In not such a distant future many hydrogen powered vehicles may fill the U.S. roads, but this will only happen after the issues concerning the recharging of hydrogen will have been solved. The challenge is to recharge the hydrogen quickly, safely and affordably.
Chemical hydrogen storage systems can be recharged, but the real challenge is to come up with a method that decreases the costs and increases the safety of these processes, so it can be used outside the laboratories. The current processes are based on molten sodium, which doesn’t meet the safety and cost requirements. PNNL scientists demonstrated in their early work that rhodium complexes could be used, but rhodium is far too expensive.
Dr. Tom Autrey, a chemist at PNNL who participated in the study said that “The hardest part is getting the hydrogen back onto the storage material, you can’t just pump it back in. So, we needed to develop a chemical process where we can do it cost effectively.”
Scientists from Pacific Northwest National Laboratory showed in one of their recent studies that an amine borane-based hydrogen storage system can be made from abundant and inexpensive metals.
They discovered cobalt and nickel complexes that activate hydrogen, allowing the spent fuel to be recycled. Both of these materials are common and affordable and because of this they can hold the key for efficient and cheap refueling.
“We took a rational approach—mindful of the chemistry and how it impacts the refueling process,” said PNNL chemist Dr. Michael Mock, who led the study.
Using the NWChem software, the team performed extensive electronic structure calculations to predict the reactivity of a large number of potential reaction schemes. Dr. Don Camaioni, who led the theoretical portion of the research said that the calculations let them screen targets fast. “We quickly learned what influenced reactivity and what didn’t.”
“We can’t just pressurize the spent fuel with hydrogen. You have to work with Mother Nature and use a chemical process to put the hydrogen back,” said Autrey.
After they determined the properties, benefiting from the use of resources in EMSL, the researchers focused on the synthesis of a select number of cobalt and nickel complexes. Analyzing the effectiveness of these complexes confirmed to them that they are able to perform the task at reasonable temperatures and pressures.
These tests allow the PNNL researchers to come one step closer to answering fundamental questions surrounding molecular catalysis. A greater challenge is being undertaken by Mock, in the Center for Molecular Electrocatalysis, who will soon be answering fundamental questions regarding the complex multi-electron reduction that takes nitrogen gas to ammonia for fertilizer. Camaioni and Autrey are also using the data obtained from these studies to investigate the potential of using non-metal complexes to catalytically activate hydrogen for energy storage applications.
To put it in Dr Autrey’s words, “This is a very good step forward.”