A new study has demonstrated an environmentally friendly approach to converting atmospheric carbon dioxide into batteries, improved technology that could lead to the development of electric vehicles that are carbon-neutral and also carbon-negative, therefore lessening the amount of atmospheric CO2 produced as they operate.

The study, a collaboration between Vanderbilt University and George Washington University, published in the journal ACS Central Science [Licht et al. ACS Cent. Sci. (2016) DOI: 10.1021/acscentsci.5b00400], showed how the graphite electrodes used could be replaced by carbon material from the atmosphere. The team has developed a new solar thermal electrochemical process (STEP) to convert atmospheric or smokestack CO2 into carbon nanotubes (CNTs), which can then be incorporated into advanced batteries such as lithium-ion used in electric vehicles and electronic devices as well as the more inexpensive sodium-ion batteries being developed for larger applications.

"our new electrochemical synthesis, STEP, provides a strong economic incentive to remove the greenhouse gas CO2"Stuart Licht

STEP uses solar energy to provide the electrical and thermal energy required to break down carbon dioxide into carbon and oxygen, as well as provide stable, flexible, conductive and robust CNTs. The technology helps transform the greenhouse gas CO2 into valuable products, and offers an alternative to greenhouse gas emissions from industrial and transportation fossil fuel processes. For commercial lithium-ion batteries, the CNTs could improve upon the performance of the carbon anode; for sodium-ion batteries, minor defects in the carbon (which can be tuned using STEP) were shown to offer stable and much better storage performance than those with graphite electrodes.

Both CNT batteries were exposed to the same amount of continuous charging and discharging without displaying any fatigue. They estimated that CO2 as a battery material is up to six times more valuable than when it is converted to methanol. In addition, unlike methanol, combining batteries with solar cells can offer renewable energy that involves no greenhouse emissions.

It is claimed the STEP process could be combined with a natural gas powered electrical generator to produce electricity and heat, as well as a concentrated source of CO2 to boost the performance of the STEP process. The oxygen released during the process could be returned to the generator to boost its combustion efficiency, as this would compensate for the amount of electricity that the STEP process consumes, and potentially result in a fossil fuel electrical power plant with zero net CO2 emissions. The team will also explore applications of the STEP CNTs made from CO2, including carbon composites for strong and lightweight construction materials, sports equipment and vehicle bodies.