Abstract

nserting underlying reduced graphene oxide (rGO) into Co aims to regulate the chemical integrity and catalytic ability of the Co upper-layer for hydrogen evolution reaction (HER) as a green-hydrogen goal. Consequently, an operando mass spectrometer indicates 3.8 times more considerable hydrogen (m/z = 2) generation in Co/rGO than in the Co at the potential of -2.12 V vs Ag/AgCl. The other operando spectroscopical approaches in the soft and hard X-ray illustrate the chemical oxidation evolution of electronic Co-3d and Co-4p states in terms of the underlying rGO contribution, varied with dynamic chemical adsorption of Co-O(H), Co-Hads, and H2 molecules desorption. The two-dimensional R-k domain in the Co/rGO sample indicates two significant blocks of metal Co and Co-O(H) shifted with the functions of the time- and potential-related utilization, compared to a slight change in the Co sample. A unique examination through the cathodic potential and catalytic process is regarded as the phase transition from the initial middle oxidation state to high oxidation (Co- O(H)) and to de-oxidation (Co-H) in the lattice structure coordination and oxidation state, particularly the intermediate Co⁰ existence and H2 generation. Incorporating rGO provides the regeneration, sustained stability, and decreasing energy barrier of Co-Hads catalysts under density functional theory (DFT) calculation, thereby augmenting the HER enhancement through the alternative Volmer-Heyrovsky process. Combination of in-situ mass spectrometer, soft, and hard X-ray provides novel evidence regarding HER enhancement of the Co/rGO nanocomposite. This study offers insights into the chemical composition, electronic structure, and active role of Co bonded with/without the extinct OH and H bonds, advancing our comprehension of electrocatalytic reactions, thus taking our knowledge of composite materials to stepwise electrocatalytic reactions forward. This cutting-edge experiment under in-situ environment and DFT studies gives critical information regarding the catalytic mechanism and chemical stability of the Co and rGO materials.