Mechanistic insights into hydrogen production from formic acid catalyzed by Pd@N-doped graphene: The role of the nitrogen dopant

The catalytic decomposition of formic acid (HCOOH) is a crucial process for hydrogen production technologies. Herein, periodic density functional theory (DFT) calculations were employed to explore the effect of N-doping on the decomposition of formic acid. We designed a series of single Pd-atoms deposited in the single vacancy of N-doped graphene sheets, namely Pd-DGr, Pd–N1Gr, Pd–N2Gr, and Pd–N3Gr, as the proposed catalysts. Our findings show that H2 production from HCOOH dehydrogenation on these surfaces proceeds via the formate (HCOO) pathway (Path-I) rather than the carboxylate (COOH) pathway (Path-II). Furthermore, the Pd–N3Gr catalyst shows the greatest catalytic reactivity toward HCOOH dehydrogenation via Path-I, requiring an activation energy (Ea) of 0.38 eV. On the other hand, the undesirable dehydration of HCOOH to carbon monoxide (CO) through COOH (Path-IIIA) or formyl (HCO) (Path-IIIB) intermediates is unlikely to occur on Pd–N3Gr due to a large activation energy. We found that the active species on the catalyst surface increased with N-doping concentration. Additionally, microkinetic simulations of the HCOOH decomposition on these surfaces confirmed the high activity and selectivity of the Pd–N3Gr catalyst toward HCOOH dehydrogenation (Path-I). These calculated results highlight that the Pd–N3Gr catalyst is a promising candidate for the formic acid decomposition reaction to yield hydrogen.