Flame growth of nickel-based cocatalyst for efficient solar water splitting of BiVO4 photoanode†

The low charge separation efficiency and slow water oxidation kinetics of bismuth vanadate (BiVO₄, BVO) limit its performance for solar water splitting. Here, a flame growth method has been developed to rapidly grow a nickel-based cocatalyst (NiO_x) on the surface of the worm-like BVO films. After 20 s flame growth, the NiO_x cocatalyst, which is comprised of Ni, NiO, and NiOOH, can be uniformly and rapidly synthesized. The NiO_x/BVO composite photoanode achieves a photocurrent density of 3.80 mA cm⁻² at 1.23 V vs. RHE in a neutral electrolyte, which is 6.67 times higher than that of the pristine BiVO₄. Under the assistance of polyacrylamide hydrogel coating, the photocurrent of the NiO_x/BVO photoanode can be well maintained at 62.26% after a 24 h long-term stability test. The performance improvement can be mainly attributed to the fact that the NiO_x layer reduces the resistance of the charge transfer and the energy barrier of the oxygen evolution reactions, and introduces a large number of oxygen vacancies. This research confirms that the flame growth of cocatalysts is an efficient method for preparing the cocatalytic layer on the nanostructure photoelectrode, which can well maintain the nanostructures.