MOF‐Mediated Fabrication of a Porous 3D Superstructure of Carbon Nanosheets Decorated with Ultrafine Cobalt Phosphide Nanoparticles for Efficient Electrocatalysis and Zinc–Air Batteries

Electron regulation of CeO2 on CoP multi-shell hetero-junction micro-sphere towards highly efficient water oxidation

CeO2 has been identified as a significant cocatalyst to enhance the electrocatalytic activity of transition metal phosphides (TMPs). However, the electrocatalytic mechanism by which CeO2 enhances the catalytic activity of TMP remains unclear. In this study, we have successfully developed a unique CeO2-CoP-1-4 multishell microsphere heterostructure catalyst through a simple hydrothermal and calcination process. CeO2-CoP-1-4 exhibits great potential for electrocatalytic oxygen evolution reaction (OER), requiring only an overpotential of 254 mV to achieve a current density of 10 mA cm-2. Moreover, CeO2-CoP-1-4 demonstrates excellent operating durability lasting for 55 h. The presence of CeO2 as a cocatalyst can regulate the microsphere structure of CoP, the resulting multishell microsphere structure can shorten the mass transfer distance, and improve the utilization rate of the active site. Furthermore, in situ Raman and ex situ characterizations, and DFT theoretical calculation results reveal that CeO2 can effectively regulates the electronic structure of Co species, reduces the reaction free energy of rate-limiting step, thus increase the reaction kinetic. Overall, this study provides experimental and theoretical evidence to better comprehend the mechanism and structure evolution of CeO2 in enhancing the OER performance of CoP, offering a unique design inspiration for the development of efficient hollow heterojunction electrocatalysts.

Streamlined synthesis of superstructure Ni-benzimidazole MOFs: Glucose electrochemical analysis

The design and synthesis of efficient electrochemical sensors are crucial transformation technologies in electrochemistry. We successfully synthesize a three-dimensional Ni-metal-organic framework (MOF) nanostructured material with a superior architecture using benzimidazole and nickel nitrate as precursors at room temperature which is being applied in glucose electrochemical sensors. The reaction mechanism of M-6 during glucose detection is thoroughly studied using various characterization techniques, such as in situ Raman spectroscopy, in situ ultraviolet-visible spectrophotometry, synchrotron radiography, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The research findings demonstrate that the M-6 material exhibits high sensitivity for glucose detection, with a sensitivity of 2199.88 mA M-1 cm-2. This study provides an important reference for designing more efficient electrochemical reaction systems and optimizing material performance. Furthermore, the superstructural design offers new ideas and possibilities for the development and application of similar materials.

Single Atom Ru Doped Ni2P/Fe3P Heterostructure for Boosting Hydrogen Evolution for Water Splitting

Modulating the chemical composition and structure has been considered as one of the most promising strategies for developing high-efficient water splitting catalysts. Here, a single-atom Ru doped Ni2P/Fe3P catalyst is synthesized by introducing the dispersed Ru atoms to adjust Ni2P/Fe3P heterostructure. Single atom Ru provides effective hydrogen evolution reaction (HER) active sites for boosting catalytic activities. The catalyst with only 0.2 wt.% content of Ru exhibits an overpotential of 19.3 mV at 10 mA cm-2, which is obviously lower than 146.1 mV of Ni2P/Fe3P. Notably, an alkaline overall water electrolyzer based on Ru-Ni2P/Fe3P catalysts achieves a cell voltage of 1.47 V and operates over 600 h at 10 mA cm-2, which is superior to that of benchmark RuO2//Pt/C (1.61 V). The theoretical calculations further confirm that Ru single atom doping can effectively optimize the hydrogen/water adsorption free energy of the active site and therefore improve the HER activity of heterostructure. This work provides a valuable reference to design high-activity and durability catalyst for water splitting through the double modulation of interface-effect and atomic doping.

In Situ Construction of Highly Dispersed Pd on Cobalt Nanoparticle on Hollow Functional Cubic Graphene by Double Framework for ORR

Developing advanced functional carbon materials is essential for electrocatalysis, caused by their vast merits for boosting many key energy conversion reactions. Herein, the covalent organic frameworks (COFs) is utilized on metal-organic frameworks (MOFs) as the template, under the controllable metal atoms thermal migration process successfully in situ constructs Pd-Co alloy nanoparticles on hollow cubic graphene. The electrocatalytic oxygen reduction reaction (ORR) evaluation showed excellent performances with a half-wave potential of 0.866 V, and a limited current density of 4.975 mA cm-2, that superior to the commercial Pt/C and Co nanoparticles. The contrast experiments and X-ray absorption spectrum demonstrated the aggregated electrons at highly dispersed Pd atoms on Co nanoparticle that promoted the main activities. This work not only enlightens the novel carbon materials designing strategies but also suggests heterogeneous electrocatalysis.

MoNP-doped Defective Carbon Fibers with Bark-like Nanosurface as Effective Bifunctional Electrocatalysts for Zn-air Batteries

The flexible air electrode with high oxygen electrocatalytic performance and outstanding stability under various deformations plays a vital role in high-performance flexible Zn-air batteries (ZABs). Herein, a self-supported Mo, N, and P co-doped carbon cloth (CC) denoted as MoNP@CC with bark-like surface structure is fabricated by a facile two-step approach via a one-pot method and pyrolysis. The surface of the electrode shows a nanoscale "rift valley" and uniformly distributed active sites. Taking advantage of the nano-surface as well as transition metal and heteroatom doping, the self-supported electrocatalysis air electrode exhibits considerable oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) performance in terms of low overpotential (388 mV at 10 mA cm-2) for OER and a much positive potential (0.74 V) at 1.0 mA cm-2 for ORR. Furthermore, MoNP@CC is further used for the flexible ZAB to demonstrate its practical application. The MoNP@CC-based ZAB displays a good cycling performance for 2800 min and an open-circuit voltage of 1.44 V. This work provides a new approach to the construction of a high-performance, self-supported electrocatalysis electrode used for a flexible energy storage device.

I Single-Atom Doped P-Rich CoPn Nanocluster@CoP with Enhanced HER

Constructing I single-atom (ISA) doped CoP electrocatalyst for HER is extremely challenging and has not been reported to date. Herein, an ISA doping-phosphatization strategy is proposed to prepare a novel I single-atom doped P-rich CoPn nanocluster@CoP electrocatalyst (ISA-CoPn/CoP) with enhanced HER performance first. ISA-CoPn/CoP shows a low overpotential of only 44 and 81 mV in 0.5 m H2SO4 solution, to drive a current density of 10 and 100 mA cm-2. ISA and P-rich CoPn nanocluster show unique synergies, which can optimize the H adsorption energy and accelerate the kinetics of HER in the CoP system. The intermediate I─H bond vibration peak is directly observed through in situ Raman testing, demonstrating that ISA doping helps accelerate the HER process. Additionally, the ΔGH of ISA-CoPn/CoP is only 0.05 eV by density functional theory (DFT) calculation, which is conducive to H2 evolution.

