Atomically Dispersed Manganese on Carbon Substrate for Aqueous and Aprotic CO2 Electrochemical Reduction

Engineering the regulation strategy of active sites to explore the intrinsic mechanism over single‑atom catalysts in electrocatalysis

The development of efficient and sustainable energy sources is a crucial strategy for addressing energy and environmental crises, with a particular focus on high-performance catalysts. Single-atom catalysts (SACs) have attracted significant attention because of their exceptionally high atom utilization efficiency and outstanding selectivity, offering broad application prospects in energy development and chemical production. This review systematically summarizes the latest research progress on SACs in five key electrochemical reactions: hydrogen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, and oxygen evolution reaction. Initially, a brief overview of the current understanding of electrocatalytic active sites in SACs is provided. Subsequently, the electrocatalytic mechanisms of these reactions are discussed. Emphasis is placed on various modification strategies for SAC surface-active sites, including coordination environment regulation, electronic structure modulation, support structure regulation, the introduction of structural defects, and multifunctional site design, all aimed at enhancing electrocatalytic performance. This review comprehensively examines SAC deactivation and poisoning mechanisms, highlighting the importance of stability enhancement for practical applications. It also explores the integration of density functional theory calculations and machine learning to elucidate the fundamental principles of catalyst design and performance optimization. Furthermore, various synthesis strategies for industrial-scale production are summarized, providing insights into commercialization. Finally, perspectives on future research directions for SACs are highlighted, including synthesis strategies, deeper insights into active sites, the application of artificial intelligence tools, and standardized testing and performance requirements.

High-Performance Aprotic Li-CO2 Battery Enabled by the Ru Heterophase Catalyst

Aprotic Li-CO2 batteries (LCBs) hold promise for mitigating the greenhouse effect while generating electric power, yet their development remains nascent due to the sluggish CO2 activation and irreversible discharge product formation, requiring efficient catalysts to address these challenges. Herein, we developed ∼5.5 nm fcc + hcp Ru heterophase nanoparticles on a Ketjen black (KB) matrix (Rufcc+hcp/KB) as a dual-functional catalyst for LCBs. X-ray absorption spectroscopy revealed charge redistribution in the fcc + hcp heterophase and under-coordinated Ru sites, which serve as abundant active sites to boost catalytic activity. Theoretical calculations evidenced that the heterophase interface lowers the free energy barriers of the desorption of the *Li2CO3 step (*Li2CO3 → Li2CO3) and the decomposition of the *Li2C2O4 step (*Li2C2O4 → *LiC2O4 + Li), facilitating both the nucleation and decomposition of Li2CO3. Thus, the Rufcc+hcp/KB catalyst exhibited a low overpotential of 0.73 V and long-term cycling stability exceeding 2260 h (at 100 mA g-1 with a capacity of 1000 mA h g-1), outperforming Rufcc/KB (1.14 V, 1260 h), Ruhcp/KB (0.90 V, 1480 h), and previously reported Ru-based catalysts. Our findings highlight crystalline phase engineering as an effective strategy to enhance catalytic performance in LCBs.

Continuous coordination modulation with different heteroatoms unveils favorable single-atom Ni sites for near-unity CO selectivity in CO2 electroreduction

Coordination modulation is a key strategy for enhancing the catalytic activity of single-atom catalysts (SACs) in CO2 electroreduction. However, achieving such modulation within the same framework by incorporating an array of heteroatoms with differing electronic properties remains unexplored, despite its potential for optimizing active sites. Here, we investigate unprecedentedly three Ni-based SACs (N3Ni-C, N3Ni-N, and N3Ni-O), where varying coordinating atoms (C, N, and O) modulate continuously the electronic structure to explore their effects on CO2 electroreduction. Compared to the N3Ni-N catalyst with classic Ni-N4 coordination, N3Ni-C demonstrates significantly enhanced CO2 conversion, achieving remarkably a near-unity Faradaic efficiency for CO (99.3%) at -0.7 VRHE in the H-cell and a CO partial current density of 396.8 mA cm-2 at -1.15 VRHE in the flow cell, whereas N3Ni-O exhibits inferior performance. Operando and computational investigations reveal that both C- and O-coordination enhance CO2 hydrogenation by elevating the Ni d-band center, thereby strengthening *COOH intermediate adsorption. However, the concurrent promotion of the hydrogen evolution reaction competes with CO2 reduction, ultimately leading to opposite effects on performance. This work provides atomic-level insights into CO2 electroreduction mechanisms and offers compelling strategies for improving SAC performance via coordination modulation with heteroatoms.

