Effect of Base on the Facile Hydrothermal Preparation of Highly Active IrO_x Oxygen Evolution Catalysts

The efficient electrochemical splitting of water is limited by the anodic oxygen evolution reaction (OER). IrO₂ is a potential catalyst with sufficient activity and stability in acidic conditions to be applied in water electrolyzers. The redox properties and structural flexibility of amorphous iridium oxo-hydroxide compared to crystalline rutile-IrO₂ are associated with higher catalytic activity for the OER. We prepared IrO_x OER catalysts by a simple hydrothermal method varying the alkali metal base (Li₂CO₃, LiOH, Na₂CO₃, NaOH, K₂CO₃, KOH) employed during the synthesis. This work reveals that the surface area, particle morphology, and the concentration of surface hydroxyl groups can be controlled by the base used and greatly influence the catalyst activity and stability for OER. It was found that materials prepared with bases containing lithium cations can lead to amorphous IrO_x materials with a significantly lower overpotential (100 mV @ 1.5 mA·cm^-2) and increased stability compared to materials prepared with other bases and rutile IrO₂. This facile method leads to the synthesis of highly active and stable catalysts which can potentially be applied to larger scale catalyst preparations.