A pillar-layered Ni2P-Ni5P4-CoP array derived from a metal-organic framework as a bifunctional catalyst for efficient overall water splitting

Interfacial engineering emerges as a potent strategy for regulating the catalytic reactivity of metal phosphides. Developing a facile and cost-effective method to construct bifunctional metal phosphides for highly efficient electrochemical overall water splitting remains an essential and challenging issue. Here, a multiphase transition metal phosphide is constructed through the direct phosphorization of a Ni-Co metal-organic framework grown on nickel foam (Ni-Co-MOF/NF), which is prepared by utilizing nickel foam as conductive substrate and nickel source. The resulting transition metal phosphide manifests a pillar-layered morphology, wherein CoP, Ni2P, and Ni5P4 nanoparticles are embedded within each carbon sheet and these carbon sheets assemble into a pillar-shaped structure on the nickel foam (Ni2P-Ni5P4-CoP-C/NF). The heterogeneous Ni2P-Ni5P4-CoP-C/NF with multiple interfaces serves as a highly efficient bifunctional electrocatalyst with overpotentials of -100 mV and 293 mV in the hydrogen evolution reaction and oxygen evolution reaction, respectively, at 50 mA cm-2 in alkaline media. This superior catalytic performance should mainly be ascribed to its enriched active centers and multiphase synergy. When directly applied for alkaline overall water splitting, the Ni2P-Ni5P4-CoP-C/NF couple demonstrates satisfactory activity (1.55 V @10 mA cm-2) along with sustained durability over 18 hours. This method brings fresh enlightenment to the economical and controllable preparation of multi-metal phosphides for energy conversion.

Metal-Organic Framework (MOF)-Based Clean Energy Conversion: Recent Advances in Unlocking its Underlying Mechanisms

Carbon neutrality is an important goal for humanity . As an eco-friendly technology, electrocatalytic clean energy conversion technology has emerged in the 21st century. Currently, metal-organic framework (MOF)-based electrocatalysis, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), hydrogen oxidation reaction (HOR), carbon dioxide reduction reaction (CO2RR), nitrogen reduction reaction (NRR), are the mainstream energy catalytic reactions, which are driven by electrocatalysis. In this paper, the current advanced characterizations for the analyses of MOF-based electrocatalytic energy reactions have been described in details, such as density function theory (DFT), machine learning, operando/in situ characterization, which provide in-depth analyses of the reaction mechanisms related to the above reactions reported in the past years. The practical applications that have been developed for some of the responses that are of application values, such as fuel cells, metal-air batteries, and water splitting have also been demonstrated. This paper aims to maximize the potential of MOF-based electrocatalysts in the field of energy catalysis, and to shed light on the development of current intense energy situations.

Polymetal-Chelated Fabrication of Bimetallic Nanophosphides as Electrocatalysts for Zinc-Air Batteries

Bimetallic phosphides are considered as promising electrocatalysts for zinc-air batteries toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). To address the semi-conductor inherent low electronic conductivity and catalytic activity, a polymetal-chelated strategy is employed to in situ fabricate bimetallic nanophosphides within carbon matrix anchoring by chemical bonding. The employment of biomolecule polydopamine (PDA) efficiently anchors various transition metal ions due to its strong chelating capability via inherent functional groups. Furthermore, the chelation of multi-metal ion is proved to promote the formation of graphitic nitrogen. The bimetallic FexCoyP phosphides nanoparticles are intimately encapsulated in carbon matrix through in situ carbonization and phosphatization processes. When utilized in Zinc-air batteries, Fe0.20Co0.80P anchored within N, P co-doped sub-microsphere (Fe0.20Co0.80P /PNC) exhibit a maximum power density of 167 mW cm-2 and cycle life up to 270 cycles, with a round-trip voltage of 0.955 V. The mechanisms for catalytic activity passivation are ascribed to the etching of nitrogen and oxidation of phosphorus in carbon matrix, as well as the oxidation of the surface phosphide on the sub-microspheres. This study presents a promising candidate for advancing the further development of energy conversation catalysis.

Functionalized hydrogen-bonded organic superstructures via molecular self-assembly for enhanced uranium extraction

Effective uranium extraction from water is essential for the development of nuclear power industry and the protection of human health and environment. Nevertheless, it still remains challenging to realize efficient and cost-effective uranium extraction. Herein, a fast and simple method for the direct fabrication of novel functionalized hydrogen-bonded organic superstructures via molecular self-assembly is reported. The as-constructed flower-like superstructures (MCP-5) can allow the exposure of adsorption sites and facilitate the transport of uranyl ions, while synergism between amino and phosphate groups can realize selective uranium extraction. Consequently, MCP-5 possesses excellent uranium adsorption ability with a high saturated adsorption capacity of 950.52 mg g-1, high utilization rate of adsorption sites and adsorption equilibrium time of simply 5 min in uranium-spiked aqueous solution. Furthermore, MCP-5 offers selective uranium adsorption over a broad range of metal ions. The facile synthesis and low-cost raw materials make it have promising potential for uranium capture. Simultaneously, this study opens a design avenue of functionalized hydrogen-bonded organic material for efficient uranium extraction.

Non-noble metal single-atoms for oxygen electrocatalysis in rechargeable zinc-air batteries: recent developments and future perspectives

Ever-growing demands for zinc-air batteries (ZABs) call for the development of advanced electrocatalysts. Single-atom catalysts (SACs), particularly those for isolating non-noble metals (NBMs), are attracting great interest due to their merits of low cost, high atom utilization efficiency, structural tunability, and extraordinary activity. Rational design of advanced NBM SACs relies heavily on an in-depth understanding of reaction mechanisms. To gain a better understanding of the reaction mechanisms of oxygen electrocatalysis in ZABs and guide the design and optimization of more efficient NBM SACs, we herein organize a comprehensive review by summarizing the fundamental concepts in the field of ZABs and the recent advances in the reported NBM SACs. Moreover, the selection of NBM elements and supports of SACs and some effective strategies for enhancing the electrochemical performance of ZABs are illustrated in detail. Finally, the challenges and future direction in this field of ZABs are also discussed.

