Active Site Engineering in Porous Electrocatalysts

Polyphenol-Derived Carbonaceous Frameworks with Multiscale Porosity for High-Power Electrochemical Applications

With the escalating global demand for electric vehicles and sustainable energy solutions, increasing focus is placed on developing electrochemical systems that offer fast charging and high-power output, primarily governed by mass transport. Accordingly, porous carbons have emerged as highly promising electrochemically active or supporting materials due to expansive surface areas, tunable pore structures, and superior electrical conductivity, accelerating surface reaction. Yet, while substantial research has been devoted to crafting various porous carbons to increase specific surface areas, the optimal utilization of the surfaces remains underexplored. This review emphasizes the critical role of the fluid dynamics within multiscale porous carbonaceous electrodes, leading to substantially enhanced pore utilization in electrochemical systems. It elaborates on strategies of using sacrificial templates for incorporating meso/macropores into microporous carbon matrix, while exploiting the unique properties of polyphenol moieties such as sustainable carbons derived from biomass, inherent adhesive/cohesive interactions with template materials, and facile complexation capabilities with diverse materials, thereby enabling adaptive structural modulations. Furthermore, it explores how multiscale pore configurations influence pore-utilization efficiency, demonstrating advantages of incorporating multiscale pores. Finally, synergistic impact on the high-power electrochemical systems is examined, attributed to improved fluid-dynamic behavior within the carbonaceous frameworks, providing insights for advancing next-generation high-power electrochemical applications.

Defect-engineered chiral metal-organic frameworks

Chirality has an important impact on chemical and biological research, as most active substances are chiral. In recent decades, metal-organic frameworks (MOFs), which are assembled from metal ions or clusters and organic linkers via metal-ligand bonding, have attracted considerable scientific interest due to their high crystallinity, exceptional porosity and tunable pore sizes, high modularity, and diverse functionalities. Since the discovery of the first functional chiral metal-organic frameworks (CMOFs), CMOFs have been involved in a variety of disciplines such as chemistry, physics, optics, medicine, and pharmacology. The introduction of defect engineering theory into CMOFs allows the construction of a class of defective CMOFs with high hydrothermal stability and multi-stage pore structure. The introduction of defects not only increases the active sites but also enlarges the pore sizes of the materials, which improves chiral recognition, separation, and catalytic reactions, and has been widely investigated in various fields. This review describes the design and synthesis of various defective CMOFs, their characterization, and applications. Finally, the development of the materials is summarized, and an outlook is given. This review should provide researchers with an insight into the design and study of complex defective CMOFs.

2D PtRhPb Mesoporous Nanosheets with Surface-Clean Active Sites for Complete Ethanol Oxidation Electrocatalysis

The development of active and selective metal electrocatalysts for complete ethanol oxidation reaction (EOR) into desired C1 products is extremely promising for practical application of direct ethanol fuel cells. Despite some encouraging achievements, their activity and selectivity remain unsatisfactory. In this work, it is reported that 2D PtRhPb mesoporous nanosheets (MNSs) with anisotropic structure and surface-clean metal site perform perfectly for complete EOR electrocatalysis in both three-electrode and two-electrode systems. Different to the traditional routes, a selective etching strategy is developed to produce surface-clean mesopores while retaining parent anisotropy quasi-single-crystalline structure without the mesopore-forming surfactants. This method also allows the general synthesis of surface-clean mesoporous metals with other compositions and structures. When being performed for alkaline EOR electrocatalysis, the best PtRhPb MNSs deliver remarkably high activity (7.8 A mg-1) and superior C1 product selectivity (70% of Faradaic efficiency), both of which are much better than reported electrocatalysts. High performance is assigned to multiple structural and compositional synergies that not only stabilized key OHads intermediate by surface-clean mesopores but also separated the chemisorption of two carbons in ethanol by adjacent Pt and Rh sites, which facilitate the oxidation cleavage of stable C─C bond for complete EOR electrocatalysis.

Hierarchically Ordered Pore Engineering of Metal-Organic Framework-Based Materials for Electrocatalysis

Ordered pore engineering that embeds uniform pores with periodic alignment in electrocatalysts opens up a new avenue for achieving further performance promotion. Hierarchically ordered porous metal-organic frameworks (HOP-MOFs) possessing multilevel pores with ordered distribution are the promising precursors for the exploration of ordered porous electrocatalysts, while the scalable acquisition of HOP-MOFs with editable components and adjustable pore size regimes is critical. This review presents recent progress on hierarchically ordered pore engineering of MOF-based materials for enhanced electrocatalysis. The synthetic strategies of HOP-MOFs with different pore size regimes, including the self-assembly guided by reticular chemistry, surfactant, nanoemulsion, and nanocasting, are first introduced. Then the applications of HOP-MOFs as the precursors for exploring hierarchically ordered porous electrocatalysts are summarized, selecting representatives to highlight the boosted performance. Especially, the intensification of molecule and ion transport integrated with optimized electron transfer and site exposure over the hierarchically ordered porous derivatives are emphasized to clarify the directional transfer and integration effect endowed by ordered pore engineering. Finally, the remaining scientific challenges and an outlook of this field are proposed. It is hoped that this review will guide the hierarchically ordered pore engineering of nanocatalysts for boosting the catalytic performance and promoting the practical applications.

Enzymatic Mesoporous Metal Nanocavities for Concurrent Electrocatalysis of Nitrate to Ammonia Coupled with Polyethylene Terephthalate Upcycling

Electrochemical upcycling of waste pollutants into high value-added fuels and/or chemicals is recognized as a green and sustainable solution that can address the resource utilization on earth. Despite great efforts, their progress has seriously been hindered by the lack of high-performance electrocatalysts. In this work, bimetallic PdCu mesoporous nanocavities (MCs) are reported as a new bifunctional enzymatic electrocatalyst that realizes concurrent electrocatalytic upcycling of nitrate wastewater and polyethylene terephthalate (PET) plastic waste. Abundant metal mesopores and open nanocavities of PdCu MCs provide the enzymatic confinement of key intermediates for the deeper electroreduction of nitrate and accelerate the transport of reactants/products within/out of electrocatalyst, thus affording high ammonia Faradic efficiency (FENH3) of 96.6% and yield rate of 5.6 mg h-1 mg-1 at the cathode. Meanwhile, PdCu MC nanozymes trigger the selective electrooxidation of PET-derived ethylene glycol (EG) into glycolic acid (GA) and formic acid with high FEs of >90% by a facile regulation of potentials at the anode. Moreover, concurrent electrosynthesis of value-added NH3 and GA is disclosed in the two-electrode coupling system, further confirming the high efficiency of bifunctional PdCu MC nanozymes in producing value-added fuels and chemicals from waste pollutants in a sustainable manner.

