Synthesis of Co–B in porous carbon using a metal–organic framework (MOF) precursor: A highly efficient catalyst for the oxygen evolution reaction

A Review of Transition Metal Boride, Carbide, Pnictide, and Chalcogenide Water Oxidation Electrocatalysts

Transition metal borides, carbides, pnictides, and chalcogenides (X-ides) have emerged as a class of materials for the oxygen evolution reaction (OER). Because of their high earth abundance, electrical conductivity, and OER performance, these electrocatalysts have the potential to enable the practical application of green energy conversion and storage. Under OER potentials, X-ide electrocatalysts demonstrate various degrees of oxidation resistance due to their differences in chemical composition, crystal structure, and morphology. Depending on their resistance to oxidation, these catalysts will fall into one of three post-OER electrocatalyst categories: fully oxidized oxide/(oxy)hydroxide material, partially oxidized core@shell structure, and unoxidized material. In the past ten years (from 2013 to 2022), over 890 peer-reviewed research papers have focused on X-ide OER electrocatalysts. Previous review papers have provided limited conclusions and have omitted the significance of "catalytically active sites/species/phases" in X-ide OER electrocatalysts. In this review, a comprehensive summary of (i) experimental parameters (e.g., substrates, electrocatalyst loading amounts, geometric overpotentials, Tafel slopes, etc.) and (ii) electrochemical stability tests and post-analyses in X-ide OER electrocatalyst publications from 2013 to 2022 is provided. Both mono and polyanion X-ides are discussed and classified with respect to their material transformation during the OER. Special analytical techniques employed to study X-ide reconstruction are also evaluated. Additionally, future challenges and questions yet to be answered are provided in each section. This review aims to provide researchers with a toolkit to approach X-ide OER electrocatalyst research and to showcase necessary avenues for future investigation.

Balancing Mass Transfer and Active Sites to Improve Electrocatalytic Oxygen Reduction by B,N Codoped C Nanoreactors

Mass transfer is critical in catalytic processes, especially when the reactions are facilitated by nanostructured catalysts. Strong efforts have been devoted to improving the efficacy and quantity of active sites, but often, mass transfer has not been well studied. Herein, we demonstrate the importance of mass transfer in the electrocatalytic oxygen reduction reaction (ORR) by tailoring the pore sizes. Using a confined-etching strategy, we fabricate boron- and nitrogen-doped carbon (B,N@C) electrocatalysts featuring abundant active sites but different porous structures. The ORR performance of these catalysts is found to correlate with diffusion of the reactant. The optimized B,N@C with trimodal-porous structures feature enhanced O₂ diffusion and better activity per heteroatomic site toward the ORR process. This work demonstrates the significance of the nanoarchitecture engineering of catalysts and sheds light on how to optimize structures featuring abundant active sites and enhanced mass transfer.

Mild Construction of "Midas Touch" Metal-Organic Framework-Based Catalytic Electrodes for Highly Efficient Overall Seawater Splitting

Mild construction of highly efficient and durable practical electrodes for overall water splitting (OWS) at industrial-grade current density is currently a significant challenge. Herein, metal-organic framework (MOF) materials are grown in situ on the surface of carbon cloth (CC) at 25 °C, and quickly "interspersed" by cobalt-boron (Co-B) via electroless plating for 30 min to obtain a highly efficient and stable CoB@MOF@CC self-supporting electrode. Owing to the large specific surface area, abundant active sites, and porous structure, the MOF-based CC modified by bamboo leaf-like ultrathin CoB has remarkable electrochemical catalysis efficiency. The CoB@MOF@CC electrode exhibits excellent performance during the hydrogen evolution reaction (η₁₀  = 57 mV, η₅₀₀  = 266 mV) and oxygen evolution reaction (η₁₀  = 209 mV, η₅₀₀  = 423 mV) in alkaline simulated seawater, and is durable for 2500 h at 500 mA cm^-2 . The OWS performance is obviously enhanced by employing the prepared electrode, which only requires 1.49 V to achieve 10 mA cm^-2 and is durable for over 360 h at industrial-grade current densities in alkaline high-salt, real seawater, rainwater, and urea electrolytes.

