Hydrogen generation from formic acid decomposition on Ni(2 1 1), Pd(2 1 1) and Pt(2 1 1)

Abstract

The catalytic decomposition of formic acid into carbon dioxide and hydrogen (HCO2H→CO2+H2) on M(211) (M=Ni, Pd, Pt) was investigated by using spin-polarized plane-wave based density functional theory calculations. It is found that on M(211) formic acid prefers the O (OC) atom atop adsorption and the H (HO) atom bridging two neighboring metal atoms, and formate prefers the bidentate adsorption with O atoms atop on metal surface. For M=Ni, Pd, Pt, formic acid has close adsorption energies (−0.69, −0.58, −0.61eV) and also close dissociation barriers (0.42, 0.53, 0.51eV), and the dissociation step is exothermic (−0.95, −0.44, −0.81eV). Formate dissociation into surface CO2 and H (HCOO→CO2+H) is the rate-determining step; and the effective barrier is higher on Ni(211) than on Pd(211) and Pt(211) (1.43 vs. 0.96 and 0.86eV), and formate dissociation is endothermic (0.44eV) on Ni(211), but exothermic on Pd(211) and Pt(211) (−0.09 vs. −0.19eV). On M(211), CO2 has chemisorption (−0.32, −0.13, −0.27eV for M=Ni, Pd, Pt, respectively). For formate dissociation, detailed comparisons between M(211) and M(111) show that Pd(111) and Pt(211) have the smallest effective barriers, while Pt(111) and Ni(211) have the largest effective barriers.