Improved Chloride Tolerance of PtCo/C with a Pt-Skin Structure toward the Oxygen Reduction Reaction Due to a Weakened Pt–Cl Interaction

ACS Appl. Energy Mater.

Wen

Qin

et al. 2023

Self Cite

Meeting the long-term durability target still poses a significant challenge for the large-scale commercialization of proton exchange membrane fuel cells (PEMFCs) for electric vehicle application. The air impurities (e.g., SO 2 , NO x , and halogen ions) are regarded as one of the major factors that significantly suppresses the output performance of fuel cells. Herein, we revealed the origin of halogen ions poisoning on Pt sites of the state-of-the-art Pt/C catalyst for oxygen reduction reaction (ORR) catalysis through adsorption kinetic investigation and density functional theory (DFT) calculations. Results show that the origin of halogen ions poisoning on Pt sites not only arises from the decrease of Pt reactive sites for ORR catalysis through covering the Pt surface but also depends on the tailored Pt intrinsic activity by modifying the Pt electronic structure that relies on the bonding form between the Pt and impurity. The poisoning kinetics of halogen ions follows the decrease trend of I − > Br − > Cl − > F − with poisoning rates of 1.33, 0.36, 0.20, and 0.19 h −1 , respectively. Both Br − and I − mainly bond with Pt in the form of covalent bonding that leads to occupation of the Pt 5d orbital and thus impedes the interaction with the 2p orbital of oxygen, leading to the decrease of ORR activity, while both Pt−F and Pt−Cl are the primary ionic bonding that makes the Pt 5d orbital electrons decrease and thus promotes the formation of the Pt−O bond. The ORR rate-determining step is changed from the *OH hydrogenation step (*OH → H 2 O) for normal ORR catalysis without impurities to the O 2 hydrogenation step (O 2 → *OOH) for Pt sites poisoned by Cl − , Br − , and I − . This work provides an insight into the poisoning mechanism of impurities on Pt sites and offers informative guidance for the development of robust antipoisoning catalysts for PEMFC application.

Section: Adsorption Kinetics Of Halogen Ions On Pt/cmentioning

confidence: 99%

Origin of Pt Site Poisoning by Impurities for Oxygen Reduction Reaction Catalysis: Tailored Intrinsic Activity of Pt Sites

ACS Appl. Energy Mater.

Wen

Qin

et al. 2023

Self Cite

“…Currently, the hydrogen fuel feed for PEMFC anodes still relies on fossil fuel-based feeds (mainly from natural gas, heavy oils, naphtha, and coal); thus, some impurities (e.g., CO, H 2 S, and NH 3 ) from hydrogen are inevitably introduced into the anode of PEMFCs . The presence of these fuel contaminants will poison the key materials of PEMFCs (especially the membrane electrode assembly (MEA)) and decrease their cell performance, which ultimately significantly limit the durability and competitiveness of fuel cell EVs (FCEVs), especially in heavy trucks that require a longer lifetime (∼30,000 h). , …”

Section: Introductionmentioning

confidence: 99%

“…2 The presence of these fuel contaminants will poison the key materials of PEMFCs (especially the membrane electrode assembly (MEA)) and decrease their cell performance, which ultimately significantly limit the durability and competitiveness of fuel cell EVs (FCEVs), especially in heavy trucks that require a longer lifetime (∼30,000 h). 3,4 Among these contaminants, H 2 S is regarded one of the most sensitive impurities for PEMFCs, having a serious detrimental effect on the output cell performance and durability. 5 The total sulfur limit in hydrogen is determined to be stringent for the application of PEMFCs with the limit level of 0.4 ppb according to the ISO standard (14687: 2019), 6 so the limit value of H 2 S may be equivalent or smaller, which is remarkably stricter than that of CO (0.2 ppm) and other impurities (e.g., total halide (0.05 ppm) and total hydrocarbons (2 ppm)), indicating that the poisoning extent of H 2 S on PEMFCs is the most serious among all hydrogen impurities.…”

Section: Introductionmentioning

confidence: 99%

Operatable and Efficient Mitigation Strategies for H₂S Poisoning in Proton Exchange Membrane Fuel Cells: Releasing Pt Reactive Sites for Hydrogen Oxidation

ACS Appl. Energy Mater.

Cui

et al. 2023

Self Cite

The anode feed for hydrogen fuel cell electric vehicles (FCEVs) currently still relies on the reformed fuel that inevitably contains contaminants (e.g., CO, H 2 S, and NH 3 ). As one of the most sensitive impurities, trace H 2 S in hydrogen significantly deteriorates the durability of proton exchange membrane fuel cells (PEMFCs), while there is still a lack of effective strategies to mitigate H 2 S poisoning in PEMFCs. Herein, we present two kinds of facile, operatable, and efficient strategies to mitigate a H 2 S-poisoned anode, with the aim of improving the durability of PEMFCs by releasing more Pt reactive sites for hydrogen oxidation reaction (HOR) catalysis. The first mitigation strategy is conducted by increasing the cell temperature temporarily when purging with pure hydrogen after H 2 S poisoning by means of accelerating H 2 S desorption on Pt sites under high temperatures and thus releasing more available Pt reactive sites for HOR catalysis. A higher temporary temperature leads to a larger recovery percentage of performance, outperforming the effect of the generally adopted pure hydrogen purging operation. Another mitigation strategy is called "internal oxygen permeation", based on the oxidation of sulfur-adsorbed anode by compelling air diffusion through thin PEM via constructing a pressure differential between the cathode and the anode. The cell was found to be recovered more at a high pressure differential due to the fact that more sulfur species are oxidized by a larger content of permeated oxygen, showing ∼88.7% performance recovery for 0.40 bar pressure differential. The proposed strategies with simplicity, operability, and resilience show promising potential in the application of long-term PEMFCs, which is critical for the durability improvement of FCEVs and cost reduction of hydrogen purification.

“…Hydrogen is regarded as an ideal energy carrier due to its nontoxicity, sustainability, environmental friendliness, and high calorific value, which is suitable to support large-scale power generation of renewable energy and frequency regulation of the auxiliary power grid. The application of proton-exchange membrane fuel cells (PEMFCs) as a power generator for vehicles and residential purpose is crucial to the development of hydrogen energy. − Currently, injecting green hydrogen into the natural gas network is regarded as a promising strategy for hydrogen transportation because the construction of the hydrogen delivery infrastructure or major modifications for the current nature gas pipeline are not needed. , However, trace impurities [e.g., hydrogen sulfide (H 2 S), carbon monoxide (CO), , and organic pollutants , ] are inevitably introduced into the anode H 2 stream of PEMFCs during the hydrogen transportation process. Consequently, the PEMFC anode will be poisoned by these impurities, showing suppressed output cell performance and reduced durability, which is not beneficial for the long-term application of PEMFCs.…”

Section: Introductionmentioning

confidence: 99%

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

Cui

ACS Appl. Mater. Interfaces

et al. 2022

Self Cite

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.