Before they can replace fossil fuels entirely, wind and solar power plants will need to provide electricity to the grid at all times of the day, and in unpredictable weather conditions. To ensure a consistent output, renewable sources can be coupled with energy-storing batteries. Ideally, these batteries can be charged up when excess energy is generated, and then release their energy when the grid’s demand for power outpaces its supply. However, even the most well-designed battery systems only have a limited storage capacity. If this limit is exceeded, any excess energy will simply be wasted. One possible solution to this problem is to combine electrical batteries with chemical energy storage. Read More
In particular, ‘electrochemical reduction’ reactions could use renewable electrical energy to convert carbon dioxide into other molecules that store energy in their chemical bonds. In regular electrochemical reduction reactions, electrons are transferred directly from an electrode to carbon dioxide molecules close to its surface. This ‘reduces’ the carbon dioxide molecules, priming them for chemical reactions that convert them into useful products.
For the first time, Professor Kathryn Toghill and her colleagues at Lancaster University have successfully ‘de-coupled’ the electrochemical reduction of carbon dioxide from an electrode’s surface. Their method drastically transforms the nature of the catalytic reaction, and could offer a promising new approach to renewable energy storage.
When an electrochemical reduction reaction is de-coupled, different ‘go-between’ molecules gain electrons from the electrode instead. These electrons are then transferred to a dispersed catalyst, which itself triggers the reduction of carbon dioxide molecules. A dispersed catalyst is not constrained to a two-dimensional surface, and does not need to be electrically conductive, potentially making the system more easily scalable than conventional electrolysers.
These ‘go between’ molecules are also the basis of energy storage in redox flow batteries, which when combined with this technology would create a single system capable of storing, releasing, and transforming energy.
To initiate this reaction, Professor Toghill’s team carried out a detailed study exploring different catalysts, to identify the most efficient catalyst material. In their experiments, they tested materials including copper, gold, and molybdenum carbide.
At first, these reactions mainly produced hydrogen, with minor yields of carbon dioxide reduction products. But when the researchers introduced a bismuth catalyst, the performance drastically improved. With optimisation, 85% of the reaction products were a carbon-based molecule named formic acid.
This molecule is especially well-suited for chemical energy storage, as it is liquid at room temperature, and does not require high-pressure storage containers. In addition, formic acid can be easily converted back into carbon dioxide – releasing its stored energy when required.
The team’s research demonstrates the electrochemically decoupled reduction of carbon dioxide for the very first time. This alternative solution to energy storage could allow renewable energy plants to capture and store their excess energy with greater flexibility in the face of intermittent weather. With some further improvements, the team’s approach may ultimately help to accelerate the rollout of renewable energy technologies, bringing the global goal of net-zero carbon emissions one step closer to reality.
