Hydrogen used in proton exchange membrane fuel cells (PEMFCs) mainly originates from refinery resources in which inevitable S-containing impurities possibly reduce the fuel cell life. Herein, the poisonous influence of trace impurities of H 2 S, carbon disulfide (CS 2 ), and carbonyl sulfide (COS) on the performance of Pt/C catalysts in hydrogen oxidation reaction (HOR) is investigated by a combination of electrochemical measurements, structural characterization, and DFT calculations. Rotating disk electrode (RDE) half-cell electrochemical experiments were used to determine the impact of H 2 S, CS 2 , and COS on the HOR activity and the recovery capability of a commercial Pt/C catalyst. The experimental results indicate that CS 2 even poses a more severe threat to the HOR activity than H 2 S, while COS poses a weaker threat than H 2 S. Moreover, all of H 2 S, CS 2 , and COS have a deteriorative impact on the regeneration of Pt/C catalysts. The theoretical calculation results reveal that CS 2 and COS can decrease the activity of HOR by decreasing the d-band center of Pt atoms except for occupying the active sites of Pt, while H 2 S deactivates the catalyst solely by occupying the active sites. Based on the analysis, the presence of trace CS 2 and COS, as well as H 2 S, will result in the serious degeneration of the Pt/C catalysts. These results provide insights into the deactivation mechanism of Pt-based catalysts and are significant for the practical applications of PEMFCs.

The coalescence of Pt nanoparticles during operation in a real vehicle is considered to be the main reason to weaken the ORR. The trajectories of oriented attachment were disclosed by observing the coalescence events of Pt NPs using in situ TEM.

Proton exchange membrane fuel cell (PEMFC) is one of the most promising energy conversion devices with high efficiency and zero emission. However, oxygen reduction reaction (ORR) at the cathode is still the dominant limiting factor for the practical development of PEMFC due to its sluggish kinetics and the vulnerability of ORR catalysts under harsh operating conditions. Thus, the development of high-performance ORR catalysts is essential and requires a better understanding of the underlying ORR mechanism and the failure mechanisms of ORR catalysts with in situ characterization techniques. This review starts with the introduction of in situ techniques that have been used in the research of the ORR processes, including the principle of the techniques, the design of the in situ cells, and the application of the techniques. Then the in situ studies of the ORR mechanism as well as the failure mechanisms of ORR catalysts in terms of Pt nanoparticle degradation, Pt oxidation, and poisoning by air contaminants are elaborated. Furthermore, the development of high-performance ORR catalysts with high activity, anti-oxidation ability, and toxic-resistance guided by the aforementioned mechanisms and other in situ studies are outlined. Finally, the prospects and challenges for in situ studies of ORR in the future are proposed.

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