Solar-driven water splitting to generate dihydrogen (H2) and dioxygen (O2) has long been recognized as a sustainable and renewable energy source.Recently, our group reported that an earth abundant metal complexes containing a tetradentate ligand, [CoⅡ(qpy)(H2O)]2+ (qpy =2,2:6,2":6",2(")-quaterpyridine), can function as an efficient molecular catalyst for both water oxidation and reduction.