Development of New CO Tolerant Ternary Anode Catalysts for Proton Exchange Membrane Fuel Cells

Venkataraman, Ramki; Kunz, H. R.; Fenton, James M.

doi:10.1149/1.1543567

Cited by 88 publications

(47 citation statements)

References 22 publications

(21 reference statements)

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“…An electrode coated with a film of the Re MBH possessing a binuclear Ni-Fe active site represents a previously undescribed H 2 oxidation electrocatalyst that is completely tolerant to CO; thus, even Synthesis Gas (an industrial H 2 ͞CO mixture) would provide a viable H 2 fuel source. Intriguingly, modifications to platinum surfaces that confer increased resistance to CO poisoning often depend on introduction of a second metal, as in the intermetallic materials PtBi, PtIn, or PtPb (24) or the binary alloys PtRu or PtMo (25).…”

Section: Resultsmentioning

confidence: 99%

Electrocatalytic hydrogen oxidation by an enzyme at high carbon monoxide or oxygen levels

Vincent

Cracknell

Lenz

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

249

282

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Use of hydrogen in fuel cells requires catalysts that are tolerant to oxygen and are able to function in the presence of poisons such as carbon monoxide. Hydrogen-cycling catalysts are widespread in the bacterial world in the form of hydrogenases, enzymes with unusual active sites composed of iron, or nickel and iron, that are buried within the protein. We have established that the membrane-bound hydrogenase from the ␤-proteobacterium Ralstonia eutropha H16, when adsorbed at a graphite electrode, exhibits rapid electrocatalytic oxidation of hydrogen that is completely unaffected by carbon monoxide [at 0.9 bar (1 bar ‫؍‬ 100 kPa), a 9-fold excess] and is inhibited only partially by oxygen. The practical significance of this discovery is illustrated with a simple fuel cell device, thus demonstrating the feasibility of future hydrogen-cycle technologies based on biological or biologically inspired electrocatalysts having high selectivity for hydrogen.biohydrogen ͉ electron transfer ͉ energy ͉ fuel cell ͉ hydrogenase H ydrogenases prevail throughout the microbial world and are essential to hydrogen metabolism (1). X-ray crystallography in conjunction with Fourier transform infrared spectroscopy has revealed that the active site structure of the [NiFe] hydrogenases from Desulfovibrio gigas (Dg) (2) and D. vulgaris Miyazaki F (3, 4) is a bimetallic site having Ni and Fe centers linked by bridging cysteinyl S, with the Fe additionally coordinated by one CO and two CN Ϫ ligands. Crystallographic experiments on the enzyme from D. fructosovorans involving infusion of Xe have revealed the likely positions of ''gas channels'' for transport of small molecules such as H 2 , O 2 , and CO to and from the active site (5).The vast majority of hydrogenase-containing microorganisms, including the Desulfovibrio species, live under anaerobic or semianaerobic conditions, and like their hosts, the hydrogenases are usually highly sensitive to O 2 (1). However, some bacteria are able to gain energy from H 2 oxidation under aerobic conditions. A well studied example is Ralstonia eutropha (Re, formerly Alcaligenes eutrophus) strain H16 a ␤-proteobacterium that hosts three physiologically distinct [NiFe] hydrogenases (6-8). One of these enzymes, the membrane-bound hydrogenase (MBH), is coupled via a b-type cytochrome to the respiratory chain. Sequence similarity shows that this enzyme belongs to the family of [NiFe] hydrogenases having a large subunit containing the NiOFe catalytic center and a small electron-transferring subunit accommodating three iron-sulfur clusters (9). The MBH enables Re to grow on H 2 as the sole energy source even under ambient levels of O 2 . The exceptional tolerance of Re MBH to O 2 (10) inspired us to assess its electrocatalytic activity under extremely demanding conditions, including the presence of CO, which is the classic inhibitor of hydrogen-cycling catalysts (11). This inhibition is rationalized on the basis that activation of H 2 by transition metals requires it to form a bond that involves back donation ...

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Section: Resultsmentioning

confidence: 99%

Electrocatalytic hydrogen oxidation by an enzyme at high carbon monoxide or oxygen levels

Vincent

Cracknell

Lenz

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

249

282

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“…The decomposition of methanol on platinum or its alloys is the main reaction that occurs at the anodes of DMFC's; methanol chemisorbs and reacts to form CO, which is then oxidized to CO 2 . Poisoning by CO is acute for platinum surfaces, and there is a search for more CO tolerant anode catalysts [2][3][4]. Methanol can also be used for hydrogen production via steam reforming or aqueous phase reforming processes [5].…”

