Enhanced Activity and Stability of Pt-Hf Alloy Catalysts for Electrocatalytic Oxygen Reduction

Enhanced Activity and Stability of Pt-Hf Alloy Catalysts for Electrocatalytic Oxygen Reduction
PEMFC; Pt-Hf alloy; Oxygen reduction reaction; stability
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Notwithstanding a polymer electrolyte membrane fuel cell (PEMFC) is a promising alternative device to reduce our reliance on environmentally unfriendly fossil fuel, there are several problems that should be overcome to make PEMFC more economically attractive. One of the most pivotal issues of problems is considerable overpotential associated with the slow reaction rate of the oxygen reduction at the cathode. Much effort has hitherto been devoted to understanding the kinetic and mechanism of ORR in an attempt to search for inexpensive and catalytically active electrocatalysts such as bi and multi-metallic alloys. Recently, there have been studies concerning the correlation between the electronic structure and catalytic activity of metallic alloys for the ORR. The absorption energy of oxygen is proportional to the oxygen-metal bond strength and relative level of the position of the d-band center at the Fermi level. Other tremendous challenge is the stability for electrochemical reaction, including metal dissolution and surface oxide formation, which occurs intensely in acid medium at high potential. In recent report, Markovic et al. and Adzic et al. have demonstrated the stable cathode catalyst by alloying Pt with 3-d transition metal (especially, Pt-skin surface alloys) and modifying Pt with Au cluster and emphasized the significance of stability considerations. In spite of the significant technological interest in finding active and stable catalyst for ORR condition, the direct experimental inspection of the contributions of the stability involving activity has rarely been investigated in electrochemical reduction of oxygen. Herein we report more active and stable electrocatalytic cathode materials consisting of Pt-based alloys involving late and early transition metals.
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