Screening and Understanding Lattice Silicon-Controlled Catalytically Active Site Motifs from a Library of Transition Metal-Silicon Intermetallics

Abstract

A joint theoretical and experimental study is reported to systematically explore over a library of transition metal-silicon intermetallics for understanding silicon-controlled active site motifs and discovering hydrogen-evolving electrocatalysts. On the one hand, every low-index surface termination of 115 transition metal (M)-silicon (Si) intermetallics is enumerated, followed by cataloging of stable adsorption sites and prediction of catalytic activities on the main exposed facets. It is theoretically found that silicon atoms in silicon-rich structures (especially MSi₂ and MSi) show a strong site-isolating effect, which can eliminate M-M-M hollow and M-M bridge sites with too strong hydrogen-binding ability and thereby provide great opportunities for the exposure of novel highly active sites (e.g., M-top and Si-related sites). On the other hand, solid-state redox reactions are developed to synthesize a set of 24 silicides containing 5 MSi, 13 MSi₂, and 6 others, most of which are phase-pure samples. The experimental studies demonstrate that too rich silicon content in silicides (e.g., MSi₂) leads to adverse effects, such as the formation of amorphous SiO_x layers on the silicide surface, masking the presence of active sites during electrocatalysis. Finally, 5 MSi (M = Rh, Pd, Pt, Ru, Ir) as highly active hydrogen-evolving electrocatalysts are identified.