All three-electrode electrochemical measurements were tested in a Gamry potentiostat. A Pt wire was used as the counter electrode, and an Ag/AgCl in saturated KCl solution was used as reference electrode. The rotating disc electrode (RDE) was a glassy carbon electrode with a diameter of 5 mm. Since all the HOR catalysts have a loading of 10 wt. %, to achieve low metal loadings, they were diluted by carbon black. Unless specified, all the data shown here are iR-corrected. The detailed description of electrode preparation, HOR measurements and data analysis, as well as Cu stripping and CO stripping measurements are provided in the Supplementary Information.