Implementation of Multifunctional Electrocatalysts in Photoelectrochemical Devices for Water Electrolysis

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Photoelectrochemical (PEC) water-splitting devices represent a promising and environmentally friendly technology for the emission-free production of hydrogen. A PEC device is made up of two half-reactions: at the photoanode, where the oxygen evolution reaction (OER) takes place, and at the photocathode, responsible for the hydrogen evolution reaction (HER). In PEC devices, light is absorbed by the photoelectrode material, generating electron–hole pairs. The photogenerated electrons and holes migrate to the interface to participate in PEC–HER and PEC–OER, respectively. Despite the potential of PEC devices, their practical performance faces significant challenges, including several issues such as severe recombination, large overpotential, low stability, and sluggish surface reaction. The integration of electrocatalysts (cocatalysts) with photoelectrode materials, either photoanode or photocathode, is an efficient strategy to improve the performance of PEC devices. This chapter explores the multifunctional role of cocatalysts in devices including the separation of charge carriers, reduction of the overpotential required for HER and OER, and enhancement of photostability. In addition, unbiased water-splitting devices are presented as a crucial step for practical applications. This chapter also summarizes the key insights and reflections on the challenges and opportunities that lie ahead for advancing novel cocatalysts, thus promoting the development of highly efficient PEC water-splitting devices.