High-efficiency photoelectrochemical hydrogen generation enabled by p-type semiconductor nanoparticle-decorated n-type nanotube arrays

TiO₂ nanotube arrays (TNTAs) were decorated with NiO nanoparticles via a sequential chemical bath deposition (CBD) approach to yield NiO@TNTA photoanodes. In sharp contrast to pure TNTAs, NiO@TNTAs displayed increased absorption and decreased photoluminescence. Interestingly, NiO@TNTA photoanodes exhibited a higher photoelectrochemical activity for hydrogen production than pure TNTAs. The incident-photon-to-current-conversion efficiency (IPCE) of the optimized NiO@TNTA photoanode was calculated to be 62.8%, and remarkably, the maximum hydrogen production rate reached 37.8 μmol h^-1 cm^-2, approximately 5.0 times faster than pure TNTAs. Such markedly enhanced photoelectrochemical efficiency can be attributed primarily to the efficient separation of photogenerated charge carriers at the p-n junction of the two dissimilar semiconductors, that is, p-type NiO and n-type TiO₂, in conjunction with the implementation of nanosized NiO particles with large surface area which enables a shortened charge transfer distance and in turn increased probability of reaction of charge carriers with water molecules.