The beauty of multi‐active sites

The Sabatier principle—which states that the best catalyst should be at the peak of the volcano plot, with neither too strong nor too weak intermediate binding strength—plays the golden rule in designing highly active electrocatalysts. For instance, Pt with a "just right" hydrogen adsorption free energy (ΔGH* = ∼0 eV) is the most efficient catalyst for hydrogen evolution reaction (HER).1 Nevertheless, the pressing demand for renewable energy has sparked a quest beyond the top of the volcano plot, driving the innovation towards more effective, economical, and sustainable catalysts.2-5 Among extensive endeavors, recent advancements have highlighted hydrogen spillover as a promising approach to enhance catalytic activity. This process involves the migration of chemisorbed hydrogen atoms across the catalyst's surface, leading to potential synergistic effects among various active sites.6, 7 In a compelling article published in Nature Communications, Qing Jiang and coworkers from Jilin University shed light on the potential of high entropy alloys (HEAs) to leverage the hydrogen spillover effect for remarkable HER performance.8 The team finds that the surface of HEAs has a spatially varying ΔGH*. Specifically, the ΔGH* of different adsorption sites on HEA follows a Gaussian distribution [X ∼ N(μ, σ2), where μ and σ denote expectation and standard deviation, respectively]. In such a system, proton adsorption occurs on sites with ΔGH* < μ − σ, hydrogen spillover happens on sites with moderate ΔGH* (μ − σ < ΔGH* < μ + σ), and hydrogen molecule desorption takes place on those with ΔGH* > μ + σ (Figure 1). As a result, they propose an unusual Sabatier principle, that is, a smaller absolute value of μ and a larger σ render more efficient HER catalysts. Illustration of HEA surface with a spatially varying ΔGH*. (a) Illustration of different types of hydrogen adsorption sites on HEA (111), including bridge site, FCC hollow site, and HCP hollow site. (b) Schematic diagram of the Gaussian distribution of the ΔGH* on HEA surface: the sites with ΔGH* < μ − σ, μ − σ < ΔGH* < μ + σ, and ΔGH* > μ + σ are proton adsorption sites, diffusion region, and hydrogen molecule desorption sites, respectively. (Reproduced with permission from Ref. 8 Copyright 2024, Spring Nature Publishing for Reviews and Mini reviews). FCC, face-centered cubic; HCP, hexagonal close packed; HEA, high entropy alloy. Applying this principle, they experimentally design PtFeCoNiCu HEAs with gradient composition. A typical three-electrode cell is employed to examine the HER efficiency. Notably, the HEAs exhibit electrochemical activation effects by cyclic voltammetry (CV) cycling. For instance, the overpotential at −100 mA cm−2 decreases to 30.7 mV after 5000 CV cycles for HEA with 7.1% strain, significantly lower than the initial value of 96.8 mV. Furthermore, their theoretical analysis reveals that the energy barrier of the rate-determining steps on HEA (111) is lower than that of Pt (111) for both Volmer–Heyrovsky and Volmer–Tafel mechanisms. More broadly, this principle holds the potential to be applied to other key reactions, such as the oxygen evolution reaction, CO2 reduction reaction, and nitrogen reduction reaction. Jiang et al. envisage that these findings may pave the way for novel HEA design, potentially opening new horizons in the design of highly efficient catalysts.8 Yu-Qing Wang: Writing - original draft; visualization. Sha-Sha Guo: Writing - review & editing; conceptualization. Zheng Liu: Conceptualization; writing - review & editing. Z.L. acknowledges funding from the Singapore Ministry of Education (AcRF MOE2019-362 T2-2-105 and AcRF Tier 1 RG7/21). Z.L. also acknowledges funding from the Ministry of Education, Singapore, under its Research Centre of Excellence award to the Institute for Functional Intelligent Materials (Project No. EDUNC-33-18-279-V12). Zheng Liu is an associate editor-in-chief for cMat and was not involved in the editorial review or the decision to publish this article. The authors declare no conflicts of interest. Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.