Photocatalytic technology offers the potential to provide renewable hydrogen by solar-driven water splitting or to produce hydrocarbons directly from sunlight, water and CO₂.

However, the low charge-separation efficiency due to the lack of directional driving forces strongly limits the solar-to-hydrogen efficiency or, more generally, the solar-to-fuel efficiency. Thus, understanding and exploring the driving force for charge separation is key to improving the photocatalytic performance.

Schematic showing asymmetric excitation induced charge separation and revealing the driving force caused by charge mobility differences.(Image by CHEN Ruotian)

Using surface photovoltage microscopy (SPVM), a research group led by Prof. FAN Fengtao and Prof. LI Can from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences demonstrated that the photogenerated charges could be separated effectively in a high-symmetry Cu₂O photocatalyst particle by asymmetric light irradiation.

Quantitative studies combined with theoretical simulations revealed that the huge difference of electron and hole mobilities (100-fold) was responsible for the asymmetric illumination-induced charge separation.

Therefore, the asymmetric cocatalysts assembly could be achieved on a single photocatalytic particle, leading to a significant improvement of photocatalytic performance.

These directional driving forces can improve the charge separation efficiency of photocatalysts and, in the future, may be applied in the context of solar water splitting or CO₂ reduction to increase the efficiency of solar fuel production.

Their study entitled "Charge separation via asymmetric illumination in photocatalytic Cu₂O particles" was published online in Nature Energy.

A cartoon movie showing how asymmetric excitation conditions affect the charge separation and redox reactions between light and shadow parts of a photocatalytic particle. (Video by FAN Fengtao)