Recent progress of Ni-based nanomaterials for the electrocatalytic oxygen evolution reaction at large current density

The precise design and development of high-performing oxygen evolution reaction (OER) for the production of industrial hydrogen gas through water electrolysis has been a widely studied topic. A profound understanding of the nature of electrocatalytic processes reveals that Ni-based catalysts are highly active toward OER that can stably operate at a high current density for a long period of time. Given the current gap between research and applications in industrial water electrolysis, we have completed a systematic review by constructively discussing the recent progress of Ni-based catalysts for electrocatalytic OER at a large current density, with special focus on the morphology and composition regulation of Ni-based electrocatalysts for achieving extraordinary OER performance. This review will facilitate future research toward rationally designing next-generation OER electrocatalysts that can meet industrial demands, thereby promoting new sustainable solutions for energy shortage and environment issues.

Longevous Cycling of Rechargeable Zn-Air Battery Enabled by "Raisin-Bread" Cobalt Oxynitride/Porous Carbon Hybrid Electrocatalysts

Developing commercially viable electrocatalyst lies at the research hotspot of rechargeable Zn-air batteries, but it is still challenging to meet the requirements of energy efficiency and durability in realistic applications. Strategic material design is critical to addressing its drawbacks in terms of sluggish kinetics of oxygen reactions and limited battery lifespan. Herein, a "raisin-bread" architecture is designed for a hybrid catalyst constituting cobalt nitride as the core nanoparticle with thin oxidized coverings, which is further deposited within porous carbon aerogel. Based on synchrotron-based characterizations, this hybrid provides oxygen vacancies and Co-Nx -C sites as the active sites, resulting from a strong coupling between CoOx Ny nanoparticles and 3D conductive carbon scaffolds. Compared to the oxide reference, it performs enhanced stability in harsh electrocatalytic environments, highlighting the benefits of the oxynitride. Furthermore, the 3D conductive scaffolds improve charge/mass transportation and boost durability of these active sites. Density functional theory calculations reveal that the introduced N species into hybrid can synergistically tune the d-band center of cobalt and improve its bifunctional activity. As a result, the obtained air cathode exhibits bifunctional overpotential of 0.65 V and a battery lifetime exceeding 1350 h, which sets a new record for rechargeable Zn-air battery reported so far.

MOF-on-MOF-Derived Ultrafine Fe2P-Co2P Heterostructures for High-Efficiency and Durable Anion Exchange Membrane Water Electrolyzers

The alkaline hydrogen evolution reaction (HER) in an anion exchange membrane water electrolyzer (AEMWE) is considered to be a promising approach for large-scale industrial hydrogen production. Nevertheless, it is severely hampered by the inability to operate tolerable HER catalysts consistently under low overpotentials at ampere-level current densities. Here, we develop a universal ligand-exchange (MOF-on-MOF) modulation strategy to synthesize ultrafine Fe2P and Co2P nanoparticles, which are well anchored on N and P dual-doped carbon porous nanosheets (Fe2P-Co2P/NPC). In addition, benefiting from the downshift of the d-band center and the interfacial Co-P-Fe bridging, the electron-rich P site is triggered, which induces the redistribution of electron density and the swapping of active centers, lowering the energy barrier of the HER. As a result, the Fe2P-Co2P/NPC catalyst only requires a low overpotential of 175 mV to achieve a current density of 1000 mA cm-2. The solar-driven water electrolysis system presents a record-setting and stable solar-to-hydrogen conversion efficiency of 20.36%. Crucially, the catalyst could stably operate at 1000 mA cm-2 over 1000 h in a practical AEMWE at an estimated cost of US$0.79 per kilogram of H2, which achieves the target (US$2 per kg of H2) set by the U.S. Department of Energy (DOE).

Hierarchically Superstructured Anisotropic Carbon Particles by Multiscale Assembly Driven by Spinodal Decomposition

Hierarchical superstructures have novel shape-dependent properties, but well-defined anisotropic carbon superstructures with controllable size, shape, and building block dimensionality have rarely been accomplished thus far. Here, a hierarchical assembly technique is presented that uses spinodal decomposition (SD) to synthesize anisotropic oblate particles of mesoporous carbon superstructure (o-MCS) with nanorod arrays by integrating block-copolymer (BCP) self-assembly and polymer-polymer interface behaviors in binary blends. The interaction of major and minor phases in binary polymer blends leads to the formation of an anisotropic oblate particle, and the BCP-rich phase enables ordered packing and unidirectional alignment of carbon nanorods. Consequently, this approach enables precise control over particles' size, shape, and over the dimensionality of their components. Exploiting this functional superstructure, o-MCS are used as an anode material in potassium-ion batteries, and achieve a notable specific capacity of 156 mA h g-1 at a current density of 2 A g-1 , and long-term stability for 3000 cycles. This work presents a significant advancement in the field of hierarchical superstructures, providing a promising strategy for the design and synthesis of anisotropic carbon materials with controlled properties, offering promising applications in energy storage and beyond.

Terrace-Like 2D Hierarchically Porous Iron/Cobalt Metal-Organic Framework: Ambient Fast Synthesis and Efficient Oxygen Evolution Reaction Application

It is urgent to design a low-cost electrocatalyst with high activity to enhance the efficiency of oxygen evolution reaction (OER), which is limited by the slow four-electron transfer kinetics process. Nevertheless, traditional synthetic methods, including calcination and solvothermal, of the electrocatalysts are high-cost, low-yield, and energy-hogging, which limits their industrial application. Herein, an ambient fast synthetic method is developed to prepare terrace-like Fe/Co bimetal-organic framework (TFC-MOF) electrocatalyst materials in gram scale in 1 h. The method in this paper is designable based on coordination chemistry. Fe and Co ions can coordinate with the carboxyl groups on benzene-1,3,5-tricarboxylic acid (H3 BTC) to form a 2D-MOF structure. Structural characterizations, including SEM, TEM, and XRD are conducted to verify that the TFC-MOF is a terrace-like layered structure with uniform-sized mesoporous, which reduces the adsorption steric hindrance and facilitates the mass and electron transfer efficiency of OER. The TFC-MOF shows low overpotential, 255 mV at a current density of 10 mA cm-2 , and a low Tafel slope of 49.9 mV dec-1 , in an alkaline solution. This work provides a planar coordination strategy to synthesize 2D-MOF OER electrocatalyst on a large scale with low cost and low energy consumption, which will promote its practical OER applications.

Application of Conductive MOF in Zinc-Based Batteries

The use of conductive MOFs (c-MOFs) in zinc-based batteries has been a popular research direction. Zinc-based batteries are widely used with the advantages of high specific capacity and safety and stability, but they also face many problems. c-MOFs have excellent conductivity compared with other primitive MOFs, and therefore have better applications in zinc-based batteries. In this paper, the transfer mechanisms of the unique charges of c-MOFs: hop transport and band transport, respectively, are discussed and the way of electron transport is further addressed. Then, the various ways to prepare c-MOFs are introduced, among which solvothermal, interfacial synthesis, and postprocessing methods are widely used. In addition, the applications of c-MOFs are discussed in terms of their role and performance in different types of zinc-based batteries. Finally, the current problems of c-MOFs and the prospects for their future development are presented.

