Optimizing annealing treatment of mesoporous MoO₂ nanoparticles for enhancement of hydrogen evolution reaction

Various strategies have been adopted to enhance the characteristics of the MoO2 nanoparticles electrode structures. Meanwhile the alkaline medium exhibits the sluggish kinetic and an acidic medium can donate the excess protons to promote the hydrogen evolution reaction. The annealing temperature may sputter the environmental oxygen from the surface and enhance the characteristics of the electrocatalysts. MoO2 nanoparticles have been synthesized successfully using the hydrothermal process; later on, the synthesized structure was treated at temperatures of 400 and 600 degree celsius under the flow of N-2 gas for 6 h. The heat treatment process at 600 degree celsius influenced the characteristics of MoO2 nanoparticles and enhanced the electrical conductivity, electrochemical and specific surface area and mesoporous features of MoO2-600 nanoparticles. Owing to boosted characteristics, MoO2-600 nanoparticles reveal a good overpotential of 56 mV at the current density of 10 mA cm(-2) in 0.5 M H2SO4 due to the excess availability of the protons, which is better than pre-annealed MoO2-basic and MoO2-400 nanoparticles. MoO2-600 nanoparticles exhibit a good Tafel slope of 22 mV dec(-1) and follow the Tafel mechanism, while MoO2-600 nanoparticles show a Tafel slope of 64 and 67 mV dec(-1) in buffer solution and 1 M KOH electrolyte, respectively. Moreover, the turnover frequency of MoO2-600 nanoparticles has been found as 191 ms(-1) at the fixed reversible hydrogen potential of 800 mV(RHE) in 0.5 M H2SO4, which is greater than the buffer solution and 1 M KOH electrolyte. The results indicate that MoO2-600 nanoparticles are an effective electrocatalyst for hydrogen evolution reactions.