Structurally Disordered Phosphorus-Doped Pt as a Highly Active Electrocatalyst for an Oxygen Reduction Reaction
Bang‐An Lu, Linfan Shen, Jia Liu, Qinghua Zhang, Liyang Wan, David J. Morris, Ruixiang Wang, Zhi‐You Zhou, Gen Li, Tian Sheng, Lin Gu, Peng Zhang, Na Tian, Shi‐Gang Sun
Abstract
The application of Pt alloy catalysts for oxygen reduction reactions (ORRs) in proton-exchange membrane fuel cells is severely impeded by base metal leaching, since the produced metal ions can result in the degradation of a Nafion membrane by replacing H+ and inducing a Fenton reaction. Doping Pt with nonmetal elements can significantly mitigate such problems due to the relative harmlessness of the corrosion products of anions. Herein, we developed a phosphorus-doping strategy, which can greatly boost the ORR performance of Pt. Phosphorus was introduced into the near-surface of commercial Pt/C (denoted as PNS-Pt/C) via a surfactant-free method. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and X-ray photoelectron spectrum (XPS) tests indicate that the introduction of phosphorus induced distortion of the Pt lattice and the downshift of the d-band center. In situ electrochemical Fourier transform infrared (FTIR) spectroscopy with adsorbed CO as a molecule probe further revealed that the introduction of phosphorus can lower the adsorption ability. The ORR mass activity of PNS-Pt/C is as high as 1.00 mA μgPt–[email protected] V, which is enhanced by 7 times in comparison with the initial Pt/C catalyst. Meanwhile, the durability is also enhanced. After 10 000 potential cycles, PNS-Pt/C only lost 14% of the ORR mass activity, while Pt/C lost 51%. More importantly, a H2–air fuel cell with a PNS-Pt/C cathode achieves a power density of 1.06 W cm–2 at a current density of 2.0 A cm–2 with a low Pt loading of 0.15 mg cm–2. The current density at 0.60 V (practical working potential) is 1.54 A cm–2, 2 times higher than that of commercial Pt/C. Density functional theory (DFT) calculations indicate that near-surface phosphorus doping can induce the distortion of the Pt surface, on which some concave Pt sites have optimal binding energy of OH for the ORR. Furthermore, this phosphorus-doping strategy is also valid for a PtNi alloy catalyst to further boost the ORR performance.