The influence of chloride impurities on Pt/C fuel cell catalyst corrosion

The effect of Cl − on Pt dissolution under both potentiostatic and potential cycling conditions is reported, using a channel-flow multielectrode (CFME) as an in situ detection method. To avoid the contamination of the entire CFME system by Cl − , a liquid-phase chloride ion gun is placed upstream of the double electrode. Under potentiostatic conditions, Cl − enhances Pt dissolution by forming PtCl 4 2− at potentials below 1.0 V and PtCl 6 2− above 1.2 V. Under potential cycling conditions, Cl − accelerates Pt dissolution above 1.2 V by the enhanced formation of both PtCl 6 2− and PtCl 4 2− . The cathodic dissolution of Pt 2+ during PtO 2 reduction is also increased in the presence of Cl − . A mechanism for the effect of Cl − on Pt dissolution is proposed.Chloride (Cl − ) is a major fuel cell contaminant 1 that can be introduced into the cell through airborne salts. Moreover, the Pt-based catalysts may also contain a trace of Cl − that is not completely removed after synthesis using chloride-containing precursors. 2 The Cl − impurity is detrimental to the performance of proton exchange membrane fuel cells (PEMFCs). [3][4][5] The presence of Cl − enhances platinum (Pt) dissolution, 6-8 which accelerates the degradation of the Pt/C catalyst. 9-11 In spite of significant evidence of this effect, 6-8 the mechanism remains unclear, especially in the potential region in which PEMFC cathodes operate (<1.0 V vs. standard hydrogen electrode, SHE). Therefore, investigating the effect of Cl − on Pt dissolution is important for the development of PEMFCs.Recent data on the effect of Cl − on Pt dissolution were primarily obtained from electrochemical quartz crystal microbalance (EQCM) measurements. 6-8 Lam et al. reported a dramatic loss of ECA under cyclic voltammetry (CV) conditions in presence of 1000 mg/L Cl − . 6 Yadav et al. reported significant mass loss due to Pt dissolution above 1.2 V in a CV anodic scan in the presence of 100 mg/L Cl − . 7 Below 1.2 V, the adsorption of oxygen (O) and Pt-O formation on the Pt surface resulted in a continuous mass increase; mass loss caused by Pt dissolution could not be distinguished. Under potentiostatic conditions at 1.2 V, Ofstad et al. reported enhanced Pt loss in presence of 10 mg/L Cl − over a 24-hour period. 8 The Pt loss increased with increasing Cl − concentration. Mitsushima et al. also reported increased Pt/PtO solubility in 1.0 M H 2 SO 4 in the presence of Cl − . 12 Recently, Pavlišič et al reported that Pt dissolution was enhanced by Cl − in both anodic and cathodic scans, 13 using a electrochemical flow cell. 14,15 Dissolution of Pt were quantified by in-situ ICP-MS measurement. Their findings suggested that the dissolution mechanism changes in chloride electrolyte. To investigate the mechanism of Pt dissolution in presence of Cl − , knowledge of the valences of the dissolved species would be instrumental, as stated by Xing et al. 16 In a previous study, 17 we established an in situ electrochemical system based on a channel-flow double electrode (CFDE) and elucidated t...

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“…Pt + PtCl 6 2− + 2Cl − → 2PtCl 4 2− [13] In the cathodic scan, Pt 4+ dissolution continues until 1.2 V, as represented by the I C in Fig. 10b.…”

Section: Resultsmentioning

confidence: 97%

In Situ Analysis of Chloride Effect on Platinum Dissolution by a Channel-Flow Multi-Electrode System

