Hydrogen evolution activity of NiMo-MoO2 produced by mechanical milling

Abstract

In this study, mechanical alloying was done by a high-energy planetary ball milling technique. A mixture of NiO, MoO₃ and graphite powders were used as initial materials. After milling of powder mixture with 40 wt.% additional graphite, a temperature of 400, 550 and 1000 °C for 1 h was considered for the heat treatment of powder mixture. Also, powder mixtures containing 60, 80 and 100 wt.% additional graphite was heat-treated at 1000 °C for 1 h. The results of the thermodynamic analysis showed that full reduction of molybdenum-nickel oxide at ambient temperature during milling does not occur and thermal activation is required for complete reduction of mixed metal oxide. Investigation of hydrogen release through the electrochemical test in 1 M electrolyte solution of KOH at 28 °C showed that the reduced sample containing 60 wt.% additional graphite with ~187 mV additional potential in current density of ~10 mAcm^-2, has the most activity in the release of hydrogen. This sample showed the lowest R_ct of 17 ohm which means the good electrochemical characteristics of Ni-Mo alloy due to the good electrical conduction pathways and high access for the electrolyte solution with the high electrochemically active surface area.