A Lithium Dendrite Inhibitor in Graphite Anodes Enabling Fast-Charging and Low-Temperature Lithium-Ion Pouch Cells

Under harsh conditions, such as high-rate and low-temperature charging, part of Li ions cannot intercalate into the graphite (Gr) particles and will form dendrite-like Li plating, causing capacity fading and serious safety hazards in commercial lithium-ion batteries (LIBs). Herein, instead of eliminating the Li plating, a Li plating regulation strategy that transforms dead Li plating into reversible active Li plating is proposed by using a lithium dendrite inhibitor to realize safe and long-lifespan LIBs. Remarkably, only 1 wt.% single-atom manganese (SAMn) in the Gr anode (Gr-SAMn) is sufficient to achieve a significant improvement, thus both the volumetric and mass-energy density remain roughly unaffected. The amount of dead Li on the Gr anode can be reduced by 90%, thereby enabling much-improved pouch cell performance at high rates and low temperatures. The capacity retention of the Gr-SAMn||NCM811 pouch cell is 86.2% (23.0% higher than that of the pristine Gr||NCM811 pouch) for 1500 cycles at 2 C, and the cell can even be cycled at 5C charge. Even cycling at -20 °C, the average coulombic efficiency (CE) can be improved from 97.95% to 99.94% by using SAMn additive. Hence, this promising strategy provides a novel alternative to solve the Li plating issue.

Boosting Li-CO2 Battery Performance via High-Entropy Alloy Catalysts: Insights into Configurational Entropy Effect

Li-CO2 batteries have attracted considerable attention for their ability to combine CO2 fixation and conversion with high-density energy storage. However, sluggish kinetics of CO2 reduction and evolution reactions at cathodes lead to large overpotentials and poor cyclic stability. To address this issue, it is critical to develop advanced cathode catalysts. High-entropy alloys (HEAs), a new class of catalysts, have exhibited exceptional catalytic activities in various electrochemical reactions. Nevertheless, the intrinsic relationship between mix configurational entropy (▵Smix) and catalytic properties of HEAs remains unclear. Herein, we prepared a series of quinary FeCoNiCuRu alloys with different ▵Smix values supported on carbon nanofibers as cathode catalysts in Li-CO2 batteries. Experimental and computational results reveal a positive correlation between ▵Smix and catalytic activity, attributed to charge redistribution among elements with different electronegativities. The Li-CO2 battery using the alloy catalyst with the maximum ▵Smix value delivers the largest capacity of 6160 mAh g-1, the lowest charge potential plateau below 4.0 V, and remarkable cycling stability (550 cycles/5500 h), surpassing most reported Ru-based catalysts. Furthermore, fabrication of pouch cells with low noble metal loading demonstrates the practical potential of HEAs for Li-CO2 batteries. This work provides insights into high-entropy engineering for advanced electrocatalysts in Li-CO2 batteries.

A Single-Atom Mn/MoO3- x Nanoagonist for Cascade cGAS/STING Activation in Tumor-Specific Catalytic Metalloimmunotherapy

