Preparation of Alkali Metal Iridates as Oxygen Evolution Catalysts Via Thermal Transformation of Amorphous Iridium (oxy)hydroxides.

Achieving efficient water-splitting under acidic conditions for hydrogen production is severely limited by the anodic oxygen evolution reaction (OER). Overcoming this obstacle is vital to realise effective electrolysers and deliver a hydrogen-driven economy. Iridium oxides remain one of the only viable catalysts under acidic conditions due to their corrosion resistance, however, a fine balance exists between the activity and stability of differing oxide morphologies. We have previously shown that heat-treating high-activity amorphous iridium oxyhydroxide in the presence of residual lithium carbonate leads to the formation of lithium-layered iridium oxide, suppressing the formation of low-activity crystalline rutile IrO2. We now report our recent work on the synthesis of similar compounds, Na-IrOx and K-IrOx, featuring similarly layered crystalline structures. Electrocatalytic tests confirm Li-IrOx has similar electrocatalytic activity as commercial amorphous IrO2·2H2O and with increasing size of the intercalated cation, the activity towards the OER decreases. However, the synthesised electrocatalysts show greater stability than crystalline rutile IrO2 and amorphous IrO2·2H2O, suggesting these compounds could be viable alternatives for industrial PEM electrolysers where durability is a key performance criterion.