The United States Department of Energy has invested $100 million in the development of artificial photosynthesis. This technology takes inspiration from the process through which plants convert sunlight, carbon dioxide, and water into
energy in order to produce clean and sustainable fuels.
Over the past 50 years, global carbon dioxide emissions have risen by 90%, with fossil fuels contributing to 78% of this increase. In 2020 alone, almost 35 billion tonnes of carbon dioxide (CO2) were produced from burning fossil
fuels,
compared to only six billion in 1950.
Former United States Secretary of Energy, Dr Steven Chu, visiting Berkeley Lab, a Department of Energy laboratory working on artificial energy. | Berkeley Lab / Flickr
Our overreliance on non-renewables is unsustainable. It contributes to the ever-growingly damaging effects of climate change that are mediated by greenhouse gases such as carbon dioxide, and these resources, as their name
suggests, are
bound to eventually run out.
Thus, we are faced with an urgent need to shift to renewable energy production methods, and one of the best ways to do this is to employ biomimetic: taking inspiration from nature.
For 500 million years, plants have been thriving self-sufficiently through photosynthesis. This process consists of plants absorbing sunlight through chlorophyll molecules, in order to convert carbon dioxide into glucose.
The process also involves the splitting of water into hydrogen and oxygen (photolysis), which provides the concentration gradient needed to produce energy from the reaction. Whilst this is an impressive jigsaw of well-fitting pathway
components, natural photosynthesis is not an optimal process.
‘Natural photosynthesis is not an optimal process.’
For example, black leaves rather than green would allow for the absorption of all light waves, resulting in more light being absorbed. Furthermore, plants only convert sunlight to energy with a 2% efficiency rate, whereas to be economically
feasible, artificial photosynthesis harnessed by man must reach at least 5% to 10% efficiency. Therefore, the ideal scenario for scientists would be to adapt and optimise photosynthesis for human use.
A technology harnessing the energy of the sun to make electricity already exists: solar power. However, a major challenge associated with photovoltaic cells is their reliance on the weather, as energy can only be harnessed during the day
and with favourable weather conditions.
Similarly, our society still relies on machinery needing fuel, not electricity, such as planes and most cars. Therefore, there is a need to design a novel system enabling the production of fuels from sunlight which can also be stored when
light is absent.
Solar power station in Gars am Kamp, Austria. | Raphael Cruz / Unsplash
Artificial photosynthesis mimics the basics of energy production in plants, whilst aiming to optimise the process. It consists of three main components: a light absorption mechanism, a catalysis step (i.e. the chemical breakdown of water
and carbon dioxide into fuels), and a tool to link it together, known as a photocatalyst. In this technology, an ‘artificial leaf’, or cell, absorbs the sunlight, whilst a catalyst splits water into oxygen, and most importantly, hydrogen.
The latter has been growing as a clean fuel in recent years and can be used in fuel cells without emitting greenhouse gases. Alternatively, formic acid, ethylene, or methanol are other fuels which can be produced via artificial
photosynthesis.
Current research is also focussing on efforts to convert waste carbon dioxide from industry into fuel or ethylene, which can be used as a plastic precursor. This utopic idea of generating and storing fuel directly from sunlight would be a
serious
opponent to fossil fuels.
‘Whilst this technology is promising, several major challenges still stand in the way of the deployment of artificial photosynthesis.’
Currently, numerous different mechanisms have been employed and are still being developed at each step of the technology. An example of such is a sheet covered with solar cells can be rolled out on a flat surface (such as a rooftop) to
collect
light and water. Then, the sheet can be moved into a tank full of catalysts that will convert the carbon dioxide into a fuel, which can then be stored.
Other researchers have integrated photosynthetic bacteria or microalgae into their artificial photosynthesis models—the possibilities are endless.
Whilst this technology is promising, several major challenges still stand in the way of the deployment of artificial photosynthesis. Splitting water is the hardest step in the reaction and the catalysts used for this are often made of
manganese (like in plants), titanium oxide, and most recently cobalt oxide. However, these have limited stability as they are quickly corroded by the acidification of water that takes place within the reaction.
A team at Brookhaven National Laboratory, of the United States Department of Energy, investigating artificial photosynthesis. The aim is to produce fuel from photosynthesis.| Brookhaven National Laboratory / Flickr
Similarly, sunlight itself is corrosive and often damages the equipment, incurring extra costs to the system. Overall, at the present moment, catalysts are too expensive and inefficient, rendering the overall technology of artificial
photosynthesis unsuitable for large-scale application.
Despite extensive work being carried out to greatly improve the components of the artificial photosynthesis system, there is still a long way to go before they can harmoniously work as a united system to rival wind or solar power.
Nonetheless, governments and research bodies truly believe that this is a feasible method to reduce our over-reliance on fossil fuels in the coming years and take steps to mitigate the effects of climate change.
‘This utopic idea of generating and storing fuel directly from sunlight would be a serious opponent to fossil fuels.’
In 2020, the United States Department of Energy announced an investment of $100 million in artificial photosynthesis research over five years. This money has been assigned to two main projects with diverging yet complementary focusses: the
Center for Hybrid Approaches in Solar Energy to Liquid Fuels (CHASE) and the Liquid Sunlight Alliance (LISA). Whilst LISA focusses on theoretically enhancing every step of the process, CHASE aims to develop an effective final product.
Professor Erwin Reisner, an active researcher on artificial photosynthesis at the University of Cambridge, stated: ‘I really believe that artificial photosynthesis will be one part of that energy portfolio over the next two decades’.
Now, we will just have to wait and see.
Featured Image: Clay Banks | Unsplash
Edenhofer O. (2014) ‘Climate Change 2014: Mitigation of Climate Change.’ Intergovernmental Panel on Climate Change. Available at: https://www.ipcc.ch/report/ar5/wg3/ [Accessed February 21st, 2022]
Haas T., Krause R., Weber R., Demler M., Schmid G. (2018) Technical photosynthesis involving CO2 electrolysis and fermentation. Nature Catalysis. Volume 1, pages 32-39.
