N-Ni-S coordination sites of NiS/C3N4 formed by an electrochemical-pyrolysis strategy for boosting oxygen evolution reaction

The rational design and fabrication of distinctive coordination sites is an attractive and challenging approach to develop electrocatalysts with superior activity toward oxygen evolution reaction (OER). Constructing N-doped carbon shells coordinated with transitional metal composites can greatly enhance the OER activity of electrocatalysts. Herein, a facile electrochemical-pyrolysis strategy is applied to synthesize NiS/C3N4 composite with N-Ni-S coordination sites by in-situ crystallization on copper foam (CF). A detailed characterization, especially synchrotron-based X-ray absorption fine structure (XAFS) clearly unravels the N-Ni-S coordination mode is successfully formed. As a result, NiS/C3N4 presents excellent OER performance with a low overpotential of 334 mV at a current density of 10 mA cm−2, a Tafel slope of 45 mV dec−1, and robust electrochemical stability for 50 h in basic media, outperforming some recently reported conventional transitional metal electrocatalysts. The outstanding electrocatalytic performance of NiS/C3N4 mainly originates from the N-Ni-S coordination sites, which can provide abundant catalytic active sites, facilitate charge transfer, and enhance electronic conductivity. Furthermore, by tuning the two important experimental parameters of electrodeposition potential and electropolymerization time, the relationship between morphology and electrocatalytic performance of catalysts is deeply explored. This work demonstrates the validity of improving electrocatalytic performance by elaborately tailoring the coordination sites, thereby opening up an applicable and inspiring avenue forward in the design of advanced electrocatalysts for water splitting.