Nanofiber Electrodes with Low Platinum Loading for High Power Hydrogen/Air PEM Fuel Cells

PEFC electrodes manufactured using inkjet printing are investigated. Cell performance, Tafel slope, reaction order and local oxygen transport resistance of electrodes with varying Pt loadings of 0.014 to 0.113 mg/cm 2 are studied in order to understand the nonlinear relationship between loading and performance. The performance increase with Pt loading was substantially reduced above Pt loadings of 0.08 mg/cm 2 . Electrochemical active area of the electrodes decreased from 66.4 to 40.4 m 2 /g as the Pt loading increased from 0.026 to 0.113 mg/cm 2 . Below the transition voltage of 0.8 V i R f ree , the Tafel slope was found to be a function of the Pt loading and oxygen partial pressure. The kinetic performance dependence on p O 2 was quantified by measuring the total reaction order. Oxygen transport resistance evaluated from limiting current experiments revealed its dependence on the inlet relative humidity of the reactants. The local oxygen transport resistance was found to drop from 5.93 ± 3.16 s/cm to 3.43 ± 1.67 s/cm as the humidity increased from 50% to 90%. Hydrogen polymer electrolyte fuel cells (PEFCs) are a zero emission and efficient energy conversion technology for transportation, stationary and electronic applications. The current generation of fuel cell vehicles provide quick start-up, long-range and increased durability. The high and unstable cost of platinum (Pt), which is the commonly used catalyst, however hinders its commercial prospects, especially when compared to the internal combustion engine. The cost of Pt is responsible for over 34% of the fuel cell stack cost.1 Less than 10-20% of the catalyst is however estimated to be utilized during the operation of a conventional catalyst layer (CL) due to mass and charge transport limitations.2 Re-designing the CL to improve these transport limitations has the potential to achieve better Pt utilization, i.e., generate more current per gram of catalyst. The CL fabrication process governs its utilization efficiency, microstructure and Pt loading in the electrodes.The effect of Pt loading on electrodes manufactured by spraying, using film applicators, sputtering as well as inkjet printing has been studied in the literature. [3][4][5][6][7][8][9][10][11][12][13][14][15] Results show that fuel cell performance is severely degraded at low Pt loading, 3,6,12,16 and that an optimal value of Pt loading exists above which the performance gains are not very significant. 4,12 The reason for the reduced performance of low loading electrodes has thus far mainly been attributed to a high oxygen mass transport resistance at the reaction site. 12,[17][18][19][20][21][22] The source of this resistance is still under debate. Oxygen dissolution in the ionomer, 23 densification of the ionomer layer near the ionomer/Pt interface, 24 and catalyst/oxygen interactions at the catalyst site 20 have been proposed as causes for this local mass transport barrier. These results indicate that in order to understand the performance degradation of low loading electrodes, and to comp...

show abstract

“…Refs. 5,7,8,11,12. Even for conventional electrodes, the oxygen reaction order has usually been reported only at open circuit voltage, e.g. Refs.…”

mentioning

confidence: 99%

Analysis of Inkjet Printed PEFC Electrodes with Varying Platinum Loading

Shukla

Stanier

Saha

et al. 2016

J. Electrochem. Soc.

View full text Add to dashboard Cite

show abstract

“…2 In a series of recent papers, Pintauro and coworkers have shown that an electrospun nanofiber cathode, composed of Pt/C particles and a binder of Nafion + poly(acrylic acid) (abbreviated as PAA) performs remarkably well in a hydrogen/air proton exchange membrane fuel cell. [3][4][5] For example, a nanofiber electrode MEA with 0.055 mg Pt /cm 2 at the cathode and 0.059 mg Pt /cm 2 at the anode (Johnson Matthey Pt/C catalyst) produced more than 900 mW/cm 2 at maximum power in a H 2 /air fuel cell at 80…”

mentioning

confidence: 99%

Power Output and Durability of Electrospun Fuel Cell Fiber Cathodes with PVDF and Nafion/PVDF Binders

