Intriguing H<sub>2</sub>S Tolerance of the PtRu Alloy for Hydrogen Oxidation Catalysis in PEMFCs: Weakened Pt–S Binding with Slower Adsorption Kinetics
Shaojie Ke, Bolan Cui, Chaoyong Sun, Yufeng Qin, Jiakun Zhang, Meiling Dou
Abstract
High quality of hydrogen is the key to the long lifetime of proton-exchange membrane fuel cell (PEMFC) vehicles, while trace H2S impurities in hydrogen significantly affect their durability and fuel expense. Herein, we demonstrate a robust PtRu alloy catalyst with an intriguing H2S tolerance as the PEMFC anode, showing a stronger antipoisoning capability toward hydrogen oxidation reaction compared with the Pt/C anode. The PtRu/C-based single PEMFC shows approximately 14.3% loss of cell voltage after 3 h operation with 1 ppm of H2S in hydrogen, significantly lower than that of Pt/C-based PEMFCs (65%). By adopting PtRu/C as the anode, the H2S limit in hydrogen can be increased to 1.7 times that of the Pt/C anode, assuming that the PEMFC runs for 5000 h, which is conductive for the cost reduction of hydrogen purification. The three-electrode electrochemical test indicates that PtRu/C exhibits a slower adsorption kinetics toward S2– species with poisoning rates of 0.02782, 0.02982, and 0.03682 min–1 at temperatures of 25, 35, and 45 °C, respectively, all lower than those of Pt/C. X-ray absorption fine structure spectra indicate the weakened Pt–S binding for PtRu/C in comparison to Pt/C with a longer Pt–S bond length. Density functional theory calculation analyses reveal that adsorption energy of sulfur on the Pt surface was reduced for PtRu/C, showing 1–10% decrease at different Pt sites for (111), (110), and (100) planes, which is ascribed to the downshifted Pt d-band center caused by the ligand and strain effects due to the introduction of second metallic Ru. This work provides a valuable guide for the development of the H2S-tolerant catalysts for long-term application of PEMFCs.