« Obama Administration proposes $4B to accelerate development and adoption of autonomous vehicles; policy update | Main | Mammoet switches Dutch operations to Shell GTL fuel » Researchers at the University of Delaware, with a colleague at the Beijing University of Chemical Technology, have developed a composite catalyst—nickel nanoparticles supported on nitrogen-doped carbon nanotubes—that exhibits hydrogen oxidation activity in alkaline electrolyte similar to platinum-group metals. An open access paper on their work is published in the journal Nature Communications. Although nitrogen-doped carbon nanotubes are a very poor hydrogen oxidation catalyst, as a support, they increase the catalytic performance of nickel nanoparticles by a factor of 33 (mass activity) or 21 (exchange current density) relative to unsupported nickel nanoparticles, the researchers reported. Owing to its high activity and low cost, the catalyst shows significant potential for use in low-cost, high-performance fuel cells, the team suggested. Polymer electrolyte membrane (PEM) fuel cells are based on two half-cell reactions: hydrogen oxidation reaction (HOR) at the anode and oxygen reduction reaction (ORR) at the cathode. Pt is the most active catalyst for both HOR and ORR; the high price of the metal (~$50 g−1) has hindered fuel cell commercialization. This, in turn, has compelled engineers to (1) work to reduce the platinum loading in the membrane assemblies and (2) find alternate, lower-cost catalysts that offer comparable performance to platinum. Although the various efforts have managed to reduce the total content of platinum-group metals (PGMs) in the state-of-the-art proton exchange membrane fuel cell (PEMFC) stacks, more than 0.137 g Pt kW−1 is still needed, the University of Delaware team said. One promising approach to reduce the cost of fuel cells is to switch the operating environment from an acidic to a basic one (that is, a hydroxide exchange membrane fuel cell, HEMFC), thus opening up the possibility of using PGM-free catalysts and other cheaper components. For the cathode of the HEMFC, some PGM-free and metal-free ORR catalysts have been developed that show comparable activity to Pt in alkaline media. However, for the anode side, only a few PGMs (for example, Pt, Ir and Pd) show adequate activity. The HOR catalyzed by Pt is very fast in acidic conditions so that a very low loading of the Pt catalyst could be used relative to the cathode side in PEMFCs. However, the HOR activities of PGMs are ~100 times slower in alkaline solutions. As a result, a much higher loading of the HOR catalyst is required (0.4 mg Pt cm−2 in a HEMFC compared with 0.03 mg Pt cm−2 in a PEMFC) to achieve similar performance. Thus, it is highly desirable to develop PGM-free anode catalysts for the HOR in alkaline electrolyte. Unlike its reverse reaction (hydrogen evolution reaction, HER), only a few PGM-free HOR catalysts have been reported. One possibility is to use Raney Ni as the HOR catalyst in liquid alkaline fuel cells. However, it is functional only under very high alkalinity (6 M KOH) while the activity remains low. It is not catalytically active for a HEMFC, which can be mimicked as 0.1–1 M KOH. Efforts have been made to improve the HOR activity of the Ni-based catalyst in the last decade. Ni alloys, such as NiMo and NiTi, have been shown to enhance the HOR activity. Our recent work has also shown that electrochemically deposited NiCoMo on an Au substrate has a high HOR activity. Zhuang and co-workers decorated Ni particles with CrOx to weaken the Ni–O bond and stabilize the Ni catalysts. A HEMFC incorporating this PGM-free catalyst has been fabricated, and it exhibits a peak power density of 50 mW cm−2. Although the power density is still low (compared with the peak power density of more than 1,000 mW cm−2 for PEMFCs), it demonstrates the possibility to fabricate low-cost PGM-free fuel cells. However, their activities are still incomparable with PGM-based catalysts. In the Nature Communications study, the team synthesized Ni nanoparticles supported on N-doped carbon nanotubes (Ni/N-CNT) using a wet chemical method. The nanotubes are not only the support for the Ni nanoparticles, but also a promoter for the catalytic activity. Using density functional theory (DFT) calculations to understand the interaction between the Ni nanoparticle and the N-CNT support, the team found that, when nitrogen dopants are present at the edge of the nanoparticle, the Ni nanoparticle is stabilized on the support and locally activated for the HOR because of modulation of the Ni d-orbitals. The experimental work was supported by the ARPA-E program of the US Department of Energy under Award Number DE-AR0000009. The computational work was financially supported by the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001004. Stephen Giles was supported by a fellowship from the University of Delaware Energy Institute. The research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Abstract: "Planes, Trains and Automobiles" is a popular comedy from the 1980s, but there's nothing funny about the amount of energy consumed by our nation's transportation sector. This sector -- which includes passenger cars, trucks, buses, and rail, marine, and air transport -- accounts for more than 20 percent of America's energy use, mostly in the form of fossil fuels, so the search is on for environmentally friendly alternatives. The two most promising current candidates for cars are fuel cells, which convert the chemical energy of hydrogen to electricity, and rechargeable batteries. The University of Delaware's Yushan Yan believes that fuel cells will eventually win out. "Both fuel cells and batteries are clean technologies that have their own sets of challenges for commercialization," says Yan, Distinguished Engineering Professor in the Department of Chemical and Biomolecular