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The discovery and identification of novel active sites are paramount for deepening the understanding of the catalytic mechanism and driving the development of remarkable electrocatalysts. Here, we reveal that the genuine active sites for the hydrogen evolution reaction (HER) in LaRuSi are Si sites, not the usually assumed Ru sites. Ru in LaRuSi has a peculiar negative valence state, which leads to strong hydrogen binding to Ru sites. Surprisingly, the Si sites have a Gibbs free energy of hydrogen adsorption that is near zero (0.063 eV). The moderate adsorption of hydrogen on Si sites during the HER process is also validated by in situ Raman analysis. Based on it, LaRuSi exhibits an overpotential of 72 mV at 10 mA cm−2 in alkaline media, which is close to the benchmark of Pt/C. This work sheds light on the recognition of real active sites and the exploration of innovative silicide HER electrocatalysts. [ABSTRACT FROM AUTHOR]

Optimizing the hydrogen adsorption Gibbs free energy (ΔGH) of active sites is essential to improve the overpotential of the electrocatalytic hydrogen evolution reaction (HER). We doped graphene‐like Co0.85Se with sulfur and found that the active sites are reversed (from cationic Co sites to anionic S sites), which contributed to an enhancement in electrocatalytic HER performance. The optimal S‐doped Co0.85Se composite has an overpotential of 108 mV (at 10 mA cm−2) and a Tafel slope of 59 mV dec−1, which exceeds other reported Co0.85Se‐based electrocatalysts. The doped S sites have much higher activity than the Co sites, with a hydrogen adsorption Gibbs free energy (ΔGH) close to zero (0.067 eV), which reduces the reaction barrier for hydrogen production. This work provides inspiration for optimizing the intrinsic HER activity of other related transition metal chalcogenides. [ABSTRACT FROM AUTHOR]