Durable Oxide-Based Catalysts for Application as Cathode Materials in Polymer Electrolyte Fuel Cells (PEFCs)

Rabis, Annett; Fabbri, Emiliana; Foelske, Annette; Horisberger, M.; Kötz, R.; Schmidt, Thomas J.

doi:10.1149/05036.0009ecst

Cited by 15 publications

(19 citation statements)

References 12 publications

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“…By the use of a Pt ring electrode held at a constant potential of 0.4 V (RHE), where H 2 oxidation is purely under mass transport limited control, it was possible to exclude the hypothesis that H 2 evolution occurred from the Sb-SnO 2 surface. After À0.4 V (RHE) being reached, upon the subsequent anodic sweep a peak at about 0.35-0.4 V (RHE) appeared; the latter was already observed for SnO 2 samples 13 and was mostly associated with SnO 2 re-oxidation.…”

Section: Sb-sno 2 Supports: Electrochemical Characterizationmentioning

confidence: 93%

“…At the lowest measured potential (50 mV RHE) the H 2 O 2 production reached up to 13%, while it progressively decreased to 7% at 0.1 V (RHE) and went to almost zero at potential higher than B0.6 V (RHE), similar to relatively low Pt loading catalysts. 13,52 The small amount of hydrogen peroxide formation indicates that the ORR on Pt supported on Sb-SnO 2 mostly involves a 4-electron transfer process. From the Levich-Koutecky relationship, a first order dependence of ORR kinetics and a 4-electron transfer process could be confirmed for the Pt/Sb-SnO 2 catalyst.…”

Section: Sb-sno 2 Supports: Electrochemical Characterizationmentioning

confidence: 99%

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Pt nanoparticles supported on Sb-doped SnO₂ porous structures: developments and issues

Fabbri

Rabis

Kötz

et al. 2014

Phys. Chem. Chem. Phys.

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In this work, high surface area antimony doped tin oxide (Sb-SnO2) has been synthesized using a modified sol-gel synthesis method. The bulk and surface properties of the metal oxide support have been investigated as a function of the processing conditions. A change in the Sb-SnO2 processing conditions, while preserving an overall invariant bulk composition, led to substantial modification of the surface stoichiometry. Accelerated stability test protocols have shown that the surface composition represents a crucial parameter for the electrochemical stability of Sb-SnO2. Model Pt/Sb-SnO2 electrodes have been developed depositing Pt nanoparticles by magnetron sputtering on the optimized Sb-SnO2 porous surface. A significant enhancement in the corrosion stability upon 1000 potential cycles between 0.5 and 1.5 V (RHE) at 50 mV s(-1) has been observed for the Pt/Sb-SnO2 system compared to Pt/carbon.

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Section: Sb-sno 2 Supports: Electrochemical Characterizationmentioning

confidence: 93%

Section: Sb-sno 2 Supports: Electrochemical Characterizationmentioning

confidence: 99%

Pt nanoparticles supported on Sb-doped SnO₂ porous structures: developments and issues

Fabbri

Rabis

Kötz

et al. 2014

Phys. Chem. Chem. Phys.

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“…For experimental details of the sputtering process, we refer to our previous publications. 18,19 For comparison with a standard Pt/C catalyst, a 47 wt-% Pt/HSAC (high surface area carbon, TKK) was used for reference thin-film electrodes with a Pt loading of 24 μg Pt cm −2 . The electrodes were immersed under potential control inside a three electrode glass cell in 0.1 M HClO 4 electrolyte, prepared from Suprapur 70% perchloric acid (Merck KGaA) and ultrapure Milli-Q water.…”

mentioning

confidence: 99%

Determination of the Electrochemically Active Surface Area of Metal-Oxide Supported Platinum Catalyst

Binninger

Fabbri

Kötz

et al. 2013

J. Electrochem. Soc.

162

148

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The electrochemically active surface area (ECSA) of metal-oxide supported platinum catalysts as obtained from hydrogen underpotential deposition (H upd ) and from carbon monoxide stripping experiments was investigated. It was demonstrated that both methods fail to give meaningful values of the ECSA if they are performed in the conventional way as known for pure Pt and carbon supported Pt catalysts, respectively. For both methods, the reason for this failure is the lack of a correct baseline for the integration of the associated charges. It was found that the cyclic voltammogram recorded in CO saturated electrolyte gives an improved baseline for the H upd analysis. For CO stripping, a novel baseline method was developed by performing a "CO stripping simulation" (COSS) experiment in CO-free electrolyte. The first cycle of this COSS-experiment is an improved baseline for the integration of the CO stripping peak, since possible support reduction/oxidation currents can be accounted for. With these modifications, H upd and CO stripping voltammetry can be used for metal-oxide supported platinum to yield true, reproducible and consistent values for the ECSA. In recent years, an increased attention in the research on oxygen reduction reaction (ORR) catalysts for polymer electrolyte fuel cells (PEFC) has been focused on metal-oxide supported platinum catalysts.1 The reason for this interest is the potentially higher stability of the metal-oxide support in the oxidative electrochemical environment of a PEFC cathode in comparison with the carbon support of standard Pt/C catalysts for ORR. The resistance of the support toward corrosion is especially important under load cycling and start/stop conditions with cathode potentials reaching values up to 1.5 V vs. the adjacent electrolyte.2,3 State-of-the-art cathodes made of Pt nanoparticles supported on high surface area carbon suffer from severe corrosion at potentials above 1.1 V due to the oxidation of the carbon support. [4][5][6] The consequent detachment of Pt catalyst nanoparticles or their dissolution leads to a strong degradation of PEFC performance. 7,8 Replacing the carbon support by suitable metal-oxides in an oxidation state which is thermodynamically stable at PEFC cathode potentials can help to mitigate this degradation mode on the materials side. Furthermore, it is well established in heterogeneous catalysis that metal-oxide supports can possibly influence the intrinsic activity of the supported Pt catalyst toward ORR due to so-called strong metal-support interactions, SMSI.9-12 Thus, metal-oxides may offer a way to kill two birds with one stone: Enhancing the cathode stability and enhancing the cathode catalyst kinetics toward the ORR.In order to experimentally assess both the stability and the ORR activity properties of metal-oxide supported Pt catalyst, the determination of the electrochemically active Pt surface area (ECSA) is inevitable due to its widespread use as an important descriptor of the state of the degraded catalyst and electrode. Measuring the ECS...