Transition Metal Non-Oxides as Electrocatalysts: Advantages and Challenges

The identification of hydrogen as green fuel in the near future has stirred global realization toward a sustainable outlook and thus boosted extensive research in the field of water electrolysis focusing on the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). A huge class of compounds consisting of transition metal-based nitrides, carbides, chalcogenides, phosphides, and borides, which can be collectively termed transition metal non-oxides (TMNOs), has emerged recently as an efficient class of electrocatalysts in terms of performance and longevity when compared to transition metal oxides (TMOs). Moreover, the superiority of TMNOs over TMOs to effectively catalyze not only OERs but also HERs and ORRs renders bifunctionality and even trifunctionality in some cases and therefore can replace conventional noble metal electrocatalysts. In this review, the crystal structure and phases of different classes of nanostructured TMNOs are extensively discussed, focusing on recent advances in design strategies by various regulatory synthetic routes, and hence diversified properties of TMNOs are identified to serve as next-generation bi/trifunctional electrocatalysts. The challenges and future perspectives of materials in the field of energy conversion and storage aiding toward a better hydrogen economy are also discussed in this review.

Critical Review, Recent Updates on Zeolitic Imidazolate Framework-67 (ZIF-67) and Its Derivatives for Electrochemical Water Splitting

Design and construction of low-cost electrocatalysts with high catalytic activity and long-term stability is a challenging task in the field of catalysis. Metal-organic frameworks (MOF) are promising candidates as precursor materials in the development of highly efficient electrocatalysts for energy conversion and storage applications. This review starts with a summary of basic concepts and key evaluation parameters involved in the electrochemical water-splitting reaction. Then, different synthesis approaches reported for the cobalt-based Zeolitic imidazolate framework (ZIF-67) and its derivatives are critically reviewed. Additionally, several strategies employed to enhance the electrocatalytic activity and stability of ZIF-67-based electrocatalysts are discussed in detail. The present review provides a succinct insight into the ZIF-67 and its derivatives (oxides, hydroxides, sulfides, selenides, phosphide, nitrides, telluride, heteroatom/metal-doped carbon, noble metal-supported ZIF-67 derivatives) reported for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water splitting applications. Finally, this review concludes with the associated challenges and the perspectives on developing the best economic, durable electrocatalytic materials.

Electrochemically activated Co-Prussian blue analogue derived amorphous CoB nanostructures: Efficient electrocatalyst for oxygen evolution reaction

The oxygen evolution reaction is a kinetically sluggish half-cell reaction plays an important role in tuning the efficiency of various electrochemical energy conversion systems. However, this process can be facilitated...

Efficient electrocatalytic water splitting by bimetallic cobalt iron boride nanoparticles with controlled electronic structure

Developing an efficient bifunctional catalyst for Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) in water splitting technology is very attractive for clean energy. Here, a new Co-Fe-B ternary catalyst with improved crystallinity is successfully synthesized by combining the chemical reduction and subsequent solid-state reaction method. Synchrotron-based X-ray absorption near-edge structure (XANES) and X-ray photoelectron spectroscopy (XPS) indicate the electronic structure redistribution is favor for the improved performance. The overpotential is only 129 mV and 280 mV for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline condition, the corresponding Tafel slope is 67.3 mV dec^-1 and 38.9 mV dec^-1. Density functional theory calculations distinguish that the ternary crystalline Co-Fe-B catalysts are thermodynamically favorable for HER and OER. The actual active species of the ternary catalyst in OER is the CoOOH and FeOOH as indicated in ex situ Raman spectra. The present work may introduce promising crystallinity borides material for the anode and cathode of water splitting device.

Nanostructured Metal Borides for Energy-Related Electrocatalysis: Recent Progress, Challenges, and Perspectives

The discovery of durable, active, and affordable electrocatalysts for energy-related catalytic applications plays a crucial role in the advancement of energy conversion and storage technologies to achieve a sustainable energy future. Transition metal borides (TMBs), with variable compositions and structures, present a number of interesting features including coordinated electronic structures, high conductivity, abundant natural reserves, and configurable physicochemical properties. Therefore, TMBs provide a wide range of opportunities for the development of multifunctional catalysts with high performance and long durability. This review first summarizes the typical structural and electronic features of TMBs. Subsequently, the various synthetic methods used thus far to prepare nanostructured TMBs are listed. Furthermore, advances in emerging TMB-catalyzed reactions (both theoretical and experimental) are highlighted, including the hydrogen evolution reaction, the oxygen evolution reaction, the oxygen reduction reaction, the carbon dioxide reduction reaction, the nitrogen reduction reaction, the methanol oxidation reaction, and the formic acid oxidation reaction. Finally, challenges facing the development of TMB electrocatalysts are discussed, with focus on synthesis and energy-related catalytic applications, and some potential strategies/perspectives are suggested as well, which will profit the design of more efficient TMB materials for application in future energy conversion and storage devices.

