Solution Combustion Synthesis of Equiatomic Fe-Co-Mo Mixed-Metal Oxide with Mo 5+ for Alkaline Oxygen Evolution Reaction

Oxygen evolution reaction (OER) is the key step in water-splitting devices and rechargeable metal-air batteries. Hence, there is an urgent need for stable and low-cost materials for efficient OER. In the present investigation, a ternary mixed metal oxide of Fe, Co and Mo (FCMO) with equimolar composition is prepared using solution combustion synthesis. The combination of two-phase oxides, AB2O4-spinel and ABO4-monoclinic, have evolved and been investigated as electrocatalysts for the OER in alkaline solutions. Herein, after activation by a few sweeps of linear sweep voltammetry (LSV), FCMO exhibits a low overpotential of 300 mV vs. RHE to achieve a current density of 10 mA/cm2 in 1M KOH. The Tafel slope at low overpotentials for FCMO is ~33 mV/dec. The performance of FCMO comes in the ideal OER catalyst category, which is between 200 to 300 mV @10 mA/cm2. To find the reason behind the excellent OER activity of FCMO its constituents are studied separately. The other possible monoclinic molybdate and spinel phases are also prepared and their electrochemical activity is observed. This study indicates that the presence of Fe supports reduction of Mo in the FCMO mixed metal oxide (MMO) synthesized at 700°C, which enhances the conductivity of the material. The combinations of this MMO, the effect of Fe content and synthesis temperature, are also studied.