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Solar power and other sources of renewable energy can help combat global warming but they have a drawback: they don’t produce energy as predictably as generating plants powered by oil, coal, or natural gas. Solar panels only produce electricity when the sun is shining, and wind turbines are only productive when the wind is brisk. Ideally, alternative energy sources would be complemented with massive systems to store and dispense power—think batteries on steroids. Reversible fuel cells have been envisioned as one such storage solution.
Fuel cells use oxygen and hydrogen as fuel to create electricity; if the process were run in reverse, the fuel cells could be used to store electricity, as well. But like the renewable energy sources they seek to complement, fuel cells also have a drawback: the chemical reactions that cleave water into hydrogen and oxygen or join them back together into water are not fully understood—at least not to the degree of precision required to make utility-grade storage systems practical.
Now, Professor William Chueh, a member of the Stanford Institute of Materials and Energy Sciences, working with researchers at Stanford National Accelerator Laboratory (SLAC), Lawrence Berkeley National Laboratory (LBNL), and Sandia National Laboratories (SNL), has studied the chemical reactions in a fuel cell in a new and important way. In a paper published in Nature Communications, Chueh and his team describe how they observed the hydrogen-oxygen reaction in a specific type of high-efficiency solid-oxide fuel cell.
While the fuel cell was running, the SLAC-LBNL-SNL team applied high-brilliance X-rays produced by Berkeley Lab’s Advanced Light Source (ALS) to illuminate the routes the oxygen ions took in the catalyst. Access to the ALS tool and the cooperation of the staff enabled the researchers to create “snapshots” revealing just why ceria is such a superb catalytic material: it is, paradoxically, defective. The knowledge gained from this first-of-its-kind analysis may lead to even more efficient fuel cells that could, in turn, make utility-scale alternative energy systems more practical.
“It turns out that a poor catalytic material is one where the atoms are very densely packed, like billiard balls racked for a game of eight ball,” Chueh said. “That tight structure inhibits ion flow. But ions are able to exploit the abundant vacancies in ceria. We can now probe these vacancies; we can determine just how and to what degree they contribute to ion transfer. That has huge implications. When we can track what goes on in catalytic materials at the nanoscale, we can make them better—and, ultimately, make better fuel cells and even batteries.”