The design of electrocatalysts for polymer electrolyte membrane fuel cells must satsify two equally important fundamental principles: optimization of electrocatalytic activity and long-term stability in acid media (pH <1) at high potential (0.8 V). We report here a solution-based approach to the preparation of Pt-based alloy with early transition metals and realistic parameters for the stability and activity of Pt(3)M (M = Y, Zr, Ti, Ni, and Co) nanocatalysts for oxygen reduction reaction (ORR). The enhanced stability and activity of Pt-based alloy nanocatalysts in ORR and the relationship between electronic structure modification and stability were studied by experiment and DFT calculations. Stability correlates with the d-band fillings and the heat of alloy formation of Pt(3)M alloys, which in turn depends on the degree of the electronic perturbation due to alloying. This concept provides realistic parameters for rational catalyst design in Pt-based alloy systems.
Interesting phenomena were observed during an investigation on the accelerating effects of 3-mercapto-1-propane sulfonic acid ͑MPSA͒, i.e., different aging times of MPSA result in different filling profiles. When MPSA was added to the electrolyte immediately before electrodeposition, subconformal deposits appeared, whereas MPSA aged over 12 h enabled superfilling. From UV-visible analysis, over 99% MPSA was converted to bis͑3-sulfopropyl͒disulfide ͑SPS͒ within 12 h through the reaction with Cu 2ϩ , which means that SPS was, in terms of ''visible'' superfilling, the real accelerator. This arose from the fact that SPS experienced adsorption first, while MPSA underwent Cu 2ϩ reduction first at the trench entrance.
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