In this article, we will analyse the concept of artificial photosynthesis and how we will apply it in Photo2Fuel.
The field of renewable energies and sustainability is moving into many different directions, always looking for the most innovative solutions to reach the goal of lowering emissions by 2030. In Photo2Fuel, we are working to produce sustainable biofuels using CO2 and sunlight. Read more here.
Artificial photosynthesis: replicating what nature does to save it
Artificial photosynthesis is an emerging technology that enables the synthesis of organic molecules, mimicking natural photosynthesis. It uses sunlight to initiate a complex reaction sequence that can produce to convert sunlight, water, and carbon dioxide into carbohydrates, oxygen, hydrogen or hydrocarbons, without making use of biomass or an external electricity network. The term “artificial photosynthesis” is commonly used to refer to any scheme for capturing and storing the energy from sunlight in the chemical bonds of a fuel, also defined solar fuel.
The functioning is similar to the natural photosynthesis system:
- Light harvesting: the collection of light particles (photons) by antenna molecules and the concentration of the collected energy in a reaction centre.
- Charge separation: at the reaction centre, the collected sunlight is used to separate positive (‘holes’) and negative (electrons) charges from each other.
- Water splitting: positive charges are directly injected into catalytic centres where they are used to split water into hydrogen ions (protons) and oxygen.
- Fuel production: electrons from step 2 are given more energy from new photons and subsequently combined with the hydrogen ions and possibly CO2 to produce either hydrogen or a carbon-based fuel. [1]
The carbon-based fuels that may be produced by means of artificial photosynthesis are not complex molecules like carbohydrates, but simpler molecules such as methane, methanol and carbon monoxide [2].
This technology is very attractive and could be the answer for a sustainable transition from fossil to renewable fuels, promoting energy independence and decentralisation, as well as being a solution for energy storage.
Semi-synthetic approach for the production of biochemicals
Photo2Fuel’s technology lies in one branch of artificial photosynthesis's main research area, the so-called “semi-synthetic” systems, an interesting new approach that is a hybrid of biological (enzymes, microorganisms, yeast, etc.) and artificial components.
For instance, a biological component (such as bacteria and archaea strains used in Photo2Fuel) that harvests light and splits water could be modified chemically or by synthetic biology and tethered to a suitable scaffold. This complex could then be linked to a hydrogen-producing enzyme or a catalyst, similarly optimized by chemical or biochemical synthesis. Alternatively, chlorophyll molecules could be modified and combined with semi-artificial components. The advantage of such an approach is that biological components can be very efficient and no biomass is used to obtain the final products [2].
These biosynthetic pathways are under dynamic regulation to keep cellular functionality in tune with physiological needs at different conditions. These features allow microbes to synthesise complex products from the simplest and most stable feedstocks (e.g., H2O, CO2, N2, etc.) and render microbial catalysis resilient to environmental variations [3].
The overall advantage of using hybrid systems is to benefit from the high efficiency of live organisms developed over millions of years, combined with the latest technological advancements in synthetic materials. This hybrid approach is still in its infancy, though, and, therefore, there is a huge space for development in several sub-areas that apply different techniques that will be explored by Photo2Fuel.
How is artificial photosynthesis used in the Photo2Fuel project
In the Photo2Fuel project, a hybrid reactor will be built and tested to obtain two main products: biomethane and acetic acid. For the production of biomethane, the methanosarcina barkeri archaea are used, while, for the production of acetic acid, the bacteria moorella thermoacetica is employed. The TZE University is in charge of finding the most suitable bacteria for the purposes of the Photo2Fuel project. Bacteria are then mixed with biopolymers and CO2, after being chemically optimised and characterised. The biopolymers, or polymer dots, are the speciality of the University of Uppsala and ICCAS University in China research teams involved in Photo2Fuel. The hybrid system is placed into a photo-micro reactor running only with sunlight. Thanks to the reactor designed by the University of Amsterdam, the system will be able to run even at night and under variant solar irradiance, in case of cloudy skies, converting solar energy into a narrow and steady spectral distribution. While other solar photoreactors were designed to filter the solar spectrum and concentrate only the portion of radiation needed by the reaction, the luminescent solar concentrator photo-microreactor developed by the University of Amsterdam is the only reactor design that actively down-converts high-energy UV photons to longer wavelengths, the ones needed to mimic natural photosynthesis.
Conclusion
Overall, these research areas represent promising avenues for advancing renewable energy technologies and addressing climate change by utilizing solar energy to produce sustainable fuels and reduce carbon emissions. However, specific advancements and the current state of research in these areas would require referring to the latest scientific literature and developments in the field.
[1] Ball, P. 1999 Reinventing the leaf. Nature News 1999; http://www.nature.com/news/1999/991004/full/news991007-3.html
[2] Purchase, R.; Vriend, H.; de Groot, H.; Harmsen, P.F.H.; Bos, H.L. 2015. Artificial photosynthesis: for the conversion of sunlight to fuel. Leiden University (Groene grondstoffen ). Research report. https://edepot.wur.nl/353079
[3] Xin Fang, Shafeer Kalathil, and Erwin Reisner, ‘Semi-Biological Approaches to Solar-to-Chemical Conversion’, Chemical Society Reviews, 49.14 (2020), 4926–52. https://doi.org/10.1039/c9cs00496c