Without a doubt, the sun is the most abundant resource in our solar system. In one hour of the day, the fraction of its energy that reaches the earth’s surface could power the human race for a whole year. Our future, and the future of life on earth, may soon depend on our ability to capture and use this seemingly unlimited source of energy.
A profound idea is emerging from the frontier of science; a vision of the future in which artificial photosynthesis will enable us to shift from the anthropocene into a ‘sustainocene’. An age of existence in which ‘governance structures and scientific endeavour coordinate to achieve the social virtues of ecological sustainability and environmental integrity’ 
The first step to achieving this vision is finding a way to replicate photosynthesis through technology. Teams of scientist from across the world are well on the way to doing this. Amongst the highest profile might be the Joint Centre for Artificial Photosynthesis, the Solar-H2 network, and Dan Nocera’s Artificial Leaf.
Already a large variety of systems have been invented that can carry out parts of the processes within photosynthesis; light capture, charge separation, electron transfer, water splitting, and to some extent CO2 reduction. What is more, these separate processes are claimed to be enhancements of nature’s version. However, this separation into parts highlights one of the many challenges in taking artificial photosynthesis into society; to create an integrated system, scalable and adaptable for commercial and industrial use.
Depending on how you look at it, this may not be that big of a problem. The difference between what we can realistically achieve with artificial photosynthesis, in comparison to the real thing, can be reduced to what we can and can’t do after splitting water with the sun’s energy.
In plants, algae and other photosynthesisers, water is split to produce oxygen and hydrogen. The hydrogen formed in natural photosynthesis is in the form of protons; positively charged hydrogen ions. These protons are captured by an enzyme which drives a molecular rotor to create ATP; the universal energy vector for life. The molecules of ATP then go on to drive a series of process which transforms carbon dioxide into sugars.
In artificial photosynthetic water splitting, the hydrogen produced is in the form of a gas. Gases can’t be captured by enzymes, and so the hydrogen obtained can’t be combined with carbon dioxide in a similar manner to nature. With our current technology and scientific knowledge, attempting to transform hydrogen and carbon dioxide into sugar-based fuels would be a misdirected effort. The complexity of the process in nature is astounding, and to replicate would potentially require more energy than that stored in the sugars produced.
It is however possible to combine hydrogen with carbon dioxide under very high temperatures and pressures to form ethanol; a fuel already widely used in Brazil and the USA as a petrol additive. This approach is often considered as a step in the right direction, owing to it having the capacity to remove CO2 from the atmosphere. Paradoxically however, upon combustion, CO2 is released back into the atmosphere, which would leave us with little progress in tackling our global warming problems.
This leaves us then with a choice. Do we use the hydrogen to make ethanol, a fuel which contributes little to the vision of a sustainocene? Or can we find a way to make direct use of hydrogen?
If you’ve been paying attention to this blog, you should have read James’ blog post on the hydrogen economy; a concept of an energy infrastructure, and thus economy, based on the production and use of hydrogen as a fuel. Hydrogen has three times the energy content of petrol, and upon combustion yields only water as a product. If we could establish a hydrogen powered civilisation, using artificial photosynthesis to produce hydrogen, our energy needs as a species could be sourced entirely from the sun’s energy.
Many challenges still lay ahead for the construction of a sustainocene based on artificial photosynthesis. As well as those mentioned above, artificial photosynthesis systems will need to be made from abundant non-toxic materials which can operate in a range of environments and conditions. Further ahead lies challenging the accepted norms of a fossil fuelled society, shaping governmental and political debate, and maybe most challengingly, fighting the power yielded by the oil and gas corporations that monopolise our energy infrastructures. [1, 2]
Intentionally shifting our planet into a new epoch is by no means an easy feat. However, it is absolutely possible. In the last 200 years we have already forced such a change. Our species’ interference with our planet’s natural systems has left profound impacts on almost every aspect of nature; the land, seas, atmosphere, ecosystems, climate, are just a few.
Even with the will and determination of people like Dan Nocera and Thomas Faunce, and the productivity of internationally collaborating scientists, creating a sustainable solar powered future won’t be possible without the efforts and intentions of the people across our planet. Supporting the creation of a universal declaration which would give natural and artificial photosynthesis the status of ‘common heritage of humanity’, much like those protecting outer space, our seas and the genome, will limit its private exploitation and facilitate its use to benefit life on earth. Once the science and technology is further established, its integration into everyday life will be a matter of its acceptance into society, and might hinge upon the voice of the people to calling for a hydrogen powered civilisation.
1. ‘Towards a global solar fuels project- Artificial photosynthesis and the transition from anthropocene to sustainocene’, Thomas Faunce, 2012.
2.’Artificial photosynthesis as a frontier technology for energy sustainability’, Thomas Faunce et al, 2013.