Photoelectrode nanomaterials for photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is among the most promising approaches for energy conversion due to its practical efficiency. Unfortunately, many works simply test typical cases without profound insight, and this does not lead us very far. Two concepts are usually neglected: (i) the rate-determining step is usually the electrocatalytic process conducting the water splitting, and thus, the interfacial reaction at the electrode surface can be practically more important that the absorption of photons by the semiconductors, and (ii) the architecture of nanomaterials can directly control both photon absorption and electrochemical catalysis. While narrating the importance of the first concept the primary focus of the present review focuses on the second concept to summarize the general effects of nanostructures on the PEC performance. The nano-architecture has a larger impact on the electrocatalytic properties of the photoelectrode rather than light harvesting capability, but this feature is usually neglected. In fact, designing a nano-architecture is a tuning process to balance a series of different processes, which are in competition in a complicated system, for optimizing the PEC performance. The most important task is to maximize the number of electrocatalytic sites and forming a more effective electrode/electrolyte interface while reducing the number of charge recombination centers. Nano structuring is normally in favor of the former while unfavorably supporting the latter. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.