Kristina Wedege is a PhD student from the Department of Engineering at Aarhus University in Denmark, where she also did her MSc. in Chemical and Biological Engineering. In Denmark, more than 40% of the electricity is generated by renewable sources, but the security of electricity supply remains high, which causes her research interests to mainly include energy storage technologies and materials engineering for the future green energy transition. She is expected to finish her PhD on the subject of organic, aqueous batteries for solar energy storage in the middle of 2018.
In one hour the radiation from the sun supplies about the total annual energy consumption on Earth. Being our most abundant source of energy, naturally there is enormous interest in developing technologies to both harvest and store solar energy, so that supply and demand can be balanced safely and efficiently in a future all-renewable energy system. Semiconductors – or photoelectrodes in this context – can be applied to this purpose, because the energy of light can be converted directly into electricity (the photovoltaic effect) as evidenced by the immensely growing number of solar cells currently being installed worldwide. However, solar cells do not have the build-in functionality to store the photogenerated electricity, which is a major problem in terms of grid stability. To remedy this, since the 1970s immense research effort has been put into developing materials and systems for photoelectrochemical water splitting; ultimately with the aim to produce hydrogen and oxygen gas to be used in fuel cells and thereby achieve the desired time-delay from photovoltaic energy production to consumption. However, the photoelectrochemical water splitting reaction is very challenging to drive, due to both high thermodynamic and kinetic required photopotential of the photoelectrodes. Additionally, hydrogen can be difficult to safely store and transport.
Another approach is to use the semiconductors to carry out electrochemical reactions with better kinetics and less required potential, thereby converting the electricity to readily useful chemical energy (the solar fuel approach). In this project, we use semiconductors originally developed for water splitting to photoelectrochemically charge liquid state batteries i.e. redox flow batteries. Flow batteries are an emerging type of battery, which is useful in stationary applications, such as in energy neutral buildings, due to a relatively low cost and low energy density. Electroactive compounds in aqueous solution are stored in external tanks and pumped through electrochemical flow cells when charging and discharging is necessary, thus decoupling the power and capacity of the system. The combination of suitable semiconductors with suitable flow battery chemistries could result in simple photovoltaic energy harvesting+storage systems, potentially of very low cost. In this talk, two experimental proof-of-concept studies are presented and discussed.
Audience Take away:
• Insight into the new and expanding research field of solar flow batteries.
• Increased understanding of the imminent energy storage challenge for the transition to renewable energy.
• Inspiration for alternative use of semiconductor materials.