Methods for Characterizing the Structure and Electrochemical Behavior of Teflon-Bonded Pt Electrodes

Giner, J.; Parry, J. M.; Smith, Scott R.; Turchan, M.

doi:10.1149/1.2411664

Cited by 45 publications

(19 citation statements)

References 4 publications

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“…The use of a porous gas diffusion electrode allows for reactant gas to be supplied directly to the catalyst, while the electrode remains in a three-electrode configuration and the desired half-reaction is isolated on the working electrode. This “floating electrode” setup was initially employed − and theoretically modeled − for phosphoric acid fuel cells in the 1960–1980s and was later adapted for hydrogen PEM fuel cells. ,− Realizing that the electrode thickness and roughness of the interface was impeding the performance of the electrodes, Kucernak and co-workers ,,, revised the FE setup for intrinsic studies of supported Pt catalysts by moving to a support which was both orders of magnitude thinner (∼15 μm), much flatter, and with well-defined gas pore geometry allowing production of submicron thick catalyst layers using standard carbon supported catalysts . These studies investigated catalyst loadings of 0.16–10 μg cm –2 , uniquely situating the catalyst particles around the pores of the track-etched membrane substrate (tortuosity = 1), by vacuum filtration, to allow for effective gas transportation to the catalyst surface and better catalyst utilization .…”

Section: Introductionmentioning

confidence: 99%

Toward Understanding the Utilization of Oxygen Reduction Electrocatalysts under High Mass Transport Conditions and High Overpotentials

et al. 2021

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There is currently a disconnect between the high electrocatalyst oxygen reduction reaction (ORR) performance measured ex situ, using the rotating disc electrode (RDE), and the in situ membrane electrode assembly (MEA) performance. The disconnect in the electrocatalyst performance raises questions both about the pitfalls of the RDE technique at extrapolating the performance to higher overpotentials and how to improve the in situ catalyst layer performance to meet ambitious fuel cell targets. This work aims to bridge the gap by measuring the ORR ex situ performance under high mass transport conditions, at high overpotentials, using the floating electrode (FE) technique. Here, we determine the performance of three Pt/C electrocatalysts using the FE in 1 M HClO4 and 1 M H2SO4 to show that the MEA activities measured at 80 °C, 150 kPag were substantially lower than the room temperature and pressure performance of the same catalyst in 1 M HClO4 using the RDE and FE methods and also lower than the FE in 1 M H2SO4, implying MEA limitations are not purely due to sulfonate adsorption from the Nafion. Finally, FE and MEA data was modeled which obtained j o values on the FE (oxide free conditions) which were 4–6× larger, at 11–26 μA cm–2, than those measured on the MEA. The difference is interpreted as due to better water removal in the FE system. This work shows that MEA catalyst layers are vastly underutilized, due to poor water transport, and current densities equivalent to 10–16 A cm–2 at 0.65 V for 400 μgPt cm–2 (25–40 A mg–1) are achievable, whereas the current mass activity of MEAs is <40% of this value at 25 and 80 °C, 150 kPag.

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Section: Introductionmentioning

confidence: 99%

Toward Understanding the Utilization of Oxygen Reduction Electrocatalysts under High Mass Transport Conditions and High Overpotentials

et al. 2021

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“…22 In this way, the kinetics of the ORR and HOR can be measured over a much wider potential window which includes the typical cell potential window of PEFC operation (0.6-0.8 V vs. RHE for the cathode). Extensive experimental studies of these 'floating electrodes' for the phosphoric acid fuel cell have been conducted in the 1960's-1980's [22][23][24][25] and were augmented with theoretically models. [26][27][28] More recently, the floating electrode has been adapted for PEFC studies.…”

Section: Introductionmentioning

confidence: 99%

Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport

Zalitis

Kramer

Kucernak

2013

Phys. Chem. Chem. Phys.