(Fe-Co-Ni-Zn)-Based Metal-Organic Framework-Derived Electrocatalyst for Zinc-Air Batteries

Zinc-air batteries (ZABs) have garnered significant interest as a viable substitute for lithium-ion batteries (LIBs), primarily due to their impressive energy density and low cost. However, the efficacy of zinc-air batteries is heavily dependent on electrocatalysts, which play a vital role in enhancing reaction efficiency and stability. This scholarly review article highlights the crucial significance of electrocatalysts in zinc-air batteries and explores the rationale behind employing Fe-Co-Ni-Zn-based metal-organic framework (MOF)-derived hybrid materials as potential electrocatalysts. These MOF-derived electrocatalysts offer advantages such as abundancy, high catalytic activity, tunability, and structural stability. Various synthesis methods and characterization techniques are employed to optimize the properties of MOF-derived electrocatalysts. Such electrocatalysts exhibit excellent catalytic activity, stability, and selectivity, making them suitable for applications in ZABs. Furthermore, they demonstrate notable capabilities in the realm of ZABs, encompassing elevated energy density, efficacy, and prolonged longevity. It is imperative to continue extensively researching and developing this area to propel the advancement of ZAB technology forward and pave the way for its practical implementation across diverse fields.

A General "In Situ Etch-Adsorption-Phosphatization" Strategy for the Fabrication of Metal Phosphides/Hollow Carbon Composite for High Performance Liquid/Flexible Zn-Air Batteries

Benefiting from the admirable energy density (1086 Wh kg-1 ), overwhelming security, and low environmental impact, rechargeable zinc-air batteries (ZABs) are deemed to be attractive candidates for lithium-ion batteries. The exploration of novel oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts is the key to promoting the development of zinc-air batteries. Transitional metal phosphides (TMPs) especially Fe-based TMPs are deemed to be a rational type of catalyst, however, their catalytic performance still needs to be further improved. Considering Fe (heme) and Cu (copper terminal oxidases) are nature's options for ORR catalysis in many forms of life from bacteria to humans. Herein, a general "in situ etch-adsorption-phosphatization" strategy is designed for the fabrication of hollow FeP/Fe2 P/Cu3 P-N, P codoped carbon (FeP/Cu3 P-NPC) catalyst as the cathode of liquid and flexible ZABs. The liquid ZABs manifest a high peak power density of 158.5 mW cm-2 and outstanding long-term cycling performance (≈1100 cycles at 2 mA cm-2 ). Similarly, the flexible ZABs deliver superior cycling stability of 81 h at 2 mA cm-2 without bending and 26 h with different bending angles.

Sustainable zinc-air battery chemistry: advances, challenges and prospects

Sustainable zinc-air batteries (ZABs) are considered promising energy storage devices owing to their inherent safety, high energy density, wide operating temperature window, environmental friendliness, etc., showing great prospect for future large-scale applications. Thus, tremendous efforts have been devoted to addressing the critical challenges associated with sustainable ZABs, aiming to significantly improve their energy efficiency and prolong their operation lifespan. The growing interest in sustainable ZABs requires in-depth research on oxygen electrocatalysts, electrolytes, and Zn anodes, which have not been systematically reviewed to date. In this review, the fundamentals of ZABs, oxygen electrocatalysts for air cathodes, physicochemical properties of ZAB electrolytes, and issues and strategies for the stabilization of Zn anodes are systematically summarized from the perspective of fundamental characteristics and design principles. Meanwhile, significant advances in the in situ/operando characterization of ZABs are highlighted to provide insights into the reaction mechanism and dynamic evolution of the electrolyte|electrode interface. Finally, several critical thoughts and perspectives are provided regarding the challenges and opportunities for sustainable ZABs. Therefore, this review provides a thorough understanding of the advanced sustainable ZAB chemistry, hoping that this timely and comprehensive review can shed light on the upcoming research horizons of this prosperous area.

One-Step Electrodeposition of a Mesoporous Ni/Co-Imidazole-Based Bimetal-Organic Framework on Pyramid-like NiSb with Abundant Coupling Interfaces as an Ultra-Stable Heterostructural Electrocatalyst for Water Splitting

The exploration of highly efficient metal-organic framework (MOF)-based electrocatalysts is a research topic of high significance owing to their potential applications in sustainable and clean energy production. Herein, a mesoporous MOF containing Ni and Co nodes along with 2-methylimidazole (Hmim) ligands has been directly grown on the surface of the pyramid-like NiSb through a convenient cathodic electrodeposition strategy and evaluated as the catalyst for water splitting catalysis. Tailoring catalytically active sites through porous well-arranging architecture and the coupled interface offers a catalyst with exquisite performance that displays ultra-low Tafel constant of 33 and 42 mV dec^-1 toward the hydrogen evolution reaction and oxygen evolution reaction, sequentially, and also enhanced durability at high current densities over 150 h in a 1 M KOH medium. The success of the synthesized NiCo-MOF@NiSb@GB electrode is explained by the intimate contact between the NiCo-MOF and NiSb with well-tailored phase interfaces, the positive coupling effect between Ni and Co metal centers in the MOF, and the porous structure with abundant active sites toward electrocatalysis. Importantly, the present work provides a new technical reference for the electrochemical synthesis of heterostructural MOFs as a promising candidate for energy-related applications.

Replacing Oxygen Evolution with Hydrazine Borane Oxidation for Energy-Saving Electrochemical Hydrogen Production

Electrochemical water splitting is a green strategy for hydrogen (H₂) production but is severely hindered by the sluggish anodic oxygen evolution reaction (OER). Therefore, replacing the sluggish anodic OER with more favorable oxidation reactions is an energy-saving approach for hydrogen production. Hydrazine borane (HB, N₂H₄BH₃) is considered a potential hydrogen storage material due to its easy preparation, nontoxicity, and high chemical stability. Furthermore, the complete electrooxidation of HB has a unique characteristic of a much lower potential compared to that of OER. All these make it an ideal alternative for energy-saving electrochemical hydrogen production, however, which has never been reported so far. Herein, HB oxidation (HBOR)-assisted overall water splitting (OWS) is proposed for the first time for energy-saving electrochemical hydrogen production. The as-synthesized NiCoP@CoFeP nanoneedle array catalyst exhibited superefficient OER, hydrogen evolution reaction (HER), and HBOR performance. Impressively, NiCoP@CoFeP serves as both anodic and cathodic electrocatalysts for HB-assisted OWS, only requires a low cell voltage of only 0.078 V to achieve a current density of 10 mA cm^-2, which was 1.4 V lower than that for HB-free OWS, indicating the highly energy-saving H₂ production.

