Ternary Pdnimo Alloy as Bifunctional Nanocatalysts for Oxygen Reduction Reaction and Hydrogen Revolution Reaction

Abstract

Proton exchange membrane (PEM) electrolyzers are one of the most significant technologies for producing green hydrogen energy, in which the nanostructured catalysts occupy an important position. At commercial densities, the nanocatalysts on the cathode side in PEM electrolyzers often suffer from the undesirable oxidation with the slight oxygen passing from the membrane. In this work, we designed an ultra-small ternary Mo x Pd y Ni nanocatalyst supported on N-doped carbon (NC) from pyrolysis of ZIF-8 toward hydrogen revolution reaction (HER), avoiding the loss of the activity toward oxygen reduction reaction (ORR). Taking advantage of the ultrasmall size and the charge redistribution among these elements, the representative Mo 0.2 Pd 3 Ni/NC exhibited a low overpotential (η 10 = 53 mV) toward HER with a low Tafel slope of 35.8 mV dec -1 in H 2 SO 4 . Additionally, Mo 0.2 Pd 3 Ni/NC also exhibited a half-wave potential of 0.90 V toward ORR with a mass activity of 0.78 A mg Pd -1 , which was much higher than that of Pt/C (0.38 A mg Pt -1 ). Micro-structured analyses and density functional theory calculations revealed that the d band center of Pd down-shifted by the synergistic effect between Ni and Mo, which weakened the binding energy of the intermediates with Pd, thus lowering the energy barrier toward HER and ORR. This strategy significantly enhanced the HER stability in PEM electrolyzers, which could be extended to design other bifunctional nanocatalysts in other reactions.

Keywords: Bifunctional nanocatalyst, Charge redistribution, HER, Ternary alloy, ORR