Ceria-Optimized Oxygen-Species Exchange in Hierarchical Bimetallic Hydroxide for Electrocatalytic Water Oxidation

The utilization of rare earth elements to regulate the interaction between catalysts and oxygen-containing species holds promising prospects in the field of oxygen electrocatalysis. Through structural engineering and adsorption regulation, it is possible to achieve high-performance catalytic sites with a broken activity-stability tradeoff. Herein, this work fabricates a hierarchical CeO2/NiCo hydroxide for electrocatalytic oxygen evolution reaction (OER). This material exhibits superior overpotentials and enhanced stability. Multiple potential-dependent experiments reveal that CeO2 promotes oxygen-species exchange, especially OH- ions, between catalyst and environment, thereby optimizing the redox transformation of hydroxide and the adsorption of oxygen-containing intermediates during OER. This is attributed to the reduction in the adsorption energy barrier of Ni to *OH facilitated by CeO2, particularly the near-interfacial Ni sites. The less-damaging adsorbate evolution mechanism and the CeO2 hierarchical shell significantly enhance the structural robustness, leading to exceptional stability. Additionally, the observed "self-healing" phenomenon provides further substantiation for the accelerated oxygen exchange. This work provides a neat strategy for the synthesis of ceria-based complex hollow electrocatalysts, as well as an in-depth insight into the co-catalytic role of CeO2 in terms of oxygen transfer.

Fabrication of a wearable and foldable photodetector based on a WSe2-MXene 2D-2D heterostructure using a scalable handprint technique

Several studies on semiconductor material-based single-band, high-performance photosensitive, and chemically stable photodetectors are available; however, the lack of broad spectral response, device flexibility, and biodegradability prevents them from being used in wearable and flexible electronics. Apart from that, the selection of the device fabrication technique is a very crucial factor nowadays in terms of equipment utilization and environmental friendliness. This report presents a study demonstrating a straightforward solvent- and equipment-free handprint technique for the fabrication of WSe2-Ti3C2TX flexible, biodegradable, robust, and broadband (Vis-NIR) photodetectors. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX), UV-visible spectroscopy, and X-ray photoelectron spectroscopy (XPS) confirm the formation of a WSe2-Ti3C2TX film. The WSe2-Ti3C2TX van der Waals heterostructure plays a key role in enhancing the optoelectrical properties. The as-prepared photodetector exhibits efficient broadband response with a photoresponsivity and a detectivity of 0.3 mA W-1 and 6.8 × 1010 Jones, respectively, under NIR (780 nm) irradiation (1.0 V bias). Under various pressure and temperature conditions, the device's flexibility and durability were tested. The biodegradable photodetector prepared through the solvent- and equipment-free handprint technique has the potential to attract significant interest in wearable and flexible electronics in the future.

Addressing the Carbonate Issue: Electrocatalysts for Acidic CO2 Reduction Reaction

Electrochemical CO2 reduction reaction (CO2RR) powered by renewable energy provides a promising route to CO2 conversion and utilization. However, the widely used neutral/alkaline electrolyte consumes a large amount of CO2 to produce (bi)carbonate byproducts, leading to significant challenges at the device level, thereby impeding the further deployment of this reaction. Conducting CO2RR in acidic electrolytes offers a promising solution to address the "carbonate issue"; however, it presents inherent difficulties due to the competitive hydrogen evolution reaction, necessitating concerted efforts toward advanced catalyst and electrode designs to achieve high selectivity and activity. This review encompasses recent developments of acidic CO2RR, from mechanism elucidation to catalyst design and device engineering. This review begins by discussing the mechanistic understanding of the reaction pathway, laying the foundation for catalyst design in acidic CO2RR. Subsequently, an in-depth analysis of recent advancements in acidic CO2RR catalysts is provided, highlighting heterogeneous catalysts, surface immobilized molecular catalysts, and catalyst surface enhancement. Furthermore, the progress made in device-level applications is summarized, aiming to develop high-performance acidic CO2RR systems. Finally, the existing challenges and future directions in the design of acidic CO2RR catalysts are outlined, emphasizing the need for improved selectivity, activity, stability, and scalability.

N-Doping Effects On Electrocatalytic Water Splitting of Non-Noble High-Entropy Alloy Nanoparticles Prepared by Inert Gas Condensation

The unique catalytic activities of high-entropy alloys (HEAs) emerge from the complex interaction among different elements in a single-phase solid solution. As a "green" nanofabrication technique, inert gas condensation (IGC) combined with laser source opens up a highly efficient avenue to develop HEA nanoparticles (NPs) for catalysis and energy storage. In this work, the novel N-doped non-noble HEA NPs are designed and successfully prepared by IGC. The N-doping effects of HEA NPs on oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are systematically investigated. The results show that N-doping is conducive to improving the OER, but unfavorable for HER activity. The FeCoNiCrN NPs achieve an overpotential of 269.7 mV for OER at a current density of 10 mA cm-2 in 1.0 M KOH solution, which is among the best reported values for non-noble HEA catalysts. The effects of the differences in electronegativity, ionization energy and electron affinity energy among mixed elements in N-doped HEAs are discussed as inducing electron transfer efficiency. Combined with X-ray photoelectron spectroscopy and the extended X-ray absorption fine structure analysis, an element-design strategy in N-doped HEAs electrocatalysts is proposed to improve the intrinsic activity and ameliorate water splitting performance.

CuOx/Cu nanorod skeleton supported Ru-doped CoO/NC nanocomposites for overall water splitting

High overpotential and low stability are major challenges for hydrogen evolution reaction (HER)/oxygen evolution reaction (OER). Tuning the electronic structure of catalysts is regarded as a core strategy to enhance catalytic activity. Herein, we report CuOx/Cu nanorod skeleton supported Ru doped cobalt oxide/nitrogen-doped carbon nanocomposites (Ru-CoO/NC/CuOx/Cu, denoted as RCUF) as bifunctional catalysis. The one-dimensional/three-dimensional (1D/3D) nanostructure and defect-rich amorphous/crystalline phases of RCUF facilitates active site exposure and electron transport. Experimental characterization and density functional theory (DFT) calculation results indicate that Ru doping can optimize the electronic structure, which accelerates the water dissociation process and reduces the Gibbs free energy of the reaction intermediates. As expected, the optimal RCUF-900 exhibits low overpotential (25/205 mV at 10 mA cm-2) and high stability (100/100 h) for HER/OER. RCUF-900 has low voltage (1.54 V at 10 mA cm-2) and high stability (100 h) for overall water splitting. This work provides new insights into the design of advanced catalysts for overall water splitting.

Diamondoid Ni(II) Coordination Polymer as an Electrocatalyst for Hydrogen and Oxygen Evolution Reactions and Overall Water Splitting

We have successfully synthesized a new Ni(II)-based coordination polymer (CP) [Ni2(cis-1,4-chdc)2(4,4'-bpy)3(H2O)2] (1); (cis-1,4- H2chdc=cis-1,4-cyclohexanedicarboxylic acid and 4,4'-bpy=4,4'-bipyridine) employing slow diffusion method in a single pot technique. The connectivity of Ni(II) ions and bridging cis-1,4-chdc ligand gives rise to a three-dimensional (3D) framework with 2-fold interpenetrated diamondoid topology. Interestingly, the synthesized CP acts as efficient catalyst for electrocatalytic water splitting. The water oxidation activity of compound 1 exhibits Tafel slope equivalent to 361.48 mV.dec-1 for hydrogen evolution reaction (HER) and 353.53 mV.dec-1 for oxygen evolution reaction (OER) in an alkaline medium while almost similar values of Tafel slope for HER and OER equivalent to 287.33 mV.dec-1 and 289.93 mV.dec-1 respectively in acidic medium. Thus, the compound 1 has excellent efficacy in catalyzing HER and OER in acidic as well as alkaline medium, which is ascribed to its distinctive 3D architecture.

