· Iridium oxide (IrO2) and Ruthenium oxide (RuO2): These are considered state-of-the-art OER catalysts due to their high activity and stability in acidic media. However, their high cost and scarcity limit their large-scale applications.

· Nickel-based materials: Nickel oxides, hydroxides, and alloys have shown good OER performance in alkaline media. They are earth-abundant and relatively inexpensive, making them attractive alternatives to IrO2 and RuO2.

· Cobalt-based materials: Similar to nickel, cobalt oxides, hydroxides, and alloys exhibit promising OER activity, particularly in alkaline solutions.

· Perovskite oxides: These materials have gained significant attention due to their tuneable composition and structure, which allows for optimizing their catalytic properties. Some perovskite has shown comparable OER activity to IrO2 in alkaline media.

· Metal-organic frameworks (MOFs): These porous materials can be designed with specific functionalities for OER catalysis. They offer high surface area and tuneable active sites, leading to enhanced performance