180

194

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An alternative approach to the rotating disk electrode (RDE) for characterising fuel cell electrocatalysts is presented. The approach combines high mass transport with a flat, uniform, and homogeneous catalyst deposition process, well suited for studying intrinsic catalyst properties at realistic operating conditions of a polymer electrolyte fuel cell (PEFC). Uniform catalyst layers were produced with loadings as low as 0.16 μg Pt cm -2 and thicknesses as low as 200 nm. Such ultra thin catalyst layers are considered 10 advantageous to minimize internal resistances and mass transport limitations. Geometric current densities as high as 5.7 A cm -2 Geo were experimentally achieved at a loading of 10.15 μgPt cm -2 for the hydrogen oxidation reaction (HOR) at room temperature, which is three orders of magnitude higher than current densities achievable with the RDE. Modelling of the associated diffusion field suggests that such high performance is enabled by fast lateral diffusion within the electrode. The electrodes operate over a wide 15 potential range with insignificant mass transport losses, allowing the study of the ORR at high overpotentials. Electrodes produced a specific current density of 31 ± 9 mA cm -2Spec at a potential of 0.65 V vs. RHE for the oxygen reduction reaction (ORR) and 600 ± 60 mA cm -2 Spec for the peak potential of the HOR. The mass activities of Pt/C catalysts towards the ORR was found to exceed a range of literature PEFC mass activities across the entire potential range. The HOR also revealed fine structure in 20 the limiting current range and an asymptotic current decay for potentials above 0.36 V. These characteristics are not visible with techniques limited by mass transport in aqueous media such as the RDE. IntroductionUnderstanding the kinetics of the oxygen reduction reaction 25 (ORR) and hydrogen oxidation reaction (HOR) on platinum nano-particles is vital for polymer electrolyte fuel cell (PEFC) development. Each platinum nano-particle within the electrode should have optimal proton access, gas access and an electronic path to study intrinsic electrocatalytic properties of the catalyst. 30 These three criteria should be maintained throughout the working conditions (e.g., temperature, humidity and potential). If a reaction site is starved for any of the three, its activity will be reduced, which skews the average activity and introduces an error. It is paramount to minimize the number of underperforming 35 catalyst sites to determine intrinsic catalyst properties. Ideally, the catalyst layer should be made as thin as possible. Thus, all the catalyst particles will be close to the perfluorosulfonic acid (PFSA) membrane for ionic access and close to the gas diffusion layer (GDL) for gas access and an electronic path, removing 40 internal limitations. Mass transport limitations lead to concentration polarization across thick electrodes, 1-3 limiting the active thickness to about 5 μm at high current densities, regardless of how thick the catalyst layer is. 1 The majority of ORR and ...

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13] In these initial studies, PTFE bonded catalyst layers (~200 µm) were coated on a gas diffusion layer (GDL); the electrode was positioned so that it was in contact with the acid electrolyte but not immersed and flooded. 4 Some of the pores in the catalyst layer and GDL functioned as gas phase O 2 transport pathways due to the hydrophobic nature of PTFE; due to hydrophilicity of the catalyst interface with the electrolyte, proton transport pathways are also present. Since O 2 transport takes place predominantly through the gas phase, O 2 diffusion-limited currents are typically large in these systems and this method has been successfully used to screen novel electrocatalyst for PAFCs and reasonably high values of activity have been obtained.…”

Section: Introductionmentioning

confidence: 99%

Benchmarking the oxygen reduction reaction activity of Pt-based catalysts using standardized rotating disk electrode methods

Shinozaki

Zack

Pylypenko

et al. 2015

International Journal of Hydrogen Energy

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Methods for Characterizing the Structure and Electrochemical Behavior of Teflon-Bonded Pt Electrodes

Cited by 45 publications

References 4 publications

Toward Understanding the Utilization of Oxygen Reduction Electrocatalysts under High Mass Transport Conditions and High Overpotentials

Toward Understanding the Utilization of Oxygen Reduction Electrocatalysts under High Mass Transport Conditions and High Overpotentials

Electrocatalytic performance of fuel cell reactions at low catalyst loading and high mass transport

Benchmarking the oxygen reduction reaction activity of Pt-based catalysts using standardized rotating disk electrode methods

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