Brodt

Dale

Pintauro

2016

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

Membrane-electrode-assemblies (MEAs) with electrospun nanofiber mat electrodes (0.10 mg/cm 2 Pt loading) and a Nafion 211 membrane were prepared and tested in a H 2 /air fuel cell at 100% and 40% relative humidity. The cathode binder was either neat poly(vinylidene fluoride) (PVDF) or a Nafion/PVDF blend (20 to 80 wt% Nafion) and the anode binder was Nafion with poly(acrylic acid). Polarization curves were recorded at 80 • C and ambient pressure before, intermittently, and after a carbon corrosion voltage cycling experiment. The Nafion/PVDF cathode MEA with the smallest amount of PVDF (80/20 Nafion/PVDF weight ratio) produced the highest maximum power at beginning-of-life (BoL), 545 mW/cm 2 at 100% RH, which was 35% greater than that for a conventional MEA with a neat Nafion binder. Carbon corrosion scaled inversely with cathode PVDF content, with a 33/67 Nafion/PVDF cathode binder MEA producing the highest end-of-life (EoL) power (330 mW/cm 2 ). MEAs with < 50 wt% PVDF in the cathode binder exhibited a power density decline during carbon corrosion, whereas the power increased during/after carbon corrosion for nanofiber cathodes with binders containing > 50 wt% PVDF due to favorable increases in the hydrophilicity of the carbon support and Pt mass activity, coupled with a lower carbon loss. The hydrogen/air proton-exchange membrane fuel cell is a promising candidate for emission-free automotive power plants, but issues remain regarding the high cost and durability of membrane-electrodeassemblies (MEAs).1 For commercialization, the Pt loading of fuel cell MEAs (particularly the cathode) must be reduced while maintaining high power output and the catalytic activity of the cathode for electrochemical oxygen reduction must be maintained during long-term operation with various power cycles and numerous stack start-ups and shut-down events. 2In a series of recent papers, Pintauro and coworkers have shown that an electrospun nanofiber cathode, composed of Pt/C particles and a binder of Nafion + poly(acrylic acid) (abbreviated as PAA) performs remarkably well in a hydrogen/air proton exchange membrane fuel cell.3-5 For example, a nanofiber electrode MEA with 0.055 mg Pt /cm 2 at the cathode and 0.059 mg Pt /cm 2 at the anode (Johnson Matthey Pt/C catalyst) produced more than 900 mW/cm 2 at maximum power in a H 2 /air fuel cell at 80• C, 100% RH, and high feed gas flow rates at 2 atm backpressure. 4 In a recent collaborative study between Vanderbilt University and Nissan Technical Center North America, Brodt et al. 5 showed that MEAs with an electrospun particle/polymer cathode generated high beginning-of-life power and also exhibited excellent durability, as determined from end-of-life polarization curves after an accelerated start-stop voltage cycling (carbon corrosion) test. Thus, after 1,000 simulated start-stop cycles, a nanofiber MEA with Johnson Matthey Pt/C catalyst and a binder of Nafion + PAA maintained 53% of its initial power at 0.65 V and 85% of its maximum power, as compared to a 28% power retention at 0.65...

show abstract

“…17 The excellent performance of nanofiber fuel cell electrodes is attributed to facile oxygen and proton transport to catalytic sites and efficient product water removal, which is a direct consequence of the unique nanofiber electrode morphology, with significant inter-fiber and intrafiber porosity and a well-mixed dispersion of catalyst powder and ionomer binder.…”

mentioning

confidence: 99%

Fabrication, In-Situ Performance, and Durability of Nanofiber Fuel Cell Electrodes

Brodt

Han

Dale

et al. 2014

J. Electrochem. Soc.

Self Cite

View full text Add to dashboard Cite

A series of electrospun nanofiber mat electrodes with two different commercial Pt/C catalysts and a binder of Nafion and poly(acrylic acid) were fabricated and evaluated. The electrodes were assembled into membrane-electrode-assemblies (MEAs) using Nafion 211 as the membrane. Variations in catalyst type, nanofiber composition (the ratio of Pt/C to Nafion), and fiber diameter had little or no impact on hydrogen/air fuel cell power output. 25 cm 2 nanofiber and sprayed gas diffusion electrode MEAs were compared in terms of beginning of life (BoL) and end of life (EoL) performance after automotive-specific load cycling (Pt dissolution) and start-stop cycling (carbon corrosion) cathode durability protocols. Nanofiber electrode MEAs (0.10 mg/cm 2 Pt loading for the anode and cathode) were clearly superior to sprayed MEAs; they produced more power at BoL and maintained a higher percentage of their power after the carbon corrosion durability protocol, resulting in much higher EoL fuel cell performance. On the other hand, there was no effect of electrode morphology on MEA durability for the Pt dissolution test. The higher MEA power output after carbon corrosion with electrospun electrodes is attributed to better oxygen and water transport within the nanofiber electrode and a higher electrochemical surface area for the fiber cathode. The hydrogen/air proton-exchange membrane fuel cell is a promising candidate for emission-free automotive power plants due to its high power output, efficiency of energy conversion, and quick start-up. The successful integration of a sizable fleet of Electric Vehicles into the transportation sector would greatly diminish localized air pollution and alleviate our dependency on depleting oil reserves. Presently, mass commercialization of fuel cell vehicles is challenging due in large part to issues related to the cost and durability of membraneelectrode-assemblies (MEAs). 1A principal strategy to reduce the cost of MEAs is to minimize the amount of the platinum catalyst in the electrodes without sacrificing power generation. In this regard, recent R&D efforts have been directed at the investigation of platinum metal alloys, 2 core-shell nanostructures, 3 and the use of platinum-free metal-nitrogen-carbon catalysts. 4,5 Although these studies have shown some promise in terms of catalytic activity and potential cost savings, they do not currently meet automotive power density and durability targets.Carbon support corrosion in Pt/C catalysts during fuel cell startup/shut-down is another ongoing issue that has drawn considerable research attention. In particular, when a hydrogen-air mixture is present in the anode during start-up, the cathode potential spikes as high as 1.5 V vs. SHE, resulting in severe carbon corrosion of the cathode catalyst layer. 6 Researchers have worked to mitigate carbon corrosion at the materials level by investigating catalyst that can better withstand the harsh automotive operating environment. Current efforts are focused on metal oxides and thermally treated carbon sup...

show abstract

Nanofiber Electrodes with Low Platinum Loading for High Power Hydrogen/Air PEM Fuel Cells

Cited by 62 publications

References 25 publications

Analysis of Inkjet Printed PEFC Electrodes with Varying Platinum Loading

Analysis of Inkjet Printed PEFC Electrodes with Varying Platinum Loading

Power Output and Durability of Electrospun Fuel Cell Fiber Cathodes with PVDF and Nafion/PVDF Binders

Fabrication, In-Situ Performance, and Durability of Nanofiber Fuel Cell Electrodes

Contact Info

Product

Resources

About