Two-dimensional materials as novel co-catalysts for efficient solar-driven hydrogen production

Hydrogen has attracted extensive attention due to its versatile applications in various fields. As the starting step, hydrogen production is a critical technique for the practical application of hydrogen-related technologies. Solar-driven water splitting is considered one of the cleanest methods for hydrogen production because solar power is abundant and clean, and the products are only hydrogen and oxygen. Consequently, strategies to increase the efficiency of solar-to-hydrogen conversion have been widely explored. Based on the basic requirements, loading of co-catalysts for photocatalysis is emerging as an effective method to improve the efficiency of solar-driven water splitting. In this review, we shall systematically discuss the recent developments in two-dimensional (2D) materials, including graphene, 2D transition-metal dichalcogenides (TMDs), and MXenes, for their application as co-catalysts in photocatalytic/photoelectrochemical H-2 evolution. It is noted that highly efficient electrocatalysts for the hydrogen evolution reaction (HER) by electrocatalysis can be used as superior co-catalysts for photocatalysis. Therefore, various methods to improve the HER activity of co-catalysts, such as phase-control, doping, defect engineering, hybridization, and functionalization, have been adopted to increase the photocatalytic performances of decorated photocatalysts, which are also systematically discussed. Through a comprehensive literature review, we summarize and propose this concept, that is, electrocatalysts can be used as co-catalysts in photocatalysis for the improvement of solar-driven H-2 evolution. We believe that this concept will shed light on the development of technologies in photocatalytic hydrogen production for practical applications. At the same time, we trust that efficient, inexpensive and stable co-catalysts will be designed and fabricated not only to promote the efficiency of solar-driven hydrogen production on a large scale, but also to be beneficial for other catalytic processes.