High Crystalline MxSby (M═Fe, Co, and Ni) Nanocrystals Tuned by Antimony for Boosting Overall Water Splitting Catalysis

Six types of M_xSb_y compounds (Fe, Co, and Ni antimonides) are synthesized in form of mono-dispersed nanocrystallites (NCs) via a hot-injection metathesis-reduction. Various contents of Sb atoms are found to drive crystallographic structure and re-coordination in the M_xSb_y materials, leading to rhythmical changes of orthorhombic M₃Sb→hexagonal MSb→monoclinic (or orthorhombic) MSb₂. The crystallography is identified as crucial factor in electrocatalysis of water splitting at cathodic and anodic electrodes, respectively. Owning to the in-plane microstrain distributed along (001) plane, the synthesized Ni₃Sb NCs are more suitable to catalyzing hydrogen evolution reaction (HER), sharing overpotential (η₁₀) of 93 mV@10 mA cm⁻² with Tafel slope of 45 mV dec⁻¹, and extremely low hydrogen adsorption resistance (0.019 Ω) is obtained. The orthorhombic FeSb₂ NCs featured with larger deprotonation capacity of 13.71 mC V⁻¹ excelled in oxygen evolution reaction (OER) electrolysis, and is confirmed to facilitate minimal deformation of the OOH^*. The integrated devices (FeSb₂‖Ni₃Sb) are tested as efficient catalyst for overall water splitting (1.58 V@10 mA cm⁻²) with long stability. Density functional theory (DFT) calculations elucidated the particular coordination of Sb with proper electronegativity (2.05) is able to adjust active sites, relax electronic attraction, and benefit electrochemical reactions.