Composition-Dependent Effect of the Calcination of Cobalt-, Nickel-, and Gallium-Based Layered Double Hydroxides to Mixed Metal Oxides in the Oxygen Evolution Reaction

Mixed cobalt and nickel based layered double hydroxides (LDHs) with Ga as the third cation and the mixed metal oxides (MMOs) resulting from their thermal decomposition were synthesized in various compositions through constant pH coprecipitation and calcination. The structural and textural properties of the catalysts with variable Co/Ni ratios were assessed by N-2 physisorption, powder X-ray diffraction, and electron microscopy. The obtained materials exhibit electrocatalytic activity for the oxygen evolution reaction in alkaline solution. The highest activity was found for catalysts containing both transition-metal cations, Co and Ni. However, comparison of the LDH precursors and the calcined MMOs revealed a composition-dependent effect of calcination. Co-rich LDH tends to lose activity when calcined, whereas Ni-rich LDH gains activity. The optimal cation composition of the LDH was Co1.5Ni0.5Ga with an overpotential of 382 mV. The highest performance among the MMOs, on the other hand, has been encountered for the Co0.5Ni1.5Ga composition, reaching a similar overpotential.