In this blog post, we will examine how artificial photosynthesis utilizes solar energy to simultaneously alleviate the problems of energy depletion and environmental pollution, and provide a detailed overview of the technical possibilities presented by the latest research.
Can abundant energy and a clean environment truly coexist? Various forms of environmental pollution arise during the energy production process. Gases emitted when resources are burned cause air pollution and global warming, while substances generated during the processing of certain energy sources, such as shale gas, lead to complex environmental pollution, including water and soil contamination. Furthermore, the depletion of energy resources has emerged as a serious problem. While global energy demand increases every year, major energy sources such as coal, oil, and natural gas have limited reserves and are gradually being depleted. To address this energy depletion issue, the world has been striving to develop new underground resources, such as the aforementioned shale gas; however, it is becoming clear that this, too, cannot serve as a fundamental solution due to the limitations of its reserves.
As a way to simultaneously address the dual challenges of limited energy and environmental pollution, we can consider utilizing solar energy, which is effectively an infinite resource available to us. Artificial photosynthesis has garnered attention not only for its ability to produce usable energy from solar energy but also for its capacity to synthesize various high-value-added materials in an environmentally friendly manner. Furthermore, just like natural photosynthesis, it absorbs carbon dioxide during the process of producing materials or energy, thereby contributing to the mitigation of global warming. However, due to the limitations of having to overcome barriers related to efficiency and economic viability, practical application has been difficult, and as a result, artificial photosynthesis had to remain at the experimental stage or the level of theoretical discussion for some time. Nevertheless, with a series of significant research achievements emerging worldwide recently, the path toward commercialization is gradually opening up. Before examining the development process of artificial photosynthesis, we will first understand its principles and then examine the current state of the technology through two representative research cases.
Artificial photosynthesis, as the name suggests, is a process that mimics natural photosynthesis to artificially produce substances. Therefore, to understand artificial photosynthesis, it is necessary to first grasp the principles of natural photosynthesis. Natural photosynthesis is the process by which plants and certain organisms use light energy to synthesize substances necessary for life; fundamentally, it uses carbon dioxide and water to produce glucose and oxygen. This process consists of two stages: the light reaction and the dark reaction. The light reaction occurs in the thylakoid membrane of chloroplasts and is divided into the photolysis of water and the photophosphorylation reaction. In the photolysis of water, water is broken down to produce electrons, hydrogen ions, and oxygen, while the photophosphorylation reaction primarily generates ATP and NADPH2, which are necessary for the dark reaction. Since both reactions rely on light energy absorbed by chlorophyll, the light reaction does not occur in the absence of light. The dark reaction takes place in the chloroplast stroma, where ATP and NADPH2 produced during the light reaction are used to synthesize glucose from carbon dioxide via the Calvin cycle.
Artificial photosynthesis also proceeds in a manner similar to natural photosynthesis, and the general process is as follows. In artificial photosynthesis, solar cells perform the function corresponding to the light-dependent reaction stage of natural photosynthesis. Instead of producing electricity as intended, solar cells play the role of synthesizing NADPH₂ from NADP, just as in natural photosynthesis. Redox enzymes are used in the dark reaction stage of natural photosynthesis. Although numerous enzymes are involved in the Calvin cycle, in artificial photosynthesis, these complex enzymatic reactions are replaced by redox enzymes. Artificial photosynthesis is thus implemented by mimicking the light and dark reactions of natural photosynthesis through human technology; however, unlike natural photosynthesis, it does not stop at producing only oxygen and glucose but can produce a wide variety of products according to human needs. For example, artificial photosynthesis can not only be used to store energy for human use but also to selectively synthesize high-value-added chemicals, such as raw materials for diabetes or AIDS treatments.
All technologies undergo a process of continuously improving efficiency and economic viability from the initial development stage through to commercialization, and artificial photosynthesis was no exception. As mentioned earlier, artificial photosynthesis is divided into energy storage and material production methods depending on the final product. Let us examine the challenges faced in each method and the recent research achievements made to address them. First, in the method of storing energy using artificial photosynthesis, issues arose regarding energy conversion efficiency. When hydrogen is produced via artificial photosynthesis, it must be stored and transported in a usable form of energy. However, because hydrogen is extremely light and unstable, a device capable of absorbing it stably and efficiently was required. Previously, bacteria that absorb hydrogen and store it as hydrocarbon-based substances were utilized; however, these systems could only store about 1% of the input energy, falling far short of the approximately 10% efficiency considered the benchmark for commercialization. However, in June 2016, a research team at Harvard University succeeded in raising the energy conversion efficiency to around 10% by genetically engineering bacteria to increase their hydrogen absorption rate and developing a new catalyst that allowed these bacteria to survive stably. This research served as a significant milestone in advancing energy storage methods using artificial photosynthesis to the commercialization stage. Subsequent studies through the late 2020s have reported efficiencies in the 12–15% range based on this technology, further demonstrating the potential of artificial photosynthesis-based hydrogen production and storage technologies. However, since additional verification and technical improvements—such as long-term operational stability, scalability to large-scale systems, and resistance to contamination—are still required for industrial application, commercialization is currently at a stage of gradual yet steady progress.
Next, in methods for producing high-value-added materials through artificial photosynthesis, the efficiency and cost-effectiveness of water-splitting catalysts have emerged as key challenges. While the water-splitting stage is essential for producing high-value-added chemicals from water and carbon dioxide, this process requires significant energy. Therefore, catalysts are used to reduce energy consumption; however, to ensure commercial viability, both low cost and high performance must be achieved simultaneously. However, low-cost catalysts suffered from poor performance, while high-performance catalysts were excessively expensive, persistently undermining economic viability. For this reason, the method of producing chemicals using artificial photosynthesis remained confined to theoretical possibilities for a long time. Then, in September 2017, news was announced that a research team at the Korea Institute of Science and Technology (KIST) had developed an artificial photosynthesis catalyst that was both low-cost and high-performance. The team synthesized a catalyst called nickel oxyhydroxide using stainless steel components. Not only is it capable of mass production through a simple process, but it also achieves a 20–30% increase in efficiency compared to existing catalysts, thereby simultaneously resolving the issues of efficiency and cost-effectiveness in water-splitting catalysts. Since the late 2020s, research related to artificial photosynthesis—including low-cost metal-based catalysts, photoelectrochemical semiconductor materials, and carbon resource utilization technologies—has rapidly expanded globally, further increasing the potential for commercialization.
In summary, artificial photosynthesis technology—which mimics natural photosynthesis to produce energy and materials for human use—is moving closer to commercialization as recent active research has improved its efficiency and economic viability. While some achievements have emerged that could be considered commercially viable in terms of overall efficiency, separate challenges regarding mass production and cost reduction remain throughout the entire artificial photosynthesis process, beyond the water splitting process mentioned earlier. Of course, raising the energy efficiency of artificial photosynthesis from around 1% to 10% is undoubtedly a remarkable advancement. However, considering that the energy conversion efficiency of natural photosynthesis exceeds 40%, the efficiency of artificial photosynthesis is likely to improve even further in the future. Artificial photosynthesis has the distinct advantage of converting solar energy—a nearly limitless resource—into a form that humans can utilize in an environmentally friendly manner. If we can not only improve energy efficiency but also establish mass production systems and reduce costs, we will be able to dramatically improve the global energy depletion crisis and the environmental pollution caused by energy development that humanity currently faces. Furthermore, since artificial photosynthesis enables not only energy production but also the selective production of various high-value-added chemicals, it is expected to establish itself as a key technology that further enhances the quality of human life across various industrial sectors, including pharmaceutical development.