CO2 Electrolyzers

CO2 electrolyzers have progressed rapidly in energy efficiency and catalyst selectivity toward valuable chemical feedstocks and fuels, such as syngas, ethylene, ethanol, and methane. However, each component within these complex systems influences the overall performance, and the further advances needed to realize commercialization will require an approach that considers the whole process, with the electrochemical cell at the center. Beyond the cell boundaries, the electrolyzer must integrate with upstream CO2 feeds and downstream separation processes in a way that minimizes overall product energy intensity and presents viable use cases. Here we begin by describing upstream CO2 sources, their energy intensities, and impurities. We then focus on the cell, the most common CO2 electrolyzer system architectures, and each component within these systems. We evaluate the energy savings and the feasibility of alternative approaches including integration with CO2 capture, direct conversion of flue gas and two-step conversion via carbon monoxide. We evaluate pathways that minimize downstream separations and produce concentrated streams compatible with existing sectors. Applying this comprehensive upstream-to-downstream approach, we highlight the most promising routes, and outlook, for electrochemical CO2 reduction.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

Ir-Doped CuPd Single-Crystalline Mesoporous Nanotetrahedrons for Ethylene Glycol Oxidation Electrocatalysis: Enhanced Selective Cleavage of C-C Bond

The development of highly efficient electrocatalysts for complete oxidation of ethylene glycol (EG) in direct EG fuel cells is of decisive importance to hold higher energy efficiency. Despite some achievements, their progress, especially electrocatalytic selectivity to complete oxidated C1 products, is remarkably slower than expected. In this work, we developed a facile aqueous synthesis of Ir-doped CuPd single-crystalline mesoporous nanotetrahedrons (Ir-CuPd SMTs) as high-performance electrocatalyst for promoting oxidation cleavage of C-C bond in alkaline EG oxidation reaction (EGOR) electrocatalysis. The synthesis relied on precise reduction/co-nucleation and epitaxial growth of Ir, Cu and Pd precursors with cetyltrimethylammonium chloride as the mesopore-forming surfactant and extra Br- as the facet-selective agent under ambient conditions. The products featured concave nanotetrahedron morphology enclosed by well-defined (111) facets, single-crystalline and mesoporous structure radiated from the center, and uniform elemental composition without any phase separation. Ir-CuPd SMTs disclosed remarkably enhanced electrocatalytic activity and excellent stability as well as superior selectivity of C1 products for alkaline EGOR electrocatalysis. Detailed mechanism studies demonstrated that performance improvement came from structural and compositional synergies, which kinetically accelerated transports of electrons/reactants within active sites of penetrated mesopores and facilitated oxidation cleavage of high-energy-barrier C-C bond of EG for desired C1 products. More interestingly, Ir-CuPd SMTs performed well in coupled electrocatalysis of anode EGOR and cathode nitrate reduction, highlighting its high potential as bifunctional electrocatalyst in various applications.

Key role of subsurface doping in optimizing active sites of IrO2 for the oxygen evolution reaction

The oxygen evolution reaction (OER) over a family of metal-doped rutile IrO2 catalysts is theoretically investigated by controlling the species and position of doped elements. The subsurface substitution doping is demonstrated to efficiently regulate the eg-filling of surface iridium sites and lower the adsorption strength of oxygen intermediates, improving the catalytic activity for the OER. Finally, based on screening, subsurface Cu- and Li-doped IrO2 models stand near the top of the volcano plot and display high levels of structural stability toward acidic OER.

One-pot gram-scale rapid synthesis of MN4 complexes with 14-membered ring macrocyclic ligand as a precursor for carbon-based ORR and CO2RR catalysts

Herein, CoN4, CuN4, and NiN4 complexes with a 14-membered ring hexaazamacrocycle ligand H2HAM were synthesised as precursors for ORR and CO2RR catalysts via a one-pot, gram-scale synthesis procedure, which involved microwave heating for only 10 min. Detailed structures of the obtained 14MR-MN4 complex were revealed by single-crystal X-ray diffraction measurements.

A new method for the preparation of MgAl layered double hydroxide-copper metal-organic frameworks structures: application to electrocatalytic oxidation of formaldehyde

In this research, we present a novel design protocol for the in-situ synthesis of MgAl layered double hydroxide-copper metal-organic frameworks (LDH-MOFs) nanocomposite based on the electrocoagulation process and chemical method. The overall goal in this project is the primary synthesis of para-phthalic acid (PTA) intercalated MgAl-LDH with Cu (II) ions to produce the paddle-wheel like Cu-(PTA) MOFs nanocrystals on/in the MgAl-LDH structure. The physicochemical properties of final product; Cu-(PTA) MOFs/MgAl-LDH, were characterized by the surface analysis and chemical identification methods (SEM, EDX, TEM, XRD, BET, FTIR, CHN, DLS, etc.). The Cu-(PTA) MOFs/MgAl-LDH nanocomposite was used to modification of the carbon paste electrode (CPE); Cu-(PTA) MOFs/MgAl-LDH/CPE. The electrochemical performance of Cu-(PTA) MOFs/MgAl-LDH/CPE was demonstrated through the utilization of electrochemical methods. The results show a stable redox behavior of the Cu (III)/Cu (II) at the surface of Cu-(PTA) MOFs/MgAl-LDH/CPE in alkaline medium (aqueous 0.1 M NaOH electrolyte). Then, the Cu-(PTA) MOFs/MgAl-LDH/CPE was used as a new electrocatalyst toward the oxidation of formaldehyde (FA). Electrochemical data show that the Cu-(PTA) MOFs/MgAl-LDH/CPE exhibits superior electrocatalytic performance on the oxidation of FA. Also the diffusion coefficient, exchange current density (J°) and mean value of catalytic rate constant (Kcat) were found to be 1.18 × 10-6 cm2 s-1, 23 mA cm-2 and 0.4537 × 104 cm3 mol-1 s-1, respectively. In general, it can be said the Cu-(PTA) MOFs/MgAl-LDHs is promising candidate for applications in direct formaldehyde fuel cells.

Engineering core-shell hollow-sphere Fe3O4@FeP@nitrogen-doped-carbon as an advanced bi-functional electrocatalyst for highly-efficient water splitting

Given the rapidly increasing energy demand and environmental pollution, to achieve energy conservation and emission reduction, hydrogen production has emerged as a promising alternative to traditional fossil fuels because of its high gravimetric energy density, and renewable and environmentally friendly characteristics. Herein, a core-shell hollow-sphere Fe3O4@FeP@nitrogen-doped-carbon (labeled as H-Fe3O4@FeP@NC) with a dual-interface, novel morphology, and superior conductivity is prepared as an advanced bi-functional electrocatalyst for electrochemical overall water splitting using a collaborative strategy comprising of facile self-assembly and phosphating. The prepared catalyst exhibits superior electrocatalytic activity compared to H-Fe3O4@NC and H-Fe3O4 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Additionally, the overpotential of H-Fe3O4@FeP@NC for OER/HER (258/165 mV at 10 mA/cm2) is significantly lower than those of H-Fe3O4@NC (274/209 mV) and H-Fe3O4 (287/213 mV) at 10 mA/cm2. Meanwhile, the as-synthesized H-Fe3O4@FeP@NC, as an electrode pair, displays a low cell voltage of 1.69 V at 10 mA/cm2 and excellent stability after 100 h, indicating its practical application for overall water splitting. This work presents a practical and economical strategy toward the fabrication of catalyst for efficient water splitting and fuel cell.