Pencil-like Hollow Carbon Nanotubes Embedded CoP-V4P3 Heterostructures as a Bifunctional Catalyst for Electrocatalytic Overall Water Splitting

Electrocatalytic water splitting is one of the most efficient ways of producing green hydrogen energy. The design of stable, active, and efficient electrocatalysts plays a crucial role in water splitting for achieving efficient energy conversion from electrical to hydrogen energy, aimed at solving the lingering energy crisis. In this work, CNT composites modified with CoP-V₄P₃ composites (CoVO-10-CNT-450P) were formed by carbonising a pencil-like precursor (Co₃V₂O₈-H₂O) and growing carbon nanotubes in situ, followed by in situ phosphorylation on the carbon nanotubes. In the HER electrocatalytic process, an overpotential of only 124 mV was exhibited at a current density of 10 mA cm^-2. In addition, as an OER catalyst, a low overpotential of 280 mV was attained at a current density of 10 mA cm^-2. Moreover, there was no noticeable change in the performance of the catalyst over a 90 h test in a continuous total water splitting experiment. The unique electronic structure and hollow carbon nanotube structure of CoVO-10-CNT-450P effectively increased the catalytic active sites, while also significantly improving the electrocatalytic activity. This work provides theoretical guidance for the design and synthetic route of high-performance non-precious metal electrocatalysts, and actively promotes the commercial application of electrochemical water splitting.

Recent advances in interface engineering of Fe/Co/Ni-based heterostructure electrocatalysts for water splitting

Among various methods of developing hydrogen energy, electrocatalytic water splitting for hydrogen production is one of the approaches to achieve the goal of zero carbon emissions. It is of great significance to develop highly active and stable catalysts to improve the efficiency of hydrogen production. In recent years, the construction of nanoscale heterostructure electrocatalysts through interface engineering can not only overcome the shortcomings of single-component materials to effectively improve their electrocatalytic efficiency and stability but also adjust the intrinsic activity or design synergistic interfaces to improve catalytic performance. Among them, some researchers proposed to replace the slow oxygen evolution reaction at the anode with the oxidation reaction of renewable resources such as biomass to improve the catalytic efficiency of the overall water splitting. The existing reviews in the field of electrocatalysis mainly focus on the relationship between the interface structure, principle, and principle of catalytic reaction, and some articles summarize the performance and improvement schemes of transition metal electrocatalysts. Among them, few studies are focusing on Fe/Co/Ni-based heterogeneous compounds, and there are fewer summaries on the oxidation reactions of organic compounds at the anode. To this end, this paper comprehensively describes the interface design and synthesis, interface classification, and application in the field of electrocatalysis of Fe/Co/Ni-based electrocatalysts. Based on the development and application of current interface engineering strategies, the experimental results of biomass electrooxidation reaction (BEOR) replacing anode oxygen evolution reaction (OER) are discussed, and it is feasible to improve the overall electrocatalytic reaction efficiency by coupling with hydrogen evolution reaction (HER). In the end, the challenges and prospects for the application of Fe/Co/Ni-based heterogeneous compounds in water splitting are briefly discussed.

Advances of Electroactive Metal-Organic Frameworks

The preparation of electroactive metal-organic frameworks (MOFs) for applications of supercapacitors and batteries has received much attention and remarkable progress during the past few years. MOF-based materials including pristine MOFs, hybrid MOFs or MOF composites, and MOF derivatives are well designed by a combination of organic linkers (e.g., carboxylic acids, conjugated aromatic phenols/thiols, conjugated aromatic amines, and N-heterocyclic donors) and metal salts to construct predictable structures with appropriate properties. This review will focus on construction strategies of pristine MOFs and hybrid MOFs as anodes, cathodes, separators, and electrolytes in supercapacitors and batteries. Descriptions and discussions follow categories of electrochemical double-layer capacitors (EDLCs), pseudocapacitors (PSCs), and hybrid supercapacitors (HSCs) for supercapacitors. In contrast, Li-ion batteries (LIBs), Lithium-sulfur batteries (LSBs), Lithium-oxygen batteries (LOBs), Sodium-ion batteries (SIBs), Sodium-sulfur batteries (SSBs), Zinc-ion batteries (ZIBs), Zinc-air batteries (ZABs), Aluminum-sulfur batteries (ASBs), and others (e.g., LiSe, NiZn, H⁺ , alkaline, organic, and redox flow batteries) are categorized for batteries.

Proton-Conductive Supramolecular Hydrogen-Bonded Organic Superstructures for High-Performance Zinc-Organic Batteries

With fast (de)coordination kinetics, the smallest and the lightest proton stands out as the most ideal charge carrier for aqueous Zn-organic batteries (ZOBs). Hydrogen-bonding networks with rapid Grotthuss proton conduction is particularly suitable for organic cathodes, yet not reported. We report the supramolecular self-assembly of cyanuric acid and 1,3,5-triazine-2,4,6-triamine into organic superstructures through in-plane H-bonds and out-of-plane π-π interaction. The supramolecular superstructures exhibit highly stable lock-and-key H-bonding networks with an ultralow activation energy for protonation (0.09 eV vs. 0.25 eV of zincification). Then, high-kinetics H⁺ coordination is prior to Zn²⁺ into protophilic C=O sites via a two-step nine-electron reaction. The assembled ZOBs show high-rate capability (135 mAh g^-1 at 150 A g^-1 ), high energy density (267 Wh kg^-1 _cathode ) and ultra-long life (50 000 cycles at 10 A g^-1 ), becoming the state-of-the-art ZOBs in comprehensive performances.

Hollow Heterostructured Nanocatalysts for Boosting Electrocatalytic Water Splitting

The implementation of electrochemical water splitting demands the development and application of electrocatalysts to overcome sluggish reaction kinetics of hydrogen/oxygen evolution reaction (HER/OER). Hollow nanostructures, particularly for hollow heterostructured nanomaterials can provide multiple solutions to accelerate the HER/OER kinetics owing to their advantageous merit. Herein, the recent advances of hollow heterostructured nanocatalysts and their excellent performance for water splitting are systematically summarized. Starting by illustrating the intrinsically advantageous features of hollow heterostructures, achievements in engineering hollow heterostructured electrocatalysts are also highlighted with the focus on structural design, interfacial engineering, composition regulation, and catalytic evaluation. Finally, some perspective insights and future challenges of hollow heterostructured nanocatalysts for electrocatalytic water splitting are also discussed.

