Correlation between theoretical descriptor and catalytic oxygen reduction activity of graphene supported palladium and palladium alloy electrocatalysts

• Published in: Journal of power sources 2015-12, Vol.300, p.1-9
• Main Authors: Seo, Min Ho, Choi, Sung Mook, Lee, Dong Un, Kim, Won Bae, Chen, Zhongwei
• Format: Article
• Language: English
• Subjects: Density functional theory; Dissolution potential; Electrocatalyst; Graphene; Oxygen reduction reaction; Palladium
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2015.08.079

The oxygen reduction reaction, ORR, performances of graphene-supported palladium (Pd) and palladium alloys (Pd3X: X = Ag, Co and Fe) catalysts with highly dispersed catalyst particles are investigated in acidic and alkaline conditions using a rotating disk electrode, RDE. Graphene nanosheet, GNS, supported Pd based catalysts are fabricated without surfactant through the impregnation of Pd and 2nd metal precursors on GNS, leading to small and uniformly dispersed nanoparticles, even when high metal loading of up to 60 wt.% are deposited on supports. The ab-initio density functional theory, DFT, calculations, which are based on the d-band center theory, have been applied to correlate with the results of the ORR performances obtained by half-cell tests. Additionally, the cohesive energy, Ecoh, and dissolution potential, Um, for the Pd nanoparticles have been calculated to understand thermodynamic stability. To elucidate the d-band center shift, the Pd 3d5/2 core-level binding energies for Pd/GNS, Pd3Ag/GNS, Pd3Fe/GNS and Pd3Co/GNS have been investigated by X-ray photoelectron spectroscopy, XPS. The GNS-supported Pd, or Pd-based alloy-nanoparticle catalyst shows good ORR activity under acidic and alkaline conditions, suggesting it may offer potential replacement for Pt for use in cathode electrodes of anion-exchange membrane fuel cell, AEMFC, and acid based polymer electrolyte fuel cell, PEMFC. [Display omitted] •Highly dispersed Pd and Pd alloy nanoparticles on graphene at loadings up to 60 wt.%.•The experimental measurements of Pd3d core level with DFT calculation.•Identifying the d band center of Pd atom in the Pd and Pd3X alloy by DFT calculation.•A descriptor for ORR activity by the electronic structure of bimetallic Pd alloys.•A fundamental relationship on Pd and Pd alloy for ORR in acidic and alkaline media.