Electrocatalytic activity of layered oxides SrLaAl1/2M1/2O4 (M = Mn, Fe, Co) for hydrogen- and oxygen-evolution reactions

A series of quasi-2D oxides, with formula SrLaAl1/2M1/2O4 (M = Mn, Fe, Co), have been synthesized and their electrocatalytic activity has been investigated for both half reactions of water splitting, namely oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). These layered oxides consist of octahedrally coordinated Al/M metals, where the octahedra are separated by alkaline earth/rare earth cations. Among the synthesized materials, SrLaAl1/2Co1/2O4 shows the best performance, evident from considerably lower overpotentials for OER and HER, as well as faster reaction kinetics, evaluated by the Tafel method. The improved performance of SrLaAl1/2Co1/2O4 is explained in terms of a combination of factors, including the greater bond covalency due to the higher electronegativity of Co than Mn and Fe, as well as the favorable electronic configuration of trivalent cobalt. Importantly, the electrical conductivity studies indicate a correlation between charge transport and the electrocatalytic activity, where the most active catalyst also shows the highest electrical conductivity.