Recent Advancement of p- and d-Block Elements, Single Atoms, and Graphene-Based Photoelectrochemical Electrodes for Water Splitting

Solar-assisted photoelectrochemical (PEC) water splitting to produce hydrogen energy is considered the most promising solution for clean, green, and renewable sources of energy. For scaled production of hydrogen and oxygen, highly active, robust, and cost-effective PEC electrodes are required. However, most of the available semiconductors as a PEC electrodes have poor light absorption, material degradation, charge separation, and transportability, which result in very low efficiency for photo-water splitting. Generally, a promising photoelectrode is obtained when the surface of the semiconductor is modified/decorated with a suitable co-catalyst because it increases the light absorbance spectrum and prevents electron–hole recombination during photoelectrode reactions. In this regard, numerous p- and d-block elements, single atoms, and graphene-based PEC electrodes have been widely used as semiconductor/co-catalyst junctions to boost the performances of PEC overall water splitting. This review enumerates the recent progress and applications of p- and d-block elements, single atoms, and graphene-based PEC electrodes for water splitting. The focus is placed on fundamental mechanism, efficiency, cells design, and various aspects that contribute to the large-scale prototype device. Finally, future perspectives, summary, challenges, and outlook for improving the activity of PEC photoelectrodes toward whole-cell water splitting are addressed.