Loosening CO Limit 25-Fold for Hydrogen: Coupling Material Development and Operation Optimization of Proton-Exchange Membrane Fuel Cells

Abstract

Assurance of high-quality hydrogen is critical for end usage in proton-exchange membrane (PEM) fuel cell (PEMFC) electric vehicles with a long lifetime and low cost as a trace amount of CO impurities in hydrogen significantly affects the durability and fuel expense. Herein, we demonstrate an effective strategy to reduce the total ownership cost of PEMFC vehicles by coupling material development and operation optimization, aiming to obtain the optimal tolerance limit for hydrogen impurities. An electrochemical hydrogen pump was used to accurately determine the poisoning-caused overpotential by eliminating interferences from cathode polarization and the permeated oxygen from thin PEM. The quantitative relations of overpotential versus influencing factors (e.g., type of catalysts, CO concentration, and temperature) were established. The results indicate that PtRu/C demonstrates alleviated CO poisoning, exhibiting approximately 12.8 mV lower overpotential than Pt/C after 100 h test (PtRu/C: 6 mV; Pt/C: 18.8 mV) with a CO concentration of 0.2 ppm specified by ISO standards (14687: 2019) and its increase rate of overpotential is reduced to 1/3-fold. Only the electronic effect induced by Pt–Ru interactions is responsible for the improved CO tolerance of PtRu/C under ultra-low CO concentrations, whereas the widely recognized bi-functional effect due to the reaction of Ru–OH with neighboring Pt–CO species does not work, leading to over 10% decrease of CO–Pt(111) adsorption energy for PtRu/C compared with Pt/C. By means of the synergistic effect of the alternative PtRu/C catalyst and an elevated cell temperature at 85 °C, the CO limit can be loosened to 25-fold from currently recommended 0.2 to 5 ppm, which will remarkably decrease the cost of hydrogen purification. This work offers an insight for the cost reduction of hydrogen mobility and the future optimization of hydrogen quality and also provides valuable guidance for the design of robust anti-poisoning CO catalysts for the long-term application of PEMFCs.

Intriguing H2S Tolerance of the PtRu Alloy for Hydrogen Oxidation Catalysis in PEMFCs: Weakened Pt–S Binding with Slower Adsorption Kinetics

“…To further investigate the difference in resistance to S 2− poisoning between PtRu/C and Pt/C, the physical and chemical characteristics of both catalysts were compared to reveal the relation between the electronic structure and affinity of S 2− to Pt sites. Figure 8 displays the XPS spectra for the two catalysts before and after 50 μM S 2− poisoning for 1 h. Notably, the binding energy of the Pt 4f peak in PtRu/C is shifted positively by 0.4 eV in comparison to Pt/C, suggesting a modification in the Pt electronic structure caused by Ru alloying 16 (Figure 8a). The introduction of Ru atoms into the Pt lattice was reported to induce the strain and ligand effects that involve the lattice change in metal and the modification of the Pt electronic structure, respectively, resulting in the change in the Pt d-band center to move toward or away from the Fermi level.…”

“…Among these impurities, H 2 S and CO are regarded as the key poisons that severely affect the durability of the carbon-supported Pt (Pt/C) catalyst for the PEMFC anode. For CO poisoning, extensive investigations have been performed on the mechanism exploration of the CO harmful effect on PEMFCs and also the development of mitigation strategies (e.g., oxygen bleeding, electrochemical oxidation, and employment of alternative catalysts [e.g., platinum (Pt)-ruthenium (Ru)/C)]). − However, for H 2 S impurity, several literature − studies have been conducted on its detrimental effect on PEMFCs, which showed that trace H 2 S can be strongly absorbed on Pt reactive sites and it is easier to severely poison the Pt/C catalyst. The poisoning of Pt/C by H 2 S impurity results in a significant decrease in available Pt reactive sites for anode hydrogen oxidation reaction (HOR) catalysis, which ultimately affects the output performance and durability of PEMFCs.…”