Batteries that breath air are a possible future for electric vehicles, as they might significantly cut the weight of energy storage.

Called metal-air batteries, during discharge they react a metal (lithium, zinc, magnesium or aluminium, amongst other options) with oxygen from the atmosphere to deliver energy. During charge, they emit the oxygen.

A catalyst is required to get oxygen to cooperate during both charge and discharge, and Korean university UNIST has created a one that avoids the need for expensive metals like platinum.

It comes in the form of a thin layer of metal oxide films that self-construct on the surface of a less-well-performing perovskite catalyst. “The interface naturally formed between the two catalysts enhances the overall performance and stability of the new catalyst,” according to the university.

In detail, a cobalt oxide catalyst (Co3O4), which performs well in charging, is atomic-layer deposited on a manganese-based perovskite catalyst known as LSM (La0.5Sr0.5MnO3) which performs well in discharge.

As it is done, through manganese (Mn) diffusion from the perovkite, a third material (MnCo2O4 with a ‘spinel’ crystal structure) spontaneously grows under the cobalt oxide (see diagram).

“During the repeated deposition and oxidation cycles of atomic layer deposition process, the Mn cations diffuse into Co3O4 from LSM, and therefore, the catalyst is composed of LSM encapsulated with the self-reconstructed spinel interlayer [Co3O4/MnCo2O4/LSM],” according to UNIST chemical engineer Arim Seong. “And this has enhanced the catalytic activitiy of the hybrid catalyst, leading to superior electrochemical performances in alkaline solutions.”

The hybrid catalyst has been dubbed ‘LSM-20-Co’, and it was tried out in an alkaline zinc-air cell.

“To the best of our knowledge, this is the first study to investigate the self-reconstructed interlayer induced by the in-situ cation diffusion during ALD process for designing an efficient and stable bi-functional catalyst for alkaline zinc-air batteries,” according to the research team.

“Our findings provide the rational design strategy of self-reconstructed interlayer for efficient electro-catalyst,” said fellow engineer Professor Guntae Kim. “Therefore, this work can provide insight into the rational design strategy of metal oxide with perovskite materials.”

UNIST worked with the University of Pennsylvania.

The work is published as “Self-reconstructed interlayer derived by in-situ Mn diffusion from La0.5Sr0.5MnO3 via atomic layer deposition for an efficient bi-functional electrocatalyst” in Nano Energy.

For the electrochemically inclined, according to the paper: “the LSM-20-Co catalyst showed comparable Tafel slope for both the ORR (65mV/dec) and OER (82mV/dec) comparing with the Pt/C (58mV/dec) and IrO2 (114mV/dec), along with stable cycling performance over 450 min for alkaline zinc-air battery.”