Research Theme: Solar-Driven Artificial Carbon Cycle (SDAC2)

The goal of our research is to develop inorganic materials for energy and environmental applications, at the intersection of chemistry, physics and materials science. We develop new synthetic and fabrication approaches based on the rational control of size, shape, structure and composition at the atomic level. As the project unfolds, we investigate the physicochemical properties intrinsically associated with the precisely controlled structures at molecular and electronic levels, and implement their functionality in different application systems. Ultimately this research will emphasize integration of nanoscale building blocks into complex functional systems.

Currently our research centers on solar-driven artificial carbon cycle through the combination of four routes -- photocatalysis, electrocatalysis, photoelectrochemical system and plasmonic catalysis, based on the rationally designed inorganic materials and devices. In our research, we employ ultrafast or operando spectroscopic techniques, combined with theoretical simulations, to depict the charge dynamics and molecule reaction processes. This multidisciplinary research across the boundaries can reveal the essential mechanisms involved in molecular activation and selective conversion in complex energy coupling systems.

To achieve artificial carbon cycle, we specifically develop the following chemical transformations:

1. Carbon dioxide reduction.

Increasing levels of atmospheric carbon dioxide (CO2) have been recognized as the principal cause of current trends in global warming. To reduce this environmental pollution, efforts are being made to capture and sequester CO2 and to recycle it as a fuel feedstock that can also meet future energy demands. Currently, the major obstacle preventing efficient conversion of CO2 into energy-bearing products is the lack of catalysts that can readily couple an abundant energy source (e.g., electricity from solar, or direct solar radiation) with inexpensive reducing agents (e.g., hydrogen derived from water) to achieve rapid and selective cleavage of C-O bonds in CO2 and formation of C-H and C-C bonds in the products.

2. Methane conversion.

The direct conversion of methane into value-added liquid fuels or chemical products is a highly promising technical approach to the utilization of methane resource. However, achieving both high activity and selectivity under mild conditions is a grand challenge to direct methane conversion, which requires the development of new catalytic mechanisms and energy coupling modes. Our research develops hybrid structures by integrating photoelectrochemical system with plasmonic photothermal conversion, which can build a photo-electro-thermal energy coupling and conversion system for efficient direct methane conversion.

3. Nitrogen fixation.

Ammonia is one of the most important manmade chemicals due to its enormous applications in fertilizer production and energy carrier.  The production of ammonia mainly relies on the traditional Haber–Bosch process under high temperature and pressure, leading to a massive energy consumption and notable environmental issues.  Recently, electrocatalytic and photocatalytic nitrogen (N2) fixation have emerged for achieving green production of ammonia owing to their features of environmental friendliness and cost effectiveness.  However, ammonia production through electrocatalytic and photocatalytic is still far away from practical applications.  To facilitate the practical applications, a thorough understanding on nitrogen fixation is highly desired for the future design of high-efficiency catalysts.

4. Water splitting.

Exploiting sustainable energy systems is essentially important for solving the issues of increasingly severe energy crisis and environmental pollution. Sunlight-driven water splitting provides a promising approach to transform solar energy into hydrogen fuel. Since the photocatalytic splitting of water at TiO2 electrodes was first reported by Honda and Fujishima in 1972, photocatalysis has demonstrated wide-ranging potential applications in such areas for solving the world energy crisis. However, the low overall efficiency impedes the development of industrial-scale solar-driven photocatalytic water splitting systems. Therefore, developing highly efficient photocatalysts is the vital task for the scientists of the time. In parallel, water splitting can be achieved through electrocatalysis or photoelectrochemical system.

5. Organic chemical production.

Solar- or electro-driven organic synthesis has received tremendous attention for the development of renewable energy conversion and sustainable chemical manufacturing. Light- or electro-driven catalysis can significantly increase reaction rates, diminish side reactions, and even alter reaction pathways. Although homogeneous photocatalysis has shown splendid talents, heterogeneous catalysts (including semiconductor photocatalysts, plasmonic metals and electrocatalysts) bloom more promising prospects, owing to their merits such as easy separation from reaction products, applicability to continuous chemical industry and recyclability.