Structurally Disordered Phosphorus-Doped Pt as a Highly Active Electrocatalyst for an Oxygen Reduction Reaction

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–1@0.90 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.