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.

Interface Catalysts of Ni3Fe1 Layered Double Hydroxide and Titanium Carbide for High-Performance Water Oxidation in Alkaline and Natural Conditions

The electrocatalytic oxygen evolution reaction (OER) is important for many renewable energy technologies. Developing cost-effective electrocatalysts with high performance remains a great challenge. Here, we successfully demonstrate our novel interface catalyst comprised of Ni₃Fe₁-based layered double hydroxides (Ni₃Fe₁-LDH) vertically immobilized on a two-dimensional MXene (Ti₃C₂T_x) surface. The Ni₃Fe₁-LDH/Ti₃C₂T_x yielded an anodic OER current of 100 mA cm^-2 at 0.28 V versus reversible hydrogen electrode (RHE), nearly 74 times lower than that of the pristine Ni₃Fe₁-LDH. Furthermore, the Ni₃Fe₁-LDH/Ti₃C₂T_x catalyst requires an overpotential of only 0.31 V versus RHE to deliver an industrial-level current density as high as 1000 mA cm^-2. Such excellent OER activity was attributed to the synergistic interface effect between Ni₃Fe₁-LDH and Ti₃C₂T_x. Density functional theory (DFT) results further reveal that the Ti₃C₂T_x support can efficiently accelerate the electron extraction from Ni₃Fe₁-LDH and tailor the electronic structure of catalytic sites, resulting in enhanced OER performance.

Density Functional Theory Approximations and Experimental Investigations on Co1-xMoxTe2 Alloy Electrocatalysts Tuning the Overall Water Splitting Reactions

Understanding the relationship between electronic structure, surface characteristic, and reaction process of a catalyst helps to architect proficient electrodes for sustainable energy development. The highly active and stable catalysts made of earth-abundant materials provide a great endeavor toward green hydrogen production. Herein, we assembled the Co_1-xMo_xTe (x = 0-1) nanoarray structures into a bifunctional electrocatalyst to achieve high-performance hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics under alkaline conditions. The designed Co_0.75Mo_0.25Te and Co_0.50Mo_0.50 electrocatalysts require minimum overpotential and Tafel slope for high-efficacy HER and OER, respectively. Furthermore, we constructed a Co_0.50Mo_0.50Te₂∥Co_0.50Mo_0.50Te₂ device for overall water splitting with an overpotential of 1.39 V to achieve a current density of 10 mA cm^-2, which is superior to noble electrocatalyst performance, with stable reaction throughout the 50 h continuous process. Density functional theory approximations and Gibbs free energy calculations validate the enhanced water splitting reaction catalyzed by the Co_0.50Mo_0.50Te₂ nanoarrays. The partial replacement of Co atoms with Mo atoms in the Co_0.50Mo_0.50Te₂ structure substantially enhances the water electrolysis kinetics through the synergistic effects between the combined metal atoms and the bonded chalcogen.

Boosting cobalt ditelluride quantum-rods anode materials for excellent potassium-ion storage via hierarchical physicochemical encapsulation

The exploration of anode materials that can store large-sized K-ion to solve the poor kinetics and large volume expansion issues has become the key scientific bottlenecks hindering the development of potassium-ion batteries (PIBs). Herein, ultrafine CoTe₂ quantum rods physiochemically encapsulated by graphene and nitrogen-doped carbon (CoTe₂@rGO@NC) are regarded as anode electrodes for PIBs. Dual physicochemical confinement and quantum size effect not only enhance electrochemical kinetics but also restrain large lattice stress during repeated K-ion insertion/extraction process. Superior electronic conductivity, K-ion adsorption, and diffusion ability can be acquired for CoTe₂@rGO@NC, confirmed through first-principles calculations and kinetics study. K-ion insertion/extraction proceeds via a typical conversion mechanism relying on Co as the redox site, where the robust chemical bond of COCo plays an important role in maintaining the electrode stability. Accordingly, CoTe₂@rGO@NC contributes a high initial capacity of 237.6 mAh·g^-1 at 200 mA·g^-1, a long lifetime over 500 cycles with low-capacity decay of 0.10% per cycle. This research will lay the materials science foundation for the construction of quantum-rod electrodes.

Recent Advances in Transition Metal Tellurides (TMTs) and Phosphides (TMPs) for Hydrogen Evolution Electrocatalysis

The hydrogen evolution reaction (HER) is a developing and promising technology to deliver clean energy using renewable sources. Presently, electrocatalytic water (H₂O) splitting is one of the low-cost, affordable, and reliable industrial-scale effective hydrogen (H₂) production methods. Nevertheless, the most active platinum (Pt) metal-based catalysts for the HER are subject to high cost and substandard stability. Therefore, a highly efficient, low-cost, and stable HER electrocatalyst is urgently desired to substitute Pt-based catalysts. Due to their low cost, outstanding stability, low overpotential, strong electronic interactions, excellent conductivity, more active sites, and abundance, transition metal tellurides (TMTs) and transition metal phosphides (TMPs) have emerged as promising electrocatalysts. This brief review focuses on the progress made over the past decade in the use of TMTs and TMPs for efficient green hydrogen production. Combining experimental and theoretical results, a detailed summary of their development is described. This review article aspires to provide the state-of-the-art guidelines and strategies for the design and development of new highly performing electrocatalysts for the upcoming energy conversion and storage electrochemical technologies.

