High surface area lanthanum cobaltate and its A and B sites substituted derivatives for electrocatalysis of O2 evolution in alkaline solution

Co-based perovskite oxides with molecular formulae, La1−xSrxCoO3 (0⩽x⩽0.5) and La0.7Sr0.3Co1−yByO3 (B=Cu, Fe, Ni, Cr or Mn; 0.05⩽y⩽0.2) were prepared at 700°C, using a carbonate precipitation method, and reproduced in the film forms on pretreated Ni supports by an oxide slurry painting technique. The study showed that the partial substitution of La by Sr in the LaCoO3 matrix increased the electrochemically effective area (RF), as well as the apparent electrocatalytic activity (ia) but it decreased the true catalytic efficiency (it). Small substitutions at the B site by Ni seemed to slightly improve the electrochemically active area. On the contrary, all other substitutions, namely, Cr, Mn, Fe and Cu had the adverse effect. It is noteworthy that 0.1 mol Fe substitution considerably improved both the apparent as well as the true catalytic activity of the oxide, while other substitutions except Cu, had detrimental effect on the electrocatalysis of O2 evolution. The oxygen evolution reaction (OER) followed first-order kinetics with respect to OH− ion concentration. The Tafel slope (b) values at low potentials ranged between 60 and 80 mV decade−1 and that they increased slightly with increasing temperature. The electrochemical apparent activation energy (ΔHel#) of OE was observed to decrease on increasing the potential across the catalyst/1 M KOH interface. The ΔS# values for the reaction were largely negative. Based on these results a suitable mechanism for O2 evolution is proposed.