Formic acid dehydrogenation over Pd single atom or cluster supported on nitrogen-doped graphene: A DFT study

Formic acid (FA, HCOOH) is one of the most promising hydrogen carriers. Developing cost-effective dehydrogenation catalyst for formic acid is the key to the application of formic acid as hydrogen storage compound. In this study, we systematically studied the catalytic performance of nitrogen-doped graphene supported Pd1 single-atom and Pd4 single-cluster for dehydrogenation of formic acid by density functional theory calculations. Three types of nitrogen-dopants (pyridinic N, pyrrolic N and graphitic N) were introduced into graphene to determine which N dopant plays an important role in catalytic dehydrogenation of formic acid. The results showed that HCOOH decomposition proceeds via the formate (HCOO) intermediate to yield product CO2 and H2, so all catalysts have 100 % H2 selectivity. On graphN3 support, the catalytic activity of Pd4 single-cluster catalyst (SCC) is better than that of Pd1 single-atom catalyst (SAC), while on pyriN3 and pyrroN3, the catalytic activity of Pd1 SAC is better. Compared with traditional Pd(1 1 1), the present SACs and SCCs exhibit higher HCOOH dehydrogenation activity, and Pd4@graphN3 has the best catalytic performance with an energetic span of 0.75 eV, much lower than 1.33 eV of Pd(111). Our work provides an insight into the effects of the coordination environment of N-doped graphene support and active center size on FA dehydrogenation performance.