Enhancing hydrogen evolution reaction activity on cobalt oxide in alkaline electrolyte by doping inactive rare-earth metal

Abstract

In order to reduce the energy consumption of hydrogen evolution reaction (HER), a series of lanthanum-doped cobalt oxide (x%La–Co3O4–T, where x% represents the La doping molar ratio and T represents the annealing temperature) electrocatalysts are successfully synthesized by a co-precipitation process, followed by annealing in air. Through X-ray diffraction (XRD) refinements, La3+ is doped into Co3O4 lattice, which decreases the crystallinity of Co3O4. It inhibits the aggregation and growth of Co3O4 grains. 2%La–Co3O4-350 is the optimized sample to show the lowest overpotential of 98 mV at 10 mA cm−2 with the corresponding Tafel slope of 72.8 mV dec−1 in 1 M KOH. Although La is an inactive rare-earth metal element for HER, it enhances the HER activity of Co3O4 efficiently. From further studies, the high HER catalytic activity of 2%La–Co3O4-350 can be owing to three aspects: (i) The highly dispersed and small-size Co3O4 nanoparticles caused by La doping own high specific surface area and electrochemically active surface area (ECSA), which benefits exposing more Co3+ active sites to electrolyte. (ii) La dopants make 2%La–Co3O4-350 own more oxygen vacancies that facilitating the water dissociation step of HER. (iii) La doping leads to improved conductivity and charge transfer efficiency of 2%La–Co3O4-350 during HER.