High‐entropy alloys and compounds for electrocatalytic energy conversion applications

Abstract

High‐entropy materials, composed of five or more elements in near‐equiatomic percentage, have been attracting tremendous interests due to their advantageous properties in a variety of applications. Recently, electrocatalysis on high‐entropy alloys (HEAs) and high‐entropy compounds (HECs) has emerged as a new and promising material owing to the tailored composition and the disordered configuration of HEAs and HECs. Though extensive efforts have been devoted to investigating the catalytic nature of HEAs and HECs, the details related to the active sites and intrinsic activity of such catalysts still remain uncertain due to the complexity of the multicomponent systems. In this review, the recent progress of HEAs and HECs is systematically reviewed in terms of their synthetic strategies and electrocatalytic applications. Importantly, the computationally assisted methods (e.g., density functional theory [DFT]) are also presented to discover and design the optimum HEA‐ and HEC‐based catalysts. Subsequently, the applications of HEAs and HECs in electrocatalytic energy conversion reactions will be discussed, including hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, nitrogen reduction reaction, methanol oxidation reaction, and ethanol oxidation reaction (EOR). Moreover, the prospects and future opportunities for this research field are cautiously discussed. A series of upcoming challenges and questions are thoroughly proposed from the experimental and theoretical aspects as well as other future applications in electrocatalysis.

General Synthesis of Transition‐Metal‐Based Carbon‐Group Intermetallic Catalysts for Efficient Electrocatalytic Hydrogen Evolution in Wide pH Range

“…By contrast with SSAs, the IMAs have well-defined atomic arrangements and fixed stoichiometry, therefore uniform active centers on the same surface plane. [15][16][17] As a result, the ordered IMAs are promising for practical applications but are fairly difficult to synthesize because the high-temperature pyrolysis needed for atom ordering inevitably accelerates metal sintering, which leads to larger crystallites.…”

High‐entropy alloy stabilized and activated Pt clusters for highly efficient electrocatalysis

“…[25][26][27][28][29][30][31] Compared with pure metal and fewer-element alloys, HEA has a more flexible composition range and complex multielement synergy, therefore, enabling widely tunable electronic structures and adsorption energy toward high-performance catalysis. [32][33][34][35] In addition, originated from the unique HEA structure, the thermodynamics (△G = △H−T△S) and kinetic stability (slow diffusion) promise good stability under catalytic conditions. [36][37][38][39][40] Therefore, in theory, HEAs can act as the ideal support for noble metals (e.g., Pt) owing to the following advantages: (1) HEA with intrinsic structural stability can effective disperse and stabilize Pt on the surface by forming strong metal-metal bonds, and (2) their multicomponent composition can easily adjust Pt's electronic structure and improve its catalytic activity, thus, achieving uniform Pt dispersion, strong bonding, and synergistic interaction toward improved activity and stability.…”

“…Recently, high entropy alloy (HEA) nanoparticles, consisting of five or more principal elements in a single‐phase solid solution, have emerged as novel catalytic material and attracted wide attention 25–31 . Compared with pure metal and fewer‐element alloys, HEA has a more flexible composition range and complex multielement synergy, therefore, enabling widely tunable electronic structures and adsorption energy toward high‐performance catalysis 32–35 . In addition, originated from the unique HEA structure, the thermodynamics (△ G = △ H − T △ S ) and kinetic stability (slow diffusion) promise good stability under catalytic conditions 36–40 .…”

Surface‐Decorated High‐Entropy Alloy Catalysts with Significantly Boosted Activity and Stability

“…Despite the considerable promise, the rational design of HEA catalysts remains challenging owing to the almost unlimited compositional space and the lack of understanding of the structure‐activity correlations, hindering their rapid exploration. [ 7,14,33–35 ] The complex composition and distribution of the multitude of elements in the HEA are reported to substantially affect the catalytic activity mainly through the ligand effect, that is, synergy from the random spatial distribution of different metal elements. [ 36,37 ] In addition, most HEA catalysts are based on extremely non‐equilibrium synthesis (e.g., 2000 K, 55 ms) to enable homogeneous mixing.…”