The Role of Discrepant Reactive Intermediates on Ru-Ru2 P Heterostructure for pH-Universal Hydrogen Oxidation Reaction

Developing highly efficient electrocatalysts for hydrogen oxidation reaction (HOR) under alkaline media is essential for the commercialization of alkaline exchange membrane fuel cell (AEMFC). However, the kinetics of HOR in alkaline media is complicated, resulting in orders of magnitude slower than that in acid, even for the state-of-the-art Pt/C. Here, we find that Ru-Ru₂ P/C heterostructure shows HOR performance with a non-monotonous variation in a whole pH region. Unexpectedly, an inflection point located at pH≈7 is observed, showing an anomalous behavior that HOR activity under alkaline media surpasses acidic media. Combining experimental results and theoretical calculations, we propose the roles of discrepant reactive intermediates for pH-universal HOR, while H* and H₂ O* adsorption strengths are responsible for acidic HOR, and OH* adsorption strength is essential for alkaline HOR. This work not only sheds light on fundamentally understanding the mechanism of HOR but also provides new designing principles for pH-targeted electrocatalysts.

Self-Supporting Metal-Organic Framework-Based Nanoarrays for Electrocatalysis

The replacement of powdery catalysts with self-supporting alternatives for catalyzing various electrochemical reactions is extremely important for the large-scale commercial application of renewable energy storage and conversion technologies. Metal-organic framework (MOF)-based nanoarrays possess tunable compositions, well-defined structure, abundant active sites, effective mass and electron transport, etc., which enable them to exhibit superior electrocatalytic performance in multiple electrochemical reactions. This review presents the latest research progress in developing MOF-based nanoarrays for electrocatalysis. We first highlight the structural features and electrocatalytic advantages of MOF-based nanoarrays, followed by a detailed summary of the design and synthesis strategies of MOF-based nanoarrays, and then describe the recent progress of their application in various electrocatalytic reactions. Finally, the challenges and perspectives are discussed, where further exploration into MOF-based nanoarrays will facilitate the development of electrochemical energy conversion technologies.

Regulating the coordination capacity of ATMP using melamine: facile synthesis of cobalt phosphides as bifunctional electrocatalysts for the ORR and HER

Due to the complexity of the synthetic process of cobalt phosphides (CoP), ongoing efforts concentrate on simplifying the preparation process of CoP. In this work, amino tris(methylene phosphonic acid) (ATMP, L1) and melamine (MA, L2) are assembled into two-dimensional (2D) organic nanostructures by hydrogen bonding and ionic interactions via a supramolecular assembly, which greatly weakens the coordination ability of L1 with Co²⁺. As the introduced L2 is rich in carbon and nitrogen, it allows the cobalt-organophosphate complex to be placed under a strongly reducing atmosphere during the high-temperature calcination process to achieve an in situ phosphating purpose. The resulting catalyst (N-CoP/NC) exhibits the sought-after enhanced oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) performance. For the ORR in 0.1 M KOH, an enhanced onset potential (0.908 V vs. RHE) and diffusion limiting current (6.280 mA cm^-2) can be obtained, which is comparable to those of 20% Pt/C (0.911 V vs. RHE, 5.380 mA cm^-2). For the HER in 0.5 M H₂SO₄, an overpotential of 150 mV is required to drive a current of 10 mA cm^-2. Moreover, Density Functional Theory (DFT) calculations reveal the catalytic pathway of N-CoP/NC.

Texture Regulation of Metal-Organic Frameworks, Microwave Absorption Mechanism-Oriented Structural Optimization and Design Perspectives

Texture regulation of metal-organic frameworks (MOFs) is essential for controlling their electromagnetic wave (EMW) absorption properties. This review systematically summarizes the recent advancements in texture regulation strategies for MOFs, including etching and exchange of central ions, etching and exchange of ligands, chemically induced self-assembly, and MOF-on-MOF heterostructure design. Additionally, the EMW absorption mechanisms in approaches based on structure-function dependencies, including nano-micro topological engineering, defect engineering, interface engineering, and hybrid engineering, are comprehensively explored. Finally, current challenges and future research orientation are proposed. This review aims to provide new perspectives for designing MOF-derived EMW-absorption materials to achieve essential breakthroughs in mechanistic investigations in this promising field.

In Situ Growth of Self-Supporting MOFs-Derived Ni2P on Hierarchical Doped Carbon for Efficient Overall Water Splitting

The in situ growth of metal organic framework (MOF) derivatives on the surface of nickel foam is a novel type of promising self-supporting electrode catalyst. In this paper, this work reports for the first time the strategy of in situ growth of Ni-MOF, where the metal source is purely provided by a nickel foam (NF) substrate without any external metal ions. MOF-derived Ni2P/NPC structure is achieved by the subsequent phosphidation to yield Ni2P on porous N, P-doped carbon (NPC) backbone. Such strategy provides the as-synthesized Ni2P/NPC/NF electrocatalyst an extremely low interfacial steric resistance. Moreover, a unique three-dimensional hierarchical structure is achieved in Ni2P/NPC/NF, providing massive active sites, short ion diffusion path, and high electrical conductivity. Directly applied as the electrode, Ni2P/NPC/NF demonstrates excellent electrocatalytic performance towards both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), with low overpotentials of only 58 mV and 208 mV to drive 10 mA cm−2, respectively, in 1 M KOH. Furthermore, Ni2P/NPC/NF acting as the overall water splitting electrodes can generate a current density of 10 mA cm−2 at an ultralow cell voltage of 1.53 V. This simple strategy paves the way for the construction of self-supporting transition metal-based electrocatalysts.

Emerging Heterogeneous Supports for Efficient Electrocatalysis

Electrocatalysis plays a fundamental role in many fields, such as metallurgy, medicine, chemical industry, and energy conversion. Anchoring active electrocatalysts with controllable loading and uniform dispersion onto suitable supports has become an attractive topic. This is because the supports can not only have the potential to improve catalytic activity and stability through the interaction between support and catalytic center, but also can reduce precious metal consumption by improving atomic utilization. Herein, recent theoretical and experimental progresses concerning the development of supports to anchor electrocatalytic materials are first reviewed. Next, their controllable syntheses, characterization techniques, metal-support electronic interactions, and structure-performance relationships are presented. Some representative carbon supports and non-carbonaceous supports, as well as recently reported star supports such as 2D supports, single atom catalysts, and self-supported catalysts are also summarized. In addition, the significant role of support in stabilizing and regulating catalytic active sites is particularly emphasized. Finally, challenges, opportunities, key problems, and further promising solutions for supported catalysts are proposed.

