Modulation of photogenerated holes for enhanced photoelectrocatalytic performance

Utilizing clean energy derived from photoelectrocatalytic reactions is expected to be an excellent choice to fundamentally solve the problem of the human energy crisis. Photoelectrochemical (PEC) cell can effectively promote charge separation and improve solar energy conversion efficiency since it combines the advantages of photocatalysis and electrocatalysis. However, the hole transfer and subsequent oxidation reaction in the PEC process are slow, resulting in the rapid recombination of photogenerated electron-hole pairs and low PEC performance. The half-oxidation reaction involving photogenerated holes is the bottleneck of PEC water splitting. Therefore, hole modulation has been an important research area in the field of catalysis. However, compared with electron modulation, research on hole modulation is limited and still faces great challenges. It is therefore of great significance to develop effective modulation strategies for photogenerated holes. This review summarizes the hole modulation strategies developed in the last five years, including hole sacrificial agents, nanostructural modification, heterostructure construction and cocatalyst modification. Hole modulation dynamics studies, such as transient absorption spectroscopy, time-resolved photoluminescence spectroscopy, transient photovoltage and scanning electrochemical microscopy, are also summarized. Moreover, relevant conclusions and an outlook are proposed.