Suppression of oxygen reduction reaction activity on Pt-based electrocatalysts from ionomer incorporation

Shinozaki, Kazuma; Morimoto, Yu; Pivovar, Bryan S.; Kocha, Shyam S.

doi:10.1016/j.jpowsour.2016.06.062

Cited by 135 publications

(142 citation statements)

References 40 publications

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“…Spinel type metal oxides possess a reasonable electronic conductivity and are studied without addition of carbon. Since no additives are added to the cavity during the electrochemical investigation, neither the employed double layer capacitance by cyclic voltammetry is affected by carbon, nor the evaluation of the ORR activity is influenced by the addition of an ionomer . Thus, the intrinsic activity of the metal oxides can be extracted by referring the determined activity to the real surface area of the catalysts.…”

Section: Introductionsupporting

confidence: 79%

Oxygen Reduction Reaction Activity of Mesostructured Cobalt‐Based Metal Oxides Studied with the Cavity‐Microelectrode Technique

Behnken

Deng

et al. 2019

ChemElectroChem

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Cobalt oxides are known as abundant and stable catalysts for the oxygen reduction reaction (ORR) in an alkaline environment. Here, the ORR activity of Co3O4 and mixed metal oxides NiCo2O4 and CuCo2O4 was studied. Synthesis by using the nanocasting procedure resulted in a mesostructured spinel phase with uniform morphology and high surface area. However, the evaluation of the specific activity of this material class is often hampered by limitations in determining the real surface area. The cavity‐microelectrode technique did not require the addition of any additives to the catalytic material. Thus, measuring the double layer capacitance was used to assess the surface area. This approach showed comparable and reliable values for all samples and different cavity depths. Furthermore, the in situ derived surface area enabled the determination of the specific ORR activity, which is more accurate than utilizing the geometric and nitrogen absorption derived surface area. Although the activity of Co3O4 was rather low, the presence of Ni2+ and Cu2+ in the mixed metal oxides led to a substantial activity enhancement, possibly by providing additional active sites.

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Section: Introductionsupporting

confidence: 79%

Oxygen Reduction Reaction Activity of Mesostructured Cobalt‐Based Metal Oxides Studied with the Cavity‐Microelectrode Technique

Behnken

Deng

et al. 2019

ChemElectroChem

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“…The obtained mass and specific activities are in good agreement with the literature for Nafion-free films. 27 Table III shows that the ORR mass activity of the catalyst with the functionalized support (Pt/V-NH x ) is the same as that of the non-functionalized support (Pt/V), both also displaying the same Tafel slope (see Table III and Figure S5). The specific activity of the Pt/V-NH x catalyst is slightly higher than that of the Pt/V catalyst due to the difference in the ECSA (see Table III).…”

mentioning

confidence: 84%

The Key to High Performance Low Pt Loaded Electrodes

Orfanidi

Madkikar

El‐Sayed

et al. 2017

J. Electrochem. Soc.

215

252

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The effect of ionomer distribution on the oxygen mass transport resistance, the proton resistivity of the cathode catalyst layer, and the H 2 /air fuel cell performance was investigated for catalysts with surface modified carbon supports. By introducing nitrogen containing surface groups, it was shown that the ionomer distribution in the cathodic electrode can be optimized to decrease mass transport related voltage losses at high current density. The in house prepared catalysts were fully characterized by TEM, TGA, elemental analysis, and XPS. Thin-film rotating disk electrode measurements showed that the carbon support modification did not affect the oxygen reduction activity of the catalysts, but exclusively affects the ionomer distribution in the electrode during electrode preparation. Limiting current measurements were used to determine the pressure independent oxygen transport resistance -primarily attributed to oxygen transport in the ionomer film -which decreases for catalysts with surface modified carbon support. Systematically lowering the ionomer to carbon ratio (I/C) from 0.65 to 0.25 revealed a maximum performance at I/C = 0.4, where an optimum between ionomer thickness and proton conductivity within the catalyst layer is obtained. From this work, it can be concluded that not only ionomer film thickness, but more importantly ionomer distribution is the key to high performance low Pt loaded electrodes.

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“…In comparison, the ionomer‐free Pt black electrode is more sensitive to RH changes that yield differences in the ECSA. Although not conclusive, it is likely that the higher current at 100 % RH with the ionomer‐free electrode versus that with ionomer is due to the lack of surface poisoning by the ionomer's sulfonic acid anions as has been observed in RDE studies …”

Section: Resultsmentioning

confidence: 95%

“…In addition, the possibly reduced proton concentration in liquid water may kinetically hinder the ORR. Alternatively, it has been shown for liquid rotating disk electrode cells that Pt surfaces not covered by ionomer feature more active ORR kinetics since they are not partially poisoned by the ionomer's anions . Ionomer coverage also increases the oxygen‐transport resistance with low Pt loading and at high current density …”

Section: Introductionmentioning

confidence: 99%

Ionic Conductivity over Metal/Water Interfaces in Ionomer‐Free Fuel Cell Electrodes

Zhang

Babu

et al. 2019

ChemElectroChem

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Ion conduction and oxygen reduction reaction (ORR) kinetics at metal/water interfaces are important in determining the performance of proton exchange membrane fuel cells (PEMFCs). However, the coupled ion transport and electrochemical reactions in ionomer‐free domains of catalyst layers are still unclear. In this work, we deconvolute the ion transport and oxygen reduction reaction (ORR) by studying metal/water interfaces of platinum (Pt) and gold (Au) ionomer‐free porous cathodes. In our experiments, a conventional membrane electrode assembly (MEA) was used for electrochemical characterization of ionomer‐free electrodes. Cyclic voltammetry (CV) and polarization curve measurements at different relative humidity (RH) conditions show that active surface area and ORR current density increases with RH. We also use microstructured electrode scaffold (MES) apparatus for measurement of the ionic conductivity in the cathode. The results show that the ionic conductivity increases with the RH and water coverage. The potential dependence of ionic conductivity for Au approximately follows the classical Guoy‐Chapman electrical double layer (EDL) behavior, while the ionic conductivity of the Pt electrode did not show a strong potential dependence, indicating that it could also be affected by other mechanisms, such as formation of surface oxide and diffusion of adsorbed hydrogen on its surface.

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Suppression of oxygen reduction reaction activity on Pt-based electrocatalysts from ionomer incorporation

Cited by 135 publications

References 40 publications

Oxygen Reduction Reaction Activity of Mesostructured Cobalt‐Based Metal Oxides Studied with the Cavity‐Microelectrode Technique

Oxygen Reduction Reaction Activity of Mesostructured Cobalt‐Based Metal Oxides Studied with the Cavity‐Microelectrode Technique

The Key to High Performance Low Pt Loaded Electrodes

Ionic Conductivity over Metal/Water Interfaces in Ionomer‐Free Fuel Cell Electrodes

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