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Compositionally complex solid solutions (CCSS), often called high-entropy alloys (HEA) have emerged as a promising platform for electrocatalysts for the hydrogen evolution reaction (HER). However, due to their complexity, the interplay among surface composition, structure, and catalytic activity remains insufficiently understood. Herein, noble-metal-based CCSS thin-film materials libraries, prepared by combinatorial magnetron sputtering, are employed as a platform to elucidate how HER activities of CCSS electrocatalysts are linked to their volume composition through surface segregation and crystal structure. High-throughput investigations of three CCSS material libraries, Ir–Pd–Pt–Rh–Ru, Ag–Au–Pd–Pt-Ru, and Ag–Au–Cu–Pd-Pt, were conducted to assess their structural, compositional, and electrochemical properties, using high-throughput X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS) coupled with Gaussian process regression, and long-range scanning electrochemical cell microscopy (SECCM). Correlative data analysis revealed that the composition-dependent surface segregation, driven by surface energy differences, modulates the distribution of active sites on the surface. We identified Ir10Pd15Pt46Rh12Ru17 as the most active volume composition for HER which corresponds to a surface composition of Ir6Pd17Pt50Rh11Ru16. Moreover, the HER trends were governed not only by the intrinsic activity of the constituent elements but also by unexpected synergetic effects between them. The findings offer direct insights into composition–structure–activity relationships in compositionally complex electrocatalysts.
Pukhareva et al. (2025) studied this question.