Engineering. "The key difference, however, is that the problems facing battery cars, such as short driving range and long battery charging time, are left with the customers. By contrast, fuel cell cars demand almost no change in customer experience because they can be charged in less than 5 minutes and be driven for more than 300 miles in one charge. And these challenges, such as hydrogen production and transportation, lie with the engineers." Yan is prepared to address the biggest challenge fuel cells do face -- cost. He and colleagues recently reported a breakthrough that promises to bring down the cost of hydrogen fuel cells by replacing expensive platinum catalysts with cheaper ones made from metals like nickel. The work is documented in a paper published Jan. 14 in Nature Communications. The researchers achieved the breakthrough by switching the operating environment from acidic to basic, and they found that nickel matched the activity of platinum. "This new hydroxide exchange membrane fuel cell can offer high performance at an unprecedented low cost," Yan says. "Our real hope is that we can put hydroxide exchange membrane fuel cells into cars and make them truly affordable -- maybe $23,000 for a Toyota Mirai. Once the cars themselves are more affordable, that will drive development of the infrastructure to support the hydrogen economy." ### About the research The experimental work was supported by the ARPA-E program of the U.S. Department of Energy under Award Number DE-AR0000009. The computational work was financially supported by the Catalysis Center for Energy Innovation, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001004. Stephen Giles was supported by a fellowship from the University of Delaware Energy Institute. The research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Vlachos D.G.,University of Delaware |
Vlachos D.G.,Catalysis Center for Energy Innovation |
Chen J.G.,University of Delaware |
Chen J.G.,Catalysis Center for Energy Innovation |
And 6 more authors.
Catalysis Letters | Year: 2010
Production of energy and chemicals from biomass is of critical importance in meeting some of the challenges associated with decreasing availability of fossil fuels and addressing global climate change. In the current article, we outline a perspective on key challenges of biomass processing. We also introduce the Catalysis Center for Energy Innovation (CCEI), one of the 46 Energy Frontier Research Centers established by the Department of Energy in the spring of 2009, and CCEI's overall research strategies and goals along with its cross-cutting research thrusts that can enable potential technological breakthroughs in the utilization of biomass and its derivatives. The center focuses on developing innovative heterogeneous catalysts and processing schemes that can lead to viable biorefineries for the conversion of biomass to chemicals, fuels, and electricity. In order to achieve this goal, a group of over twenty faculty members from nine institutions has been assembled to bring together complementary expertise covering novel materials synthesis, advanced characterization, multiscale modeling, surface science, catalytic kinetics, and microreactors. © 2010 Springer Science+Business Media, LLC. Source
Do P.T.M.,Catalysis Center for Energy Innovation |
Do P.T.M.,Honeywell |
McAtee J.R.,University of Delaware |
Watson D.A.,University of Delaware |
Lobo R.F.,Catalysis Center for Energy Innovation
ACS Catalysis | Year: 2013
The reaction of 2,5-dimethylfuran and ethylene to produce p-xylene represents a potentially important route for the conversion of biomass to high-value organic chemicals. Current preparation methods suffer from low selectivity and produce a number of byproducts. Using modern separation and analytical techniques, the structures of many of the byproducts produced in this reaction when HY zeolite is employed as a catalyst have been identified. From these data, a detailed reaction network is proposed, demonstrating that hydrolysis and electrophilic alkylation reactions compete with the desired Diels-Alder/dehydration sequence. This information will allow the rational identification of more selective catalysts and more selective reaction conditions. © 2012 American Chemical Society. Source
Lee W.-S.,University of Minnesota |
Lee W.-S.,Catalysis Center for Energy Innovation |
Wang Z.,University of Minnesota |
Wang Z.,Catalysis Center for Energy Innovation |
And 6 more authors.
Catalysis Science and Technology | Year: 2014
Vapor phase hydrodeoxygenation (HDO) of furfural over Mo2C catalysts at low temperatures (423 K) and ambient pressure showed high/low selectivity to CO bond/C-C bond cleavage, resulting in selectivity to 2-methylfuran (2MF) and furan of ~50-60% and <1%, respectively. Efficient usage of H2 for deoxygenation, instead of unwanted sequential hydrogenation, was evidenced by the low selectivity to 2-methyltetrahydrofuran. The apparent activation energy and H2 order for 2MF production rates were both found to be invariant with furfural conversion caused by catalyst deactivation, suggesting that (1) the measured reaction kinetics are not influenced by the products of furfural HDO and (2) the loss of active sites, presumably by formation of carbonaceous species observed by TEM analysis, is the reason for the observed catalyst deactivation. The observed half order dependence of 2MF production rates on H2 pressure at different furfural pressures (~0.12-0.96 kPa) and the 0-0.3 order dependence in furfural pressure support the idea of two distinct sites required for vapor phase furfural HDO reactions on Mo2C catalysts. The invariance of 2MF production rates normalized by the number of catalytic centers assessed via ex situ CO chemisorption suggests that metal-like sites on Mo2C catalysts are involved in selective HDO reactions. © 2014 the Partner Organisations. Source