The research team led by Dr. Hyung-Suk Oh and Dr. Woong Hee Lee at the Clean Energy Research Center at Korea Institute of Science and Technology (KIST, President Sang-Rok Oh) has developed a silver-silica composite catalyst capable of reversible local pH control through a silica-hydroxide cycle, inspired by Earth's natural cycles. This research draws inspiration from the carbonate-silicate cycle, known as the Earth's inorganic carbon cycle, where carbon dioxide (CO₂) maintains balance. CO₂ is removed from the atmosphere as it is stored in weathered minerals, then released back into the atmosphere through volcanic activity. During the weathering of silicate rocks, dissolved silica (SiO₂) is produced, leading to carbonate rock formation, which eventually recycles back into silicate rock through volcanic activity, impacting Earth's temperature regulation. The key substance in this cycle, silica, was applied to electrochemical CO₂ conversion reactions.
Among the catalysts used in CCU technology, silver catalysts are highly effective at converting CO₂ into carbon monoxide (CO), a valuable raw material for petrochemical products. However, silver catalysts are not yet commercially viable, as they exhibit issues at high current densities, such as agglomeration or clumping of particles on the catalyst surface, which rapidly reduces selectivity for CO.
To maintain the performance of the silver catalyst, the research team developed a silver-silica composite catalyst. During reactions, hydroxide ions (OH⁻) generated interact with silica, dissolving into a silicate form and precipitating back under neutral conditions, thereby controlling the pH. This approach addresses performance degradation issues at higher current densities without altering the catalyst's physical structure, relying solely on a chemical approach.
The newly developed silver-silica composite catalyst showed near 100% selectivity even at a higher current density of 1 A cm⁻², compared to commercial silver catalysts that drop to about 60% selectivity at 800 mA cm⁻². Additionally, the catalyst boosted CO₂ conversion to CO by around 47%, achieving high efficiency even at elevated current densities.
This silver-silica composite catalyst successfully enhances CO₂ reduction performance and durability at high current densities, significantly advancing the commercial potential of CCU technology for electrochemical CO₂ conversion. Its high CO selectivity and durability due to reversible cycling enable sustained performance over extended periods, improving productivity and economic feasibility. Moving forward, the team plans to optimize production processes for high-efficiency catalysts and conduct long-term durability testing for potential application in industrial facilities, such as power plants and petrochemical factories.
Dr. Oh from KIST stated, "The research provides a significant direction in enhancing catalyst reversibility and environmental control strategies for electrochemical systems. It is expected to contribute to the future demonstration and commercialization of electrochemical systems."
