Effect of molybdenum doping Zn-Co spinel oxide microspheres for efficient electrocatalytic hydrogen production in alkaline media and study supported by DFT

TL;DR: Molybdenum doping in Zn-Co spinel oxide microspheres enhances hydrogen evolution reaction (HER) activity in alkaline media, with 6% Mo-doping exhibiting exceptional HER activity, high stability, and improved electrochemical surface area and charge transfer kinetics.

Abstract: The rational design of efficient transition metal-based electrocatalysts for the hydrogen evolution reaction (HER) is critical for the water-splitting process. Industrial water-alkali electrolysis requires large current densities at low overpotentials, which are always limited by the intrinsic activity. Here, ZnCo2−xMoxO4 (x ≤ 0.10) spinel oxide microsphere electrocatalysts were synthesized for the process in alkaline media. Mo doping in the ZnCo2O4 crystal structure enhanced the active sites, which were responsible for the enhancement in the HER process. The ZnCo2−xMoxO4 (x = 0.06) electrocatalyst exhibited exceptional HER activity, as evidenced by an overpotential of 195 mV, Tafel slope of 81.4 mVs−1 and high stability for 40 h with 1000 cycles linear sweep voltammetry. The surface and electrochemical characterization revealed that 6% Mo-doping exhibits improved the HER activity due to a significantly higher electrochemical surface area and accelerated charge transfer kinetics at the semiconductor electrolyte interface. Density functional theory (DFT) for exploring and explaining the effect of the Mo dopants on the HER activity elucidated that hydrogen and water molecules are adsorbed on the surface of the Mo-doped ZnCo2O4 slab structures. The results show that Mo dopants enhance the chemical activity, due to water adsorption, and HER activity for enhanced electrocatalytic processes. This work provides a new insight into low-metal-cost materials for efficient and durable HER electrocatalysts and successfully showcases the catalyst model for a detailed mechanistic insight into the HER process.