Sodium Hexa-Titanate Nanowires Modified with Cobalt Hydroxide Quantum Dots as an Efficient and Cost-Effective Electrocatalyst for Hydrogen Evolution in Alkaline Media

A novel electrocatalyst with high activity and enhanced durability toward the hydrogen evolution reaction (HER) in alkaline media has been designed and fabricated based on sodium hexa-titanate (Na₂Ti₆O₁₃) nanowires synthesized by a hydrothermal process and modified with Co(OH)₂ quantum dots (QDs) by a facile chemical bath deposition (CBD) method. The current response of the developed Ti/Na₂Ti₆O₁₃/Co(OH)₂ nanocomposite electrode attained 10 mA cm^-2 at an overpotential of 159 mV. The nanocomposite electrode exhibited a high stability at an applied current of 100 mA cm^-2. The remarkable catalytic behavior was achieved with a loading amount of ca. 0.06 mg cm^-2 cobalt hydroxide. This is attributed to the high electrochemically active surface area (EASA) gained by the nanowire-structured substrate and considerable enhancement of electrochemical conductivity with the use of Co(OH)₂ quantum dots as an active material. The superior catalytic activity and high stability show that the developed catalyst is a promising candidate for hydrogen production in alkaline media.

MOF-derived nanoarrays as advanced electrocatalysts for water splitting

Developing efficient, nanostructured electrocatalysts with the desired compositions and structures is of great significance for improving the efficiency of water splitting toward hydrogen production. In this regard, metal-organic framework (MOF) derived nanoarrays have attracted great attention as promising electrocatalysts because of their diverse compositions and adjustable structures. In this review, the recent progress in MOF-derived nanoarrays for electrochemical water splitting is summarized, highlighting the structural design of the MOF-derived nanoarrays and the electrocatalytic performance of the derived composite carbon materials, oxides, hydroxides, sulfides, and phosphides. In particular, the structure-performance relationships of the MOF-derived nanoarrays and the modulation strategies toward enhanced catalytic activity for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are discussed, providing insights into the development of advanced catalysts for the HER and OER. The challenges and prospects in this promising field for future industrial applications are also addressed.

Urea-oxidation-assisted electrochemical water splitting for hydrogen production on a bifunctional heterostructure transition metal phosphides combining metal-organic frameworks

Electrocatalyzed urea-assisted wastewater splitting is a promising approach for sustainable hydrogen production. However, the lack of cost-efficient electrocatalysts hinders its practical application. Herein, bimetal phosphide (NiCoP_x) nanowire arrays decorated with ultrathin NiFeCo metal-organic framework (NiFeCo-MOF) nanosheets on porous nickel foam (NF) were designed for urea-assisted wastewater splitting. The core-shell NiCoP_x@NiFeCo-MOF hybrids were prepared via successive hydrothermal, gas-phase phosphorization and hydrothermal strategies. Encouragingly, the novel NiCoP_x@NiFeCo-MOF/NF electrode served as an excellent bifunctional electrocatalyst for both the cathodic hydrogen evolution reaction (HER) and the anodic urea oxidation reaction (UOR) in urea-assisted water splitting, which merely required an overpotential of 44 mV to deliver a current density of 10 mA cm^-2 for HER and a voltage of 1.37 V to deliver a current density of 100 mA cm^-2 for UOR in 1.0 M KOH + 0.5 M urea. Benefiting from the highly exposed electroactive sites in exquisite three-dimensional (3D) hierarchical structure, multicomponent synergistic effect, accelerated electron transfer, easy electrolyte access and diffusion of released gas bubbles, the as-fabricated NiCoP_x@NiFeCo-MOF/NF exhibited outstanding electrocatalytic performance. The mechanism of water splitting was elucidated by density functional theory calculations. Interestingly, NiFeCo-MOF possessed optimized COO* adsorption ability on Ni sites that were beneficial to UOR intermediates. More significantly, this work paves the way for the design and fabrication of bifunctional electrocatalysts for urea-containing wastewater treatment and sustainable hydrogen production.

Nanoemulsion-Coated Ni-Fe Hydroxide Self-Supported Electrode as an Air-Breathing Cathode for High-Performance Zinc-Air Batteries

To improve the energy conversion efficiency and durability of zinc-air batteries (ZABs) for large-scale implementations, here we propose an "air-breathing" strategy to significantly enlarge triple-interfaces with intensified mass transfer. By dip-coating the aerophilic perfluorochemical compounds (PFC) and amphiphilic ionomers into the self-supported electrodes, (1) the high solubility of O₂ in the PFC nanoemulsions greatly increases triple-phase boundaries and facilitates the efficient supply/removal of O₂ from the electrolyte; (2) the ionomers with hydrophobic and hydrophilic functionalities enable fast gas, water, and ion transport to the triple-phase boundaries; and (3) the self-supported electrode without binder ensures fast electron transfer while the firm integration prevents catalyst shedding. By applying this strategy, the ZABs show a high power density of 115 mW cm^-2 and a narrow discharge/charge gap of 0.64 V at 10 mA cm^-2 and a long-cycling durability (over 1000 h). This work provides a universal approach to promote gas-evolving reactions for electrochemical applications.

A Kinetically Superior Rechargeable Zinc-Air Battery Derived from Efficient Electroseparation of Zinc, Lead, and Copper in Concentrated Solutions

Zinc electrodeposition is currently a hot topic because of its widespread use in rechargeable zinc-air batteries. However, Zn deposition has received little attention in organic solvents with much higher ionic conductivity and current efficiency. In this study, a Zn-betaine complex is synthesized by using ZnO and betainium bis[(trifluoromethyl)sulfonyl]imide and its electrochemical behavior for six organic solvents and electrodeposited morphology are studied. Acetonitrile allowed dendrite-free Zn electrodeposition at room temperature with current efficiencies of up to 86 %. From acetonitrile solutions in which Zn, Pb, and Cu complexes are dissolved in high concentrations, Zn and Pb/Cu are efficiently separated electrolytically under potentiostatic control, allowing the purification of solutions prepared directly from natural ores. Additionally, a highly flexible Zn anode with excellent kinetics is obtained by using a carbon fabric substrate. A rechargeable zinc-air battery with these electrodes shows an open-circuit voltage of 1.63 V, is stable for at least 75 cycles at 0.5 mA cm^-2 or 33 cycles at 20 mA cm^-2 , and allows intermediate cycling at 100 mA cm^-2 .

Freestanding Metal-Organic Frameworks and Their Derivatives: An Emerging Platform for Electrochemical Energy Storage and Conversion

Metal–organic frameworks (MOFs) have recently emerged as ideal electrode materials and precursors for electrochemical energy storage and conversion (EESC) owing to their large specific surface areas, highly tunable porosities, abundant active sites, and diversified choices of metal nodes and organic linkers. Both MOF-based and MOF-derived materials in powder form have been widely investigated in relation to their synthesis methods, structure and morphology controls, and performance advantages in targeted applications. However, to engage them for energy applications, both binders and additives would be required to form postprocessed electrodes, fundamentally eliminating some of the active sites and thus degrading the superior effects of the MOF-based/derived materials. The advancement of freestanding electrodes provides a new promising platform for MOF-based/derived materials in EESC thanks to their apparent merits, including fast electron/charge transmission and seamless contact between active materials and current collectors. Benefiting from the synergistic effect of freestanding structures and MOF-based/derived materials, outstanding electrochemical performance in EESC can be achieved, stimulating the increasing enthusiasm in recent years. This review provides a timely and comprehensive overview on the structural features and fabrication techniques of freestanding MOF-based/derived electrodes. Then, the latest advances in freestanding MOF-based/derived electrodes are summarized from electrochemical energy storage devices to electrocatalysis. Finally, insights into the currently faced challenges and further perspectives on these feasible solutions of freestanding MOF-based/derived electrodes for EESC are discussed, aiming at providing a new set of guidance to promote their further development in scale-up production and commercial applications.

