A universal, green, and self-reliant electrolytic approach to high-entropy layered (oxy)hydroxide nanosheets for efficient electrocatalytic water oxidation

High-entropy layered double hydroxide with advanced structural regulation for electrochemical water splitting

Electrochemical water splitting (EWS) serves as a pivotal technology for green hydrogen production. However, its practical application is limited by the high cost and scarcity of noble metal-based catalysts. High-entropy layered double hydroxides (HE-LDHs) have emerged as a novel class of high-entropy materials attracting significant attention for their exceptional electrocatalytic performance. Compared with traditional bimetallic layered double hydroxides, HE-LDHs possess unique configurational entropy and "four core effects" (high-entropy effect, delayed diffusion effect, lattice distortion effect, and cocktail effect). In this review, we firstly introduced the concept of HE-LDHs and summarized their different synthesis methods such as the hydrothermal method, co-precipitation method, electrodeposition method and template etching method. Then, we presented advanced regulation strategies of HE-LDHs, including geometric structure design, single-atom doping, inert component doping and vacancy creation. Finally, we further explored the current important challenges and corresponding solutions to promote the practical development of HE-LDH catalysts.

Entropy Engineering of 2D Materials

Entropy, a measure of disorder or uncertainty in the thermodynamics system, has been widely used to confer desirable functions to alloys and ceramics. The incorporation of three or more principal elements into a single sublattice increases the entropy to medium and high levels, imparting these materials a mélange of advanced mechanical and catalytic properties. In particular, when scaling down the dimensionality of crystals from bulk to the 2D space, the interplay between entropy stabilization and quantum confinement offers enticing opportunities for exploring new fundamental science and applications, since the structural ordering, phase stability, and local electronic states of these distorted 2D materials get significantly reshaped. During the last few years, the large family of high-entropy 2D materials is rapidly expanding to host MXenes, hydrotalcites, chalcogenides, metal-organic frameworks (MOFs), and many other uncharted members. Here, the recent advances in this dynamic field are reviewed, elucidating the influence of entropy on the fundamental properties and underlying elementary mechanisms of 2D materials. In particular, their structure-property relationships resulting from theoretical predictions and experimental findings are discussed. Furthermore, an outlook on the key challenges and opportunities of such an emerging field of 2D materials is also provided.

Future prospects of high-entropy alloys as next-generation industrial electrode materials

The rapid advancement of electrochemical processes in industrial applications has increased the demand for high-performance electrode materials. High-entropy alloys (HEAs), a class of multicomponent alloys with unique properties, have emerged as potential electrode materials owing to their enhanced catalytic activity, superior stability, and tunable electronic structures. This review explores contemporary developments in HEA-based electrode materials for industrial applications and identifies their advantages and challenges as compared to conventional commercial electrode materials in industrial aspects. The importance of tuning the composition, crystal structure, different phase formations, thermodynamic and kinetic parameters, and surface morphology of HEAs and their derivatives to achieve the predicted electrochemical performance is emphasized in this review. Synthetic procedures for producing potential HEA electrode materials are outlined, and theoretical discussions provide a roadmap for recognizing the ideal electrode materials for specific electrochemical processes in an industrial setting. A comprehensive discussion and analysis of various electrochemical processes (HER, OER, ORR, CO2RR, MOR, AOR, and NRR) and electrochemical applications (batteries, supercapacitors, etc.) is included to appraise the potential ability of HEAs as an electrode material in the near future. Overall, the design and development of HEAs offer a promising pathway for advancing industrial electrode materials with improved performance, selectivity, and stability, potentially paving the way for the next generation of electrochemical technology.

Elucidating the Geometric Active Sites for Oxygen Evolution Reaction on Crystalline Iron-Substituted Cobalt Hydroxide Nanoplates

Transition-metal (oxy)hydroxides are among the most active and studied catalysts for the oxygen evolution reaction in alkaline electrolytes. However, the geometric distribution of active sites is still elusive. Here, using the well-defined crystalline iron-substituted cobalt hydroxide as a model catalyst, we reported the scanning electrochemical cell microscopy (SECCM) study of single-crystalline nanoplates, where the oxygen evolution reaction at individual nanoplates was isolated and evaluated independently. With integrated prior- and post-SECCM scanning electron microscopy of the catalyst morphology, correlated structure-activity information of individual electrocatalysts was obtained. Our result reveals that while the active sites are largely located at the edges of the pristine Co(OH)₂ nanoplates, the Fe lattice incorporation significantly promotes the basal plane activities. Our approach of correlative imaging provides new insights into the effect of iron incorporation on active site distribution across nano-electrocatalysts.

Lattice-disordered high-entropy metal hydroxide nanosheets as efficient precatalysts for bifunctional electro-oxidation

Electro-oxidation reactions (EORs) are important half reactions in overall and assisted water electrolysis, which are crucial in achieving economic and sustainable hydrogen production and realizing simultaneous wastewater treatment. Current studies indicate that the high-valence metal ions that are locally enriched in the catalysts or generated in situ during the anodic preoxidation process are active species for EORs. Hence, designing (pre)catalysts with enriched local active sites and boosted preoxidation is of great importance. In this work, with a focus on improving the EOR performance toward the oxygen evolution reaction (OER) and the urea oxidation reaction (UOR), we fabricated a lattice-disordered high-entropy FeCuCoNiZn hydroxide nanoarray catalyst that exhibits robust bifunctional OER and UOR behavior. The high-entropy feature could bring in a unique catalytic ensemble effect and remarkably improve the intrinsic OER/UOR activity. The lattice-disordered structure could not only enrich the local high-valence metal ions as active sites but also provide abundant reactive surface sites to accelerate the preoxidation process, thus leading to enriched active sites for the OER and UOR. Benefitting from the structural merits, the lattice-disordered high-entropy catalyst exhibits excellent OER and UOR activity with low overpotential, large current density and enhanced intrinsic activity, and no performance degradation but dramatic 35.3% and 88.7% enhancement in activity can be achieved during the long-term OER and UOR tests, respectively. The robust OER and UOR performance makes the lattice-disordered high-entropy catalyst a promising candidate for overall and urea-assisted water electrolysis from industrial, agricultural and sanitary wastewater.

Designing strategies and enhancing mechanism for multicomponent high-entropy catalysts

High-entropy materials (HEMs) are new-fashioned functional materials in the field of catalysis owing to their large designing space, tunable electronic structure, interesting "cocktail effect", and entropy stabilization effect. Many effective strategies have been developed to design advanced catalysts for various important reactions. Herein, we firstly review effective strategies developed so far for optimizing HEM-based catalysts and the underlying mechanism revealed by both theoretical simulations and experimental aspects. In light of this overview, we subsequently present some perspectives about the development of HEM-based catalysts and provide some serviceable guidelines and/or inspiration for further studying multicomponent catalysts.