Cobalt sulphide microtube array as cathode in photoelectrochemical water splitting with photoanodes

We report on a cobalt sulphide (CoS) electrode prepared by simple and scalable chemical bath deposition (CBD), which performs as a highly efficient and robust electrocatalyst for the H₂ evolution reaction (HER) in both neutral and pH 13 electrolyte solution at a small overpotential (η < 90 mV). At η = 390 mV, turnover frequencies of 38.8 ± 1.9 and 52.1 ± 2.0 mol H₂ (mol Co)^-1 h^-1 were achieved with high stability (Faradaic efficiency >95% for at least 72 h) and turnover numbers of approximately 2600 and 3400 in neutral and basic electrolyte solution, respectively. The rate of HER per geometric area is further enhanced by employing a CoS microtube array (microCoS), which is prepared by sulphurisation of a cobalt hydroxide carbonate nanorod array template using CBD. MicroCoS shows excellent HER activity when it is coupled with a cadmium sulphide sensitised zinc oxide photoanode in the presence of sodium sulphide and a nanostructured hematite (α-Fe₂O₃) photoanode from photoelectrochemical water splitting in basic electrolyte solution.