Mesoporous RE0.5Ce0.5O2-x Fluorite Electrocatalysts for the Oxygen Evolution Reaction

Developing highly active and stable electrocatalysts for the oxygen evolution reaction (OER) is key to improving the efficiency and practical application of various sustainable energy technologies including water electrolysis, CO2 reduction, and metal air batteries. Here, we use evaporation-induced self-assembly (EISA) to synthesize highly porous fluorite nanocatalysts with a high surface area. In this study, we demonstrate that a 50% rare-earth cation substitution for Ce in the CeO2 fluorite lattice improves the OER activity and stability by introducing oxygen vacancies into the host lattice, which results in a decrease in the adsorption energy of the OH* intermediate in the OER. Among the binary fluorite compositions investigated, Nd2Ce2O7 is shown to display the lowest OER overpotential of 243 mV, achieved at a current density of 10 mA cm-2, and excellent cycling stability in an alkaline medium. Importantly, we demonstrate that rare-earth oxide OER electrocatalysts with high activity and stability can be achieved using the EISA synthesis route without the incorporation of transition and noble metals.

Surface Reconstruction Facilitated by Fluorine Migration and Bimetallic Center in NiCo Bimetallic Fluoride Toward Oxygen Evolution Reaction

Oxygen evolution reaction (OER) is a critical anodic reaction of electrochemical water splitting, developing a high-efficiency electrocatalyst is essential. Transition metal-based catalysts are much more cost-effective if comparable activities can be achieved. Among them, fluorides are rarely reported due to their low aqueous stability of coordination and low electric conductivity. Herein, a NiCo bimetallic fluoride with good crystallinity is designed and constructed, and significantly enhanced catalytic activity and conductivity are observed. The inevitable oxidation of transition metal ions at high potential and the dissociation of F- are attributed to the low aqueous stability of coordination. The theoretical researches predicte that transition metal fluorides should have a strong tendency to electrochemical reconstruction. Therefore, based on the observations on their electrochemical behavior, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and bode plots, it is further demonstrated that surface reconstruction occurred during the electrochemical process, meanwhile a significant increase of electrochemically active area, which is created by F migration, are also directly observed. Additionally, DFT calculation results show that the electronic structure of the catalysts is modulated by the bimetallic centers, and this reconstruction helps optimizing the adsorption energy of oxygen-containing species and improves OER activity.

Nitrogen sites prevail over textural properties in N-doped carbons for the oxygen reduction reaction

Nitrogen-doped carbon-based electrodes are among the most promising alternatives to platinum-based electrodes in the cathode of fuel cells and metal-air batteries, where the oxygen reduction reaction (ORR) takes place. Among the approaches for improving ORR activity, nitrogen functionalities and well-developed textural properties have proved very effective. Nonetheless, the question of which between nitrogen active sites or textural properties are more crucial in N-doped carbon materials remains unanswered. This work proposes a comparative and critical approach through the selective functionalization of four commercial activated carbons with different textural properties. This study highlights the greater importance of N-doping in relation to the textural properties of carbon materials, and provides fundamental insights for conclusively addressing the ongoing debate within the carbon community about the significance of these two factors in the context of ORR.

Metal-Free Covalent Organic Frameworks for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is the key reaction in metal air and fuel cells. Among the catalysts that promote ORR, carbon-based metal-free catalysts are getting more attention because of their maximum atom utilization, effective active sites and satisfactory catalytic activity and stability. However, the pyrolysis synthesis of these carbons resulted in disordered porosities and uncontrolled catalytic sites, which hindered us in realizing the catalysts' design, the optimization of catalyst performance and the elucidation of structure-property relationship at the molecular level. Covalent organic frameworks (COFs) constructed with designable building blocks have been employed as metal-free electrocatalysts for the ORR due to their controlled skeletons, tailored pores size and environments, as well as well-defined location and kinds of catalytic sites. In this Concept article, the development of metal-free COFs for the ORR is summarized, and different strategies including skeletons regulation, linkages engineering and edge-sites modulation to improve the catalytic selectivity and activity are discussed. Furthermore, this Concept provides prospectives for designing and constructing powerful electrocatalysts based on the catalytic COFs.

Crystal-Phase Engineering in Heterogeneous Catalysis

The performance of a chemical reaction is critically dependent on the electronic and/or geometric structures of a material in heterogeneous catalysis. Over the past century, the Sabatier principle has already provided a conceptual framework for optimal catalyst design by adjusting the electronic structure of the catalytic material via a change in composition. Beyond composition, it is essential to recognize that the geometric atomic structures of a catalyst, encompassing terraces, edges, steps, kinks, and corners, have a substantial impact on the activity and selectivity of a chemical reaction. Crystal-phase engineering has the capacity to bring about substantial alterations in the electronic and geometric configurations of a catalyst, enabling control over coordination numbers, morphological features, and the arrangement of surface atoms. Modulating the crystallographic phase is therefore an important strategy for improving the stability, activity, and selectivity of catalytic materials. Nonetheless, a complete understanding of how the performance depends on the crystal phase of a catalyst remains elusive, primarily due to the absence of a molecular-level view of active sites across various crystal phases. In this review, we primarily focus on assessing the dependence of catalytic performance on crystal phases to elucidate the challenges and complexities inherent in heterogeneous catalysis, ultimately aiming for improved catalyst design.

Design of Boron and Transition Metal Embedded Two-Dimensional Porous Carbon Nitride for Electrocatalytic Synthesis of Urea

Electrocatalytic coupling of CO and N2 to synthesize urea under ambient conditions is considered a promising strategy to replace traditional industrial technology. It is crucial to find efficient electrocatalysts that can adsorb and activate N2 and promote the C-N coupling reaction. Herein, a new two-dimensional porous carbon nitride material with multiactive sites is designed, in which boron and transition metal are embedded. Through a series of screening, B2Cr2, B2Mn2, and B2Os2 are predicted to be potential electrocatalysts for urea synthesis. Mechanistic studies are performed on bidentate metal-metal and metal-boron sites, and both NCON and CO mechanisms are explored. The electronic structure analysis shows that there is a strong N2 chemical adsorption within the bidentate site and that the N≡N bond is significantly activated. A new mechanism where free CO is inserted for C-N coupling within the two-dimensional porous structure is proposed.

