Catalysts with both excellent thermodynamic stability and robust physical adhesion to substrates are required to ensure long-term stability under these harsh conditions. 2) High overpotential at large current densities. At high current densities, high activation energy is required to drive HER because of the rapidly consumed H3O + near the catalyst surface and the blocked active sites by the high-level H2 bubble coverage at catalyst surfaces , leading to increased overpotential and reduced energy efficiency.