One-Pot Synthesis of B/P-Codoped Co-Mo Dual-Nanowafer Electrocatalysts for Overall Water Splitting

Exploring electrocatalysts with satisfactory activity and durability has remained a long-lasting target for electrolyzing water, which is particularly significant for sustainable hydrogen fuel production. Here, we report a quaternary B/P-codoped transition metal Co-Mo hybrid as an efficient alternative catalyst for overall water splitting. The Co-Mo-B-P/CF dual nanowafers were deposited on a copper foam by double-pulse electrodeposition, which is favorable for achieving a nanocrystalline structure. The Co-Mo-B-P/CF catalyst shows a high catalytic activity along with good long-term stability in 1.0 M KOH solutions for both the hydrogen and oxygen evolution reactions, requiring 48 and 275 mV to reach 10 mA cm^-2, respectively. The synergetic effect between Co-Mo and doped B and P elements is mainly attributed to the excellent bifunctional catalysis performance, while the dual-nanowafer structure endows Co-Mo-B-P with numerous catalytical active sites enhancing the utilization efficiency of atoms. Moreover, the catalytic capability of Co-Mo-B-P/CF as a bifunctional electrocatalyst for the overall water splitting is proved, with the current density of 10 mA cm^-2 accomplished at 1.59 V. After the stability test for overall water splitting at 1.59 V for 24 h, the activity almost remains unchanged. The features of excellent electrocatalytic activity, simple preparation, and inexpensive raw materials for Co-Mo-B-P/CF as a bifunctional catalyst hold great potentials for overall water splitting.

Hierarchical ultrathin defect-rich CoFe2O4@BC nanoflowers synthesized via a temperature-regulated strategy with outstanding hydrogen evolution reaction activity

Graphical illustration of the synthesis and the electrocatalytic performance of CoFe₂O₄@BC 500 °C nanoflowers.

Designing transition-metal-boride-based electrocatalysts for applications in electrochemical water splitting

Investigating renewable and clean energy materials as alternatives to fossil fuels can be foreseen as a potential solution to the global problems of energy shortages and environmental pollution. Recently, transition metal boride (TMB)-based materials have emerged as the rising star as efficient electrocatalysts for hydrogen evolution reaction (HER) and/or oxygen evolution reaction (OER). In this review, an overview of the most recent developments in the use of TMB-based materials as electrocatalysts for HER/OER or overall water splitting has been presented. Initially, we provide a comprehensive introduction of the fundamentals of electrochemical water splitting. Then, the synthesis approaches of TMB materials are summarized and compared. Emphasis is put on the various strategies for further improving the electrocatalytic performance of TMBs. Finally, challenges and future perspectives for TMBs in water-splitting applications are proposed.

Coral-like hierarchical architecture self-assembled by cobalt hexacyanoferrate nanocrystals and N-doped carbon nanoplatelets as efficient electrocatalyst for oxygen evolution reaction

It is challenging to develop novel oxygen evolution reaction (OER) electrocatalysts with high performance and low cost to replace the noble metal-based catalysts for large-scale electrochemical water splitting. To settle such issue, herein, self-assembled porous coral-like architecture constructed by cobalt hexacyanoferrate (CoHCF) nanocrystals and nitrogen-doped carbon (NC) nanoplatelets network is fabricated for the first time by a facile electroless deposition approach. The porous coral-like CoHCF/NC hybrid exhibits an excellent OER electrocatalytic activity in alkaline medium with an ultra-low onset overpotential of 165 mV (vs. RHE) and a small Tafel slope of 73.97 mV dec^-1, which are much lower than that of bare CoHCF (onset overpotential of 296 mV and Tafel slope of 113.25 mV dec^-1); it also exhibits a lower overpotential of 357 mV (vs. RHE) at current density of 10 mA cm^-1 and superior durability even after 16 h. The excellent electrocatalytic performance of CoHCF/NC hybrid can be assigned to its unique coral-like architecture self-assembled by CoHCF nanocrystals and NC nanoplatelets network, which significantly increases the electrochemical active surface area and remarkably facilitates the electron and ion transfer. This work offers rational design and facile synthesis strategy for transition metal hexacyanoferrate-based nonprecious electrocatalysts with unique nano-architecture and excellent electrocatalytic efficiency towards OER.

