Neighboring V atom as a catalytic switch: Reversing the active site for exceptional water splitting

Due to the different reaction substrates are involved in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), bifunctional catalysts with diverse active sites are crucial for electrochemical water splitting. However, it is extremely difficult to design sites that are catalytically active for both H- and O-containing intermediates. Herein, neighboring V site on poor-active FeN4 site can reverse the active center of HER from Fe sites to N sites and simultaneously boost the activity of Fe sites for OER. Water splitting on FeV-NC requires only 1.57 V to achieve 10 mA cm−2 along with an overpotential of 233.2 mV for OER and 88.8 mV for HER. Theoretical calculations reveal that the presence of neighboring V site shifts the pz centres of the bridging N atoms positively and intensifies the electronic spin and 3d orbital of Fe atoms, which optimizes the interaction of the H/O-containing reactant/intermediate on N and Fe sites.