Researchers at Purdue University have found that nickel-based perovskites have exceptional properties for use as solid electrolytes in fuel cells. Unlike conventional electrolytes, these nickel-based perovskites are chemically stable in the fuel cell's environment, which could lead to higher performing and longer lasting fuel cells.
Schematic of the perovskite samarium nickelate (SNO)-electrolyte solid-oxide fuel cell.
Solid-oxide fuel cells are considered as one of the most efficient types of fuel cells. They typically use polymers or ceramics as an electrolyte, but finding an effective solid electrolyte'one that conducts protons but blocks electrons'at low operating temperatures of 300'500°C has been a challenge. Most materials, when exposed to low pressure, start to lose oxygen and become electron conductors; The electrolyte separator becomes leaky so it can short circuit the fuel cell or it can start to crack and allow fuel to mix with oxygen.
The researchers used samarium nickelate (SmNiO3) as the fuel cell electrolyte instead of the typically used yttria-stabilized zirconia. This oxide has a perovskite crystal structure, and conducts protons and electrons on its own. It also has a strongly correlated electron system, in which electrons interact with each other and influence the material's properties. The researchers found that when samarium nickelate is exposed to hydrogen, an electron from the hydrogen atom gets incorporated into the nickel atom's orbital. This restructuring of the electron arrangement suppressed the electron conductivity by a factor of almost a billion.
They made freestanding membranes of the material and found that they had high ionic conductivity. So, unlike conventional solid electrolytes, samarium nickelate becomes better at shutting out electrons while still allowing ions to pass through in a hydrogen fuel environment.
According to the team, fuel cells made with the samarium nickelate membrane had an output power of 225 mW/cm2, which is comparable to the best-performing proton-conducting fuel cells. And these cells have not been optimized yet so it can go a long way with more development. The perovskite membrane should, said the team, be easy to make in large quantities, making it very robust for practical applications.