The cyclic GMP-AMP synthase (cGAS)/stimulator of interferon genes (STING) pathway plays a crucial role in initiating anti-tumor immunity. Despite the development of various STING agonists, their effectiveness is often limited by suboptimal activation efficiency and poor sustainability. To address this, a Mn/MoO3- x nanoagonist featuring Mn single-atom sites is presented, designed for cascade cGAS/STING activation in tumor-specific catalytic metalloimmunotherapy. The single-atom nanoagonist (SANA) is meticulously crafted by doping Mn atoms into defective molybdenum oxide (MoO3- x), enabling robust peroxidase-mimicking catalysis and inducing severe double-stranded DNA (dsDNA) damage in tumors. Of note, Mn2+ and MoO4 2- can be responsively released from Mn/MoO3- x SANA and enhance the sensitivity of cGAS to dsDNA. Importantly, MoO4 2- with a relatively slow-release profile and facile cellular accumulation compensates for Mn2+ that has poor cellular accumulation due to continuous efflux, thus continuatively triggering the secretion of type I interferon for beyond 72 h. Remarkably, Mn/MoO3- x SANA significantly inhibits tumor growth and metastasis without supplementary STING agonists or external stimulation. This study offers a promising cascade cGAS/STING activation approach to enhance the efficacy and sustainability of catalytic metalloimmunotherapy.

Planar chlorination engineering induced symmetry-broken single-atom site catalyst for enhanced CO2 electroreduction

Breaking the geometric symmetry of traditional metal-N4 sites and further boosting catalytic activity are significant but challenging. Herein, planar chlorination engineering is proposed for successfully converting the traditional Zn-N4 site with low activity and selectivity for CO2 reduction reaction (CO2RR) into highly active Zn-N3 site with broken symmetry. The optimal catalyst Zn-SA/CNCl-1000 displays a highest faradaic efficiency for CO (FECO) around 97 ± 3% and good stability during 50 h test at high current density of 200 mA/cm2 in zero-gap membrane electrode assembly (MEA) electrolyzer, with promising application in industrial catalysis. At -0.93 V vs. RHE, the partial current density of CO (JCO) and the turnover frequency (TOF) value catalyzed by Zn-SA/CNCl-1000 are 271.7 ± 1.4 mA/cm2 and 29325 ± 151 h-1, as high as 29 times and 83 times those of Zn-SA/CN-1000 without planar chlorination engineering. The in-situ extended X-ray absorption fine structure (EXAFS) measurements and density functional theory (DFT) calculation reveal the adjacent C-Cl bond induces the self-reconstruction of Zn-N4 site into the highly active Zn-N3 sites with broken symmetry, strengthening the adsorption of *COOH intermediate, and thus remarkably improving CO2RR activity.

Zn and Cl Coregulated MXene Catalyst Enhances Li-CO2 Battery Reversibility

MXenes are promising cathodes for Li-CO2 batteries owing to their high electrical conductivity and efficient CO2 activation function. However, the effects of adsorption and electronic structures of MXene on the full life cycle of Li-CO2 batteries have been rarely investigated. Here, we employ a coregulation approach to enhance the adsorption-decomposition of lithium carbonate (Li2CO3) by introducing Zn and Cl surface groups onto the Ti3C2 MXene (Zn-Ti3C2Cl2) catalyst. The incorporation of Cl surface groups enhances Li2CO3 adsorption on the MXene catalyst surface, resulting in the formation of small-sized and uniform Li2CO3. Additionally, the introduction of Zn shifts the d-band centers of titanium and promotes CO2 evolution reaction (CO2ER) activity, thereby facilitating the decomposition of discharge products. As a result, the Li-CO2 battery based on the Zn-Ti3C2Cl2 catalyst exhibits an ultralow overpotential (0.72 V) at 200 mA g-1 and stable cycling for up to 1500 h. This work validates the efficacy of promoting reversibility in Li-CO2 batteries by adjusting the adsorption-decomposition process.

Cation migration in layered oxide cathodes for sodium-ion batteries: fundamental failure mechanisms and practical modulation strategies

Sodium-ion batteries (SIBs) are regarded as competitive candidates for the next generation of electrochemical energy storage (EES) systems due to their low cost and abundant sodium resources. Layered oxide cathodes have attracted much interest owing to their simple preparation process, high specific capacity and environmental friendliness. However, undesired cation migration during electrochemical reactions can lead to irreversible phase transitions and structural degradation of layered oxide cathode materials, resulting in a sharp decrease in specific capacity and energy density. Therefore, in order to find effective strategies to suppress cation migration, the fundamental failure mechanism of layered oxides and the practical approaches to solve this key scientific issue are thoroughly investigated, and herein the history and current status of developments in this field are also reviewed. Elemental doping and structural design can directionally modify the electronic structure, energy band structure and electronic density of states in layered oxides and enhance cation migration barriers, which benefits the improvement of electrochemical performance and structural stability during the whole sodiation/desodiation process. The summary and prospects of inhibiting cation migration in layered oxides provide insights into the development of advanced cathode materials with high energy density and excellent structural stability for the commercialization of SIBs.

