Artificial photosynthesis: A new way of renewable energy?
The concept of artificial photosynthesis is to imitate this fundamental process that occurs within natural organisms and manipulate it to fit our societal needs. The term can refer to any scheme which captures and stores solar energy in the chemical bonds of a fuel. Hence, rather than producing glucose, valuable fuels such as hydrogen or methanol are created. The general goal behind this effort is to establish a way of making energy renewable, reliable, and storable without impacting the environment in a negative way. Although the notion has not been accomplished in an industrial sense, there have been many notable successes on the lab scale.
Hydrogen fuel
Artificial photosynthesis can produce two types of fuel: hydrocarbons such as methanol and formic acid, or simply pure hydrogen. Hydrogen is emerging as a clean fuel option that can either be consumed in a fuel cell or used directly as a liquid fuel itself . It can be utilized for transportation (for example, in certain cars), to power homes, or other applications to substitute fossil fuels. When channeled into a fuel cell, it can also generate electricity. This type of fuel is produced using a number of methods, artificial photosynthesis appearing as one of them. Other techniques include thermal processes, electrolysis, biological processes, or other solar-driven systems.
Essential components:
There are three major components to an artificial photosynthesis device for which there is a need to develop: light capture and electron transport, water splitting (into hydrogen and oxygen), and the reduction of carbon dioxide . Researchers have established a handful of systems that are able to carry out these important processes. The components of these systems are synthetically designed to function as corresponding elements in the reaction centers of natural photosynthesis, such as pigment molecules and electron transport chains.
Limitations and challenges:
When attempting to replicate the functionality of autotrophs in a practical way, researchers have run into several limitations. For instance, although natural photosynthesis exhibits an almost perfect quantum efficiency (efficient charge separation) , it does not in most cases demonstrate a high overall chemical conversion efficiency. In fact, most natural plants can only produce a solar-to-biomass efficiency of about 1% , owing to the fact that they have evolved to only be capable of performing enough energy conversion to sustain their own survival . However, it has been determined that the conversion of solar to chemical energy of an industrially feasible artificial photosynthesis system should demonstrate an efficiency of 10% or higher . This has posed as a challenge for this field, being that all of the fabricated devices which have successfully achieved a high conversion efficiency have been made from rare and expensive materials, thus disabling the practicality of scaling up these systems.
Furthermore, this ties into the ongoing search for materials that are capable of acting as suitable catalysts for the uphill reactions that artificial photosynthesis entails. Since the processes involved in artificial photosynthesis involve the breaking and forming of chemical bonds, catalysts are necessary to drive this reaction. However, one of the main bottlenecks associated with this area of research is establishing a cost-effective, efficient, and stable catalyst material. A significant issue among studied catalysts such as organic-based is their tendency to be unstable for multiple uses [2, 22]. Many variations have a habit of corroding or degrading the system equipment, while some lose their energy upon several cycles. While plants intrinsically perform self-repair mechanisms, artificial systems most often do not hold this characteristic . Alternative metal-oxide catalysts show good promise, but the ones that have sufficient speed lack abundance and financial viability . Meanwhile, it has been determined that an applicable device should demonstrate stability for at least 10 years . Thus, the search for an appropriate catalyst which exhibits each of these proper functions is ongoing.
Another notable challenge within the area of mimicking a natural process is the complex molecular geometry found in photosynthesizing organisms. Researchers are having a great deal of trouble replicating the level of intricacy that it entails. However, with the help of supramolecular strategies and nanotechnology, scientists are able to easily manipulate the workings of their devices through the structural and molecular composition. Although it is difficult to match the details present in natural photosynthesis, these techniques allow the field to advance toward a viable system.
