A Reverse-Current Decay Mechanism for Fuel Cells

Reiser, Carl; Bregoli, L. J.; Patterson, Timothy; Yi, Jung S.; Yang, Jangsik; Perry, Mike; Jarvi, T. D.

doi:10.1149/1.1896466

Cited by 998 publications

(847 citation statements)

References 3 publications

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“…However, the higher potentials (≥ 1.4 V) would be applied to cathodes for automotive applications wherein frequent start/stop cycling is expected; this phenomenon, caused by the partial coverage of hydrogen and oxygen in the anode, would be the most hazardous one in PEMFC operations 20,21 . Tolerance under such high potentials is the key requirement for practical cathodes.…”

Section: Structure Of Pt ML /Pdau/c Electrocatalystmentioning

confidence: 99%

Highly stable Pt monolayer on PdAu nanoparticle electrocatalysts for the oxygen reduction reaction

et al. 2012

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stability is one of the main requirements for commercializing fuel cell electrocatalysts for automotive applications. Platinum is the best-known catalyst for oxygen reduction in cathodes, but it undergoes dissolution during potential changes while driving electric vehicles, thus hampering commercial adoption. Here we report a new class of highly stable, active electrocatalysts comprising platinum monolayers on palladium-gold alloy nanoparticles. In fuel-cell tests, this electrocatalyst with its ultra-low platinum content showed minimal degradation in activity over 100,000 cycles between potentials 0.6 and 1.0 V. under more severe conditions with a potential range of 0.6-1.4 V, again we registered no marked losses in platinum and gold despite the dissolution of palladium. These data coupled with theoretical analyses demonstrated that adding a small amount of gold to palladium and forming highly uniform nanoparticle cores make the platinum monolayer electrocatalyst significantly tolerant and very promising for the automotive application of fuel cells.

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Section: Structure Of Pt ML /Pdau/c Electrocatalystmentioning

confidence: 99%

Highly stable Pt monolayer on PdAu nanoparticle electrocatalysts for the oxygen reduction reaction

et al. 2012

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“…The problem is enhanced during fuel cell start-stop cycles and fuel starvation conditions, when part of the anode is covered by fuel and part is still covered by air or water. This situation can result in corrosion of the cathode of a H2-PEMFC [97] and anode of a DMFC [98,99], which decreases the fuel cell performance and hydrophobicity of the CL. Moreover, the presence of Pt and Ru increases the oxidation rate [100].…”

Section: The Role Of Carbon Supportmentioning

confidence: 99%

Silicon nanograss as micro fuel cell gas diffusion layer

et al. 2010

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Direct methanol fuel cells (DMFC) produce electrical energy directly from chemical energy. They are a promising candidate for power sources of portable devices due to the high energy density of methanol and the quick recharging procedure by fuel insertion. However, the problem areas of the DMFC are the slow electro-oxidation of methanol and the permeated methanol reacting at the cathode. New catalysts are constantly searched but they are often tested only for catalytic activity and the DMFC testing is omitted even though the catalyst layer (CL) structure has a large impact on the performance. Miniaturization of the system is also necessary for portable applications. Silicon etching can be used to fabricate small structures for fuel cells replacing or enhancing the functions of laboratory-scale components.In the first part of this thesis, new catalysts for the DMFC are studied with the emphasis on the CL structure. Different carbon supports for the anode were studied: standard carbon black and alternative few-walled carbon nanotubes (FWCNT) and graphitized carbon nanofiber (GNF). The alternative supports showed better DMFC performance but their stability was lower than with carbon black. However, the CL formed with GNF showed a very porous structure enhancing the mass transfer, so that higher binder content could be used improving the stability to the level of carbon black and the performance by 30%. The FWCNTs were also investigated as a platform for enzymatic methanol oxidation by studying the electrochemical properties of an immobilized cofactor pyrroloquinoline quinone (PQQ). A large amount of PQQ was adsorbed having a strong redox response and good stability in a wide pH window. For the cathode, a methanol-tolerant, Pt-free nitrogen-doped FWCNTs were tested in an alkaline DMFC as such testing is not often made. Its performance was remarkably 4 times better than with Pt when synthetic air was used as the oxidant.In the second part of thesis, an integrated gas diffusion layer (GDL) consisting of Si nanoneedles (nanograss) was tested in a micro fuel cell (MFC). The layer functioned properly at low current densities. For high power applications, a standard carbon cloth GDL was tested with the nanograss as a contact surface reducing the resistance between the GDL and the flow field. The use of the nanograss improved the MFC performance and stability. Finally, the MFCs were used as a catalyst testing platform and the results were compared with a similar test in a laboratory-scale DMFC. The results varied showing that the DMFC components also have a large impact on catalyst testing.Keywords direct methanol fuel cell, carbon nanomaterials, micro fuel cells, catalyst layer Tiivistelmä Suorametanolipolttokennot (SMPK) tuottavat sähköenergiaa suoraan kemiallisesta energiasta. Ne ovat lupaava vaihtoehto kannettavien laitteiden voimanlähteeksi, koska metanolilla on korkea energiatiheys ja lataaminen tapahtuu nopeasti polttoainelisäyksellä. SMPK:lla on kuitenkin rajoitteina metanolin hidas hapetusreaktio ja katodi...

