Formic acid dehydrogenation over PdNi alloys supported on N-doped carbon: synergistic effect of Pd-Ni alloying on hydrogen release

Bimetallic Pd 1 Ni x alloys supported on nitrogen-doped carbon (Pd 1 Ni x /N-C, x = 0.37, 1.3 and 3.6) exhibit higher activities than Pd/N-C towards dehydrogenation of formic acid (HCO 2 H, FA). Density functional theory (DFT) calculations provided electronic and atomic structures, energetics and reaction pathways on Pd(111) and Pd 1 Ni x (111) surfaces of different Pd/Ni compositions. A density of states (DOS) analysis disclosed the electronic interactions between Pd and Ni revealing novel active sites for FA dehydrogenation. Theoretical analysis of FA dehydrogenation on Pd 1 Ni x (111) ( x = 0.33, 1 and 3) shows that the Pd 1 Ni 1 (111) surface provides optimum H 2 -release efficiency via a favorable 'HCOO pathway', in which a hydrogen atom and one of the two oxygen atoms of FA interact directly with surface Ni atoms producing adsorbed CO 2 and H 2 . The enhanced efficiency is also attributed to the blocking of an unfavorable 'COOH pathway' through which a C-O bond is broken and side products of CO and H 2 O are generated. Among the various Pd 1 Ni x alloys ( x = 0.33, 1 and 3) supported on nitrogen-doped carbon, Pd 1 Ni 1 /N-C has the highest activity for formic acid (HCO 2 H, FA) dehydrogenation as a result of synergistic interactions between Pd and Ni atoms.