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confidence: 99%

“…Mitigation strategies can be divided into two categories. One is focused on developing new materials, such as carbon free electrodes [14][15][16] or selective hydrogen oxidation catalysts. [17][18][19] The second category consists of system strategies, for instance flow rate adjustements, 20,21 cell potential control 8 or nitrogen purging.…”

mentioning

confidence: 99%

On the Positive Effect of CO during Start/Stop in High-Temperature Polymer Electrolyte Fuel Cells

Engl

Käse

Gubler

et al. 2014

ECS Electrochemistry Letters

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The influence of CO in the fuel gas on cathode carbon corrosion during start/stop cycles in high temperature polymer electrolyte fuel cells (HT-PEFC) was investigated. The fuel cell underwent simulated start/stop cycles with a constant time interval, reactant gas flow rate and temperature by switching between H 2 /CO mixtures and O 2 at the fuel electrode. The results reveal that increasing amounts of CO in the fuel gas reduce the amount of carbon corrosion at the air electrode. Therefore, HT-PEFC operation with CO containing fuel has the benefit of mitigating start/stop induced degradation effects. One of the most beneficial and unique features of a hightemperature polymer electrolyte fuel cell (HT-PEFC) is the capability to tolerate orders of magnitude lager amounts of CO (up to 3%) 1,2 compared to a LT-PEFC (approx. 10 ppm).3 Therefore, the system can be used to generate electricity from hydrogen-rich reformate gases without complex and energy intensive CO-cleanup.Nevertheless, the HT-PEFC can suffer from numerous degradation effects in different locations of the membrane electrode assembly (MEA), 4 e.g. pinhole formation in the membrane, acid evaporation and membrane thinning. 5,6 Electrodes can also represent a major area of degradation. Interestingly, specific degradation mechanisms, such as carbon corrosion, catalyst detachment and catalyst particle growth (Ostwald-ripening) can be found in the LT-PEFC as well. Additionally, structural changes and acid flooding of the porous layers of the cell can occur. All degradation mechanisms are complex functions of the specific operation conditions, making their individual identification challenging. Hence, it is necessary to gain insight into limitations of MEA lifetime, which is the key to successful development of mitigation strategies to reach the desired lifetimes, i.e. >40.000 hours 6 for stationary applications.One of the specific degradation triggers is known as "reversecurrent decay" or "start/stop"-mechanism, respectively. 7-9 This degradation mode is induced during fuel cell start-up or shut-down, when air or pure oxygen and fuel gas co-exist in the fuel electrode compartment (see Figure S1 and its description in the supplemental material). This mechanism can be one of the main reasons for carbon corrosion at the air electrode. The number of start/stop cycles is closely related to the overall lifetime of the fuel cell if the induced degradation effects are not mitigated. If, for instance, a HT-PEFC is used in a combined heat and power (CHP) 10-12 system, it is conceivable that several hundred cycles will be accumulated, which can lead to a rapid and irreversible damage of the stack.13 It is necessary, therefore, to improve the understanding of the start/stop mechanism in order to deduce appropriate mitigation strategies. Mitigation strategies can be divided into two categories. One is focused on developing new materials, such as carbon free electrodes [14][15][16] or selective hydrogen oxidation catalysts. 17-19The second category consists of system st...

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Durable Oxide-Based Catalysts for Application as Cathode Materials in Polymer Electrolyte Fuel Cells (PEFCs)

Cited by 15 publications

References 12 publications

Pt nanoparticles supported on Sb-doped SnO₂ porous structures: developments and issues

Pt nanoparticles supported on Sb-doped SnO₂ porous structures: developments and issues

Determination of the Electrochemically Active Surface Area of Metal-Oxide Supported Platinum Catalyst

On the Positive Effect of CO during Start/Stop in High-Temperature Polymer Electrolyte Fuel Cells

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Durable Oxide-Based Catalysts for Application as Cathode Materials in Polymer Electrolyte Fuel Cells (PEFCs)

Cited by 15 publications

References 12 publications

Pt nanoparticles supported on Sb-doped SnO2 porous structures: developments and issues

Pt nanoparticles supported on Sb-doped SnO2 porous structures: developments and issues

Determination of the Electrochemically Active Surface Area of Metal-Oxide Supported Platinum Catalyst

On the Positive Effect of CO during Start/Stop in High-Temperature Polymer Electrolyte Fuel Cells

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Product

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Pt nanoparticles supported on Sb-doped SnO₂ porous structures: developments and issues

Pt nanoparticles supported on Sb-doped SnO₂ porous structures: developments and issues