The generation of solar fuels is a way of producing fuel based on generating chemical reactions using the radiation of solar energy. These chemical processes allow energy to be generated that would otherwise come from a fossil fuel source or from nuclear power.
A great advantage of solar fuel generation is that it can be easily transported and stored. However, adding a step in the generation of electrical energy (fuel generation) implies a reduction in efficiency: adding an additional step between energy storage and electricity production drastically decreases the efficiency of the overall process.
The result is a liquid fuel generated from a renewable and sustainable energy source.
Types of Solar Chemical Reactions
Chemical reactions induced by the Sun can be divided into:
A thermochemical reaction is a chemical reaction in which a thermodynamic transformation is undergone. In other words, it is a reaction that generates or absorbs thermal energy.
Photochemical reactions generate interactions between atoms, small molecules, and light. In photochemistry there are two very important physical laws:
The first law of photochemistry states that light must be absorbed by a chemical in order for a photochemical reaction to take place.
The second law of photochemistry states that for each photon of light absorbed by a chemical system, only one molecule is activated for a photochemical reaction.
What Is Solar Chemistry?
Solar chemistry refers to a number of possible processes that harness solar energy by absorbing sunlight in a chemical reaction. The idea is conceptually similar to photosynthesis in plants, which converts solar energy into the chemical bonds of glucose molecules, but without using living organisms.
One promising approach is to use focused sunlight to provide the energy needed to split hydrogen and oxygen from water in the presence of a metal catalyst such as zinc.
Another approach is to take the hydrogen created in this process and combine it with carbon dioxide to create methane. The benefit of this approach is that there is an infrastructure in place to transport and burn methane for power generation, which is not true for hydrogen.
The main drawback of these two approaches is common to most energy storage methods: adding an extra step between energy storage and electricity production drastically decreases the efficiency of the overall process.
What Is Artificial Photosynthesis?
Artificial photosynthesis is a chemical process that mimics the natural process of photosynthesis, which converts sunlight, water, and carbon dioxide into carbohydrates and oxygen.
The term generally refers to any system for capturing and storing the energy of sunlight in the chemical bonds of a fuel (solar fuel). Photocatalytic water splitting converts water into hydrogen and oxygen. The photochemical reduction of carbon dioxide is another process under study and reproduces the natural fixation of carbon.
Research in this field includes:
The design and construction of devices for the direct production of solar fuels
Photoelectric chemistry and its applications in fuel cells
The engineering of enzymes and photoautotrophic microorganisms for microbial biofuels and the production of biohydrogen from sunlight.
Future Prospects for Solar Fuel
One of the current challenges is the development of multi-electron catalytic chemistry involved in the manufacture of carbon-based fuels (such as methanol) from the reduction of carbon dioxide.
A viable alternative is hydrogen. This technique requires mastering the multi-electron oxidation of two water molecules to molecular oxygen.
In certain sectors, it is planned to work with solar fuel plants in metropolitan coastal areas by the year 2050.
Hydrogen production technologies have been an important area of solar chemistry research teams since the 1970s. Apart from photovoltaic or photochemical cell-driven electrolysis, various thermochemical processes have also been explored.
Another approach uses heat from solar concentrators to drive steam reforming of natural gas, increasing the overall yield of hydrogen compared to conventional reforming methods. Thermochemical cycles characterized by the decomposition and regeneration of reactants present another pathway for hydrogen production.