Hydrogen Oxidation Reaction on Metal@Pt Core-Shell Catalysts in Alkaline Electrolyte

Abstract

Hydrogen oxidation reaction (HOR) as the key reaction in hydrogen-oxygen fuel cell has been widely investigated, and ultra low loading Pt (≤0.05 mg cm–2) is required for HOR in proton exchange membrane fuel cells.(1, 2) However, the HOR kinetics becomes sluggish in base, which is at least two orders of magnitude slower than that in acid.(3) The sluggish HOR kinetics in alkaline electrolyte hinders the development of alkaline exchange membrane fuel cell, which is more commercially viable because of the potential to forego noble metal catalysts and less serious corrosion.(4) To obtain the catalysts with high HOR activity in alkaline environment, it is essential to understand the reason for this puzzling difference of HOR kinetics in acid and base. The understanding of the sluggish hydrogen oxidation reaction (HOR) kinetics in alkaline electrolyte is crucial for designing high performance electrocatalysts. Here, we report a clear and convincing result on this problem by investigating the relationship between the HOR kinetics and Pt-adsorbate energetics. Using electrochemical analysis for well-modified Pt surfaces with distinct Pt-adsorbate interactions, we establish a clear trend in activity for HOR in alkaline electrolyte, that is, the activity changes in the order Au@Pt < Pt < Pd@Pt < Ru@Pt (Figure 1a). A decisive role of Pt－Had energetics in the HOR kinetics on Pt surfaces is determined, while no favorable effects of Pt－OHad energetics in the HOR kinetics were found (Figure 1b). The in-situ XANES analysis demonstrated a higher Had coverage on the pure Pt surface than that on the Pt surface with Ru core due to more strongly bonded Had on pure Pt surface (Figure 1c,d). These findings provide us a novel aspect to understand the HOR kinetics on Pt surfaces and also provides fundamental insights into the influence of the Pt－Had interaction on the HOR mechanism. Figure Caption Figure 1. (a) HOR polarization curves normalized to the limiting current density. (b) Trend in the exchange current density for HOR in alkaline solution as a function of the Hupd coverage. Error bars stand for the variation of at least two sets of experimental repeats. (c) Magnified XANES from Pt L 3 edge of commercial Pt/C in 0.1 M KOH solution at different potentials. (d) Comparison of the relative changes in the intensity of absorption peaks for Ru@Pt/C and commercial Pt/C shown in the XANES spectra. References M. K. Debe, Electrocatalyst approaches and challenges for automotive fuel cells. Nature 486, 43-51 (2012).H. A. Gasteiger, S. S. Kocha, B. Sompalli, F. T. Wagner, Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs. Appl. Catal. B: Environ. 56, 9-35 (2005).J. Durst et al., New insights into the electrochemical hydrogen oxidation and evolution reaction mechanism. Energy Environ. Sci. 7, 2255-2260 (2014).J. R. Varcoe, R. C. T. Slade, Prospects for alkaline anion-exchange membranes in low temperature fuel cells. Fuel Cells 5, 187-200 (2005). Figure 1