Metal-CO2 batteries closer to becoming a thing

CO2 sign. (Reference image by Gerd Altmann, Pixabay.)

A China-based team of researchers discovered an innovative way to overcome the energy efficiency issues that so far have plagued metal-carbon dioxide batteries.

In detail, the scientists introduced an unconventional phase nanomaterial as a catalyst, boosting battery energy efficiency by up to 83.8%.

In a paper published in the journal Proceedings of the National Academy of Sciences, the group explains that metal-carbon dioxide batteries can provide durable electricity (high energy density) for electronics, and enable carbon dioxide fixation without extra energy consumption from an external circuit to convert CO2 greenhouse gas emissions into value-added products.

Previous research has shown that the lithium-carbon dioxide battery has a high theoretical energy density (1876 Wh kg-1), making it a promising candidate for next-generation high-performance energy conversion and storage technology.

However, metal-CO2 batteries still suffer from sluggish reaction kinetics. This causes large over-potential, that is, more voltage or energy is required than is theoretically determined to drive the oxidation-reduction reaction that makes the battery work, low energy efficiency, poor reversibility, and limited cycling stability.

“Researchers commonly consider morphology, size, constituents and distribution of metal-based components in composite cathode catalysts to be the main concerns that lead to differences in battery performance,” Fan Zhanxi, one of the lead researchers in the project, said in a media statement. “But we found preparing novel catalysts with unconventional phases to be a feasible and promising strategy to boost the energy efficiency and performance of metal-gas batteries, especially since traditional modification strategies for catalysts have encountered long-term technical hurdles.”

Fan and his team accumulated extensive experience and knowledge related to the precise regulation of the crystal phase of metal-based nanomaterials, which enabled them to select suitable elements to construct their unconventional phases and subsequently study the effect of the crystal phase of catalysts on the reaction kinetics of a certain kind of aprotic or not involving hydrogen ions metal-gas electrochemistry.

“However, this does not mean that this process is easy to realize because it involves strict requirements on the bifunctionality of cathode catalysts in an organic environment,” Fan said.

The team synthesized iridium nanostructures with an unconventional 4H/face-centred cubic (fcc) heterophase by controlling the growth kinetics of Ir on gold (Au) templates. In their experiments, the catalyst with 4H/fcc heterophase demonstrated a lower charge plateau (below 3.61 V) and higher energy efficiency up to 83.8% during cycling in aprotic Li-CO2 batteries than other metal-based catalysts (commonly with charge potential of over 3.8 V and energy efficiency up to 75%).

The combination of experiments and theoretical calculations conducted revealed that 4H/fcc Ir nanostructures created through phase engineering are more favourable for the reversible formation of amorphous/low-crystalline discharge products, thereby lowering the overpotential and promoting the cycling stability of electrochemical redox reactions. The unusual phase 4H/fcc Ir nanostructures performed much better than common fcc Ir and achieved outstanding charge potential and energy efficiency compared to other reported metal-based catalysts used in aprotic Li-CO2 batteries.

“This study reveals the great potential of phase engineering of catalysts in metal-gas electrochemistry. It opens up a new direction to design catalysts for developing sustainable electrochemical energy conversion and storage systems,” Fan said.

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