Wang

Tada

Nishikata

2014

J. Electrochem. Soc.

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“…Specifically, our approach stands on the following crucial concepts: (i) transient platinum dissolution is an aggressive corrosion process that occurs upon oxidation and reduction of a Pt surface, also referred to as anodic and cathodic Pt dissolution2122. Note that the dissolution at constant electrode potentials above the Pt dissolution onset, which could be compared with soaking in acid, is much lower compared with the transient process232425; (ii) the rate of Pt transient dissolution is accelerated by the presence of chlorides and other halides. We show that, by slowing the process of Pt passivation, chlorides dramatically increase Pt dissolution during anodic and cathodic potential excursions and, at the same time, stabilize Pt ions in the solution2526; and (iii) the presence of dissolved CO gas increases Pt cathodic dissolution due to strong Pt–CO interaction, which physically prevents any potential Pt redeposition27 that may occur when CO (or some other reducing species such as H 2 ) oxidation potential gets below Pt depostition potential.…”

mentioning

confidence: 99%

Platinum recycling going green via induced surface potential alteration enabling fast and efficient dissolution

et al. 2016

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The recycling of precious metals, for example, platinum, is an essential aspect of sustainability for the modern industry and energy sectors. However, due to its resistance to corrosion, platinum-leaching techniques rely on high reagent consumption and hazardous processes, for example, boiling aqua regia; a mixture of concentrated nitric and hydrochloric acid. Here we demonstrate that complete dissolution of metallic platinum can be achieved by induced surface potential alteration, an ‘electrode-less' process utilizing alternatively oxidative and reductive gases. This concept for platinum recycling exploits the so-called transient dissolution mechanism, triggered by a repetitive change in platinum surface oxidation state, without using any external electric current or electrodes. The effective performance in non-toxic low-concentrated acid and at room temperature is a strong benefit of this approach, potentially rendering recycling of industrial catalysts, including but not limited to platinum-based systems, more sustainable.

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“…[17][18][19][20][21][22][23] In a series of papers, Mayrhofer and co-workers showed that during potential cycling with UPL higher than 1.1 V, greater Pt dissolution occurs during the cathodic scan than during the anodic scan. 17,21,22 The amount of Pt dissolved during the cathodic scan increased with increasing UPL as well as with decreasing scan rate and occurred at potentials below 1 V in the cathodic scan.…”

mentioning

confidence: 99%

Potential Dependence of Pt and Co Dissolution from Platinum-Cobalt Alloy PEFC Catalysts Using Time-Resolved Measurements

Ahluwalia

Papadias

Kariuki

et al. 2018

J. Electrochem. Soc.

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An electrochemical flow cell system with catalyst-ionomer ink deposited on glassy carbon is used to investigate the aqueous stability of commercial PtCo alloys under cyclic potentials. An on-line inductively coupled plasma-mass spectrometer, capable of real-time measurements, is used to resolve the anodic and cathodic dissolution of Pt and Co during square-wave and triangle-wave potential cycles. We observe Co dissolution at all potentials, distinct peaks in anodic and cathodic Pt dissolution rates above 0.9 V, and potential-dependent Pt and Co dissolution rates. The amount of Pt that dissolves cathodically is smaller than the amount that dissolves anodically if the upper potential limit (UPL) is lower than 0.9 V. At the highest UPL investigated, 1.0 V, the cathodic dissolution greatly exceeds the anodic dissolution. A non-ideal solid solution model indicates that the anodic dissolution can be associated with the electrochemical oxidation of Pt and PtOH to Pt 2+ , and the cathodic dissolution to electrochemical reduction of a higher Pt oxide, PtO x (x > 1), to Pt 2+ . Pt also dissolves oxidatively during the cathodic scans but in smaller amounts than due to the reductive dissolution of PtO x . The relative amounts Pt dissolving oxidatively as Pt and PtOH depend on the potential cycle and UPL.

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The influence of chloride impurities on Pt/C fuel cell catalyst corrosion

Cited by 75 publications

References 18 publications

In Situ Analysis of Chloride Effect on Platinum Dissolution by a Channel-Flow Multi-Electrode System

In Situ Analysis of Chloride Effect on Platinum Dissolution by a Channel-Flow Multi-Electrode System

Platinum recycling going green via induced surface potential alteration enabling fast and efficient dissolution

Potential Dependence of Pt and Co Dissolution from Platinum-Cobalt Alloy PEFC Catalysts Using Time-Resolved Measurements

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