Rotating disk electrode system for elevated pressures and temperatures M. J. Fleige, G. K. H. Wiberg, and M. Arenz Citation: Review of Scientific Instruments 86, 064101 (2015); doi: 10.1063/1.4922382 View online: http://dx.doi.org/10.1063/1.4922382 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/86/6?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Gas diffusion electrode setup for catalyst testing in concentrated phosphoric acid at elevated temperatures Rev. Sci. Instrum. 86, 024102 (2015); 10.1063/1.4908169 Design, development, and demonstration of a fully LabVIEW controlled in situ electrochemical Fourier transform infrared setup combined with a wall-jet electrode to investigate the electrochemical interface of nanoparticulate electrocatalysts under reaction conditions Rev. Sci. Instrum. 84, 074103 (2013); 10.1063/1.4816826 Platinum/multiwalled carbon nanotubes-platinum/carbon composites as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell Appl. Phys. Lett. 88, 253105 (2006); 10.1063/1.2214139 Nanostructured tungsten carbide catalysts for polymer electrolyte fuel cells Appl. Phys. Lett. 86, 224104 (2005); 10.1063/1.1941473 Modulation of electrode performance and in situ observation of proton transport in Pt–RuO 2 nanocomposite thin-film electrodes J. Appl. Phys. 94, 7276 (2003); 10.1063/1.1624483
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 134.129.120.3 On: Tue, 07 Jul 2015 12:34:39
REVIEW OF SCIENTIFIC INSTRUMENTS 86, 064101 (2015)
Rotating disk electrode system for elevated pressures and temperatures M. J. Fleige, G. K. H. Wiberg, and M. Arenz Department of Chemistry and Nano-Science Center, University of Copenhagen, Universitetsparken 5, 2100 Ø Copenhagen, Denmark
(Received 10 April 2015; accepted 31 May 2015; published online 12 June 2015) We describe the development and test of an elevated pressure and temperature rotating disk electrode (RDE) system that allows measurements under well-defined mass transport conditions. As demonstrated for the oxygen reduction reaction on polycrystalline platinum (Pt) in 0.5M H2SO4, the setup can easily be operated in a pressure range of 1–101 bar oxygen, and temperature of 140 ◦C. Under such conditions, diffusion limited current densities increase by almost two orders of magnitude as compared to conventional RDE setups allowing, for example, fuel cell catalyst studies under more realistic conditions. Levich plots demonstrate that the mass transport is indeed well-defined, i.e., at low electrode potentials, the measured current densities are fully diffusion controlled, while at higher potentials, a mixed kinetic-diffusion controlled regime is observed. Therefore, the setup opens up a new field for RDE investigations under temperature and current density conditions relevant for low and high temperature proton exchange membrane fuel cells. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4922382] I. INTRODUCTION
Rotating disk electrode (RDE) measurements are widely used in electrochemistry to establish well-defined mass transport conditions in half-cell setups. In the recent years, most RDE measurements were performed to mimic processes in proton exchange membrane fuel cells (PEMFCs) under more controlled conditions.1 However, such RDE measurements are in general performed at room temperature (RT) (or up to 60 ◦C) and at an oxygen partial pressure of 1 bar limiting oxygen solubility in aqueous electrolyte (at ambient pressure). At these conditions, considerably lower current densities are obtained than in PEMFCs due to low concentrations of dissolved reactant gas and much lower diffusion coefficients of gases in liquid electrolyte than in the gas phase.2 Thus, the applied conditions in RDE setups are relatively far from realistic ones, a problem that is especially relevant for RDE simulating catalytic processes in high temperature (HT) PEMFCs (operating temperatures of up to 150 ◦C). By comparison, electrocatalyst investigations performed in single cell membrane electrode assemblies (MEAs) provide access to realistic test conditions, such as temperature, reactant gas concentration, relative humidity, and acidity levels, the catalyst is exposed to in a PEMFC; but, the complexity of MEA studies complicates extracting the intrinsic properties of the catalyst from the obtained data as the anode and cathode reactions occur in parallel and, for example, crossover of reactants (hydrogen, methanol etc.) and products via the proton conducting membrane can influence the electrochemical response.3,4 In addition, MEA catalyst studies are time consuming and costly and therefore not suited for catalyst performance screening studies. Straightforward and time-efficient techniques are therefore needed for characterizing PEMFC catalysts at relevant conditions. In recent years, several methods have been developed to meet this need, i.e., micro band electrode measurements,5 gas diffusion electrodes (GDEs),6–8 channel flow electrodes,9,10 and wall jet electrodes.11,12 In GDEs, for
