Vacancy engineering of group VI anions in NiCo2A4 (A = O, S, Se) for efficient hydrogen production by weakening the shackles of hydronium ion

Abstract Hydrogen evolution reaction (HER) has been severely suppressed by the first proton adsorption step, due to the “shackles” of the surrounding water in the form of hydronium ions (H13O6+). Here, it has been found anionic vacancies in NiCo2A4 (A = O, S, Se) can weaken the shackles of surrounding water in H13O6+, resulting into efficient capture of H+ to form a H+-enriched field. Taking selenium vacancy-rich NiCo2Se4 nanowires on nitrogen-doped carbon nanofibers as an example, it displays higher electrocatalytic activities with low overpotential of 168 mV at 10 mA cm−2 and a Tafel slope of 49.8 mV dec−1. The HER performance is strongly related to the anionic vacancy size, the larger the anionic vacancy size is (VSe > VS > VO), the higher the HER activity does. Guided by density functional theory calculations, it is found that the point defect structures can not only strengthen its interfacial linkage force with H+ by weakening the hydration force of contiguous hydronium ion, but also increase its charge density for efficient electron transfer to adsorbed H+. Therefore, this work creates a useful strategy to optimize the HER performance of traditional bimetallic compounds by engineering the solid-liquid-gas three-phase interfacial interaction.