Identification of hydrogen-evolving active sites by chemical probes

Catalysts are usually poisoned by specific small molecules, leading to the poisoning or blocking effects on the catalytically active sites. Those poisoners in turn can be utilized as chemical probes to identify the real active sites in a certain catalytic reaction, including the hydrogen evolution reaction (HER). Here, we highlighted the chemical probe methods for the identification of HER-active metal and nonmetal sites by revisiting a collection of typical studies. The related identification processes and mechanisms were described in detail. Besides, potential concerns and key scientific challenges were also proposed in this field. We believed that the identification of active sites by chemical probes would not only provide a better understanding of the nature of catalytically active sites, but also facilitate the rational design of highly active catalysts.