A trip to California to tour the Sandia National Lab in Livermore and HRL Laboratories in Malibu proved two things about the state and the state of the so-called hydrogen economy: (1) hybrid vehicles have a long way to go before they outnumber SUVs on the roadways, and (2) hydrogen storage breakthroughs are still on the horizon. The GM-funded research at these two West Coast facilities is, however, getting closer to a workable solution to the problem of hydrogen storage for fuel cell-powered vehicles.
The general belief is that the real on-board storage solution lies in the use of containers filled with highly powdered metal hydrides to which hydrogen bonds during refueling. "Metal hydride tanks are smaller, operate at lower pressures, and can store much more hydrogen than high-pressure carbon fiber containers," says Chris Moen, manager, Engineering Science and Technology Dept., Sandia National Labs. Sandia’s role is to work with GM to develop the engineering tools required to design automotive metal hydride storage systems, and solve the associated thermal management issues that arise. Because the hydrogen binds with the metal hydrides, heat—and lots of it—is required to release the hydrogen.
Experiments with sodium alanate—a prototypical hydride that behaves like materials with a higher storage capability that are under investigation at HRL—have allowed researchers to study the engineering properties of storage materials and container design, and compare these to simulations and models. "Some of the questions this work will answer are: how large the storage bed has to be for a given fuel cells, how quickly the tank can be filled, what heat removal rates are required to make this happen, and how start-up and peak demands can be met," says Moen.
"We are creating the design tools and gaining the expertise needed to design hydride beds for future storage tanks," says Jim Spearot, director, Chemical and Environmental Sciences, GM R&D, "and refining the solid-phase storage material requirements." This will lead to building and testing a full-size metal hydride storage tank using sodium alanate or a higher performance material in the near future. According to Spearot, five different storage options covering as many as 15 material systems are currently under detailed investigation with many more to be evaluated.
The hydrogen storage research at HRL Laboratories is focused on destabilizing light metal hydrides so that they more easily release the hydrogen. Its proof of concept lithium hydride silicon system, for example, uses silicon as the destabilization element (i.e., the silicon lessens the energy needed to liberate the hydrogen from its bonds with the lithium, but is not consumed in the reaction), "and lowers the temperature necessary to release the hydrogen by 400ºC," says Leslie Momoda of HRL Labs. With more than 100 chemical reactions to model, Momoda is confident her team will find the compound that meets GM’s requirements for a high-weight-percentage storage of hydrogen in a compact vessel, one that requires a low energy investment to store and remove the hydrogen. Additional research is necessary in ways to reduce refueling times to five minutes or less. This research also holds the potential to lower hydrogen release time.
"Once you have the technology, how do you drive the transformation of the industry?" asks Larry Burns, v.p., R&D and Strategic Planning at GM. "Waiting decades won’t work, because it’s not a good use resources." Burns—through the research conducted at Sandia, HRL, GM, and elsewhere—hopes to manage the process such that the route to that transformation is no more than 10 years away; a goal that gets closer with each advance made by researchers. It is still too early, however, to define just when that horizon will be reached, even in California.—CAS