▎ 摘　　要

Cobalt is one of the promising metal catalysts for hydrogen evolution reaction, and its catalytic performance can be further improved by supporting on graphene oxide and reduced graphene oxide as an active interface to the substrate. Scanning transmission X-ray microscopy (STXM) identifies the position-dependent functional groups on the membranes and chemical structure evolution of the CoxOy. The in-situ mass spectrometer analysis shows the reduction current and H2 generation of the electrocatalyst enhanced by the addition of graphene oxide and reduced graphene oxide to CoxOy, as compared to the CoxOy on the bare substrate. The best hydrogen evolution reaction performance of CoxOy at -2.5 V is correlated with the high Co3+ concentration existed on the reduced graphene oxide, as evidenced by the nano-and element-resolved capability of STXM. With the economical electro-reduction synthesis, this study provides brand-new insights into the critical role of substrate rGO and electrocatalyst CoxOy toward the design of high efficiency electrocatalyst.