The inclusion of Mo, Nb and Ta in Pt and PtRu carbon supported electrocatalysts in the quest for improved CO tolerant PEMFC anodes (original) (raw)
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Electrochemical and Solid-State Letters, 1999
We report a two-to threefold enhancement of CO tolerance in a proton exchange membrane (PEM) fuel cell, exhibited by carbon supported nanocrystalline PtMo/C as compared to the current state of the art PtRu/C electrocatalysts. The bulk of these nanocrystals were comprised of Pt alloyed with Mo in the ratio 8.7:1.3 as shown by both X-ray diffraction and in situ extended X-ray absorption fine structure measurements. Rotating disk electrode measurements and cyclic voltammetry in a PEM fuel cell indicate the onset of CO oxidation at potentials as low as 0.1 V. Further, the oxidation of CO exhibits two distinct peaks, indicating redox behavior involving oxyhydroxides of Mo. This is supported by in situ X-ray absorption near edge structure measurements at the Mo K edge.
2019
The most important challenge in Proton Exchange Membrane (PEM) fuel cells is poisoning of the anode catalyst in the presence of impurities, especially carbon monoxide (CO) in the hydrogen feed. So, synthesis of catalysts with high CO tolerance is important for the commercialization of PEM fuel cells. In this study, a common borohydride reduction method was modified to synthesize a carbon supported Platinum Nanocatalyst (Pt/C) with a higher stability in the presences of CO impurity compared to a commercial Pt/C catalyst. The catalysts were characterized by X-ray diffraction and Scanning Electron Microscopy (SEM). The electrochemical cyclic voltammetry (CV) test procedure was used to evaluate the catalyst’s resistance to long-term CO exposure. The results showed that the synthesized catalyst’s electrochemical activity for CO electro-oxidation was comparable to commercial Pt/C under the same conditions. Moreover, the endurance of our catalyst for CO electro-oxidation after 100 CV with ...
Synthesis, Characterization and CO Tolerance Evaluation in PEMFCs of Pt2RuMo Electrocatalysts
Catalysts, 2019
Pt2RuMo/C catalysts were synthesized by the modified polyol method in the presence and absence of Li(C2H5)3BH (LBH), annealed at 600 °C under H2 atmosphere to improve the reduction of Pt and Ru to provide stronger interactions between Mo and another metals. LBH affected the physico-chemical characteristics of Pt2RuMo, that is, in the presence of LBH an increment of Mo(IV) amount and a decrease in the PtRu alloying degree were observed. The catalytic activity for hydrogen oxidation in the presence and absence of CO (CO tolerance) of the Pt2RuMo/C catalysts as anodes in polymer electrolyte membrane fuel cells (PEMFCs) was compared to that of a commercial PtRu/C catalyst. The results indicated that the CO tolerance increased with an increase in Mo(IV) content, but the stability increased with an increment of the amount of Ru oxides in the catalysts.
Carbon supported nano-sized Pt–Pd and Pt–Co electrocatalysts for proton exchange membrane fuel cells
International Journal of Hydrogen Energy, 2009
Pt-Co/C Membrane-electrode assembly PEM fuel cell a b s t r a c t Nano-sized Pt-Pd/C and Pt-Co/C electrocatalysts have been synthesized and characterized by an alcohol-reduction process using ethylene glycol as the solvent and Vulcan XC-72R as the supporting material. While the Pt-Pd/C electrodes were compared with Pt/C (20 wt.% E-TEK) in terms of electrocatalytic activity towards oxidation of H 2 , CO and H 2 -CO mixtures, the Pt-Co/C electrodes were evaluated towards oxygen reduction reaction (ORR) and compared with Pt/C (20 wt.% E-TEK) and Pt-Co/C (20 wt.% E-TEK) and Pt/C (46 wt.% TKK) in a single cell. In addition, the Pt-Pd/C and Pt-Co/C electrocatalyst samples were characterized by XRD, XPS, TEM and electroanalytical methods. The TEM images of the carbon supported platinum alloy electrocatalysts show homogenous catalyst distribution with a particle size of about 3-4 nm. It was found that while the Pt-Pd/C electrocatalyst has superior CO tolerance compared to commercial catalyst, Pt-Co/C synthesized by polyol method has shown better activity and stability up to 60 C compared to commercial catalysts. Single cell tests using the alloy catalysts coated on Nafion-212 membranes with H 2 and O 2 gases showed that the fuel cell performance in the activation and the ohmic regions are almost similar comparing conventional electrodes to Pt-Pd anode electrodes. However, conventional electrodes give a better performance in the ohmic region comparing to Pt-Co cathode. It is worth mentioning that these catalysts are less expensive compared to the commercial catalysts if only the platinum contents were considered.