Microenvironment Engineering of Heterogeneous Catalysts for Liquid-Phase Environmental Catalysis

Environmental catalysis has emerged as a scientific frontier in mitigating water pollution and advancing circular chemistry and reaction microenvironment significantly influences the catalytic performance and efficiency. This review delves into microenvironment engineering within liquid-phase environmental catalysis, categorizing microenvironments into four scales: atom/molecule-level modulation, nano/microscale-confined structures, interface and surface regulation, and external field effects. Each category is analyzed for its unique characteristics and merits, emphasizing its potential to significantly enhance catalytic efficiency and selectivity. Following this overview, we introduced recent advancements in advanced material and system design to promote liquid-phase environmental catalysis (e.g., water purification, transformation to value-added products, and green synthesis), leveraging state-of-the-art microenvironment engineering technologies. These discussions showcase microenvironment engineering was applied in different reactions to fine-tune catalytic regimes and improve the efficiency from both thermodynamics and kinetics perspectives. Lastly, we discussed the challenges and future directions in microenvironment engineering. This review underscores the potential of microenvironment engineering in intelligent materials and system design to drive the development of more effective and sustainable catalytic solutions to environmental decontamination.

Creating CoRu Dual Active Sites Codecorated Stable Porous Ceria Support for Enhanced Li-CO2 Batteries Cathodes

Lithium-carbon dioxide (Li-CO2) battery represents a high-energy density energy storage with excellent real-time CO2 enrichment and conversion, but its practical utilization is hampered by the development of an excellent catalytic cathode. Here, the synergistic catalytic strategy of designing CoRu bimetallic active sites achieves the electrocatalytic conversion of CO2 and the efficient decomposition of the discharge products, which in turn realizes the smooth operation of the Li-CO2 battery. Moreover, obtained support based on metal-organic frameworks precursors facilitates the convenient diffusion and adsorption of CO2, resulting in higher reaction concentration and lower mass transfer resistance. Meanwhile, the optimization of the interfacial electronic structure and the effective transfer of electrons are achieved by virtue of the strong interaction of CoRu at the support interface. As a result, the Li-CO2 cell assembled based on bimetallic CoRu active sites achieved a discharge capacity of 19,111 mA h g-1 and a steady-state discharge voltage of 2.58 V as well as a cycle life of >175 cycles at a rate of 100 mA g-1. Further experiments combined with density-functional theory calculations achieve a deeply view of the connection between cathode and electrochemical performance and pave a way for the subsequent development of advanced Li-CO2 catalytic cathodes.

Materials Containing Single-, Di-, Tri-, and Multi-Metal Atoms Bonded to C, N, S, P, B, and O Species as Advanced Catalysts for Energy, Sensor, and Biomedical Applications

Modifying the coordination or local environments of single-, di-, tri-, and multi-metal atom (SMA/DMA/TMA/MMA)-based materials is one of the best strategies for increasing the catalytic activities, selectivity, and long-term durability of these materials. Advanced sheet materials supported by metal atom-based materials have become a critical topic in the fields of renewable energy conversion systems, storage devices, sensors, and biomedicine owing to the maximum atom utilization efficiency, precisely located metal centers, specific electron configurations, unique reactivity, and precise chemical tunability. Several sheet materials offer excellent support for metal atom-based materials and are attractive for applications in energy, sensors, and medical research, such as in oxygen reduction, oxygen production, hydrogen generation, fuel production, selective chemical detection, and enzymatic reactions. The strong metal-metal and metal-carbon with metal-heteroatom (i.e., N, S, P, B, and O) bonds stabilize and optimize the electronic structures of the metal atoms due to strong interfacial interactions, yielding excellent catalytic activities. These materials provide excellent models for understanding the fundamental problems with multistep chemical reactions. This review summarizes the substrate structure-activity relationship of metal atom-based materials with different active sites based on experimental and theoretical data. Additionally, the new synthesis procedures, physicochemical characterizations, and energy and biomedical applications are discussed. Finally, the remaining challenges in developing efficient SMA/DMA/TMA/MMA-based materials are presented.

