Interface engineered Co, Ni, Fe, Cu oxide hybrids with biphasic structures for water splitting with enhanced activity

Developing high-performance catalysts for water splitting via renewable electricity is of great significance for the clean production of hydrogen. This work reports rational design and controllable fabrication of metal oxide hybrid catalyst CoNiFe2O5·2CuO with unique biphasic microstructures for electrochemical water splitting. Benefited from the presence of CuO nanoparticles as the second phase, more defects and active sites were formed around the interfaces of CoNiFe2O5 and CuO, which led to excellent performances for electrocatalytic water splitting. In particular, the catalyst exhibited outstanding activity for hydrogen evolution reaction with a small overpotential of 30 mV to reach a current density of 10 mA cm-2 and showed a higher turnover frequency (0.3 s-1) than commercial catalyst Pt/C (0.1 s-1) under an overpotential of 50 mV. Moreover, it also displayed good activity for oxygen evolution reaction with an overpotential of 264 mV at 10 mA cm-2. Using CoNiFe2O5·2CuO as the catalyst for electrode pair to construct a cell, a very low cell voltage of 1.53 V is enough to achieve overall water splitting at 10 mA cm-2 in 1 M KOH electrolyte, and the cell could maintain the stable performance at 10 mA cm-2 within 100 h. The as-prepared metal oxide hybrids with biphasic microstructures may have promising application potentials in water splitting.