All electrochemical measurements of the HER were performed with an ECstat-302 (EC FRONTIER, Kyoto, Japan) and RRDE-3A rotating ring disk electrode apparatus (BAS, Tokyo, Japan). A rotating disk electrode (RDE, φ = 5 mm, glassy carbon) was cleaned before use. Specifically, it was polished with alumina paste and then sonicated in water. Pt coil and Ag/AgCl electrodes were used as counter and reference electrodes, respectively. In the setup, the catalyst slurry was homogenized. Specifically, it was sonicated in an ice bath for 30 min. Then, 10 µL of the slurry was carefully dropped onto the RDE and rotated in open air until it dried. Next, each electrode was placed in 0.10 mol L -1 HClO4 (pH = 1.0) electrolyte attached to an electrochemical measurement system. The electrode surface was then cleaned by bubbling N2 gas for 30 min. Then, cyclic voltammetry (CV) was performed 100 times in the region of 0.00 to -1.00 V (vs. RHE) at a scanning rate of 200 mV/s. Finally, LSV was performed in the region of 0.20 to -0.80 V (vs. RHE) at a rate of 20 mV/s under N2 gas.