Real-time determination of CO 2 production and estimation of adsorbate coverage on a proton exchange membrane fuel cell
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ORIGINAL PAPER
Real-time determination of CO2 production and estimation of adsorbate coverage on a proton exchange membrane fuel cell under oscillatory operation Pietro P. Lopes & Bruno C. Batista & Guilherme A. Saglietti & Hamilton Varela & Edson A. Ticianelli
Received: 25 November 2012 / Revised: 17 February 2013 / Accepted: 20 February 2013 / Published online: 27 March 2013 # Springer-Verlag Berlin Heidelberg 2013
Abstract A number of fuel cell relevant reactions are known to undergo kinetic instabilities under certain conditions. The majority of the experiments in such systems have been performed in liquid electrolyte systems on half-cell setups. Results for proton exchange membrane fuel cells fed with H2/CO mixtures at the anode show that there can be a range of gas flow rate and current density where spontaneous potential oscillations take place. Despite the recent developments in this area, there are still many mechanistic aspects underlying the emergence of electrochemical oscillations that remain unknown. In the present contribution, we report results on the CO2 production during the oxidation of carbon monoxide-containing hydrogen in a proton exchange membrane fuel cell, as measured by online mass spectrometry. By extensive fitting and careful consideration of the proposed mechanism, we were able to estimate the coverage of hydrogen and CO during the oscillations. As no other approach seems capable to probe the adsorbate coverage in an operando fuel cell, our analyses access experimental hidden information that can be of high value for fuel cell research.
This paper is dedicated to Prof. Wolf Vielstich on the occasion of his 90th birthday. P. P. Lopes : B. C. Batista : G. A. Saglietti : H. Varela (*) : E. A. Ticianelli (*) Institute of Chemistry of São Carlos, University of São Paulo, CP: 780, 13560-970, São Carlos, São Paulo, Brazil e-mail: [email protected] e-mail: [email protected]
Keywords Oscillations . Coverage determination . PEMFC . Mass spectrometry
Introduction Fuel cells operating with hydrogen as the anode fuel present the highest performance due the fast kinetics of the hydrogen oxidation reaction in acidic media. However, automotive onboard hydrogen production from steam reform of liquid fuels such as methanol and ethanol produces considerable amounts of CO that severely poisons the anode catalyst surface, usually Pt. The mechanisms behind poisoning and tolerance of CO have been extensively studied under real operational conditions [1], and PtRu/C appears to be one of the most successful electrocatalysts as it combines both the formation of oxygenated species at overpotentials lower than Pt [2, 3] and reduces the Pt– CO bond strength by significantly changing the Pt electronic structure [4, 5]. Given the intrinsic far-fromequilibrium nature of an operational proton exchange membrane fuel cell (PEMFC), the electrooxidation of CO-contaminated hydrogen on PtRu/C has been shown to undergo spontaneous potential oscillations under specific circumstances [6–8]. Although this type of phenomena
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