The Defects of Single Atom Co ₁ ‐N‐C Regulate the H‐Binding Energy to Achieve Divergent Hydrogen Evolution or Transfer Hydrogenation with HCOOH

Abstract 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 (Co ₁ ‐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‐CoN ₃ ) 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 (CoN ₃ ) shows optimal HER efficiency of HCOOH than def‐CoN ₃ 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 CoN ₃ and easily desorbed to generate H ₂ molecule. The regulation on defect structures of single atom Co will provide new avenue for designing catalysts in catalytic processes involving H‐atom transfer.