Engineering sub-2 nm ultrasmall high-entropy alloy nanoparticles with extremely superior performance for hydrogen evolution catalysis

Abstract

The development of intrinsically effective and low-cost catalysts is critical for the large-scale commercial applications of electrocatalytic hydrogen production. Although various electrocatalysts have demonstrated high activities for hydrogen evolution reaction (HER), it remains a formidable challenge to develop an extremely efficient and durable catalyst for practical use, especially in acidic media. Here, we report quinary ultrasmall NiCoFePtRh high-entropy alloy (us-HEA) nanoparticles (NPs) with extremely superior performance for HER. The us-HEA NPs are well dispersed on the carbon supports, with an average diameter of 1.68 nm, which is the smallest size in the reported HEAs. The us-HEA/C achieves an ultrahigh mass activity of 28.3 A mg-1noble metals (much higher than that of other reported advanced catalysts) at -0.05 V (vs the reversible hydrogen electrode, RHE) for HER in 0.5 M H2SO4 solution, which is 40.4 and 74.5 times higher than those of the commercial Pt/C and Rh/C catalysts, respectively. Moreover, the us-HEA/C demonstrates the highest reported turnover frequency of 30.1 s−1 at 50 mV overpotential (41.8 times higher than that of the Pt/C catalyst) and excellent stability with no decay after 10,000 cycles. Both operando X-ray absorption spectroscopy and theoretical calculations reveal the true active sites and a synergistic effect among five elements, which endow us-HEA/C with significantly enhanced HER activity. This work not only provides a general and facile strategy for synthesizing us-HEA NPs, highlights HEAs as sufficiently advanced materials in energy electrocatalysis, but also acts as a guidance for elucidating the actual reaction process and catalytic mechanism of complex multi-element systems.