Perovskites have shaken up the photovoltaics field. Perovskite are materials with an ABX₃ structure, and methylammonium, lead, and iodide have been the most common picks for the three components in photovoltaic perovskites. Now, researchers 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.

Fuel cells, which convert chemical energy in fuels such as hydrogen into electricity, are touted to be a clean and efficient way to power cars and portable electronics. They contain an anode and cathode separated by an electrolyte. Hydrogen fed into the anode splits into electrons and protons. The protons flow through the electrolyte and the electrons go through an outer circuit to meet the protons at the cathode.

Solid-oxide fuel cells are 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. “When you expose them to low pressure, almost all materials start to lose oxygen and become electron conductors,” says Shriram Ramanathan, a materials scientist at Purdue University. “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.”

Ramanathan, his postdoc You Zhou, and colleagues 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. “It’s very unusual to see such extraordinary changes in conductivity in this class of materials at room temperature,” Ramanathan says.

Zhou made freestanding membranes of the material and found that they had high ionic conductivity. So, unlike conventional solid electrolytes such as yttrium-doped zirconia, samarium nickelate becomes better at shutting out electrons while still allowing ions to pass through in a hydrogen fuel environment, Ramanathan explains.

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, he says. “And it hasn’t been optimized yet so it can go a long way with more development.” The perovskite membrane should be easy to make in large quantities, making it very robust for practical applications, he says.

The use of strong electron correlations to control electron flow is a new concept, says Ho Nyung Lee, a materials scientist at Oak Ridge National Laboratory. The millions-fold suppression of electron-conduction is a “dazzling surprise,” he says. “This study provides new design strategies for developing low-temperature solid-oxide fuel cells.”

Read the abstract in Nature.Nature.