In 1752, Benjamin Franklin attempted to catch lightning in a bottle with a kite, a key, and a Leyden jar. Whilst it wasn’t his purpose with these experiments, he would have been able to experience first-hand the difficulties in storing electrical energy in a jar. 270 years later, and researchers are attempting a similar but – thankfully for researchers like me – usually less dangerous venture: catching sunlight in a jar. With the growing role of intermittent sources of renewable energy (such as solar energy) in powering our society, there is an increasing need for energy storage to address the instantaneous mismatch between the power we generate and the amount we consume. But how can we capture the energy in sunlight and store it in a jar for when its needed?
Solar redox flow batteries (SFRBs) are a potential solution to this problem. SFRBs are devices that combine the harvesting of sunlight and storage of energy into an integrated device. Light is shone onto semiconductor-based photoelectrodes, and the solar energy captured is used to drive the same electrochemical reactions typically used in batteries. The charged-up electrolyte (the liquid containing the battery chemicals) is then stored in simple tanks; the solar energy has been stored and is ready for discharge when power is required. The current solar + storage alternative is to use solar farms and batteries tied together in national grids by sophisticated power conversion technology. Whilst this is efficient and cost effective at scale within well developed electricity grids with large appetites for power, this solution is not as well suited to communities with different needs. By directly converts sunlight into electrochemical energy SFRBs may represent a more affordable energy solution for remote communities. As well as the cheaper capital and maintenance costs, the technology opens-up further possible advantages such as using the flowing electrolytes to cool the light harvesters and provide a source of heat for buildings.
However, SFRBs have a long way to go before they are ready for everyday use. The principal challenges are improving the lifetimes of the photoelectrodes and electrolytes, improving the efficiency of converting solar to stored energy, and balancing these requirements without using prohibitively expensive materials. There is nothing new under the sun, and SRFBs are a combination of two other technologies: redox flow batteries and photoelectrochemical cells. By learning from the advances made in these parent-technologies and by borrowing solutions from other related technologies, the progress of SRFBs has been recently greatly accelerated. My PhD project aims to investigate SFRBs and push them further towards commercialisation by testing new device architectures, photoelectrodes, and electrolytes. By developing structured photoelectrodes and electrodes with surface coatings of metal oxide nanoparticles, I will try to make the storage of sunlight more affordable.
NanoDTC PhD Student, c2021