Highly Efficient and Stable Mo-CoP3 @FeOOH Electrocatalysts for Alkaline Seawater Splitting

The introduction of high-valence state elements and highly active species is promisingly desired to design superior electrocatalysts for water electrolysis. Exploring scalable synthetic strategies is necessary for an in-depth understanding of the mechanism of improving electrocatalytic performance. But it remains challenging. Herein, several electrocatalysts through element doping are prepared. The obtained Mo-CoP3 -2@FeOOH samples show the overpotentials (OER) of 232 mV (alkaline seawater) and 262 mV (KOH electrolyte). As HER catalyst, it also presents an excellent electrocatalytic performance. The above electrocatalysts are utilized as anode/cathode to assemble devices for alkaline seawater/water electrolysis, which delivers a cell voltage of 1.58 V and durability of 350 h. Density functional theory calculations reveal that Mo ion doping and FeOOH significantly enhance the density states of the Fermi level and tune the position of the d-band center. It expedites the charge transfer and decreases the adsorption energy of intermediates. It demonstrates that transition-metal phosphides coated with highly active FeOOH offer an effective route to fabricate high-performance and durable catalysts for seawater/water electrolysis.

A novel Nb2C MXene based aptasensor for rapid and sensitive multi-mode detection of AFB1

Rapid and accurate on-site detection of aflatoxin B1 (AFB1) is of great significance for ensuring food safety. This work developed a dual mode aptasensor and a dual channel artificial neural network (ANN) intelligent sensor detection platform for simple and convenient quantitative detection of AFB1 in food. This sensor was prepared by encoding manganese ion (Mn2+) mediated surface concave niobium carbide MXene nanomaterials (Nb2C-MNs) using fluorescent group labeled aptamers (ssDNA-FAM). Mn2+-mediated Nb2C-MNs exhibited better peroxidase-like and fluorescence quenching properties. Moreover, ssDNA-FAM as a fluorescent probe for the sensor also significantly enhanced the enzyme activity of Nb2C-MNs. When AFB1 existed, ssDNA-FAM preferentially bonded to AFB1, resulting in fluorescence signal recovery and colorimetric signal weakening. Consequently, the multimodal biosensor could achieve fluorescence/colorimetric detection without the need for material and reagent replacement. In on-site detection, both ratio fluorescence and colorimetric signals could be collected using smartphones and analyzed and modeled on the developed ANN platform, achieving visual intelligent sensing. This multimodal biosensor had a detection line as low as 0.0950 ng/mL under optimal conditions, and also had the advantages of simple operation, fast and sensitive, and high specificity, which can meet the real-time on-site detection needs of AFB1 in remote areas.

Surface-structure tailoring of Dendritic PtCo nanowires for efficient oxygen reduction reaction

Platinum-based alloy nanowire catalysts demonstrates great promise as electrocatalysts to facilitate the cathodic oxygen reduction reaction (ORR) of proton exchange membrane fuel cells (PEMFCs). However, it is still challenge to further improve the Pt atom utilization of Pt based nanowires featuring inherent structural stability. Herein, a new structure of PtCo nanowire with nanodendrites was developed using CO-assistance solvent thermal method. The dendrite structure with an average length of about 7 nm are characterized by a Pt-rich surface and the high-index facets of {533}, {331} and {311}, and grows from the ultra-fine wire structure with an average diameter of about 3 nm. PtCo nanowires with nanodendrites developed in this work shows outstanding performance for ORR, in which its mass activity of 1.036 A/mgPt is 5.76 times, 1.74 times higher than that of commercial Pt/C (0.180 A/mgPt) and PtCo nanowires without nanodendrites (0.595 A/mgPt), and its mass activity loss is only 18% under the accelerated durability tests (ADTs) for 5k cycles. The significant improvement is attributed to high exposure of active sites induced by the dendrite structure with Pt-rich surface with the high-index facets and Pt-rich surface. This structure may provide a new idea for developing novel 1D Pt based electrocatalysts.

Two-dimensional mesoporous metals: a new era for designing functional electrocatalysts

Two-dimensional (2D) mesoporous metals contribute a unique class of electrocatalyst materials for electrochemical applications. The penetrated mesopores of 2D mesoporous metals expose abundant accessible undercoordinated metal sites, while their 2D nanostructures accelerate the transport of electrons and reactants. Therefore, 2D mesoporous metals have exhibited add-in structural functions with great potential in electrocatalysis that not only enhance electrocatalytic activity and stability but also optimize electrocatalytic selectivity. In this Perspective, we summarize recent progress in the design, synthesis, and electrocatalytic performance of 2D mesoporous metals. Four main strategies for synthesizing 2D mesoporous metals, named the CO (and CO container) induced route, halide ion-oriented route, interfacial growth route, and metal oxide atomic reconstruction route, are presented in detail. Moreover, electrocatalytic applications in several important reactions are summarized to highlight the add-in structural functions of 2D mesoporous metals in enhancing electrochemical activity, stability, and selectivity. Finally, current challenges and future directions are discussed in this area. This Perspective offers some important insights into both fundamental investigations and practical applications of novel high-performance functional electrocatalysts.

Programmable catalysis by support polarization: elucidating and breaking scaling relations

The Sabatier principle and the scaling relations have been widely used to search for and screen new catalysts in the field of catalysis. However, these powerful tools can also serve as limitations of catalyst control and breakthrough. To overcome this challenge, this work proposes an efficient method of studying catalyst control by support polarization from first-principles. The results demonstrate that the properties of catalysts are determined by support polarization, irrespective of the magnitude of spontaneous polarization of support. The approach enables elucidating the scaling relations between binding energies at various polarization values of support. Moreover, we observe the breakdown of scaling relations for the surface controlled by support polarization. By studying the surface electronic structure and decomposing the induced charge into contributions from different atoms and orbitals, we identify the inherent structural property of the interface that leads to the breaking of the scaling relations. Specifically, the displacements of the underlying oxide support impose its symmetry on the catalyst, causing the scaling relations between different adsorption sites to break.

One-atom-thick hexagonal boron nitride co-catalyst for enhanced oxygen evolution reactions

Developing efficient (co-)catalysts with optimized interfacial mass and charge transport properties is essential for enhanced oxygen evolution reaction (OER) via electrochemical water splitting. Here we report one-atom-thick hexagonal boron nitride (hBN) as an attractive co-catalyst with enhanced OER efficiency. Various electrocatalytic electrodes are encapsulated with centimeter-sized hBN films which are dense and impermeable so that only the hBN surfaces are directly exposed to reactive species. For example, hBN covered Ni-Fe (oxy)hydroxide anodes show an ultralow Tafel slope of ~30 mV dec-1 with improved reaction current by about 10 times, reaching ~2000 mA cm-2 (at an overpotential of ~490 mV) for over 150 h. The mass activity of hBN co-catalyst is found exceeding that of commercialized catalysts by up to five orders of magnitude. Using isotope experiments and simulations, we attribute the results to the adsorption of oxygen-containing intermediates at the insulating co-catalyst, where localized electrons facilitate the deprotonation processes at electrodes. Little impedance to electron transfer is observed from hBN film encapsulation due to its ultimate thickness. Therefore, our work also offers insights into mechanisms of interfacial reactions at the very first atomic layer of electrodes.

