Over billions of years, plants evolved and developed the most efficient energy system in the world: photosynthesis. The process of photosynthesis converts sunlight, carbon dioxide, and water into fuel plants can use, giving out oxygen during the process. The fuel here refers to carbohydrates, fats, and proteins that plants need to survive. However, in human terms, fuel refers to petroleum and diesel we need to run our vehicles and electricity to run our houses. But, we can still look to photosynthesis to solve our non-renewable, greenhouse gas-emitting energy problems. For many years now, scientists and researchers have been trying to create a system that uses energy the same way plants do, albeit with a different end result. They call the method ‘artificial photosynthesis.’
Using only sunlight, plants convert a massive amount of energy. They convert around 1,000 billion metric tons of carbon dioxide into energy they then use to perform their daily functions.
Solar energy has remained largely untapped by us humans. Photoelectric technology does convert sunlight into electricity, but this conversion is only instantaneous, which means we cannot use this energy during the night or on rainy, cloudy days. Apart from the disadvantage of instantaneous conversion, photoelectric energy is expensive and not highly efficient. But, artificial photosynthesis (a system that simulates photosynthesis in plants) could, in theory, provide us with inexpensive, abundant, ‘clean’, and storable energy and electricity.
In this article, we will look at the process of artificial photosynthesis in detail. We’ll learn what an artificial photosynthesis system should be able to do, why it is not so easy to design, and the processes currently in use.
Approaches to Artificial Photosynthesis
To mimic the photosynthesis occurring in plants, we need to design an energy conversion system that needs to be able to perform two essential functions: harvesting sunlight and splitting water molecules.
The chlorophyll present in plants helps them accomplish these tasks. Chlorophyll captures sunlight. A combination of enzymes and proteins then uses that captured sunlight to break down H2O into oxygen, hydrogen, and electrons. The electrons and hydrogen then convert CO2 into carbohydrates, releasing oxygen in the process.
To create an artificial photosynthetic system to supply energy for human requirements, the end result needs to change. Instead of expelling just oxygen at the end, the system would also have to release liquid hydrogen. We could use that hydrogen as a liquid fuel.
The problem researchers have run into while developing an artificial photosynthesis system is not producing hydrogen or capturing sunlight. The water molecules already contain hydrogen, and many solar-powered systems capture sunlight. The hard part is splitting water molecules. We need to split water molecules to obtain electrons. Electrons play a vital role in facilitating the chemical process that produces hydrogen. We would require an energy input of around 2.5 volts to split water molecules. This process would require a catalyst, which will initiate a chemical reaction by reacting with the sun’s photons.
Over the last 5-10 years, the important catalysts that have been identified are:
Dye-sensitized titanium dioxide
Applications of Artificial Photosynthesis
The world currently has a very short supply of fossil fuels. Burning fossil fuels contributes to global warming and climate change. Burning coal pollutes the environment and harms human health. Wind turbines disturb the visual aesthetics of picturesque landscapes. Making biofuel requires enormous tracts of farmland, and solar power currently in use is expensive and not very efficient. Artificial photosynthesis offers us an ideal solution to all of our energy problems.
Artificial photosynthesis is more advantageous than the usual photoelectric cells found in solar panels today. Photoelectric cells directly convert sunlight into electricity. This happens only in the instant daylight is incident on the cells. Therefore, solar panels are time and weather-dependent energy. This is one of the reasons why solar power is expensive. However, artificial photosynthesis provides us with a way of storing energy and using it when we later need it.
Most of the alternate power generation methods produce only one type of energy. Artificial photosynthesis, on the other hand, has the potential to produce more than one type of fuel. We can tweak the photosynthetic process, making the reactions between CO2, H2O, and sunlight produce liquid hydrogen as the final output. Hydrogen-powered engines can use this liquid hydrogen in place of gasoline. Hydrogen fuel cells generate electricity. We can use this electricity to power our air conditioners and water heaters.
We can also adjust the reactions to produce methanol possibly. Instead of releasing pure hydrogen, the photoelectrochemical cells used in artificial photosynthesis could generate methanol as a fuel. We often mix methanol with commercial gasoline so that it burns relatively cleaner. Some cars even run on just methanol.
Challenges in the Development of Artificial Photosynthesis
Artificial photosynthesis works perfectly fine in the laboratory. However, it is not ready yet for mass consumption. Simulating nature’s way of converting sunlight into energy efficiently is certainly no easy task.
Efficiency is a key factor in the production of energy. Photosynthesis in plants took a billion years to work efficiently. We’re trying to replicate what plants took a billion years to develop in just a few years. Therefore, creating an artificial photosynthesis system will take a lot of trial runs.
Manganese acts as a catalyst in plants. The same manganese, however, does not work as well in an artificial environment. Scientists found manganese to not last long in an artificial environment. They also found that it doesn’t dissolve in water. Therefore, using a manganese-based energy conversion system would be impractical and inefficient. The other obstacle researchers faced when trying to mimic the photosynthetic process in plants is that plants have a unique molecular geometry – it is exact and complex. Our human systems cannot recreate that level of complexity.
In dye-sensitized cells, the catalyst is not the problem. Instead, the electrolyte solution absorbing protons from split water molecules is the challenge. The solution is a crucial component of the system, but it is composed of volatile solvents capable of eroding other system components.
In the past few years, advances in science and technology have begun addressing these issues. Researchers experimenting with dye-sensitized cells have created a non-solvent based solution that we can use in place of the corrosive one.
Artificial photosynthesis is gaining the attention of a lot of research and researchers. But it will still be at least another ten years before this system becomes a reality.
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