Nickel-based thin film on multiwalled carbon nanotubes as an efficient bifunctional electrocatalyst for water splitting.

Herein, we report electrodeposited nickel-based thin film (NiOx) on multiwalled carbon nanotubes (MWCNTs) as a highly efficient bifunctional catalyst for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Under reductive conditions (-1.2 V vs Ag/AgCl), the hydrogen evolution catalyst (H2-NiO(x)) was facilely deposited on MWCNTs. The resulting film demonstrates good catalytic activity for hydrogen production in a near-neutral aqueous solution at low overpotential. When switched to oxidative conditions (+1.1 V vs Ag/AgCl), the amorphous H2-NiO(x) film onto MWCNTs can be transformed into another amorphous material (O2-NiO(x)) to efficiently catalyze OER. The NiO(x)-MWCNTs catalyst was further characterized by scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX), and X-ray photoelectron spectroscopy (XPS). The results show that the content of oxygen in the O2-NiO(x)-MWCNTs film is higher than that in the H2-NiO(x)-MWCNTs film. The NiOx-MWCNTs catalyst has good catalytic stability, and the film is reversible when the potentials are switched between the reductive conditions and oxidative conditions. The Faradaic efficiencies of hydrogen and oxygen production are >95%.