Abstract
Electro-catalyst design with superior performance and reduced precious metal content (compared to state-of-the-art Pt/C) has been a challenge in proton exchange membrane fuel cells, preventing their widespread adoption. Metallic glasses have recently shown promising performance and large electrochemical surface area in catalytic reactions. The electro-catalytic behavior of recently developed Pt-, Pd-, and Pt/Pd-based metallic glasses was evaluated in this study using scanning electrochemical microscopy. The influence of chemistry and electronic structure on catalytic behavior was studied using scanning kelvin probe technique. The work function for the metallic glasses was lower by 75 mV to 175 mV compared to pure Pt. This resulted in higher catalytic activity for the amorphous alloys, which was attributed to the ease of charge transfer on the surface. The binding energy for the metallic glasses, measured using X-ray photoelectron spectroscopy, was higher by 0.2 eV to 0.4 eV. This explained easier removal of adsorbed species from the surface of amorphous alloys. The synergistic effect of Pt and Pd in alloys containing both the noble metals was demonstrated towards hydrogen oxidation reaction.
Highlights
A major concern in PEMFCs is the degradation and dissolution of catalysts and carbon support under fuel cell operating conditions[14], which determines a fuel cell performance in addition to catalyst chemistry
Energy level diagram of tip and substrate (BMG) when: (b) there is no electrical contact between the tip and substrate; (c) tip and the substrate are connected electrically while a contact potential difference (VCPD) is generated; and (d) an external electrical bias is applied to nullify VCPD, which is the Scanning kelvin probe (SKP) potential (Vskp)
Scanning electrochemical microscopy was utilized to evaluate the catalytic performance of several Pd- and Pt-based amorphous alloys towards hydrogen oxidation reaction, the main anodic reaction in PEM fuel cells
Summary
A major concern in PEMFCs is the degradation and dissolution of catalysts and carbon support under fuel cell operating conditions[14], which determines a fuel cell performance in addition to catalyst chemistry. The effect of different amorphous chemistries on catalytic activity is not well understood and has not been reported. Work function (WF), which is the minimum energy required for removing an electron from a material’s surface, plays a key role in the charge transfer process and shown to be correlated with catalytic activity[21,22]. Combining SKP with in-situ electroanalytical techniques such as scanning electrochemical microscopy (SECM)[27], may provide valuable insights into the underlying correlation between electronic and electro-catalytic characteristics of recently developed metallic glasses. We report on the electro-catalytic activity of a series of Pd- and Pt-based metallic glasses using SECM and SKP for hydrogen oxidation reaction (HOR). Synergistic effects of Pt/Pd toward HOR were shown for alloys containing both the noble metals
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