Polarization-dependent mass transport parameters for orr in perfluorosulfonic acid ionomer membranes: an EIS study using microelectrodes

Xie, Zhong; Holdcroft, Steven

doi:10.1016/j.jelechem.2004.01.019

Cited by 88 publications

(33 citation statements)

References 52 publications

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“…25 The equivalent circuits used to interpret the impedance results at low and high current density are shown in Figure S4. 26,27 The Nyquist plot at 50 mA/cm 2 was a single semicircle loop, indicating that the oxygen reduction reaction kinetics dominated the electrode behavior at this current density. 25 At higher current densities, a distortion of the kinetic loop was observed, resulting in two semicircles.…”

Section: Resultsmentioning

confidence: 93%

Fabrication of High Performing PEMFC Catalyst-Coated Membranes with a Low Cost Air-Assisted Cylindrical Liquid Jets Spraying System

Peng

Omasta

Rigdon

et al. 2016

J. Electrochem. Soc.

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In this work, a low cost air-assisted cylindrical liquid jets spraying (ACLJS) system was developed to prepare high-performance catalyst-coated membranes (CCMs) for proton exchange membrane fuel cells (PEMFCs). The catalyst ink was flowed from a cylindrical orifice and was atomized by an air stream fed from a coaxial slit and sprayed directly onto the membrane, which was suctioned to a heated aluminum vacuum plate. The CCM pore architecture including size, distribution and volume can be controlled using various flow parameters, and the impact of spraying conditions on electrode structure and PEMFC performance was investigated. CCMs fabricated in the fiber-type break-up regime by ACLJS achieved very high performance during PEMFC testing, with the top-performing cells having a current density greater than 1900 mA/cm 2 at 0.7 V under H 2 /O 2 flows and 700 mA/cm 2 under H 2 /Air at 1.5 bar (absolute) PEMFCs have long been considered to be among the most promising next-generation energy conversion systems for portable devices and transportation vehicles due to their zero or low pollution, high power density and low temperature operation.1-3 However, the widespread commercialization of PEMFCs remains challenged by the high cost of cell assembly and the requirement of durable performance. In the last decade, significant efforts have been launched to make the technology cost competitive and to improve the cell performance by developing new electrocatalysts and lowering the noble metal loading. 4,5 However, the catalyst composition is not the only factor to consider when creating high-performance, low cost PEMFC electrodes.The electrode pore structure plays a critical role in determining PEMFC performance, and it is a direct result of the application method. The electrode porosity and pore size distribution impact reaction kinetics and mass-transport processes, including water management and electron/proton conduction.6-8 Structural optimization can be decisive in reducing performance losses, particularly at low catalyst loading and high current density. 9 In general, the catalyst coated membrane (CCM) method has been found to be superior to the gas diffusion layer (GDL) coating process because CCM fabrication avoids catalyst particles penetrating into the pore network of the GDL, lowering resistance at the interface with the electrolyte. For the CCM method, the catalyst ink can be applied onto the polymer membrane by brushing, screen printing, spraying, reactive spray deposition as well as roll-to-roll methods.6,10-14 Among them, spraying has been commonly employed for CCM fabrication. 11,15,16 However, the effects of spraying conditions on the electrode structure and PEMFC performance are poorly understood in many systems, including the air-assisted cylindrical liquid jets spraying (ACLJS) system.The objective of this work is to investigate the influence of spraying parameters on CCM structure and performance, with a particular focus on the ACLJS system because of its ability to produce very high performance CCMs at...

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Section: Resultsmentioning

confidence: 93%

Fabrication of High Performing PEMFC Catalyst-Coated Membranes with a Low Cost Air-Assisted Cylindrical Liquid Jets Spraying System

Peng

Omasta

Rigdon

et al. 2016

J. Electrochem. Soc.

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“…20,21 The technique was subsequently used to determine kinetic and mass transport parameters for ionomers with different ion exchange capacities and polymer structures. 12,[22][23][24][25] Of note is the fact that previous works relied on conditions in which the ambient environment was fully saturated (100% RH) and where water was often wicked to the membrane to maintain its fully hydrated state. These conditions are not truly representative of PEMFC conditions but were adopted because of difficulties in overcoming high ionic resistances observed in solid state electrochemical cells under low RH conditions.…”

