The enhanced photocatalytic HER activity of in-situ reduced CoB/GCN-NS composite with a cobalt interlayer as electron transport layer

Loading noble metal-free hydrogen reduction co-catalyst on GCN-based material is a promising strategy to obtain cheap, environmentally friendly, and non-toxic materials for photocatalytic hydrogen evolution. Most existing research focuses on the replacement and separate optimization of GCN-based materials or co-catalyst materials. However, our previous studies have found a new issue: at the interface, the transfer of photogenerated electrons from the surface of GCN to co-catalyst is limited. In this study, aiming to overcome this restriction, CoB nanoparticles are loaded on the GCN NS as noble-metal-free hydrogen reduction co-catalysts by a newly developed in-situ reduction method. Detailed characterization and comparative experiments demonstrate the formation of a metallic cobalt interlayer at the interface between CoB nanoparticles and GCN–NS. This cobalt interlayer significantly enhances the charge separation performance of the in-situ reduced CoB/GCN NS composite, resulting in a 13.8-fold increase in photocatalytic hydrogen evolution rate compared to GCN NS and a 2.1-fold increase compared to the mixed CoB/GCN NS composite with similar CoB loading ratio synthesized by conventional mixing methods. Insights from solar cell research suggest that this interlayer acts as an electron transport layer (ETL), enhancing electron transfer from GCN NS to CoB. Density functional theory (DFT) calculations confirm that the Fermi level of the cobalt interlayer lies between the CBM of GCN NS and the Fermi level of CoB, meeting ETL requirements in solar cell design. This work provides the first evidence that an ETL can function in photocatalytic nanomaterials as well as in solar cells, suggesting a novel optimization strategy for broader photocatalytic material design.