17 Jul 2015
Hydrogen fuel cells promise clean cars that emit only water. Several major car manufacturers have recently announced their investment to increase the availability of fueling stations, while others are rolling out new models and prototypes. However, challenges remain, including the chemistry to produce and use hydrogen and oxygen gas efficiently. Today, in ACS Central Science, two research teams report advances on chemical reactions essential to fuel-cell technology in separate papers.
Hydrogen (H2) fuel cells react H2 and oxygen (O2) gases to produce energy. For that to happen, several related chemical reactions are needed, two of which require catalysts. The first step is to produce the two gases separately. The most common way to do that is to break down, or “split,” water with an electric current in a process called electrolysis. Next, the fuel cell must promote the oxidation of H2. That requires reduction of O2, which yields water. The catalysts currently available for these reactions, though, are either too expensive and demand too much energy for practical use, or they produce undesirable side products. So, Yi Cui’s team at Stanford University and James Gerken and Shannon Stahl at the University of Wisconsin, Madison, independently sought new materials for these reactions.
Cui’s group worked on the first reaction, developing a new cadre of porous materials for water splitting. They notably used earth abundant metal oxides, which are inexpensive. The oxides also are very stable, undergoing the reaction in water for 100 hours, significantly better than what researchers have reported for other non-precious metal materials. On the side of oxygen reduction, Gerken and Stahl show how a catalyst system commonly used for aerobic oxidation of organic molecules could be co-opted for electrochemical O2 reduction. Despite the complementary aims, the two studies diverge in their approaches, with the Stanford team showcasing rugged oxide materials, while the UW-Madison researchers exploited the advantages of inexpensive metal-free molecular catalysts. Together these findings demonstrate the power and breadth of chemistry in moving fuel-cell technology forward.
More information: The two papers will be freely available July 15, 2015, at these links:
“In Situ Electrochemical Oxidation Tuning of Transition Metal Disulfides to Oxides for Enhanced Water Oxidation” pubs.acs.org/doi/full/10.1021/acscentsci.5b00163
“High-Potential Electrocatalytic O2 Reduction with Nitroxyl/NOx Mediators: Implications for Fuel Cells and Aerobic Oxidation Catalysis” pubs.acs.org/doi/full/10.1021/acscentsci.5b00227
Did you know that there are experts who evaluate the Energy Department’s work to see if projects really are transforming clean energy economy in sectors like transportation? To gather feedback from the research community, many programs across the Department have annual merit or peer reviews where scientific experts rate projects for their value. This week from June 8 to 12, the Vehicle Technologies Office and Hydrogen and Fuel Cells Program are simultaneously holding their Annual Merit Review and Peer Evaluation Meeting in Washington, D.C., where hundreds of Energy Department-funded projects will be put to the test.
To cover almost all of the work funded by the Vehicle and Fuel Cell Technologies Offices reviewers will judge nearly 400 individual activities. The reviewers come from a variety of backgrounds, including current and former members of the vehicles industry, academia, national laboratories, and government. From back-to-back presentations to poster sessions, the days are intellectually demanding, requiring intense focus and analysis of highly technical projects.
But the valuable feedback will make the challenge worth it. Each reviewer evaluates a set of projects based on how much they contribute to or advance the Energy Department’s missions and goals. The reviewer considers the project’s breadth, depth, appropriateness, accomplishments, and potential. Considering the short and long-term benefits, he or she judges the project based on a standard set of defined metrics. Reviewers provide numeric scores and in-depth comments, creating a comprehensive project report card. After the review, the offices carefully consider the reviewers’ recommendations as they generate work plans, create long-term strategies, and formulate budgets.
Open to the public and free of charge, the Annual Merit Review and Peer Evaluation Meeting provides a great opportunity for those interested in the Energy Department’s research, development, and deployment activities in transportation to learn about the relevant programs. Merit reviews also serve two other valuable purposes: increasing transparency and building a vibrant research community.
Can’t attend? The offices will post the presentations to their websites a few weeks after the meeting. In fact, presentations from past merit reviews are available on the Vehicle Technologies Office website and the Hydrogen and Fuel Cells Program website. About three to four months after the review, the programs also post reports with the results of the review.
Because the reviews bring together breadth and depth of energy experts, they allow researchers in industry, academia, and government to learn about others’ projects. They help scientists see where their work intersects, enabling them to collaborate more effectively. They also facilitate the movement of technology from the government, labs, and universities into the private sector, which can bring them to market.
Merit and peer reviews are invaluable to the government, public and industry. They help keep projects on the right track and drive innovation forward. While the Vehicle Technologies Office and Hydrogen and Fuel Cell 2015 Annual Merit Review and Peer Evaluation meeting is only this week, it will have a positive impact for the clean energy economy of tomorrow. Find out more about the projects being reviewed by following us on Twitter with the hashtags #VTOAMR and #H2AMR.
26 Apr 2015
*** From UnderstandingNano.com ***
Catalysts are used with fuels such as hydrogen or methanol to produce hydrogen ions. Platinum, which is very expensive, is the catalyst typically used in this process. Companies are using nanoparticles of platinum to reduce the amount of platinum needed, or using nanoparticles of other materials to replace platinum entirely and thereby lower costs.
Fuel cells contain membranes that allow hydrogen ions to pass through the cell but do not allow other atoms or ions, such as oxygen, to pass through. Companies are using nanotechnology to create more efficient membranes; this will allow them to build lighter weight and longer lasting fuel cells.
Small fuel cells are being developed that can be used to replace batteries in handheld devices such as PDAs or laptop computers. Most companies working on this type of fuel cell are using methanol as a fuel and are calling them DMFC’s, which stands for direct methanol fuel cell. DMFC’s are designed to last longer than conventional batteries. In addition, rather than plugging your device into an electrical outlet and waiting for the battery to recharge, with a DMFC you simply insert a new cartridge of methanol into the device and you’re ready to go.
