The Defects of Single Atom Co1-N-C Regulate the H-Binding Energy to Achieve Divergent Hydrogen Evolution or Transfer Hydrogenation with HCOOH

HCOOH can be used as a hydrogen donor in catalytic transfer hydrogenation (CTH) or a hydrogen storage molecule. The desorption-combination of H^* species from H-binding sites after dissociation of HCOOH is necessary for hydrogen evolution reaction (HER) but undesired for CTH. In this work, it is found that the process of high-temperature calcination can cause defects in the nitrogen-doped carbon anchored single atom Co catalyst (Co₁-N-C) and adjust the electronic state of Co, thereby affecting the H-binding energy on single atom Co sites. The three-coordinated single atom Co with the most abundant defects (def-CoN₃) has best catalytic activity in CTH of nitrobenzene using FA as hydrogen donor in reductive formylation reaction. While the single atom Co with minimal defects (CoN₃) shows optimal HER efficiency of HCOOH than def-CoN₃ and four-coordinated single atom Co. Through density functional theory calculation, the defective sites promoted the dissociation of HCOOH and H^* absorption but inhibited the H^* desorption, which is conducive to CTH. The H^* is moderately absorbed on defect-free CoN₃ and easily desorbed to generate H₂ molecule. The regulation on defect structures of single atom Co will provide new avenue for designing catalysts in catalytic processes involving H-atom transfer.