The reactant concentration at the catalytic interface holds the key to the activity of electrocatalytic hydrogen evolution reaction (HER), mainly referring to the capacity of adsorbing hydrogen and electron accessibility. With hydrogen adsorption free energy (ΔG_H) as a reactivity descriptor, the volcano curve based on Sabatier principle is established to evaluate the hydrogen evolution activity of catalysts. However, the role of electron as reactant received insufficient attention, especially for noble metal-free compound catalysts with poor conductivity, leading to cognitive gap between electronic conductivity and apparent catalytic activity. Herein we successfully construct a series of catalyst models with gradient conductivities by regulating molybdenum disulfide (MoS₂) electronic bandgap via a simple solvothermal method. We demonstrate that the conductivity of catalysts greatly affects the overall catalytic activity. We further elucidate the key role of intrinsic conductivity of catalyst towards water electrolysis, mainly concentrating on the electron transport from electrode to catalyst, the electron accumulation process at the catalyst layer, and the charge transfer progress from catalyst to reactant. Theoretical and experimental evidence demonstrates that, with the enhancement in electron accessibility at the catalytic interface, the dominant parameter governing overall HER activity gradually converts from electron accessibility to combination of electron accessibility and hydrogen adsorbing energy. Our results provide the insight from various perspective for developing noble metal-free catalysts in electrocatalysis beyond HER.

To enhance the catalytic activity by designing metal particles combined with atomically dispersed non-noble metal catalyst is a huge challenge, which yet has not been studied widely in organic reactions. Herein, we describe a simple and efficient method to synthesize Fe_xC combined with Fe single atoms anchored on the N-doped porous carbon by regulating pyrolysis temperature. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy corroborate the existence of atomically dispersed Fe and the coordination number between Fe and N atoms. The Fe–N–C-800 catalyst exhibits the highest catalytic activity giving the 97% yield of quinoline in dehydration of 1,2,3,4-tetrahydroquinoline (THQ) reaction at a mild condition (60 ℃, O₂ balloon), and it shows good stability with 80% isolated yield after five consecutive dehydration reactions. Moreover, density functional theory (DFT) calculations reveal that coexistence of Fe_xC and FeN_x structure exhibits high activity owing to the lowest adsorption energy of co-adsorbed O₂ and THQ and the longest N–H bond length of THQ, that is because the existence of Fe_xC induces the charges transfer. Our work may open a new route to design metal particles combined with atomically dispersed non-noble metal catalysts with high activity in organic synthesis.