Electrochimica Acta, 2005
We present results of a combined electrochemical and in situ spectroscopy study on kinetic and mechanistic aspects of the reduction of CO 2 on Pt model electrodes and compare these with the performance of a Pt/C membrane electrode assembly (MEA) in a polymer electrolyte fuel cell (PEFC) for using pure H 2 or H 2 /CO 2 (25%) mixtures (synthetic reformate). Based on highly sensitive surface enhanced IR absorption spectrocopy (SEIRAS) measurements on a thin film Pt electrode and on-line differential electrochemical mass spectrometry (DEMS) results obtained on a carbon supported Pt catalyst electrode we conclude that (i) linearly and multiply bonded CO ad is the only adsorbed reaction product, that (ii) CO ad formation by CO 2 reduction saturates after about 30 min at coverages of about 0.45 monolayers (ML) at potentials between 0.06 and 0.2 V RHE , and drops down to zero at 0.35 V RHE , that (iii) in acidic solution CO ad formation is independent of the presence of H 2 in the electrolyte, and that (iv) even at saturation CO ad coverage (0.45 ML), under steady state conditions, hydrogen oxidation is hardly affected by the presence of CO 2 in H 2 /CO 2 (20-25%) mixtures. The results indicate that CO 2 reduction proceeds by reaction with coadsorbed H ad rather than by reaction with dissolved H 2 and is therefore favored in the H-upd region, i.e., at fuel cell relevant anode potentials. CO 2 reduction is kinetically hindered by self-poisoning and blocking of Pt ensembles at CO ad coverages, which are still low enough for H 2 oxidation. These limitations in CO 2 reduction are responsible for the relatively small performance losses for PEFCs operating on H 2 /CO 2 mixtures, compatible with a picture where H 2 oxidation proceeds in holes of the CO adlayer, which are too small for CO 2 reduction.
Nonalloyed Carbon-Supported PtRu Catalysts for PEMFC Applications
Journal of The Electrochemical Society, 2004
PtRu͑1:1͒/C catalysts were prepared by a process that was claimed previously to lead to nonalloyed Pt and Ru particles, using two different precursors, Ru nitrosyl nitrate and Ru chloride hydrate. Both X-ray diffraction and characterization by cyclic voltammetry point toward Pt and Ru being present as separate phases in the prepared, nonannealed catalysts. In combination with a high dispersion, this results in proton exchange membrane fuel cell ͑PEMFC͒ anode electrocatalysts. These PEMFCs have improved hydrogen oxidation activity and CO tolerance.
Electrocatalysis of reformate tolerance in proton exchange membranes fuel cells: Part I
Journal of Electroanalytical Chemistry, 2003
Electrocatalysis of anode electrode tolerance resulting from the presence of both CO and CO 2 in the reformer feed was investigated for Pt, Pt Á/Ru (1:1) and various atomic ratios of supported Pt:Mo electrocatalysts in proton exchange membrane fuel cells (PEMFCs). In order to elucidate the effects of CO and CO 2 in the reformer feed, separate systematic studies were conducted with varying levels of CO and CO 2 in H 2 . The results were used to explain those obtained with a fixed reformate composition: 45% H 2 , 10 ppm CO, 15% CO 2 , 1% CH 4 balanced with N 2 . Results with CO in H 2 showed that PtMo/C exhibits at least a threefold better CO tolerance as compared to PtRu/C and fourfold with respect to Pt/C. The variation of PtMo atomic composition has a negligible effect on CO tolerance. Additional surface poisoning was detected for all the electrocatalysts studied in the molar ratio (H 2 :CO 2 , 40:60 to 60:40). The presence of a reduced CO 2 species was confirmed using cyclic voltammetry. An ensemble effect was proposed to explain the variation of tolerance to CO 2 as a function of Pt: Mo atomic ratio, this is in contrast to the effect in the presence of adsorbed CO. Interestingly, the overpotential losses in the presence of H 2 :CO 2 for PtMo/C (1:1) and PtRu/C (1:1) were very close. As the Pt content of the PtMo/C alloys was increased, the overpotential losses followed those observed for pure Pt, clearly demonstrating a relationship between overpotential loss and Pt site availability. Despite similar overpotential losses between Pt/C and PtMo/C (5:1), both of which were greater than PtRu/C (1;1) the overpotential loss observed for PtMo in a CO 2 '/CO reformate mix was far better than for both PtRu/C and Pt/C.
Enhanced electrocatalytic property of Pt/C electrode with double catalyst layers for PEMFC
International Journal of Hydrogen Energy, 2019
which provides more Pt catalytic active sites to the electrolyte than those in SCL electrodes. Our observation may aid in minimizing the usage amount of Pt catalysts (~0.16 mg Pt /cm 2) compared to those in present commercial Pt/C composites (~0.3 mg Pt /cm 2) as well as maximize efficient Pt utilization. More importantly, with regard to proton exchange membrane fuel cell (PEMFC) activity as a crucial in-situ characterization of a catalyst, a membrane electrode assembly (MEA) containing S 1 E 1 as the anode electrode could generate mass maximum power density of 3.84 W/mg Pt , 3.6 times higher than the present commercial one (1.07 W/mg Pt).
Journal of The Electrochemical Society, 2004
A Pt-Co/C electrocatalyst with Pt:Co atomic ratio 85:15, prepared by a low-temperature chemical reduction with sodium borohydride, was studied as possible cathode material for polymer electrolyte membrane fuel cells ͑PEMFCs͒. The physical characterization of this electrocatalyst was performed by energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The performance of the material was evaluated by cyclic voltammetry and polarization experiments in a single PEMFC and compared with those of an unalloyed Pt/C catalyst prepared by the same method and a commercial Pt-Co/C catalyst. Both the Pt-Co/C catalysts were also submitted to a thermal treatment in a reducing atmosphere.