Machine learning-assisted optimization of multi-metal hydroxide electrocatalysts for overall water splitting

Green hydrogen produced via electrochemical water splitting is a suitable candidate to replace emission-intensive fuels. However, the successful widespread adoption of green hydrogen is contingent on the development of low-cost, earth-abundant catalysts. Herein, machine learning models built on experimental data were used to optimize the precursor ratios of hydroxide-based electrocatalysts, with the objective of improving the product's electrocatalytic performance for overall water splitting. The Neural Network-based models were found to be the most effective in predicting and minimizing the overpotentials of the catalysts, reaching a minimum in two iterations. The relatively mild reaction conditions of the synthesis procedure, coupled with its scalability demonstrated herein, renders the optimized catalyst relevant for industrial implementation in the future. The optimized catalyst, characterized to be a molybdate-intercalated CoFe LDH, demonstrated overpotentials of 266 and 272 mV at 10 mA cm-2 for oxygen and hydrogen evolution reactions respectively in alkaline electrolyte, alongside unwavering stability for overall water splitting over 50 h. Overall, our results reflect the efficacy and advantages of machine learning strategies to alleviate the time and labour-intensive nature of experimental optimizations, which can greatly accelerate electrocatalysts research.

Advances on Axial Coordination Design of Single-Atom Catalysts for Energy Electrocatalysis: A Review

Single-atom catalysts (SACs) have garnered increasingly growing attention in renewable energy scenarios, especially in electrocatalysis due to their unique high efficiency of atom utilization and flexible electronic structure adjustability. The intensive efforts towards the rational design and synthesis of SACs with versatile local configurations have significantly accelerated the development of efficient and sustainable electrocatalysts for a wide range of electrochemical applications. As an emergent coordination avenue, intentionally breaking the planar symmetry of SACs by adding ligands in the axial direction of metal single atoms offers a novel approach for the tuning of both geometric and electronic structures, thereby enhancing electrocatalytic performance at active sites. In this review, we briefly outline the burgeoning research topic of axially coordinated SACs and provide a comprehensive summary of the recent advances in their synthetic strategies and electrocatalytic applications. Besides, the challenges and outlooks in this research field have also been emphasized. The present review provides an in-depth and comprehensive understanding of the axial coordination design of SACs, which could bring new perspectives and solutions for fine regulation of the electronic structures of SACs catering to high-performing energy electrocatalysis.

A general protocol for precise syntheses of ordered mesoporous intermetallic nanoparticles

Intermetallic nanomaterials consist of two or more metals in a highly ordered atomic arrangement. There are many possible combinations and morphologies, and exploring their properties is an important research area. Their strict stoichiometry requirement and well-defined atom binding environment make intermetallic compounds an ideal research platform to rationally optimize catalytic performance. Making mesoporous intermetallic materials is a further advance; crystalline mesoporosity can expose more active sites, facilitate the mass and electron transfer, and provide the distinguished mesoporous nanoconfinement environment. In this Protocol, we describe how to prepare ordered mesoporous intermetallic nanomaterials with controlled compositions, morphologies/structures and phases by a general concurrent template strategy. In this approach, the concurrent template used is a hybrid of mesoporous platinum or palladium and Korea Advanced Institute of Science and Technology-6 (KIT-6) (meso-Pt/KIT-6 or meso-Pd/KIT-6) that can be transformed by the second precursors under reducing conditions. The second precursor can either be a second metal or a metalloid/non-metal, e.g., boron/phosphorus. KIT-6 is a silica scaffold that is removed using NaOH or HF to form the mesoporous product. Procedures for example catalytic applications include the 3-nitrophenylacetylene semi-hydrogenation reaction, p-nitrophenol reduction reaction and electrochemical hydrogen evolution reaction. The synthetic strategy for preparation of ordered mesoporous intermetallic nanoparticles would take almost 5 d; the physical characterization by electron microscope, X-ray diffraction and inductively coupled plasma-mass spectrometry takes ~2 days and the function characterization depends on the research question, but for catalysis it takes 1-5 h.

Design Strategies for Hydroxyapatite-Based Materials to Enhance Their Catalytic Performance and Applicability

Hydroxyapatite (HAP) is a green catalyst that has a wide range of applications in catalysis due to its high flexibility and multifunctionality. These properties allow HAP to accommodate a large number of catalyst modifications that can selectively improve the catalytic performance in target reactions. To date, many studies have been conducted to elucidate the effect of HAP modification on the catalytic activities for various reactions. However, systematic design strategies for HAP catalysts are not established yet due to an incomplete understanding of underlying structure-activity relationships. In this review, tuning methods of HAP for improving the catalytic performance are discussed: 1) ionic composition change, 2) morphology control, 3) incorporation of other metal species, and 4) catalytic support engineering. Detailed mechanisms and effects of structural modulations on the catalytic performances for attaining the design insights of HAP catalysts are investigated. In addition, computational studies to understand catalytic reactions on HAP materials are also introduced. Finally, important areas for future research are highlighted.

Tailoring Metal-Organic Frameworks and Derived Materials for High-Performance Zinc-Air and Alkaline Batteries

Developing multifunctional materials from earth-abundant elements is urgently needed to satisfy the demand for sustainable energy. Herein, we demonstrate a facile approach for the preparation of a metal-organic framework (MOF)-derived Fe₂O₃/C, composited with N-doped reduced graphene oxide (MO-rGO). MO-rGO exhibits excellent bifunctional electrocatalytic activities toward the oxygen evolution reaction (η_j=10 = 273 mV) and the oxygen reduction reaction (half-wave potential = 0.77 V vs reversible hydrogen electrode) with a low ΔE_OER-ORR of 0.88 V in alkaline solutions. A Zn-air battery based on the MO-rGO cathode displays a high specific energy of over 903 W h kg_Zn^-1 (∼290 mW h cm^-2), an excellent power density of 148 mW cm^-2, and an open-circuit voltage of 1.430 V, outperforming the benchmark Pt/C + RuO₂ catalyst. We also hydrothermally synthesized a Ni-MOF that was partially transformed into a Ni-Co-layered double hydroxide (MOF-LDH). A MO-rGO||MOF-LDH alkaline battery exhibits a specific energy of 42.6 W h kg_total mass^-1 (106.5 μW h cm^-2) and an outstanding specific power of 9.8 kW kg_total mass^-1 (24.5 mW cm^-2). This work demonstrates the potential of MOFs and MOF-derived compounds for designing innovative multifunctional materials for catalysis, electrochemical energy storage, and beyond.

Half-Electrolysis of Water with the Aid of a Supercapacitor Electrode

Half-electrolysis runs one desirable half-cell reaction with the aid of a counter supercapacitor electrode which replaces the other unwanted half-cell reaction occurred inevitably in conventional electrolysis. Herein, it is developed to complete the whole cell reaction of water electrolysis, in alternative steps, with a capacitive activated carbon (AC) electrode and an electrolysis Pt electrode. When positively charging the AC electrode, a hydrogen evolution reaction occurs at the Pt electrode. By reversing the current, the charge stored in the AC electrode is discharged to assist the oxygen evolution reaction on the same Pt electrode. Consecutive completion of the two processes realizes the overall reaction of water electrolysis. This strategy leads to stepwise production of H₂ and O₂ without the need of a diaphragm in the cell and hence results in a lower energy consumption compared with the practical conventional electrolysis.