Graphite conjugated nickel phthalocyanine for efficient CO2 electroreduction and Zn-CO2 batteries

The linking chemistry between molecular catalysts and substrates is a crucial challenge for enhancing electrocatalytic performance. Herein, we elucidate the influence of various immobilization methods of amino-substituted Ni phthalocyanine catalysts on their electrocatalytic CO2 reduction reaction (eCO2RR) activity. A graphite-conjugated Ni phthalocyanine, Ni(NH2)8Pc-GC, demonstrates remarkable electrocatalytic performance both in H-type and flow cells. In situ infrared spectroscopy and theoretical calculations reveal that the graphite conjugation, through strong electronic coupling, increases the electron density of the active site, reduces the adsorption energy barrier of *COOH, and enhances the catalytic performance. As the cathode catalyst, Ni(NH2)8Pc-GC also displays remarkable charge-discharge cycle stability of over 50 hours in a Zn-CO2 battery. These findings underscore the significance of immobilization methods and highlight the potential for further advancements in eCO2RR.

Universal Formation of Single Atoms from Molten Salt for Facilitating Selective CO2 Reduction

Clarifying the formation mechanism of single-atom sites guides the design of emerging single-atom catalysts (SACs) and facilitates the identification of the active sites at atomic scale. Herein, a molten-salt atomization strategy is developed for synthesizing zinc (Zn) SACs with temperature universality from 400 to 1000/1100 °C and an evolved coordination from Zn-N2Cl2 to Zn-N4. The electrochemical tests and in situ attenuated total reflectance-surface-enhanced infrared absorption spectroscopy confirm that the Zn-N4 atomic sites are active for electrochemical carbon dioxide (CO2) conversion to carbon monoxide (CO). In a strongly acidic medium (0.2 m K2SO4, pH = 1), the Zn SAC formed at 1000 °C (Zn1NC) containing Zn-N4 sites enables highly selective CO2 electroreduction to CO, with nearly 100% selectivity toward CO product in a wide current density range of 100-600 mA cm-2. During a 50 h continuous electrolysis at the industrial current density of 200 mA cm-2, Zn1NC achieves Faradaic efficiencies greater than 95% for CO product. The work presents a temperature-universal formation of single-atom sites, which provides a novel platform for unraveling the active sites in Zn SACs for CO2 electroreduction and extends the synthesis of SACs with controllable coordination sites.

MOF-Derived CoSe2 Nanoparticles/Carbonized Melamine Foam as Catalytic Cathode Enabling Flexible Li-CO2 Batteries with High Energy Efficiency and Stable Cycling

Rechargeable aprotic Li-CO2 batteries have aroused worldwide interest owing to their environmentally friendly CO2 fixation ability and ultra-high specific energy density. However, its practical applications are impeded by the sluggish reaction kinetics and discharge product accumulation during cycling. Herein, a flexible composite electrode comprising CoSe2 nanoparticles embedded in 3D carbonized melamine foam (CoSe2/CMF) for Li-CO2 batteries is reported. The abundant CoSe2 clusters can not only facilitate CO2 reduction/evolution kinetics but also serve as Li2CO3 nucleation sites for homogeneous discharge product growth. The CoSe2/CMF-based Li-CO2 battery exhibits a large initial discharge capacity as high as 5.62 mAh cm-2 at 0.05 mA cm-2, a remarkably small voltage gap of 0.72 V, and an ultrahigh energy efficiency of 85.9% at 0.01 mA cm-2, surpassing most of the noble metal-based catalysts. Meanwhile, the battery demonstrates excellent cycling stability of 1620 h (162 cycles) at 0.02 mA cm-2 with an average overpotential of 0.98 V and energy efficiency of 85.4%. Theoretical investigations suggest that this outstanding performance is attributed to the suitable CO2/Li adsorption and low Li2CO3 decomposition energy. Moreover, flexible Li-CO2 pouch cell with CoSe2/CMF cathode displays stable power output under different bending deformations, showing promising potential in wearable electronic devices.