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“…A reverse-current mechanism of proton exchange membrane fuel cell (PEMFC) degradation was discovered in 2005. 1 We summarize it as follows. After a period of inactivity, a PEMFC anode contains only air due to equilibration with the atmosphere.…”

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confidence: 99%

“…1 We summarize it as follows. After a period of inactivity, a PEMFC anode contains only air due to equilibration with the atmosphere.…”

mentioning

confidence: 99%

“…Here we demonstrate for the first time that HEMFCs undergo RCD when some platinum-group metals or carbon are used as anode catalysts. We adapt the model of Reiser et al 1 to predict an inverse relationship between anode ORR activity and RCD driving force. We test several monometallic catalysts and confirm that cathode corrosion is slower for anode catalysts with low ORR activity.…”

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confidence: 99%

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Reverse-Current Decay in Hydroxide Exchange Membrane Fuel Cells

Kaspar

Wittkopf

Woodroof

et al. 2016

J. Electrochem. Soc.

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In proton exchange membrane fuel cells (PEMFCs), the cathode carbon support corrodes during startup and shutdown by reversecurrent decay (RCD). We show for the first time that hydroxide exchange membrane fuel cells (HEMFCs) also undergo RCD. We find that decreasing the oxygen reduction reaction (ORR) activity of the anode catalyst mitigates RCD: a Ru anode causes less corrosion than Pt, Ir, and Pd anodes, as expected from their ORR activities. After an intensive 6 h RCD test, an HEMFC based on Ru shows six times lower internal resistance compared to Pt (1.02 vs. 6.01 cm 2 ). Due to its enhanced ORR activity in base, carbon alone can sustain RCD. To minimize RCD the carbon support should be eliminated from the anode catalyst. A reverse-current mechanism of proton exchange membrane fuel cell (PEMFC) degradation was discovered in 2005. 1 We summarize it as follows. After a period of inactivity, a PEMFC anode contains only air due to equilibration with the atmosphere. As hydrogen is introduced during device startup, distinct hydrogen and air regions form on the anode (Fig. 1a). In the hydrogen region the device operates normally: the hydrogen oxidation reaction (HOR) occurs on the anode while across the membrane, the oxygen reduction reaction (ORR) occurs on the cathode. Since the two anode regions are electrically connected, electrons produced by HOR in the hydrogen region can move to the stagnant air region and react with protons supplied by the electrolyte to reduce oxygen. Removing positive charge from the electrolyte in this manner lowers the electrolyte potential, ultimately generating an interfacial potential difference sufficient to drive the carbon oxidation reaction (COR) and oxygen evolution reaction (OER) on the cathode in the stagnant air region. This mechanism is called reverse-current decay (RCD) because reduction occurs on the anode where hydrogen is normally oxidized while oxidation occurs on the cathode where oxygen is normally reduced. Related decay processes take place during shutdown and whenever hydrogen is maldistributed on the anode.2,3 Over the course of many startup/shutdown cycles, corrosion of the cathode carbon support leads to significant performance loss. 4 Strategies to mitigate RCD include maintaining hydrogen pressure in the anode after shutdown or flushing with an inert gas, 5 shorting the electrodes to depress the cathode potential, 2 replacing carbon with a corrosion-resistant support, 6,7 and mixing OER catalysts into the cathode to reduce selectivity for COR. [8][9][10] However, these strategies add to system complexity or treat symptoms instead of resolving the underlying problem.The key issue responsible for RCD in PEMFCs is that the anode and cathode catalysts are the same. Pt is the best catalyst available for both HOR and ORR. When a mixture of gases is present at the anode, Pt catalyzes HOR as intended, but also catalyzes ORR. A direct way to stop RCD is to eliminate the interfacial potential buildup altogether by replacing Pt with a specialized anode catalyst that has no...

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A Reverse-Current Decay Mechanism for Fuel Cells

Cited by 998 publications

References 3 publications

Highly stable Pt monolayer on PdAu nanoparticle electrocatalysts for the oxygen reduction reaction

Highly stable Pt monolayer on PdAu nanoparticle electrocatalysts for the oxygen reduction reaction

Silicon nanograss as micro fuel cell gas diffusion layer

Reverse-Current Decay in Hydroxide Exchange Membrane Fuel Cells

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