NiCoP-nanocubes-decorated CoSe2 nanowire arrays as high-performance electrocatalysts toward oxygen evolution reaction

Designing effective, robust, and low-cost catalysts for oxygen evolution reaction (OER) is an urgent requirement yet challenging task in water electrolysis. In this study, a NiCoP-nanocubes-decorated CoSe₂ nanowires arrays three-dimensional/two-dimensional (3D/2D) electrocatalyst (NiCoP-CoSe₂-2) was developed for catalyzing OER via a combined selenylation, co-precipitation, and phosphorization method. The as-obtained NiCoP-CoSe₂-2 3D/2D electrocatalyst exhibits a low overpotential of 202 mV at 10 mA cm^-2 with a small Tafel slope of 55.6 mV dec^-1, which is superior to most of reported CoSe₂ and NiCoP-based heterogeneous electrocatalysts. Experimental analyses and density functional theory (DFT) calculations proof that the interfacial coupling and synergy between CoSe₂ nanowires and NiCoP nanocubes are not only beneficial to strengthen the charge transfer ability and accelerate reaction kinetics, but also facilitate the optimization of interfacial electronic structure, thereby enhancing the OER property of NiCoP-CoSe₂-2. This study offers insights for the investigation and construction of transition metal phosphide/selenide heterogeneous electrocatalyst toward OER in alkaline media and broadens the prospect of industrial applications in energy storage and conversion fields.

Dealloying of Pt1Bi2 intermetallic toward optimization of electrocatalysis on a Bi-continuous nanoporous core-shell structure

Noble metal nanoporous materials hold great potential in the field of catalysis, owing to their high open structures and numerous low coordination surface sites. However, the formation of porous nanoparticles is restricted by particle size. Herein, we utilized a Pt₁Bi₂ intermetallic nanocatalyst to develop a dealloying approach for preparing nanoparticles with a bi-continuous porous and core-shell structure and proposed a mechanism for the formation of pores. The particle size used to form the porous structure can be <10 nm, which enhances the nanocatalyst's performance for the oxygen reduction reaction (ORR). This study provides a new understanding of the formation of porous materials via a dealloying approach.

Single atomic cerium sites anchored on nitrogen-doped hollow carbon spheres for highly selective electroreduction of nitric oxide to ammonia

Electrocatalytic nitric oxide reduction reaction (NORR) at ambient environments not only offers a promising strategy to yield ammonia (NH₃) but also degrades the NO contaminant; however, its application depends on searching for high-performance catalysts. Herein, we present single atomic Ce sites anchored on nitrogen-doped hollow carbon spheres that are capable of electro-catalyzing NO reduction to NH₃ in an acidic solution, achieving a maximal Faradaic efficiency of 91 % and a yield rate of 1023 μg h^-1 mg_cat.^-1 at -0.7 V vs RHE for NH₃ formation, both of which outperform these on Ce nanoclusters and approach the best-reported results. Meanwhile, the single atomic Ce catalyst shows good structural and electrochemical stability during the 30-h NO electrolysis. Furthermore, when the single atomic Ce catalyst was used as cathodic material in a proof-of-concept of Zn-NO battery, it delivers a maximal power density of 3.4 mW cm^-2 and a high NH₃ yield rate of 309 μg h^-1 mg_cat.^-1. Theoretical simulations suggest that the Ce-N4 active moiety can not only activate NO molecules via a strong electronic interaction but also reduce the free energy barrier of *NO transition to *NOH intermediate as the limiting step, and therefore boosting the NORR kinetics and suppressing the competitive hydrogen evolution.

Nitrogen-Doped Porous Nickel Molybdenum Phosphide Sheets for Efficient Seawater Splitting

Hydrogen is emerging as an alternative clean fuel; however, its dependency on freshwater will be a threat to a sustainable environment. Seawater, an unlimited source, can be an alternative, but its salt-rich nature causes corrosion and introduces several competing reactions, hindering its use. To overcome these, a unique catalyst composed of porous sheets of nitrogen-doped NiMo₃ P (N-NiMo₃ P) having a sheet size of several microns is designed. The presence of large homogenous pores in the basal plane of these sheets makes them catalytically more active and ensures faster mass transfer. The introduction of N and Ni into MoP significantly tunes the electronic density of Mo, surface chemistry, and metal-non-metal bond lengths, optimizing surface energies, creating new active sites, and increasing electrical conductivity. The presence of metal-nitrogen bonds and surface polyanions increases the stability and improves anti-corrosive properties against chlorine chemistry. Ultimately, the N-NiMo₃ P sheets show remarkable performance as it only requires overpotentials of 23 and 35 mV for hydrogen evolution reaction, and it catalyzes full water splitting at 1.52 and 1.55 V to achieve 10 mA cm^-2 in 1 m KOH and seawater, respectively. Hence, structural and compositional control can make catalysts effective in realizing low-cost hydrogen directly from seawater.

Identification of Co-O-Mo Active Centers on Co-Doped MoS2 Electrocatalyst

Strategies for harmonizing the construction of an active site and the building of electron transport for a hybrid MoS₂ catalyst are crucial for its application in electrochemical reactions. In this work, an accurate and facile hydrothermal strategy was proposed to fabricate the active center of Co-O-Mo on a supported MoS₂ catalyst by forming a CoMoSO phase on the edge of MoS₂, yielding (Co-O)_x-MoS_y (x = 0, 0.3, 0.6, 1, 1.5, or 2.1). The results show that the electrochemical performances (hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and electrochemical degradation) of the yielded MoS₂-based catalysts were positively correlated with the Co-O bonds, verifying the significant role of Co-O-Mo as the active center. The fabricated (Co-O)-MoS_0.9 presented an extremely low overpotential and Tafel slope in both HER and OER, and it also demonstrated excellent BPA removal in the electrochemical degradation reaction. As compared with the Co-Mo-S configuration, the configuration of Co-O-Mo not only serves as the active center but also provides a conducting channel to facilitate electron conductivity with more accessible charge transfer at the electrode/electrolyte interface, which is favorable for electrocatalytic reaction. This work offers a new perspective for the active mechanism of metallic-heteroatom-dopant electrocatalysts and further boosts research on the development of noble/non-noble hybrid electrocatalysts in the future.

Alkali treatment of layered double hydroxide nanosheets as highly efficient bifunctional electrocatalysts for overall water splitting

Efficient and economic bifunctional electrocatalyst for water splitting to produce hydrogen is urgently required. The layered double hydroxides (LDHs) have shown superior activity for oxygen evolution reaction (OER) for water electrolysis, while their hydrogen evolution reaction (HER) activity remains challenging. Herein, we report an alkali hydrothermal-treatment strategy to enhance the HER as well as OER performance of NiCo-LDH. This method can create metal vacancies and newly formed Ni/Co(OH)₂ phase over NiCo-LDH, tune the electronic structure, and improve the electrical conductivity, thereby improving the electrochemical activity. The NiCo-LDH-OH catalyst delivers a current density of 10 mA cm^-2 at an overpotential of 180 mV for HER and an overpotential of 317 mV for OER, which is greatly reduced compared to the pristine NiCo-LDH (295 mV for HER and 336 mV for OER). When assembled into an electrolyzer both as a cathode and anode, it demonstrates superior activity for overall water splitting with no obvious decay after 20 h. This work paves a new path for fabricating efficient LDHs-based HER/OER bifunctional catalysts.

