A ternary PdNiMo alloy as a bifunctional nanocatalyst for the oxygen reduction reaction and hydrogen evolution reaction

Abstract

Proton exchange membrane (PEM) electrolyzers are one of the most significant technologies for producing green hydrogen energy, in which nanostructured catalysts occupy an important role. At commercial densities, the nanocatalysts on the cathode side in PEM electrolyzers often suffer from undesirable oxidation with the slight oxygen passing through the membrane. In this study, we designed a ternary Mo_xPd_yNi nanocatalyst supported on N-doped carbon (NC) from the pyrolysis of ZIF-8 toward the hydrogen evolution reaction (HER), while at the same time avoiding a loss of the activity toward the oxygen reduction reaction (ORR). Taking advantage of the charge redistribution among these elements, the representative Mo_0.2Pd₃Ni/NC exhibited a low overpotential (η₁₀ = 53 mV) toward HER with a low Tafel slope of 35.8 mV dec⁻¹ in H₂SO₄. In addition, Mo_0.2Pd₃Ni/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 twice 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 was downshifted 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 could significantly enhance the HER stability, which could be extended to the design of other bifunctional nanocatalysts for other reactions.