Nanocrystals of CuCoO2 derived from MOFs and their catalytic performance for the oxygen evolution reaction

In this work, two different solvothermal synthesis routes were employed to prepare MOF-derived CuCoO₂ (CCO) nanocrystals for electrocatalytic oxygen evolution reaction (OER) application. The effects of the reductants (ethylene glycol, methanol, ethanol, and isopropanol), NaOH addition, the reactants, and the reaction temperature on the structure and morphology of the reaction product were investigated. In the first route, Cu-BTC derived CCO (CCO1) nanocrystals with a size of ∼214 nm and a specific surface area of 4.93 m² g^-1 were prepared by using Cu-BTC and Co(NO₃)₂·6H₂O as the Cu and Co source, respectively. In the second route, ZIF-67 derived CCO (CCO2) nanocrystals with a size of ∼146 nm and a specific surface area of 11.69 m² g^-1 were prepared by using ZIF-67 and Cu(NO₃)₂·3H₂O as the Co and Cu source, respectively. Moreover, the OER performances of Ni foam supported CCO1 (Ni@CCO1) and CCO2 (Ni@CCO2) electrodes were evaluated in 1.0 M KOH solution. Ni@CCO2 demonstrates a better OER catalytic performance with a lower overpotential of 394.5 mV at 10 mA cm^-2, a smaller Tafel slope of 82.6 mV dec^-1, and long-term durability, which are superior to those of some previously reported delafossite oxide or perovskite oxide catalysts. This work reveals the preparation method and application potential of CCO electrocatalysts by using Cu-BTC/ZIF-67 as the precursor, providing a new approach for the preparation of delafossite oxide CCO and the enhancement of their OER performances.

In situ preparation of a Co4S3-based electrocatalyst by taking advantage of the controllable components of metal-organic frameworks

In order to give full play to the advantages in structure tailoring and quantitative assembly, metal-organic frameworks (MOFs) with different topological structures formed by the self-assembly of inorganic ligands containing sulfur, cobalt ions and large-size ligands were used to prepare electrocatalyst materials for hydrolysis with controllable composition and performance. According to the synthesis proposition, we can not only avoid using additional doped sulfur sources to reduce waste but also make it very convenient for Co and sulfur elements to be uniformly and controllably distributed in the whole material, and enhance the overall synergistic effects. Based on the above considerations, two-dimensional layered and three-dimensional MOFs, Co-MOF-1, and Co-MOF-2, with the same chemical compositions were utilized as the templates, and a series of Co/S-based materials with variable compositions and properties were obtained only by controlling the pyrolysis temperature. For each MOF series, it can be observed that with the increase in the pyrolysis temperature, the derivatives gradually change from Co₄S₃ to Co₉S₈ composites, which could be proven by PXRD studies. The electrocatalytic properties of two series of derivatives were also investigated, and the results indicate that the materials containing Co₄S₃ can indeed show better water-splitting performance than Co₉S₈ ones. Furthermore, the macroscopic stacking form of the MOF template also plays an important role in determining the electrocatalytic performance of the derived materials. Through an overall comparison, it is found that the electrocatalytic performance of the Co-MOF-1 series is better than that of the Co-MOF-2 series at various temperatures, which should be only caused by the natural packing modes of the pristine MOF template. For Co-MOF-1 derivatives, the retention of the two-dimensional layered structure is favorable to form an electrostatic charge separation layer and electron transport channel, which is beneficial to the intercalation and delamination of hydroxide ions, thus improving the storage capacity of materials, promoting electron transfer, and producing less electron transfer resistance. Therefore, based on the research results, the reasonable design of layered MOF materials containing the specific sulfur-containing linker as water-splitting catalysts is an applicable route for the preparation of economical, environmentally friendly, and low energy consumption electrocatalysts, which should receive increasing attention in the future.

Hydrothermal synthesized delafossite CuGaO2 as an electrocatalyst for water oxidation

Hydrogen production from water splitting provides an effective method to alleviate the ever-growing global energy crisis. In this work, delafossite CuGaO₂ (CGO) crystal was synthesized through hydrothermal routes with Cu(NO₃)₂·3H₂O and Ga(NO₃)₃·xH₂O used as reactants. The addition of cetyltrimethylammonium bromide (CTAB) was found to play an important role in modifying the morphology of CuGaO₂ (CGO-CTAB). With the addition of CTAB, the morphology of CGO-CTAB samples changed from irregular flake to typical hexagonal sheet microstructure, with an average size of 1-2 μm and a thickness of around 100 nm. Furthermore, the electrocatalytic activity of CGO-CTAB crystals for oxygen evolution reaction (OER) was also studied and compared with that of CGO crystals. CGO-CTAB samples exhibited better activity than CGO. An overpotential of 391.5 mV was shown to be able to generate a current density of 10 mA/cm². The as-prepared samples also demonstrate good stability for water oxidation and relatively fast OER kinetics with a Tafel slope of 56.4 mV/dec. This work highlights the significant role of modification of CTAB surfactants in preparing CGO related crystals, and the introduction of CTAB was found to help to improve their electrocatalytic activity for OER.

A CoNi telluride heterostructure supported on Ni foam as an efficient electrocatalyst for the oxygen evolution reaction

The excellent oxygen evolution reaction performance of a CoNi telluride heterostructure (0.4CoNi LDH@Te-180C) can be attributed to the inherent layered structure, interconnected nanoarray structures and the synergistic effect of Co and Ni species.

CoTe2–NiTe2 heterojunction directly grown on CoNi alloy foam for efficient oxygen evolution reaction

One-step fabrication of a self-supported CoTe2–NiTe2 heterojunction electrocatalyst directly grown on CoNi foam for efficient and durable oxygen evolution reactions.

Self-supported cobalt–nickel bimetallic telluride as an advanced catalyst for the oxygen evolution reaction

The Ni-doped Co@CoTe2 electrode exhibits an outstanding OER activity and excellent long-term stability and outperforms most of the well-studied Co-based dichalcogenides.