Electrocatalytic properties of new spinel-type MMoO4 (M = Fe, Co and Ni) electrodes for oxygen evolution in alkaline solutions

New spinel-type oxides with molecular formulae MMoO4 (M = Fe, Co and Ni) have been prepared by a thermal decomposition method at 650 °C and investigated as electrocatalysts for the O2 evolution reaction (OER) in KOH solutions. The results show that the new oxide electrocatalysts are highly active for the OER, but they have very low electrochemically active areas, the relative oxide roughness factor being <2. The Tafel slope values for the OER on each oxide in 1 M KOH are found to be ∼40 and ∼60 mV at low and higher potentials, respectively. The reaction order with respect to OH− concentration has been observed to be 1.18, 1.51 and 1.94 on CoMoO4, FeMoO4 and NiMoO4 electrodes, respectively. Both in 1 M KOH and practical cell solution (30 wt% KOH) at 25 °C, the performance of the FeMoO4 electrode is observed to be better than the other two electrodes.