Co9S8–Ni3S2 heterointerfaced nanotubes on Ni foam as highly efficient and flexible bifunctional electrodes for water splitting

Large-scale commercialization of water splitting is still challenging due to the lack of efficient, cost-effective and robust electrodes. In this work, Co 9 S 8 –Ni 3 S 2 heterointerfaced nanotubes on Ni foam (Co 9 S 8 –Ni 3 S 2 HNTs/Ni) have been successfully developed via a two-step hydrothermal method as a highly efficient, robust and flexible bifunctional electrodes for water splitting. Co 9 S 8 –Ni 3 S 2 HNTs are composed of inner 1D Co 9 S 8 nanotubes surrounded by outer 2D Ni 3 S 2 nanosheets . Co 9 S 8 –Ni 3 S 2 HNTs/Ni electrode achieves 10 mA cm −2 at overpotentials of 85 mV for H 2 evolution reaction (HER) and 50 mA cm −2 at overpotential of 281 mV for O 2 evolution reaction (OER) in 1 M KOH solution, substantially better than that on single-phased Co 9 S 8 nanotubes and Ni 3 S 2 nanosheets on Ni foam. The reason is most likely due to formation of defect-rich heterointerfaces between Co 9 S 8 nanotubes and Ni 3 S 2 nanosheets, and the significant change of binding energies of Co 2p and Ni 2p level between the Co 9 S 8 and Ni 3 S 2 , leading to the synergistic effect on the enhanced catalytic activity for HER and OER. The robust and flexibility of Co 9 S 8 –Ni 3 S 2 HNTs/Ni electrodes are demonstrated in an alkaline electrolyzer, delivering 10 mA cm −2 electrolysis current at a cell voltage of 1.59 V, one of the best bifunctional electrodes for water splitting. Owing to the fact that reaction occurs at the defects-rich heterointerfaces, the Co 9 S 8 -Ni 3 S 2 HNTs/Ni electrodes are structurally very stable.