Tracking photogenerated charge transfer in electrolytes

Photocatalysis involves three fundamental steps: light absorption, charge separation and transfer, and chemical reactions. These reactions occur at the solid-liquid interface where the complex charged environment influences reaction kinetics. Most research has focused on the charge transfer processes within solid catalysts.

Understanding the interplay between surface charges and charge transfer at the catalyst-electrolyte interface is critical for advancing photocatalysis. However, directly measuring surface charges in electrolytes at the nanoscale has long been a challenge.

In a recent study published in the Journal of the American Chemical Society, Prof. Fan Fengtao, Prof. Li Can and colleagues from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences developed an innovative approach to measure surface charges in liquid environments.

By using a charged probe to isolate electrostatic forces from long-range interactions, researchers mapped the electric field distribution within the electrical double layer, which enabled direct measurement of surface potential and photovoltage under realistic liquid conditions. Moreover, they uncovered a key phenomenon: Surface charges at the solid-liquid interface create an additional driving force, pulling photogenerated electrons to the surface and driving the charge transfer reaction.

Researchers quantitatively demonstrated how local surface potential in the electrolyte varies with pH, providing micro- to nanoscale observations. By relating the surface potential and reaction product flux, they demonstrated that the photocatalytic oxygen evolution reaction rate is controlled by the surface charge-induced electric field.

Researchers also identified the optimal pH range for efficient spatial separation of photogenerated electrons and holes. They visualized the entire charge transfer process from the space charge region to the active reaction sites.

“This imaging framework offers a platform to directly measure surface potential and reaction current under operational conditions, providing an idea for photocatalytic charge transfer kinetics at the nanoscale and for designing efficient photocatalysts and optimizing reaction conditions,” said Prof. Fan.

“Our findings provide valuable insights into addressing the bottleneck issues of photocatalytic reactions,” said Prof. Li.