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New Advances in Hydrogen Fuel Catalysts

Hydrogen has great potential as a fuel of future because it is an environmentally clean energy fuel and save us from the undesirable side effects of greenhouse gases. Before becoming it a fuel of the masses we need necessary infrastructure to store it and move it. We will also need fuel cells on economical scale. To make hydrogen as a popular alternative fuel some engineers are working on storage factor of hydrogen fuel. They don’t want compressed hydrogen into a tank. They want to store hydrogen fuel into a large molecule. When we want hydrogen out of the molecule we will need a catalyst. Now, researchers have new details about one such catalyst.

Scientists from the Department of Energy’s Pacific Northwest National Laboratory are working on catalysts. They are finding out the characteristics of the catalyst which are a cluster of rhodium, boron and other atoms. The catalyst chemically reacts with ammonia borane to release the hydrogen as a gas. Ammonia borane is a molecule that stores hydrogen densely. PNNL chemist and study author Roger Rousseau shares his thoughts, “These studies tell us what is the hardest part of the chemical reaction. If we can find a way to change the hard part, that is, make it easier to release the hydrogen, then we can improve this catalyst.”

Researchers and engineers are figuring out the hydrogen storage system that is safe and discharges hydrogen easily. They are “storing” hydrogen as part of a larger molecule. Ammonia borane contains hydrogen atoms and serves as structural hold-on. The catalyst’s job is to extract the hydrogen from the ammonia borane.

The PNNL chemists in the Institute for Interfacial Catalysis are banking on the rhodium-based catalyst. The scientists are working on various structural combinations that can give maximum output. Right now they are trying various shapes such as tetrahedron, or a triangular pyramid with four rhodium atoms at the core. To arrive at the ideal combination they are trying both theory and experimental work.

They employed several methods for ammonia borane reaction. They used one unusual technique operando XAFS. They X-rayed the catalysts in action instead of the usual standstill X-ray. They carried out some different experiments too in EMSL, DOE’s Environmental Molecular Sciences Laboratory on the PNNL campus. They collected important data but they require exhaustive analysis before they can make any sense. The research team used computer models to solve this data puzzle so that they can construct a theoretical molecular configuration that accounted for all the data. These computationally challenging models were calculated on computers at the National Energy Research Scientific Computing Center at Lawrence Berkeley National Laboratory in Berkeley, California.

The computer model created a structure that best integrated the experimental data. They tested the authenticity of the data too with computer simulation with the help of an operando XAFS analysis of the catalytic structure reacting with ammonia borane. The next logical step was to compare the simulated data with real data of the catalyst. The two sets of data didn’t have much difference.

The chemical character of the structure and supplementary experimental data helped the team to chart the chemical reaction occurring between the catalyst and the ammonia borane. The catalyst is always in the state of a motion so it is difficult to spot but nonetheless it is a good catalyst.

How this catalyst actually works? First it marks out hydrogen from the ammonia borane molecule. This ammonia borane consists of a nitrogen atom in the molecule holding onto two hydrogen atoms. First, the catalyst picks out one hydrogen atom. This is the hardest part of the reaction. This first step makes the bond between the remaining hydrogen and boron unstable. Now plucking off the second hydrogen atom becomes easier. Same holds true for the last two hydrogen atoms. These hydrogen atoms can be utilized in engines or fuel cells.

The team has yet to figure out the additional details but this study makes a big dent in what they need to know to design a good, inexpensive catalyst. Rousseau elaborates, “An important part about this work is that we have these kinds of DOE teams where we can start with experiments and go to theory and back again. We get a lot more information this way than doing either one alone.”

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