, we first briefly introduce electrocatalysis and biocidal applications of Cu, with the discussion on electrocatalysis geared toward the electrochemical reduction of carbon dioxide to value-added fuels and chemicals. Second, the underlying mechanisms for the enhancement of the electrocatalytic and biocidal properties by means of morphology manipulation are discussed, followed by a review of chemical and electrochemical techniques used to synthesize nanoporous Cu. Additionally, the parameters that enable fine-tuning of the sizes and structures of the resulting porosity are outlined, including the composition and crystal structure of the precursors, along with electrochemical factors such as electrolyte, applied overpotential, and treatment time. This review elucidates the crucial role that the nanostructure of Cu plays in augmenting the electrocatalytic efficiency and self-sterilizing attributes of Cu. Moreover, it provides insights into and discusses the challenges in designing advanced functional nanomaterials and synthesizing well-controlled morphologies essential for sustainable electrocatalysis and antimicrobial applications in diverse fields.

In situ characterization techniques provide insight into electrocatalyst behavior under reaction conditions. Among these, in situ X-ray absorption spectroscopy (XAS) is particularly powerful for probing oxidation states and the local atomic structures within catalysts during electrochemical reactions. However, X-ray attenuation by catalyst substrates and electrolytes remains a challenge in electrochemical cell design. This work presents laser-engraved graphitized Kapton as a conductive, X-ray transparent substrate for electrocatalysts in in situ XAS studies. A custom three-electrode electrochemical cell incorporating graphitized Kapton as both working and counter electrodes was developed, enabling XAS measurements in fluorescence and transmission modes. Using copper nanoparticles as a model catalyst for electrochemical CO2 reduction (CO2R), electrocatalytic activity and selectivity comparable to a conventional two-compartment system were measured. In situ XAS revealed potential-dependent reduction of copper oxide species to metallic copper under CO2R conditions. The tunable thickness, customizable geometry, and mechanical flexibility of graphitized Kapton enable versatile in situ XAS cell designs, providing a robust platform for mechanistic studies across diverse electrochemical systems.

Electrochemical CO2 reduction (CO2R) offers a promising approach to for decarbonizing chemical manufacturing through production of carbon-neutral fuels. However, insufficient performance and instability of the membrane electrode assembly (MEA) reactors limit the commercial viability, with both metrics directly impacted by the CO2R catalysts. Here we develop atomically dispersed nickel-nitrogen-carbon (NiNC) catalysts through a scalable synthesis approach that enables controlled dispersion of isolated Ni active sites using two different carbon supports. When using carbon nanotubes as a support, the resulting NiNCNT electrode achieves a partial current density towards CO of 558 mA cm-2 with 92% faradaic efficiency towards CO at a cell voltage of 3.2 V and an energy efficiency of 39% at a total current density of 607 mA cm-2. The MEA demonstrated stable operation at 100 mA cm-2 over 210 hours, outperforming previously reported NiNC catalysts. Focused ion beam-scanning electron microscopy (FIB-SEM) tomography reveals the critical role of catalyst support architecture in governing electrode performance. COMSOL Multiphysics simulations using the 3D reconstructed images of the catalyst layers from FIB-SEM tomography demonstrated that the higher CO2R performance of the NiNCNT electrode is due to improved CO2 diffusion and a more uniform current-density distribution compared to the NiNCB electrode prepared with carbon black as the support. These results highlight the key role of catalyst-layer morphology in governing the CO2R performance of the two catalysts, despite their similar Ni and N loadings. The stability and performance of the NiNCNT compared favourably to the state-of-the-art Ag-based catalysts, while bottom-up cost analysis estimated the projected purchase cost of the NiNCNT catalyst to be $589 USD per kg, substantially lower than $1900 USD per kg estimated for Ag-based catalysts, highlighting its potential for scalable and economically viable CO2R electrolyzers.

Rising atmospheric CO2 concentrations threaten global climate stability. Alkali hydroxide scrubbing captures CO2 as carbonate/bicarbonate-rich solutions. (Bi)carbonate-fed electrolyzers directly convert the capture solution into valuable chemicals. This research systematically explores nanostructured copper-based porous electrodes to improve the electrocatalytic conversion of (bi)carbonate to ethylene. We examine polycrystalline copper nanowires grown on copper substrates, with nanowire size, density, and distribution tuned via varied electrochemical oxidation protocols. The best-performing electrodes demonstrated Faradaic efficiencies toward ethylene of ∼37% at a current density of 150 mA cm−2 and a cell voltage of 3.3 V, stable for at least 100 h (i.e., corresponding to ∼13% energy efficiency, nearly double comparable systems). To elucidate the mechanisms behind this performance boost, we employed operando high-speed microscopy and mass transport modeling, which revealed (1) a localized increase in pH within the nanowire array and (2) the promotion of bubble growth/detachment, increasing convective CO2 transport to the electrode surface.

Rechargeable aqueous zinc-ion batteries (RAZIBs) attract major interest for deployment in grid-scale energy storage due to higher safety and lower cost when compared to lithium-ion batteries. However, currently studied cathode materials suffer from capacity fade when cycling at rates appropriate for grid-scale applications (< C/2). To address the present limitation on cathode material availability, more than 2000 previously synthesized oxides, chalcogenides, Prussian blue analogues, and polyanion materials were computationally screened for the discovery of highly stable RAZIB cathode materials. The structural, electrochemical, and chemical properties of the materials were respectively evaluated through an investigation of the available Zn^2+ percolation paths, the stability of the material in aqueous media under RAZIB operation conditions, and the attained transition metal oxidation state during cycling. The transition metal oxidation state and intercalating ion coordination environment were determined to govern the magnitude of the calculated Zn^2+ intercalation potential, with this finding guiding the development of batteries with high operation voltages. 12 materials previously unexplored as cathodes for RAZIBs were identified to have promising operational properties as cathodes, such as high Zn^2+ (de)intercalation potential, electrochemical stability, theoretical gravimetric capacity, and energy density. Finally, α-FePO_4 was experimentally tested as a RAZIB cathode, with a main redox peak observed from cyclic voltammetry matching previous results for amorphous FePO_4 as a cathode for RAZIB. However, the subpar charge storage performance highlights the necessity of further experimental investigations. Overall, the materials identified in this study present a guide for the experimental development of stable next-generation cathode materials for RAZIBs.

