Ni-N4 sites in a single-atom Ni catalyst on N-doped carbon for hydrogen production from formic acid

The purposes of this research were to synthesize single-atom 1 wt% Ni catalysts for the hydrogen production from formic acid using a simple impregnation of N-doped carbon with Ni acetate, to elucidate the nature of the Ni site using a combination of experimental methods with density functional theory calculations, to propose a reaction mechanism with this Ni site and to compare the catalytic properties of the single-atom catalysts with those of a traditional Ni catalyst with nanoparticles (3.9 nm). We found that the single Ni atom formed a Ni-N4 site in a double vacancy of curved N-doped graphene. Mass-based catalytic activities of the single-atom and traditional catalysts were close. The mechanism of the reaction involved the formation of formate through participation of the Ni and N atoms. The highest energy barrier (1.088 eV) was determined for the step of recombination of hydrogen atoms. This barrier corresponded well to the experimental apparent activation energy.