Section: Introductionmentioning

confidence: 99%

Prediction of Experimental Methanol Decomposition Rates on Platinum from First Principles

et al. 2006

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A microkinetic model for methanol decomposition on platinum is presented. The model incorporates competitive decomposition pathways, beginning with both O-H and C-H bond scission in methanol, and uses results from density functional theory (DFT) calculations [Greeley and Mavrikakis, J. Am. Chem. Soc. 124 (2002) 7193, Greeley and Mavrikakis, J. Am. Chem. Soc. 126 (2004) 3910].Results from reaction kinetics experiments show that the rate of H 2 production increases with increasing temperature and methanol concentration in the feed and is only nominally affected by the presence of CO or H 2 with methanol. The model, based on the values of binding energies, pre-exponential factors and activation energy barriers derived from first principles calculations, accurately predicts experimental reaction rates and orders. The model also gives insight into the most favorable reaction pathway, the rate-limiting step, the apparent activation energy, coverages, and the effects of pressure. It is found that the pathway beginning with the C-H bond scission (CH 3 OH fi H 2 COH fi HCOH fi CO) is dominant compared with the path beginning with O-H bond scission. The cleavage of the first C-H bond in methanol is the rate-controlling step. The surface is highly poisoned by CO, whereas COH appears to be a spectator species.

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“…Many electrode materials such as Pt with Sn, Ru, Pd, Os, Mo, W, Fe, and Au [3,[10][11][12][13][14][15][16][17][18] have been studied. Thus far, the most successful alloy characterized is the binary PtRu alloy catalyst, also known as a good catalyst to more effectively promote the electro-oxidation of methanol and ethanol [19][20][21][22][23].…”

mentioning

confidence: 99%

CO Tolerance of PEMFC Anodes: Mechanisms and Electrode Designs

2010

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This work presents a review of the current literature regarding the CO tolerance on PEM fuel cells feed with H 2 containing CO. From bulk metal alloys to nanoparticles, we summarize the present understanding of what is necessary to achieve the CO tolerance. A discussion is given on the tolerance mechanisms for binary Pt-alloys, emphasizing the achievements gained by using coupled techniques such as X-ray absorption spectroscopy and mass spectrometry. Together with the commonly accepted CO tolerance mechanisms, the so-called bifunctional and electronic mechanisms, alternative chemical pathways are presented as reactions that consume gas-phase CO and the role of such tolerance methods is assessed on the overall cell performance. A brief discussion on the perspective electrocatalysts and improved CO tolerance methods is given to account for the CO tolerance at higher CO contents in the H 2 stream, emphasizing the various ways to increase tolerance, whether by oxidation, reduction, or by changes in the CO adsorption/desorption properties.Proton exchange membrane fuel cells working with pure hydrogen fuel present very low anode overpotentials because of the very fast hydrogen oxidation reaction (HOR). However, if the hydrogen fed to the PEMFC is obtained by the steam reform of methanol, natural gas, or gasoline [1, 2], CO is naturally produced as a by-product, hence strongly poisoning the common Pt-based electrocatalyst used in the anode [3][4][5], greatly increasing the reaction overpotential. Therefore, understanding the CO poisoning mechanisms and eliminating its effect is of fundamental importance in electrocatalysis. CO tolerance studies are usually based on the ability of a given material to electro-oxidize H 2 in the presence of CO with an acceptable polarization loss.Considering that reversible potential for the CO electrooxidation is approximately 0.0 V vs. reversible hydrogen electrode (RHE), in theory the CO should be promptly removed from the surface at this potential along the H 2 oxidation process. However, the strong adsorption of this molecule on transition metals shifts positively, in a few hundred millivolts, the reversible potential for this reaction [6], hence making the CO removal step difficult.Studies on polycrystalline platinum at 25°C indicate that CO poisoning is due to its strong adsorption on the catalyst surface, blocking the surface active sites for H 2 adsorption and electro-oxidation. Under these circumstances, the H 2 oxidation current will originate on the surface vacancies present on the CO layer. Kinetic analyses have shown that the CO poisoning effect occurs through a free Pt site attack mechanism, involving essentially two kinds of adsorbed CO [3,5,7,8]: linear adsorbed (Eq. 1) through 5σ and 2π* orbitals overlapping with the Pt 5d surface states, where the π orbitals are involved in the back-donation process; and by bridge-type adsorption (Eq. 2), in which most likely σ bondings are involved with two neighbor Pt sites.2Pt þ CO ! Pt 2 À CO

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Development of New CO Tolerant Ternary Anode Catalysts for Proton Exchange Membrane Fuel Cells

Cited by 88 publications

References 22 publications

Electrocatalytic hydrogen oxidation by an enzyme at high carbon monoxide or oxygen levels

Electrocatalytic hydrogen oxidation by an enzyme at high carbon monoxide or oxygen levels

Prediction of Experimental Methanol Decomposition Rates on Platinum from First Principles

CO Tolerance of PEMFC Anodes: Mechanisms and Electrode Designs

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