The need for a sustainable alternative to fossil fuels has never been more pressing. Not only does the burning of fossil fuels emit harmful greenhouse gases that drive global warming, the world is currently facing an energy crisis, with many unable to afford to pay the high price for oil and gas. If we want to meet the goals outlined during COP26 (the global climate change summit that took place in Glasgow in 2021) to achieve net zero carbon emissions by 2050 and limit global warming below 1.5 degrees relative to pre-industrial levels, we must increase efforts to find alternative, cheap, sustainable technologies for fueling modern society.
Luckily, versatile, sustainable, electricity-generating and fuel-making factories already exist – in the form of bacteria! Cyanobacteria are abundant, photosynthetic microorganisms that are capable of sustaining themselves using sunlight and water alone – two of the most abundant resources on earth. The advantage of using microorganisms as fuel-forming catalysts is that they are capable of self-repair and reproduction and therefore can theoretically be used to produce fuels indefinitely. If we can find a way to take advantage of these natural fuel factories, this will pave the way for a sustainable future.
The caveat is that cyanobacteria have not evolved to produce fuels for human consumption but rather for their own survival. Thus, only a fraction of the high energy electrons generated during photosynthesis are fed into fuel-forming pathways, resulting in low solar-biomass conversion efficiencies. That being said, cyanobacteria do exhibit a phenomenon called exoelectrogenesis whereby electrons derived from photosynthesis are exported out of the cell. This means we can use them for electricity generation by interfacing them with electrodes.
The main limitation of systems involving cyanobacteria-based electrodes at present is their weak exoelectrogenic activity so only small currents can be generated. This is mainly attributed to membranous systems that encapsulate the photosynthetic catalysts and form a boundary between the photo-generated electrons and the electrode surface.
The first aim of my project is to boost photocurrent outputs of cyanobacteria-based electrodes by improving the electrochemical communication at the bacteria-electrode interface. I am approaching this by using redox-active or conductive polymers to “wire” the bacteria to the electrode surface. These polymers act as an electron conduit to facilitate electron transfer from the bacteria to the electrode. This strategy has been implemented to boost current outputs from an array of biocatalysts from enzymes to whole cells on electrodes. However, the cell-polymer-electrode interface is complex and often not well-understood, limiting rational interface design.
The second part of my project involves coupling exoelectrogenesis of photosynthetic microorganisms to a fuel-generating reaction at another electrode. Using cyanobacteria-based electrodes to generate electricity which is then fed into the fuel-forming pathway of another type of microorganism (with high electricity-fuel conversion efficiencies) would provide a sustainable way of harnessing energy from the sun and storing it in chemical bonds.
NanoDTC Associate, a2021