Superb Enhancement of Hydrogen Evolution in an Acidic Medium over a Cobalt Oxide Surface with Trace Incorporation of Rhodium Particles.

Integration engineering is commonly used for the morphological development of electrocatalysts for promoting hydrogen evolution reactions (HER) due to their distinctive structures, whereas modifying the crystallinity can give the electrocatalyst unique properties that enhance its performance for HER. Herein, we successfully anchored rhodium (Rh) nanoparticles in Co3O4 thin film on a graphite (GP) surface. The obtained catalyst exhibits great HER catalytic performance in a 0.5 M H2SO4 medium. Interestingly, our findings show that the electrode prepared with 1-cycle (1c) electrodeposition of Rh onto Co3O4@GP (Rh1c/Co3O4@GP) surpasses the HER performance of multiple cycles of Rh deposition onto Co3O4@GP or even a 10-cycle Rh electrodeposition Rh10c@GP electrode in the absence of Co3O4, indicating the crucial role of well-engineered Rh deposition and Co3O4 in the overall HER activity. For acidic HER, the catalyst required overpotentials of only 57 mV to deliver a current density of 10 mA cm-2, which is nearly identical to the value by commercial Pt/C. Notably, the Rh1c/Co3O4@GP shows almost no degradation even after 8 h of stability experiments. The synergistic integration of Co3O4@GP with Rh enhances the availability of active sites and improves the intrinsic catalytic activity, as a result showing outstanding HER activity and higher stability. The structural and surface characteristics of the Rh-doped Co3O4-modified graphite electrodes were examined by using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), field emission scanning electron microscopy (FESEM), and X-ray photoelectron spectroscopy (XPS).