Sunlight is an abundant renewable energy source. It can catalyze the decomposition of water to produce hydrogen and the reduction of carbon dioxide to produce solar fuel (fuel converted from solar energy, water and carbon-based compounds) through the action of photocatalysts. Chinese scientists have recently photographed the entire evolution of photogenerated charge transfer over photocatalysts, which provides a new understanding and research strategy for breaking the bottleneck of solar photocatalytic reaction and more efficient utilization of solar energy.

According to the Chinese Academy of Sciences, the research was carried out by Li Can, an academician, and Fan Fengtao, a researcher at the Dalian Institute of Chemical Sciences of the Chinese Academy of Sciences. The results were published online in the international academic journal Nature on December 12.

Time-domain in-situ dynamic image of a single photocatalytic particle during femtosecond (one quadrillion second) to second photogenerated charge separation. (Photo provided by Dalian Institute of Chemical Sciences, Chinese Academy of Sciences)

Because of the great potential of solar photocatalytic reaction in clean energy production, scientists at home and abroad have carried out a lot of research in this field for many years. However, how does the charge generated by light excitation separate, transfer, and participate in chemical reactions? The underlying science of this critical process has long been unclear.

'In photocatalysis, photogenerated electrons and holes need to be separated from the inside of the micro-nanoparticle and transferred to the surface of the catalyst to initiate chemical reactions.' Unravelling the microscopic mechanisms of this process is challenging as it spans complex space-time scales from femtosecond to second and from atom to micron, Fan said.

In this study, we integrated a variety of techniques that can be connected at the spatiotemporal scale to detect photogenerated charge transfer in photocatalyst nanoparticles in the full space-time, for the first time tracing the entire mechanism of electrons and holes in a photocatalyst particle to the surface reaction center. They also identified the essential relationship between the charge separation mechanism and the efficiency of photocatalytic water decomposition.

'The ability to track charge transfer in space and time will greatly improve the understanding of the complex mechanisms involved in energy conversion, providing new ideas and research methods for rational design of photocatalysts with better performance.' The result is expected to promote the practical application of solar photocatalytic decomposition of water to produce solar fuel, providing more clean and green energy, Li said.