Impact of operational voltage on the Pt surface area deterioration in high temperature PEM fuel cell

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F49777513%3A23640%2F17%3A43950738" target="_blank" >RIV/49777513:23640/17:43950738 - isvavai.cz</a>

Výsledek na webu

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DOI - Digital Object Identifier

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Jazyk výsledku

angličtina

Název v původním jazyce

Impact of operational voltage on the Pt surface area deterioration in high temperature PEM fuel cell

Popis výsledku v původním jazyce

High temperature fuel cell with proton-exchange membrane (HT PEM FC) is a convenient solution for efficient transformation of chemical energy stored in H2 and O2 gases to electricity. HT PEM FC’s operating temperature 120 200 °C promotes resistance against CO present in H2 produced from natural gas/fossil fuels, enhances electrochemical reaction rate and makes heat recuperation potentially interesting. Despite the mentioned significant advantages, HT PEM FC is still in the optimization stage of research due to pronounced degradation of individual cell components. Apart from membrane, degradation processes affect mainly gas-diffusion electrodes, whose electrochemically-active surface area and catalytic activity decreases with operational time. Reasons for such behaviour include degradation of catalyst support and, more importantly, increase of Pt nanoparticle size. The nanoparticle growth is especially troublesome, not fully understood phenomenon. Among the processes resulting in nanoparticle growth, surface diffusion, agglomeration and coalescence and Ostwald ripening are universally recognized. Analysis of Pt nanoparticle degradation during HT PEM FC operation is technically demanding and time-consuming. Fuel cell has to be operated at defined, realistic conditions and catalyst has to be quantitatively separated from membraneelectrode assembly. Unfortunately, due to the necessary operational time (at least 500 h), available data from literature concerning growth of Pt nanoparticles are rather scarce. Another important point is operational regime; majority of HT PEM FC tests are performed at constant current densities. Under such conditions the impact of operational voltage, which is directly related to the individual electrodes potential as the governing parameter of the electrochemically related phenomena, is often overlooked. Goal of this work was to determine the rate of Pt surface area deterioration during HT PEM FC operation in dependence on voltage used. To accurately separate catalytic layer on the cathodic and anodic side of membrane, three membrane sandwich system with two PEEK meshes separators was developed and successfully applied. HT PEM FC’s were operated at constant voltage with no interference from measurements other than impedance spectroscopy. Membranes with adhering catalytic layer were examined by the X-ray diffraction and small angle X-ray scattering. Pt surface area was calculated on the basis of average Pt crystallite size and nanoparticle size distribution in samples. From the dependence of electrochemically-active surface area decrease on the operational voltage a degradation rate was determined. Results proved significant impact of operational voltage on the Pt nanoparticle degradation and suggested the way towards further optimization of HT PEM FC operational regime and understanding of degradation mechanism.

Název v anglickém jazyce

Impact of operational voltage on the Pt surface area deterioration in high temperature PEM fuel cell

Popis výsledku anglicky

High temperature fuel cell with proton-exchange membrane (HT PEM FC) is a convenient solution for efficient transformation of chemical energy stored in H2 and O2 gases to electricity. HT PEM FC’s operating temperature 120 200 °C promotes resistance against CO present in H2 produced from natural gas/fossil fuels, enhances electrochemical reaction rate and makes heat recuperation potentially interesting. Despite the mentioned significant advantages, HT PEM FC is still in the optimization stage of research due to pronounced degradation of individual cell components. Apart from membrane, degradation processes affect mainly gas-diffusion electrodes, whose electrochemically-active surface area and catalytic activity decreases with operational time. Reasons for such behaviour include degradation of catalyst support and, more importantly, increase of Pt nanoparticle size. The nanoparticle growth is especially troublesome, not fully understood phenomenon. Among the processes resulting in nanoparticle growth, surface diffusion, agglomeration and coalescence and Ostwald ripening are universally recognized. Analysis of Pt nanoparticle degradation during HT PEM FC operation is technically demanding and time-consuming. Fuel cell has to be operated at defined, realistic conditions and catalyst has to be quantitatively separated from membraneelectrode assembly. Unfortunately, due to the necessary operational time (at least 500 h), available data from literature concerning growth of Pt nanoparticles are rather scarce. Another important point is operational regime; majority of HT PEM FC tests are performed at constant current densities. Under such conditions the impact of operational voltage, which is directly related to the individual electrodes potential as the governing parameter of the electrochemically related phenomena, is often overlooked. Goal of this work was to determine the rate of Pt surface area deterioration during HT PEM FC operation in dependence on voltage used. To accurately separate catalytic layer on the cathodic and anodic side of membrane, three membrane sandwich system with two PEEK meshes separators was developed and successfully applied. HT PEM FC’s were operated at constant voltage with no interference from measurements other than impedance spectroscopy. Membranes with adhering catalytic layer were examined by the X-ray diffraction and small angle X-ray scattering. Pt surface area was calculated on the basis of average Pt crystallite size and nanoparticle size distribution in samples. From the dependence of electrochemically-active surface area decrease on the operational voltage a degradation rate was determined. Results proved significant impact of operational voltage on the Pt nanoparticle degradation and suggested the way towards further optimization of HT PEM FC operational regime and understanding of degradation mechanism.

Druh

O - Ostatní výsledky

CEP obor

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OECD FORD obor

10405 - Electrochemistry (dry cells, batteries, fuel cells, corrosion metals, electrolysis)

Projekt

<a href="/cs/project/LO1402" target="_blank" >LO1402: CENTEM+</a><br>

Návaznosti

P - Projekt vyzkumu a vyvoje financovany z verejnych zdroju (s odkazem do CEP)

Rok uplatnění

2017

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů