This paper provides a general overview of high-entropy alloys (HEAs) as future electrocatalysts for the hydrogen evolution reaction (HER). Growing energy demands worldwide and the need to mitigate climate change have placed attention on the efficient, sustainable production of hydrogen through electrochemical water splitting. Traditional noble-metal electrocatalysts such as platinum (Pt) possess excellent HER activity but are burdened by exorbitantly inhibitive cost, scarcity, and poisoning sensitivity. High-entropy alloys that consist of five or more major components in nearly equimolar proportions offer a paradigmatic solution due to their unique structural and electronic properties. High configurational entropy, lattice distortion, sluggish diffusion, and synergistic "cocktail" effects, in combination, enhance the catalytic activity of these alloys. Improved synthesis techniques of HEAs in nanoparticle, nanowire, and porous network forms have been discovered to exhibit high HER activity with low overpotentials and long-term durability. This review critically explores the fundamental principles of HER, the design principles of HEA electrocatalysts, and their applications in catalysis, with special focus on directions for future research to realize their full potential.
Fig. 1. Crystal structures and core characteristics of high-entropy alloys (HEAs). (A) Common HEA phases: (i) FCC, (ii) BCC, and (iii) HCP. (B) Key properties of HEAs illustrated schematically .
Fig. 2. Reaction mechanism exploration by DFT calculations. (a) The adsorption distribution of ΔG H* on HEA with 5.9% compressive strain (5.9%-HEA), containing different adsorption sites (hcp hollow site, fcc hollow site, and bridge site). Red dashed circles indicate the Volmer and Heyrovsky (or Tafel) active sites, respectively. Green region is the region of adsorbed H* diffusion (DR). (b) Volmer Heyrovsky mechanism of HER on 5.9%-HEA (111) and Pt (111). (c) Volmer-Tafel mechanism of HER on 5.9%-HEA (111) and Pt (111). (d) The H* spillover on DR1 (diffusion region for the first H*) for 5.9%-HEA (111). (e) The H* spillover on DR2 (diffusion region for the second H*) for 5.9%-HEA (111) .
Title:Tailoring high-entropy alloys for cutting-edge hydrogen evolution electrocatalysis
Author:Akbar Hojjati-Najafabadi，Reza Behmadi， Yezeng He， Hesam Kamyab，Yasser Vasseghian