Membrane and Catalyst Performance Targets for Automotive Fuel Cells by FCCJ Membrane, Catalyst, MEA WG

Differential electrochemical mass spectrometry as well as online mass spectrometry in combination with singe cell testing has been used to study carbon corrosion of typical carbon materials discussed as support for electro-catalyst in fuel cells, e.g. carbon blacks or carbon nanotubes. Beside standard tests used to study the stability under automotive LT-PEMFC conditions, additional tests were performed to try to test the stability under the operating conditions of high temperature polymer electrolyte membrane fuel cells (HT-PEMFC). It was shown that under LT-PEMFC conditions a strong catalytic effect of platinum on the carbon corrosion rate is observable. High temperatures in HT-PEMFC do accelerate the corrosion rate. It was further found that corrosion does not only occur at high potentials but also to a minor amount at lower potentials. This low potential corrosion is in particular observed after a prior potential excursion of the electrode indicating that such excursions do not only lead to the direct corrosion of the support but also to the formation of unstable surface groups, which can be removed subsequently. Throughout all tests, CNT exhibited a higher stability than the tested carbon blacks. In single cell testing, the contribution of other carbon materials in particular the MPL was evaluated. It was found that it is present but small compared to the catalyst support itself. In order to reduce the expenditure of platinum group metals in polymer electrolyte membrane fuel cells the dispersion of the catalyst on a conductive support is the current state-of the art. Only few examples do not follow this approach. Most prominent among the exemptions is the Nano-Structured Thin Film (NSTF) type of catalyst developed by 3M.1 For most applications, carbon has become, however, a sort of standard support material. To accomplish the goal to reduce costs for the fuel cells, inexpensive carbon black materials like Vulcan XC72R from Cabot are used most often. However, as carbon in presence of water is thermodynamically unstable for potentials higher than 0.207 V 2 carbon corrosion can become an issue if the oxidation of the carbon is not strongly kinetically hindered e.g. via high degrees of graphitization. Consequently, carbon materials exhibiting such high degrees of graphitization like carbon nanotubes or graphene have attracted attention as alternative supports.The focus of the research on carbon corrosion is on LT-PEMFC for automotive application. With respect to carbon corrosion the reversed current decay mechanism proposed by Reiser et al.3 is an accepted cause for this type of degradation processes. This is confirmed e.g. in the review of PEMFC degradation processes published by Yu et al. 4 The process which is induced by the formation of a hydrogen oxygen front on the anode side upon hydrogen admission after longer standstill can cause potential excursions of the cathode side to potentials between 1.4 and 1.75 V.5 Accordingly, the common tests suites published by US Department of Energy (DoE) and the Fuel Ce...

“…6 Table 4 item start/stop cycling for half-cell RDE. Instead of a RDE the flow through DEMS cell was used, however, and instead of 0.1 M HClO 4 , 0.5 M H 2 SO 4 was used as electrolyte.…”

Section: Resultsmentioning

confidence: 99%

DEMS and Online Mass Spectrometry Studies of the Carbon Support Corrosion under Various Polymer Electrolyte Membrane Fuel Cell Operating Conditions

Cremers

Jurzinsky

Meier

et al. 2018

“…24,25 In argon-purged 1.0 M HClO 4 , the CV was first recorded for the evaluation of ECA. Then, the potential was stepped from the open circuit potential to +1.0 V vs. NHE, and held a the potential for 30 s. This was followed by potential cycling from +1.0 V-+1.5 V vs. NHE at a scan rate of 0.5 V/s.…”

Section: Methodsmentioning

confidence: 99%

Boron-Doped Diamond Powder as a Durable Support for Platinum-Based Cathode Catalysts in Polymer Electrolyte Fuel Cells