Blocking Polysulfide with Co2B@CNT via "Synergetic Adsorptive Effect" toward Ultrahigh-Rate Capability and Robust Lithium-Sulfur Battery

Li-S batteries have attracted great interest as the next-generation secondary batteries due to their high energy density, being environmentally friendly, and low price. However, the road to commercialization of lithium-sulfur batteries remains limited owing to the "shuttle effect" of soluble polysulfides, which results in the inferior cycle stability. Herein, a potent functional separator is developed to restrain the "shuttle effect" by coating Co₂B@carbon nanotube layer on the commercialized polypropylene separator. In merits of the coadsorption of Co sites and B sites, such Co₂B shows highly efficient polysulfides block (11.67 mg/m² for Li₂S₆). Besides, the composite also exhibits obviously catalysis from Li₂S₈ to Li₂S. By combining the fast electron transportation along the carbon nanotube, a superior rate performance is achieved with the modified separator and common carbon-sulfur cathode. Typically, the cell with Co₂B@CNT shows prominent cycling life with a capacity degradation of 0.0072% per cycle (3000 cycles) and ultrahigh-rate capability at 5 C current (1172.8 mAh/g), which outstands the previously reported polysulfides barrier layer. The cell with Co₂B@CNT can exhibit electrochemical performance at areal capacity of 5.5 mAh/cm² (0.5 C) when the sulfur loading increased to 5.8 mg/cm². This work defines an efficacious strategy to restrain the "shuttle effect" of polysulfides and shed light on the great potential of borides in Li-S battery.

Applications of Metal-Organic-Framework-Derived Carbon Materials

Carbon materials derived from metal-organic frameworks (MOFs) have attracted much attention in the field of scientific research in recent years because of their advantages of excellent electron conductivity, high porosity, and diverse applications. Tremendous efforts are devoted to improving their chemical and physical properties, including optimizing the morphology and structure of the carbon materials, compositing them with other materials, and so on. Here, many kinds of carbon materials derived from metal-organic frameworks are introduced with a particular focus on their promising applications in batteries (lithium-ion batteries, lithium-sulfur batteries, and sodium-ion batteries), supercapacitors (metal oxide/carbon and metal sulfide/carbon), electrocatalytic reactions (oxygen reduction reaction, oxygen evolution reaction, and hydrogen evolution reaction), water treatment (MOF-derived carbon and other techniques), and other possible fields. To close, some existing problem and corresponding possible solutions are proposed based on academic knowledge from the reported literature, along with a great deal of experimental experience.

Reduced graphene oxide-supported cobalt oxide decorated N-doped graphitic carbon for efficient bifunctional oxygen electrocatalysis

A high-performance composite bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) has been synthesized via in situ growth of a hybrid precursor of graphene oxide (GO) and cobalt-based zeolite imidazolium framework (ZIF-67) under hydrothermal condition, followed by calcination at elevated temperature. The as-prepared composite bifunctional catalyst is confirmed to possess a structure of N-GC/Co@CoO/rGO, with core–shell nanoparticles of Co@CoO encapsulated in nitrogen-doped graphitic carbon (N-GC) thin layers which are then overall supported by reduced graphene oxide (rGO) sheets. With N-GC furnishing high population of ORR active sites, CoO being active for OER which is further enhanced by a highly conductive metal core, rGO sheets enhancing the overall electronic conduction, as well as the multiple synergistic couplings in the composite materials, pronounced ORR and OER catalytic activities with superior stability have been achieved. The catalysts also showed excellent tolerance to the crossover effect to methanol, showing great potential in energy-related applications requiring efficient oxygen electrocatalysis.

An efficient bifunctional electrocatalyst with sandwich structure, i.e., highly nitrogen-doped graphitic carbon (N-GC/Co@CoO, carbonized from ZIF-67) on reduced graphene oxide (rGO), has been obtained through hydrothermal and carbonization treatment.

One-dimensional MoO2–Co2Mo3O8@C nanorods: a novel and highly efficient oxygen evolution reaction catalyst derived from metal–organic framework composites

One dimensional MoO₂–Co₂Mo₃O₈@C nanorods were synthesized by using MoO₃@ZIF-67 composites as a precursor and the catalyst Co₂Mo₃O₈ shows excellent OER activity.