Low-Electronegativity Vanadium Substitution in Cobalt Carbide Induced Enhanced Electron Transfer for Efficient Overall Water Splitting

Developing highly efficient electrocatalysts while revealing the active site and reaction mechanism is essential for electrocatalytic water splitting. To overcome the number and location limitations of defects in the electrocatalyst induced by conventional transition-metal atom (e.g. Fe, Co, and Ni) surface doping, we report a facile strategy of substitution with lower electronegative vanadium in the cobalt carbide, leading to larger amounts of defects in the whole lattice. The self-supported and quantitatively substituted V_xCo_3–xC (0 ≤ x ≤ 0.80) was one-step synthesized in the electrospun carbon nanofibers (CNFs) through the solid-state reaction. Particularly, the V_0.28Co_2.72C/CNFs exhibit superior hydrogen evolution reaction and oxygen evolution reaction activity and deliver a current density of 10 mA cm^–2 at 1.47 V as the alkaline electrolyzer, which is lower than the values for the Pt/C–Ir/C couple (1.60 V). The operando Raman spectra and density functional theory calculations show that the enhanced electron transfer from V to the orbit of the Co atom makes Co a local negative charge center and leads to a significant increase in efficiency for overall water splitting.