example, the catalyst layer is typically situated at the three phase boundary liquid electrolyte, solid catalyst, and gas phase, which is very similar to PEMFC in terms of mass transport of reactants.2 In the other techniques, catalyst layers supported on inert electrode surfaces are fully submerged in the liquid electrolyte, i.e., dilute aqueous solutions of the acids H3PO4, H2SO4, or HClO4. In all approaches, the mass transport resistance is minimized by applying thin films of catalyst layers (
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 134.129.120.3 On: Tue, 07 Jul 2015 12:34:39
REVIEW OF SCIENTIFIC INSTRUMENTS 86, 064101 (2015)
Rotating disk electrode system for elevated pressures and temperatures M. J. Fleige, G. K. H. Wiberg, and M. Arenz Department of Chemistry and Nano-Science Center, University of Copenhagen, Universitetsparken 5, 2100 Ø Copenhagen, Denmark
(Received 10 April 2015; accepted 31 May 2015; published online 12 June 2015) We describe the development and test of an elevated pressure and temperature rotating disk electrode (RDE) system that allows measurements under well-defined mass transport conditions. As demonstrated for the oxygen reduction reaction on polycrystalline platinum (Pt) in 0.5M H2SO4, the setup can easily be operated in a pressure range of 1–101 bar oxygen, and temperature of 140 ◦C. Under such conditions, diffusion limited current densities increase by almost two orders of magnitude as compared to conventional RDE setups allowing, for example, fuel cell catalyst studies under more realistic conditions. Levich plots demonstrate that the mass transport is indeed well-defined, i.e., at low electrode potentials, the measured current densities are fully diffusion controlled, while at higher potentials, a mixed kinetic-diffusion controlled regime is observed. Therefore, the setup opens up a new field for RDE investigations under temperature and current density conditions relevant for low and high temperature proton exchange membrane fuel cells. C 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4922382] I. INTRODUCTION
Rotating disk electrode (RDE) measurements are widely used in electrochemistry to establish well-defined mass transport conditions in half-cell setups. In the recent years, most RDE measurements were performed to mimic processes in proton exchange membrane fuel cells (PEMFCs) under more controlled conditions.1 However, such RDE measurements are in general performed at room temperature (RT) (or up to 60 ◦C) and at an oxygen partial pressure of 1 bar limiting oxygen solubility in aqueous electrolyte (at ambient pressure). At these conditions, considerably lower current densities are obtained than in PEMFCs due to low concentrations of dissolved reactant gas and much lower diffusion coefficients of gases in liquid electrolyte than in the gas phase.2 Thus, the applied conditions in RDE setups are relatively far from realistic ones, a problem that is especially relevant for RDE simulating catalytic processes in high temperature (HT) PEMFCs (operating temperatures of up to 150 ◦C). By comparison, electrocatalyst investigations performed in single cell membrane electrode assemblies (MEAs) provide access to realistic test conditions, such as temperature, reactant gas concentration, relative humidity, and acidity levels, the catalyst is exposed to in a PEMFC; but, the complexity of MEA studies complicates extracting the intrinsic properties of the catalyst from the obtained data as the anode and cathode reactions occur in parallel and, for example, crossover of reactants (hydrogen, methanol etc.) and products via the proton conducting membrane can influence the electrochemical response.3,4 In addition, MEA catalyst studies are time consuming and costly and therefore not suited for catalyst performance screening studies. Straightforward and time-efficient techniques are therefore needed for characterizing PEMFC catalysts at relevant conditions. In recent years, several methods have been developed to meet this need, i.e., micro band electrode measurements,5 gas diffusion electrodes (GDEs),6–8 channel flow electrodes,9,10 and wall jet electrodes.11,12 In GDEs, for
example, the catalyst layer is typically situated at the three phase boundary liquid electrolyte, solid catalyst, and gas phase, which is very similar to PEMFC in terms of mass transport of reactants.2 In the other techniques, catalyst layers supported on inert electrode surfaces are fully submerged in the liquid electrolyte, i.e., dilute aqueous solutions of the acids H3PO4, H2SO4, or HClO4. In all approaches, the mass transport resistance is minimized by applying thin films of catalyst layers (