Kondo

Kikuchi

Masuda

et al. 2018

Platinum nanoparticle-supported boron-doped diamond powder (Pt/BDDP) was prepared and investigated as a durable polymer electrolyte fuel cell (PEFC) cathode catalyst. The use of the nanocapsule method enabled dense deposition of Pt nanoparticles (2-5 nm in size) on a boron-doped diamond (BDD) powder <500 nm in size. The Pt/BDDP cathode catalyst showed oxygen reduction reaction activity comparable to Pt-supported carbon black (Pt/C), indicating sufficient conductivity of the BDDP as a catalyst support. Potential cycling in a highly positive potential region (+1.0-+1.5 V vs. NHE) that simulates the start-stop operations of the PEFC was performed to investigate the durability of the Pt/BDDP catalyst. Decreases in the electrochemically active surface area of the Pt/BDDP were suppressed compared to that of Pt/C. Corrosion resistance of BDD against potential cycling was demonstrated by testing a BDD thin-film electrode. The corrosion resistance should be responsible for the improved durability of the BDDP support, possibly by lowering the Pt nanoparticle association process (e.g., agglomeration The polymer electrolyte fuel cell (PEFC) is a promising power generating system for portable devices, electric vehicles, and electric transportation applications because of its low operating temperature, high power density, high theoretical energy efficiency, and fast start-up advantages. 1,2 Improvement of PEFC durability has been desired for large-scale commercialization; a major obstacle is the deterioration of the carbon support for PEFC cathode catalysts. In frequent start-stop operations, particularly for automobiles, the cathode is exposed to a highly positive potential and the carbon support can be corroded via oxidation. 1,3-6 As solutions to this durability issue, SnO 2 , Nb-SnO 2 , 7 TiO x and TiN, 8 and polymer-coated carbon nanotubes 9 have all been reported as candidates for alternative support materials with superior tolerance to corrosion from electrochemical oxidation. Boron-doped diamond (BDD) has also attracted attention as an electrode material because it possesses excellent chemical/electrochemical stability. The BDD electrode is corrosion resistant; even in electrolytic water treatment at highly positive potentials, BDD electrode exhibits long service lifetimes with stable high performance. [10][11][12][13] To apply BDD as a PEFC catalyst support, BDD powder (BDDP) should be used. Several reports exist on the application of BDDP as a catalyst support for the direct methanol fuel cell anode catalyst. The Pt or Pt-Ru particle catalysts were deposited onto BDDP, and the catalysts exhibited high activity and stability to anodic methanol oxidation. [14][15][16][17][18] Recently, Kim reported that Pt/BDDP can be useful as a durable cathode catalyst for PEFC. 19 They fabricated a unit cell using the Pt/BDDP cathode catalyst and found that the decrease in Pt loading during an accelerated long-term test (0.6 V at 90 • C) was less on the BDD support than on the Vulcan XC-72 or multi-walled carbon nanotube supports. ...

“…For instance, a standardized AST for RDE from the Fuel Cell Conference of Japan uses triangular waves between 1.0 and 1.5 V RHE for SUSD simulation and another test (square waves between 0.6 and 1.0 V RHE ) to simulate load cycling and idling. 27 The DOE also proposed two RDE ASTs designed to simulate load cycling and SUSD, also on either side of 1.0 V. The tests were part of a Request for Information, 28 but have not yet been incorporated into the DOE's hydrogen fuel cell research targets and standards. 23 However, in the interest of making the AST as aggressive as possible, a unique AST which simulates both load cycling and SUSD was developed.…”

Section: Methodsmentioning

confidence: 99%

Screening Bifunctional Pt Based NSTF Catalysts for Durability with the Rotating Disk Electrode: The Effect of Ir and Ru

Crowtz

Dahn

2018

Various amounts of Ir (<20 μg cm −2 ) and Ru (up to 12 μg cm −2 ) on a consistent base Pt loading of 85 μg cm −2 , were sputter deposited on a nanostructured thin film catalyst support to mimic a hydrogen fuel cell's cathode catalyst. The nanostructured support was grown on glassy carbon disks designed for a rotating disk electrode, which was used to simulate what happens to a fuel cell cathode during repeated start-up, operation, and shut-down. The testing protocol subjected the catalyst to a minimum potential of 0.65 V RHE and a maximum between 1.53 and 1.8 V RHE . The upper potential was achieved with a galvanostatic hold which is an alternative way to simulate potential transients on the cathode caused by start-up and shut-down. Increasing Ir loading improved the durability of both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity. When combined with Ir, Ru provided no benefit to OER durability except at an Ir loading of 10 μg cm −2 . Ru addition (no Ir present) improved the ORR durability compared to pure Pt. ORR durability was not influenced by Ru addition to Ir-containing samples. In general, ORR durability showed no dependence on Ru loading for all the Ru containing samples and ORR activity was decreased by OER catalyst addition, though more so for Ir than Ru.