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confidence: 99%

Time-Dependent Mass Transport for O2 Reduction at the Pt Perfluorosulfonic Acid Ionomer Interface

Novitski

Xie

Holdcroft

2014

ECS Electrochemistry Letters

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Chronoamperometric analysis of the oxygen reduction reaction (ORR) at Pt microelectrode | perfluorosulfonic acid (PFSA) ionomer interfaces in a solid state electrochemical cell reveals an increase in both the oxygen diffusion coefficient (D b Proton exchange membrane fuel cell (PEMFC) catalyst layers typically employ an ionomer component to reduce ionic resistance and improve electrochemical kinetics.)1,2 Recent studies reveal the ionomer in the catalyst layer may be present as an ultrathin film, and ex-situ studies have indicated that such films undergo a surface morphological reconstruction from hydrophobic to hydrophilic upon exposure to liquid water. Moreover, the reconstruction is observed to have a timedependency proportional to film thickness.3 Exposure to water vapor is found not to trigger this surface reconstruction. 3 The nature of these morphological reorganizations at the surface of the ionomer film is of considerable interest for understanding electrochemical mass transport at the ionomer | Pt interface. 4 However, there is little evidence concerning the role of these reorganizations on actual faradaic electrochemical activities. Overall, the complex morphological changes at ionomer surfaces are of increasing interest, where variables such as film thickness, substrate, and film preparation result in a markedly different outcome for the resulting ionomer properties. [5][6][7][8] Previous electrochemical studies have shown that mass transport through perfluorosulfonic acid (PFSA) ionomer membranes is dependent upon oxygen solubility in the hydrophobic, fluorinated domains and its transport into, and diffusion through, aqueous domains. 9-11The relatively high rate of oxygen permeation through PFSA ionomer is attributed to the relatively high oxygen solubility and large diffusion coefficient.9,12 The oxygen mass transport through the ionomer in a cathode catalyst layer (CCL), and its role in determining fuel cell performance, is relatively unexplored but is under increasing scrutiny. Studies based on limiting current techniques indicate that as Pt catalyst loading in the CCL is reduced, oxygen mass transport resistance in, and through, the PFSA ionomer increases, ultimately reducing the available power density of a fuel cell. [13][14][15] Other studies support this contention -that oxygen mass transport resistance through the catalyst layer ionomer plays a large role in determining the power that can be extracted from a fuel cell. 16 It has also been suggested that the total mass transport resistance is exacerbated by a mass transport resistance at the gas/ionomer interface, which becomes increasingly dominant as ionomer film thickness is reduced. [17][18][19] Understanding oxygen mass transport limitations at ionomer | Pt interfaces is therefore of growing interest.Ex-situ solid state electrochemical techniques provide a means to study ORR at Pt | ionomer interfaces under conditions of specific temperature, pressure, and RH. Pioneering work by Srinivasan and * Electrochemical Society Student Member....

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“…The total ohmic resistance does not change with the increase of current densities, while the chargetransfer resistance of the cathode decreases with the increase of current density. It can be attributed to that the increasing current density in low polarization region can enhance the electrochemical kinetics of ORR [32].…”

Section: Performance Of Single Cell and Eis Spectramentioning

confidence: 99%

Carbon-supported Pd–Pt cathode electrocatalysts for proton exchange membrane fuel cells

Tang

Zhang

Zhong

et al. 2011

Journal of Power Sources

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Polarization-dependent mass transport parameters for orr in perfluorosulfonic acid ionomer membranes: an EIS study using microelectrodes

Cited by 88 publications

References 52 publications

Fabrication of High Performing PEMFC Catalyst-Coated Membranes with a Low Cost Air-Assisted Cylindrical Liquid Jets Spraying System

Fabrication of High Performing PEMFC Catalyst-Coated Membranes with a Low Cost Air-Assisted Cylindrical Liquid Jets Spraying System

Time-Dependent Mass Transport for O2 Reduction at the Pt Perfluorosulfonic Acid Ionomer Interface

Carbon-supported Pd–Pt cathode electrocatalysts for proton exchange membrane fuel cells

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