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Novel membrane-free Mg-CO2 battery sequesters CO2 and generates electricity

Researchers at the Ulsan National Institute of Science and Technology (UNIST) have designed a membrane-free (MF) Mg-CO2 battery as an advanced approach to sequester CO2 emissions by generating electricity and value-added chemicals without any harmful by-products. A paper on the work is published in the journal Nano Energy.

Unlike existing aqueous metal-CO2 systems, the new battery is not only easier to manufacture, but also allows continuous operation with one type of electrolyte.

The newly-developed MF Mg-CO2 battery operates based on the indirect utilization of CO2 with facile hydrogen generation process, which leads to electrochemical performance of 64.8 mW cm−2 with a high Faraday efficiency (>92.0%). Over the 80 discharge-charge cycles, the outstanding cycling performance with the generation of triple gases, e.g., H2(g) under discharge and O2/Cl2(g) under charge mode, was attained without any degradation.

—Kim et al.


Schematic configuration and operation principle for each battery system from organic to membrane-free battery. Credit: UNIST

The MF Mg-CO2 battery system has a structure similar to that of hydrogen fuel cells for use in cars, since it only requires a Mg-metal negative electrode, an aqueous electrolyte, and a positive-electrode catalyst. However, unlike the existing fuel cells, they are based on aqueous electrolytes. As a result, the newly-developed MF Mg-CO2 battery had successfully sequestered CO2 emissions by generating electricity and value-added chemicals without any harmful by-products.


(a) Schematic illustration of MF Mg-CO2 battery. (b) The XRD profile of the precipitated white solid after discharge process in CO2 sat’d condition and N2 sat’d condition.

Our findings indicate great benefits for the newly-developed MF Mg-CO2 battery technology to produce various value-added chemicals of practical significance and electricity from CO2 without any wasted by-products. Through this we have opened the door to electrochemical utilization of CO2 with indirect circulation for future alternative technologies.

—Kim et al.


  • Jeongwon Kim, Arim Seong, Yejin Yang, Sangwook Joo, Changmin Kim, Dong Hyup Jeon, Liming Dai, Guntae Kim (2021) “Indirect surpassing CO2 utilization in membrane-free CO2 battery,” Nano Energy doi: 10.1016/j.nanoen.2020.105741



Can someone explain to me why this is not heaven?
I've been let down before! ;-)

The only thing I have spotted is during the charge mode there is O2/CI2 generated.

Wiki says:

' Chlorine peroxide (also known as dichlorine dioxide or ClO dimer) is a molecular compound with formula ClOOCl.[1] Chemically, it is a dimer of the chlorine monoxide radical (ClO·). It is important in the formation of the ozone hole.[2] Chlorine peroxide catalytically converts ozone into oxygen when it is irradiated by ultraviolet light.[3] '


Is there enough info there to calculate the round trip efficiency?


What is missing is the energy that is required to generate the magnesium. There is no magic. All chemical reactions (and all mechanisms) involve a loss of energy somewhere. Otherwise you could build a perpetual motion machine.


This is very interesting research in Metal-CO2 batteries.
"the newly-developed MF Mg-CO2 battery technology to produce various value-added chemicals of practical significance and electricity from CO2 without any wasted by-products."
There is a lot of research in Metal-CO2 batteries (Metal - K, Li, Na, Zn, Al now Mg) with various byproducts (methane, H2, etc.). These rechargeable batteries are energy dense and have high Faraday efficiency (>92.0% in this case).
No commercial application yet and you can read some detail here about a Li-CO2 battery. ("A Long-Cycle-Life Lithium–CO2 Battery with Carbon Neutrality", DOI: 10.1002/adma.201902518,


I had written quite an extensive post here, trying to work out or at least give the parameters of energy efficiency, but I managed to wipe it somehow.

On further consideration I find I do not have the basic tools to work out anything much.

There are two routes here, one the energy needed to turn magnesium ore into magnesium, and the other to reverse the process in the cell, and turn MgCo3 powder back into magnesium so that the reaction can run for another cycle.

MgCO3 is ideal to capture and permanently sequester CO2, as it will be retained for geologically long time.

But if the aim is to use it as a reversible battery, presumably it gets reused.

I have not been able to put useful figures on any of the reactions involved.

Hopefully some folk here much more clever than I will be able to make inputs!


At high temperatures MgCO3 decomposes to magnesium oxide and carbon dioxide

yoatmon publication 326481848_Research_Progress_of_Metallic_Carbon_Dioxide_Batteries

"Metal carbon dioxide batteries have developed rapidly in recent years. Li-CO2 batteries exhibit an extremely high discharge capacity of 17625 mAh/g and a cut-off capacity of 1000 mAh/g at a current density of 100 mA/g, running for 100 cycles at low over-potentials. Quasi-solid state Na-CO2 batteries are non-flammable and have strong electrolyte-locking capabilities. They can run 400 cycles at 500 mA/g with a fixed capacity of 1000 mAh/g in pure CO2. Their electro-chemical performance offers potential for further improvement. Al-CO2 battery has good application prospects and economic benefits due to the low cost of Al as well as great economic value of the sodium aluminate as discharge product. Mg-CO2 battery shows a discharge voltage plateau of 0.9 V when the volume ratio of CO2/O2 is 1:1, which is higher than that of pure O2."


Maybe good for some small niche, but it's best not to make CO2 and then spend money to sequester it. Law of Entropy!


Store CO2 in spent NG wells, create pipelines, make a market.

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