Cobalt Nanoparticles Anchored on N-Doped Porous Carbon Derived from Yeast for Enhanced Electrocatalytic Oxygen Reduction Reaction

Biomass-derived carbon materials have received extensive attention for use in high-performance electrocatalysts. In this study, a highly efficient electrocatalyst is developed with Co nanoparticles anchored on N-doped porous carbon material (CoNC) by using yeast as a biomass precursor through a facial activation and pyrolysis process. CoNC exhibits comparable catalytic activity with commercial 20 % Pt/C for the oxygen reduction reaction (ORR) with a half-wave potential of 0.854 V. A home-made primary Zn-air battery exhibited an open circuit potential of 1.45 V and a peak power density of 188 mW cm^-2 . Moreover, the discharge voltage of the primary battery maintained at a stable value up to 9 days. The enhanced performance of CoNC was probably ascribed to its high content of pyridinic-N and graphitic-N species, extra Co loading and porous structure, which provided sufficient active sites and channels to promote mass/electron transfer for ORR. This work provides a promising strategy to develop an efficient non-noble metal carbon-based electrocatalyst for fuel cells and metal-air batteries.

A corpus of CO2 electrocatalytic reduction process extracted from the scientific literature

The electrocatalytic CO₂ reduction process has gained enormous attention for both environmental protection and chemicals production. Thereinto, the design of new electrocatalysts with high activity and selectivity can draw inspiration from the abundant scientific literature. An annotated and verified corpus made from massive literature can assist the development of natural language processing (NLP) models, which can offer insight to help guide the understanding of these underlying mechanisms. To facilitate data mining in this direction, we present a benchmark corpus of 6,086 records manually extracted from 835 electrocatalytic publications, along with an extended corpus with 145,179 records in this article. In this corpus, nine types of knowledge such as material, regulation method, product, faradaic efficiency, cell setup, electrolyte, synthesis method, current density, and voltage are provided by either annotating or extracting. Machine learning algorithms can be applied to the corpus to help scientists find new and effective electrocatalysts. Furthermore, researchers familiar with NLP can use this corpus to design domain-specific named entity recognition (NER) models.

Noble-Metal-Metalloid Alloy Architectures: Mesoporous Amorphous Iridium-Tellurium Alloy for Electrochemical N2 Reduction

Amorphous noble metals with high surface areas have attracted significant interest as heterogeneous catalysts due to the numerous dangling bonds and abundant unsaturated surface atoms created by the amorphous phase. However, synthesizing amorphous noble metals with high surface areas remains a significant challenge due to strong isotropic metallic bonds. This paper describes the first example of a mesoporous amorphous noble metal alloy [iridium-tellurium (IrTe)] obtained using a micelle-directed synthesis method. The resulting mesoporous amorphous IrTe electrocatalyst exhibits excellent performance in the electrochemical N₂ reduction reaction. The ammonia yield rate is 34.6 μg mg^-1 h^-1 with a Faradaic efficiency of 11.2% at -0.15 V versus reversible hydrogen electrode in 0.1 M HCl solution, outperforming comparable crystalline and Ir metal counterparts. The interconnected porous scaffold and amorphous nature of the alloy create a complementary effect that simultaneously enhances N₂ absorption and suppresses the hydrogen evolution reaction. According to theoretical simulations, incorporating Te in the IrTe alloy effectively strengthens the adsorption of N₂ and lowers the Gibbs free energy for the rate-limiting step of the electrocatalytic N₂ reduction reaction. Mesoporous chemistry enables a new route to achieve high-performance amorphous metalloid alloys with properties that facilitate the selective electrocatalytic reduction of N₂.

Defective Metal Oxides: Lessons from CO2 RR and Applications in NOx RR

Sluggish reaction kinetics and the undesired side reactions (hydrogen evolution reaction and self-reduction) are the main bottlenecks of electrochemical conversion reactions, such as the carbon dioxide and nitrate reduction reactions (CO₂ RR and NO₃ RR). To date, conventional strategies to overcome these challenges involve electronic structure modification and modulation of the charge-transfer behavior. Nonetheless, key aspects of surface modification, focused on boosting the intrinsic activity of active sites on the catalyst surface, are yet to be fully understood. Engingeering of oxygen vacancies (OVs) can tune surface/bulk electronic structure and improve surface active sites of electrocatalysts. The continuous breakthroughs and significant progress in the last decade position engineering of OVs as a potential technique for advancing electrocatalysis. Motivated by this, the state-of-the-art findings of the roles of OVs in both the CO₂ RR and the NO₃ RR are presented. The review starts with a description of approaches to constructing and techniques for characterizing OVs. This is followed by an overview of the mechanistic understanding of the CO₂ RR and a detailed discussion on the roles of OVs in the CO₂ RR. Then, insights into the NO₃ RR mechanism and the potential of OVs on NO₃ RR based on early findings are highlighted. Finally, the challenges in designing CO₂ RR/NO₃ RR electrocatalysts and perspectives in studying OV engineering are provided.

Recent Progress in Surface-Defect Engineering Strategies for Electrocatalysts toward Electrochemical CO2 Reduction: A Review

Climate change, caused by greenhouse gas emissions, is one of the biggest threats to the world. As per the IEA report of 2021, global CO2 emissions amounted to around 31.5 Gt, which increased the atmospheric concentration of CO2 up to 412.5 ppm. Thus, there is an imperative demand for the development of new technologies to convert CO2 into value-added feedstock products such as alcohols, hydrocarbons, carbon monoxide, chemicals, and clean fuels. The intrinsic properties of the catalytic materials are the main factors influencing the efficiency of electrochemical CO2 reduction (CO2-RR) reactions. Additionally, the electroreduction of CO2 is mainly affected by poor selectivity and large overpotential requirements. However, these issues can be overcome by modifying heterogeneous electrocatalysts to control their morphology, size, crystal facets, grain boundaries, and surface defects/vacancies. This article reviews the recent progress in electrochemical CO2 reduction reactions accomplished by surface-defective electrocatalysts and identifies significant research gaps for designing highly efficient electrocatalytic materials.

Electrochemically Reconstructed Vanadic Oxide-Doped Cobalt Pyrophosphate as an Electrocatalyst for the Oxygen Evolution Reaction

More and more attention has been paid to the development of the efficient electrocatalysts for the oxygen evolution reaction (OER). Herein, a porous vanadic oxide-doped cobalt pyrophosphate electrocatalyst, namely V₂O₅-Co₂P₂O₇, was exploited by using the electrochemical reconstruction method in the alkaline electrolyte and selecting a cobalt vanadium phosphate Co(H₂O)₄(VOPO₄)₂ as a precursor. The reconstructed vanadic oxide-doped cobalt pyrophosphate catalyst V₂O₅-Co₂P₂O₇ exhibited efficient electrocatalytic activity for the OER in 1.0 M KOH, requiring a low overpotential of 199 mV at 10 mA cm^-2, compared to the reported pyrophosphate electrocatalysts. The porous morphology and doping of vanadic oxide after electrochemical reconstruction were beneficial to enhance the electrocatalytic performance for the OER, through improving the surface area to bring in more accessibly active sites and regulating the electronic structures. The results provided a promising strategy to prepare the pyrophosphate electrocatalysts and improve the performance of the OER catalyst.