Ruthenium Complex of sp2 Carbon-Conjugated Covalent Organic Frameworks as an Efficient Electrocatalyst for Hydrogen Evolution

It is still a great challenge to explore hydrogen evolution reaction (HER) electrocatalysts with both lower overpotential and higher stability in acidic electrolytes. In this work, an efficient HER catalyst, Ru@COF-1, is prepared by complexation of triazine-cored sp² carbon-conjugated covalent organic frameworks (COFs) with ruthenium ion. Ru@COF-1 possesses high crystallinity and porosity, which are beneficial for electrocatalysis. The large specific surface area and regular porous channels of Ru@COF-1 facilitate full contact between reactants and catalytic sites. The nitrogen atoms of triazines are protonated in the acidic media, which greatly improve the conductivity of Ru@COF-1. This synergistic effect makes the overpotential of Ru@COF-1 about 200 mV at 10 mA cm^-2 , which is lower than other reported COFs-based electrocatalysts. Moreover, Ru@COF-1 exhibits exceptionally electrocatalytic durability in the acidic electrolytes. It is particularly stable and remains highly active after 1000 cyclic voltammetry cycles. Density functional theory calculations demonstrate that tetracoordinated Ru-N₂ Cl₂ moieties are the major contributors to the outstanding HER performance. This work provides a new idea for developing protonated HER electrocatalysts in acidic media.

MOF-Derived Ultrathin Cobalt Molybdenum Phosphide Nanosheets for Efficient Electrochemical Overall Water Splitting

The development of high-performance and cost-effective earth-abundant transition metal-based electrocatalysts is of major interest for several key energy technologies, including water splitting. Herein, we report the synthesis of ultrathin CoMoP nanosheets through a simple ion etching and phosphorization method. The obtained catalyst exhibits outstanding electrocatalytic activity and stability towards oxygen and hydrogen evolution reactions (OER and HER), with overpotentials down to 273 and 89 mV at 10 mA cm⁻², respectively. The produced CoMoP nanosheets are also characterized by very small Tafel slopes, 54.9 and 69.7 mV dec⁻¹ for OER and HER, respectively. When used as both cathode and anode electrocatalyst in the overall water splitting reaction, CoMoP-based cells require just 1.56 V to reach 10 mA cm⁻² in alkaline media. This outstanding performance is attributed to the proper composition, weak crystallinity and two-dimensional nanosheet structure of the electrocatalyst.

Electrochemical Hydrogenation of Furfural in Aqueous Acetic Acid Media with Enhanced 2-Methylfuran Selectivity Using CuPd Bimetallic Catalysts

Herein, we report a series of CuPd catalysts for electrochemical hydrogenation (ECH) of furfural to 2-methylfuran (MF or FurCH₃ where Fur=furyl) in aqueous 0.1 M acetic acid (pH 2.9). The highest faradaic efficiency (FE) for MF reached 75 % at -0.58 V vs. reversible hydrogen electrode with an average partial current density of 4.5 mA cm^-2 . In situ surface-enhanced Raman spectroscopic and kinetic isotopic experiments suggested that electrogenerated adsorbed hydrogen (H_ads ) was involved in the reaction and incorporation of Pd enhanced the surface coverage of H_ads and optimized the adsorption pattern of furfural, leading to a higher FE for MF. Density functional theory calculations revealed that Pd incorporation reduced the energy barrier for the hydrogenation of FurCH₂ * to FurCH₃ *. Our study demonstrates that catalyst surface structure/composition plays a crucial role in determining the selectivity in ECH and provides a new strategy for designing advanced catalysts for ECH of bio-derived oxygenates.

Two-Dimensional Cobalt Sulfide/Iron-Nitrogen-Carbon Holey Sheets with Improved Durability for Oxygen Electrocatalysis

Transition-metal sulfide as a promising bifunctional oxygen electrocatalyst alternative to scarce platinum-group metals has attracted much attention, but it suffers activity loss over time owing to poor structural/compositional stability during catalysis. Herein, we report a self-template method for preparing a two-dimensional cobalt sulfide holey sheet superstructure with hierarchical porosity followed by the encapsulation of thin iron-nitrogen-carbon as a protective layer. The iron-nitrogen-carbon layer to some degree precludes the phase transition of cobalt sulfide underneath and preserves the structural integrity during catalysis, therefore rendering an exceptional durability in terms of no obvious activity loss after 10,000 cycles of the accelerated durability test. It also noticeably enhances the intrinsic activity of cobalt sulfide and does not influence its exposure into the electrolyte, resulting in showing an extraordinary electrochemical performance in terms of a potential difference of 0.69 V for the overall oxygen redox. A rechargeable zinc-air battery assembled by a cobalt sulfide/iron-nitrogen-carbon air cathode delivers approximately 4.2 times higher power density than that without an iron-nitrogen-carbon layer and stably operates for 300 h with a high voltaic efficiency. This work gives a facile and effective strategy for improving the long-term durability of transition-metal sulfide electrocatalysts.

Combining Multivariate Electrospinning with Surface MOF Functionalization to Construct Tunable Active Sites toward Trifunctional Electrocatalysis

The development of high-performance multifunctional electrocatalysts operating in the same electrolyte is key to reduce the material and process costs of renewable energy conversion and storage devices. Herein, the fabrication of freestanding integral electrodes by combining multivariate electrospinning with surface metal organic framework functionalization to arrest pyrolytic emissions from fiber interior is reported, resulting in the expression of rich active sites with controlled composition, for example, the tunable Co-P coordination. The as-fabricated electrode of CoP@CF-900, when used as both the cathode and anode for overall water splitting, is able to deliver 200 mA cm^-2 at a cell voltage of 1.89 V, significantly outshining the Pt/C‖RuO₂ couple; when used as the air cathode for a zinc-air battery, is able to operate more than 150 h at 10 mA cm^-2 with a nearly constant round-trip energy efficiency of ≈60%, also outperforming the Pt/C+RuO₂ benchmark. The activity and kinetics origin of the superb multi-functionality is further elucidated through extensive electroanalytical, post-mortem, and operando characterizations, which underscore the construction of robust integral electrodes through synergistic structure and composition engineering.