Fuel cells that can replace batteries in electric cars are also under development. Hydrogen is the fuel most researchers propose for use in fuel cell powered cars. In addition to the improvements to catalysts and membranes discussed above, it is necessary to develop a lightweight and safe hydrogen fuel tank to hold the fuel and build a network of refueling stations. To build these tanks, researchers are trying to develop lightweight nanomaterials that will absorb the hydrogen and only release it when needed. The Department of Energy is estimating that widespread usage of hydrogen powered cars will not occur until approximately 2020.
Fuel Cells: Nanotechnology Applications
Researchers at the University of Copenhagen have demonstrated the ability to significantly reduce the amount of platinum needed as a catalyst in fuel cells. The researchers found that the spacing between platinum nanoparticles affected the catalytic behavior, and that by controlling the packing density of the platinum nanoparticles they could reduce the amount of platinum needed.
Researchers at Brown University are developing a catalyst that uses no platinum. The catalyst is made from a sheet of graphene coated with cobalt nanoparticles. If this catalyst works out for production use with fuel cells it should be much less expensive than platinum based catalysts.
Researchers at Ulsan National Institute of Science and Technology have demonstrated how to produce edge-halogenated graphene nanoplatelets that have good catalytic properties. The researchers prepared the nanoplatelets by ball-milling graphene flakes in the presence of chlorine, bromine or iodine. They believe these halogenated nanoplatelets could be used as a replacement for expensive platinum catalystic material in fuel cells.
Researchers at Cornell University have developed a catalyst using platinum-cobalt nanoparticles that produces 12 times more catalytic activity than pure platinum. In order to achieve this performance the researchers annealed the nanoparticles so they formed a crystalline lattice which reduced the spacing between platinum atoms on the surface, increasing their reactivity.
Researchers at the University of Illinois have developed a proton exchange membrane using a silicon layer with pores of about 5 nanometers in diameter capped by a layer of porous silica. The silica layer is designed to insure that water stays in the nanopores. The water combines with the acid molecules along the wall of the nanopores to form an acidic solution, providing an easy pathway for hydrogen ions through the membrane. Evaluation of this membrane showed it to have much better conductivity of hydrogen ions (100 times better conductivity was reported) in low humidity conditions than the membrane normally used in fuel cells.
Researchers at Rensselaer Polytechnic Institute have investigated the storage of hydrogen in graphene (single atom thick carbon sheets). Hydrogen has a high bonding energy to carbon, and the researchers used annealing and plasma treatment to increase this bonding energy. Because graphene is only one atom thick it has the highest surface area exposure of carbon per weight of any material. High hydrogen to carbon bonding energy and high surface area exposure of carbon gives graphene has a good chance of storing hydrogen. The researchers found that they could store14% by weight of hydrogen in graphene.
Researchers at Stony Brook University have demonstrated that gold nanoparticles can be very effective at using solar energy to generate hydrogen from water. The key is making the nanoparticles very small. They found that nanoparticles containing less than a dozen gold atoms are very effective photocatalysts for the generation of hydrogen.
Researchers at the SLAC National Accelerator Laboratory have developed a way to use less platinum for the cathode in a fuel cell, which could significantly reduce the cost of fuel cells. They alloyed platinum with copper and then removed the copper from the surface of the film, which caused the platinum atoms to move closer to each other (reducing the lattice space). It turns out that platinum with reduced lattice spacing is more a more effective catalyst for breaking up oxygen molecules into oxygen ion. The difference is that the reduced spacing changes the electronic structure of the platinum atoms so that the separated oxygen ions more easily released, and allowed to react with the hydrogen ions passing through the proton exchange membrane.
Another way to reduce the use of platinum for catalyst in fuel cell cathodes is being developed by researchers at Brown University. They deposited a one nanometer thick layer of platinum and iron on spherical nanoparticles of palladium. In laboratory scale testing they found that an catalyst made with these nanoparticles generated 12 times more current than a catalyst using pure platinum, and lasted ten times longer. The researchers believe that the improvement is due to a more efficient transfer of electrons than in standard catalysts.
Increasing catalyst surface area and efficiency by depositing platinum on porous alumina
Allowing the use of lower purity, and therefore less expensive, hydrogen with an anode made made of platinum nanoparticles deposited on titanium oxide.
Replacing platinum catalysts with less expensive nanomaterials
Using nanostructured vanadium oxide in the anode of solid oxide fuel cells. The structure forms a battery, as well a fuel cell, therefore the cell can continue to provide electric current after the hydrogen fuel runs out.
Fuel Cells: Nanotechnology Company Directory
|QuantumSphere||Non-platinum catalyst||Reduces cost|
|MTI Micro||DMFC’s||Minimizes moving parts, reduces cost, size and weight|
|UltraCell||DMFC’s that uses an extra catalyst to convert methanol to hydrogen before reaching the core of the fuel cell||Increases power density and cell voltage|
|EDC Ovonics||Hydrogen fuel tanks using metal hydrides as the storage media||Reduce size, weight and pressure for storing hydrogen|
|Unidym||Carbon nanotube based electrodes||Improve efficiency of fuel cells by reducing resistive and mass transfer losses|
|GridShift||Hydrogen generation using nanoparticle coated electrodes||Improve efficiency of hydrogen generation by electrolysis|
|Aerogel Composite||Catalyst with platinum nanoparticles embedded in a carbon aerogel||Reduces platinum usage|
Fuel Cell Resources
California Fuel Cell Partnership
Department of Energy Hydrogen Permitting Web site
Listing of Hydrogen Fueling Station Location Worldwide