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

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.