Improving the Rechargeable Li-CO2 Battery Performances by Tailoring Oxygen Defects on Li-Ni-Co-Mn Multi-Metal Oxide Catalysts Recycled from Spent Ternary Lithium-Ion Batteries

Rechargeable Li-CO2 batteries are considered as a promising carbon-neutral energy storage technology owing to their ultra-high energy density and efficient CO2 capture capability. However, the sluggish CO2 reduction/evolution kinetics impedes their practical application, which leads to huge overpotentials and poor cyclability. Multi-element transit metal oxides (TMOs) are demonstrated as effective cathodic catalysts for Li-CO2 batteries. But there are no reports on the integration of defect engineering on multi-element TMOs. Herein, the oxygen vacancy-bearing Li-Ni-Co-Mn multi-oxide (Re-NCM-H3) catalyst with the α-NaFeO2-type structure is first fabricated by annealing the NiCoMn precursor that derived from spent ternary LiNi0.8Co0.1Mn0.1O2 cathode, in H2 at 300 °C. As demonstrated by experimental results and theory calculations, the introduction of moderate oxygen vacancy has optimized electronic state near the Fermi level (Ef), eventually improving CO2 adsorption and charge transfer. Therefore, the Li-CO2 batteries with Re-NCM-H3 catalyst deliver a high capacity (11808.9 mAh g-1), a lower overpotential (1.54 V), as well as excellent stability over 216 cycles at 100 mA g-1 and 165 cycles at 400 mA g-1. This study not only opens up a sustainable application of spent ternary cathode, but also validates the potential of multi-element TMO catalysts with oxygen defects for high-efficiency Li-CO2 batteries.

Single-Atom Mn Catalysts via Integration with Mn Sub Nano-Clusters Synergistically Enhance Oxygen Reduction Reaction

Integrating single atoms and clusters into one system represents a novel strategy for achieving the desired catalytic performance. In comparison to single-atom catalysts, catalysts combining single atoms and clusters harness the advantages of both, thus displaying greater potential. Nevertheless, constructing single-atom-cluster systems remains challenging, and the fundamental mechanism for enhancing catalytic activity remains elusive. In this study, a directly confined preparation of a 3D hollow sea urchin-like carbon structure (MnSA/MnAC-SSCNR) is developed. Mn single atoms synergistically interact with Mn clusters, optimizing and reducing energy barriers in the reaction pathway, thus enhancing reaction kinetics. Consequently, in contrast to Mn single-atom catalysts (MnSA-SSCNR), MnSA/MnAC-SSCNR exhibits significantly improved oxygen reduction activity, with a half-wave potential (E1/2) of 0.90 V in 0.1 m KOH, surpassing that of MnSA-SSCNR and Pt/C. This work demonstrates a strategy of remote synergy between heterogeneous single atoms and clusters, which not only contributes to electrocatalytic reactions but also holds potential for reactions involving more complex products.

Customizing catalyst surface/interface structures for electrochemical CO2 reduction

Electrochemical CO2 reduction reaction (CO2RR) provides a promising route to converting CO2 into value-added chemicals and to neutralizing the greenhouse gas emission. For the industrial application of CO2RR, high-performance electrocatalysts featuring high activities and selectivities are essential. It has been demonstrated that customizing the catalyst surface/interface structures allows for high-precision control over the microenvironment for catalysis as well as the adsorption/desorption behaviors of key reaction intermediates in CO2RR, thereby elevating the activity, selectivity and stability of the electrocatalysts. In this paper, we review the progress in customizing the surface/interface structures for CO2RR electrocatalysts (including atomic-site catalysts, metal catalysts, and metal/oxide catalysts). From the perspectives of coordination engineering, atomic interface design, surface modification, and hetero-interface construction, we delineate the resulting specific alterations in surface/interface structures, and their effect on the CO2RR process. At the end of this review, we present a brief discussion and outlook on the current challenges and future directions for achieving high-efficiency CO2RR via surface/interface engineering.