Copper, the most efficient catalyst for multicarbon (C2+) product generation in electrochemical CO2 reduction (CO2R), is highly susceptible to restructuring in the presence of halides. Chloride ions enhance the performance of Cu catalysts, although a detailed understanding of the morphological and chemical evolution induced by chloride remains lacking. In this work, in situ scanning transmission soft X-ray microscopy (STXM) was used to identify the morphological and chemical changes occurring in chloride-affected Cu catalysts during catalyst synthesis by electrodeposition through to electrochemical CO2 reduction conditions. The initially electrodeposited tetrahedral particles were mainly cuprous chloride (CuCl). When a CO2 saturated KHCO3 electrolyte was introduced, the particles were converted to particles with a metallic Cu core and a shell consisting of a mixture of CuCl and cuprous oxide (Cu2O) under the application of a small negative current. As increasingly negative potentials were applied under CO2R conditions, both Cu2O and CuCl progressively reduced to metallic Cu. Simultaneously, Cu-based particles on the electrode surface partially dissolved and redeposited at the edge of the electrode, along with agglomeration and reconstruction. Our results indicate that chloride does not enhance CO2R performance by stabilizing Cu+, CuCl, or oxidized species during reaction. Instead, chloride drives rapid dissolution, migration, redeposition, and agglomeration, leading to a reconstructed catalyst with highly active nanostructures characterized by increased surface roughness, abundant grain boundaries, and reduced crystallite size. This work provides in situ visualization of these changes and detailed insight into the role of chloride, including the distribution and impact of chloride on the morphological and chemical changes occurring in Cu catalysts during CO2R.

Layered manganese oxides are considered state-of-the-art cathode materials for aqueous rechargeable zinc-ion batteries (ZIBs) owing to their low cost, natural abundance, and viability for Zn2+ intercalation. However, challenges of limited capacity, rate capability, and durability need to be addressed in order for commercial uptake of ZIBs to become a reality. In this study, we investigate the use of Cu as a redox-active dopant to improve the electrochemical performance of a layered manganese oxide cathode. Through a facile synthesis method, we prepared K0.3Mn0.95Cu0.05O2, which delivered an elevated capacity of >215 mAh g(-1) owing to both the redox activity of Cu at low voltages (<1.0 V vs. Zn/Zn2+) and a reduced charge transfer resistance observed in the Cu doped material. However, the capacity gained from the redox-active Cu displayed partial irreversibility upon repeated cycling, leading to a rapid loss of capacity contributions from Cu after 50 cycles. This work highlights the benefits of Cu doping as a strategy for enhancing the capacity and rate capability of manganese oxide cathodes, while openly discussing its current limitations, including a lack of durability of this enhanced performance owing to the irreversibility of the Cu redox activity within the system.

Catalyst lifetime is a primary technical bottleneck obstructing Cu-based CO2 reduction (CO2R), with restructuring via dissolution-redeposition being a commonly reported reason for selectivity loss. Here we examine how atomistic restructuring manifests at the microlevel of gas diffusion electrode (GDE)-based systems, ultimately compromising long-term CO2R performance. Using a flow-cell CO2R electrolyzer configuration and a copper-coated PTFE GDE, we first show how voltage gradients result in directional in-plane copper migration and porosity changes, causing a decrease in CO and ethylene production due to blocked catalyst pores. By the incorporation of different ionomer and inert carbon overlayers onto copper, we then demonstrate how in-plane degradation is mitigated by modulating the local pH and voltage homogeneity of the electrode, extending ethylene lifetimes by 10-fold. Ultimately, through-plane compaction of copper then becomes the limiting degradation pathway. Combined, these results provide rationale for the paradox of why copper degradation in membrane-electrode assemblies illustrates 100-fold greater stabilities than H-cell and flow-cell architecture.

The development of high-performance metal-nitrogen-carbon (M-N-C) catalysts for electrochemical CO2 reduction (CO2RR) requires precise control over atomic dispersion and coordination environments. Here, we report a mechanochemical ball-milling strategy to synthesize an iron-nitrogen-carbon catalyst (Fe-NC-BM) featuring uniformly dispersed Fe species within a nitrogen-doped carbon matrix. Ball-milling promotes homogeneous Fe site distribution, introduces abundant defects, and modulates the electronic structure. This catalyst achieves a CO Faradaic efficiency exceeding 99% across -0.5 to -1.2 V vs RHE, with a current density of 41.7 mA cm-2 at -1.1 V, more than twice that of the non-ball-milled counterpart (17.0 mA cm-2). Aberration-corrected STEM and XPS analyses confirm that ball-milling enhances Fe dispersion, prevents aggregation during pyrolysis, and fosters Fe-N4 site formation. The mechanical forces also induce an interconnected nanostructure, increasing active site exposure and enabling efficient charge and mass transport. Defect engineering further tunes the electronic structure and lowers the reaction energy barrier, as supported by DFT calculations. This work demonstrates that ball-milling is a solvent-free and effective pretreatment strategy for simultaneously enhancing the density and intrinsic activity of active sites, providing a promising pathway for the rational design and large-scale production of next-generation CO2RR electrocatalysts.