This project's goal is to develop high-performance water electrolysis technology for producing green hydrogen using high entropy alloy-based catalysts (HEABCs). Catalytic activity, charge transfer, and mass transport in HEABCs are the essential parameters that play important roles in determining water-splitting energy consumption. Porous HEABCs will be developed based on our knowledge in hierarchical nanostructure design and high entropy alloy optimization for the reduction of charge transfer and mass transport energy consumption. With in-situ measurements, the expected outcomes will include revealing the catalytic mechanism and stability, as well as developing effective water electrolysers that enable the use of renewable energies to produce green hydrogen.