Recent Progress in Hot Spot Regulated Strategies for Catalysts Applied in Li-CO2 Batteries

As a high energy density power system, lithium-carbon dioxide (Li-CO2 ) batteries play an important role in addressing the fossil fuel crisis issues and alleviating the greenhouse effect. However, the sluggish transformation kinetic of CO2 and the difficult decomposition of discharge products impede the achievement of large capacity, small overpotential, and long life span of the batteries, which require exploring efficient catalysts to resolve these problems. In this review, the main focus is on the hot spot regulation strategies of the catalysts, which include the modulation of the active sites, the designing of microstructure, and the construction of composition. The recent progress of promising catalysis with hot spot regulated strategies is systematically addressed. Critical challenges are also presented and perspectives to provide useful guidance for the rational design of highly efficient catalysts for practical advanced Li-CO2 batteries are proposed.

Insight into Defect Engineering of Atomically Dispersed Iron Electrocatalysts for High-Performance Proton Exchange Membrane Fuel Cell

Atomically dispersed and nitrogen coordinated iron catalysts (Fe-NCs) demonstrate potential as alternatives to platinum-group metal (PGM) catalysts in oxygen reduction reaction (ORR). However, in the context of practical proton exchange membrane fuel cell (PEMFC) applications, the membrane electrode assembly (MEA) performances of Fe-NCs remain unsatisfactory. Herein, improved MEA performance is achieved by tuning the local environment of the Fe-NC catalysts through defect engineering. Zeolitic imidazolate framework (ZIF)-derived nitrogen-doped carbon with additional CO2 activation is employed to construct atomically dispersed iron sites with a controlled defect number. The Fe-NC species with the optimal number of defect sites exhibit excellent ORR performance with a high half-wave potential of 0.83 V in 0.5 M H2 SO4 . Variation in the number of defects allows for fine-tuning of the reaction intermediate binding energies by changing the contribution of the Fe d-orbitals, thereby optimizing the ORR activity. The MEA based on a defect-engineered Fe-NC catalyst is found to exhibit a remarkable peak power density of 1.1 W cm-2 in an H2 /O2 fuel cell, and 0.67 W cm-2  in an H2 /air fuel cell, rendering it one of the most active atomically dispersed catalyst materials at the MEA level.

Constructing Fe-N4 Sites through Anion Exchange-mediated Transformation of Fe Coordination Environments in Hierarchical Carbon Support for Efficient Oxygen Reduction

Metal single atoms (SAs) anchored in carbon support via coordinating with N atoms are efficient active sites to oxygen reduction reaction (ORR). However, rational design of single atom catalysts with highly exposed active sites is challenging and urgently desirable. Herein, an anion exchange strategy is presented to fabricate Fe-N4 moieties anchored in hierarchical carbon nanoplates composed of hollow carbon spheres (Fe-SA/N-HCS). With the coordinating O atoms are substituted by N atoms, Fe SAs with Fe-O4 configuration are transformed into the ones with Fe-N4 configuration during the thermal activation process. Insights into the evolution of central atoms demonstrate that the SAs with specific coordination environment can be obtained by modulating in situ anion exchange process. The strategy produces a large quantity of electrochemical accessible site and high utilization rate of Fe-N4 . Fe-SA/N-HCS shows excellent ORR electrocatalytic performance with half-wave potential of 0.91 V (vs. RHE) in 0.1 M KOH, and outstanding performance when used in rechargeable aqueous and flexible Zn-air batteries. The evolution pathway for SAs demonstrated in this work offers a novel strategy to design SACs with various coordination environment and enhanced electrocatalytic activity.