Electrochemical overall water splitting to produce H2 and O2 is one of the most promising and efficient techniques which transform electric energy into chemical energy and can be easily integrated with green and renewable energies such as solar energy and wind energy.[1], [2] Water splitting consists of two half reactions, namely, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), and normally requires two types of catalysts to overcome the large overpotential necessary to...