Young Investigator Group Operando Characterization of Solar Fuel Materials

Schematic of a photoelectrochemical cell (PEC) using an n-type semiconductor as photoanode

We are using and developing soft X-ray based methods for studying energy materials under in-situ and operando conditions at the BESSY II synchrotron facility. A special focus of our research lies on materials which are involved in the process of hydrogen generation from solar light. Technically, this process takes place in a photoelectrochemical cell (PEC), as shown schematically in figure 1. In this cell the incoming photons with energies greater than the semiconductor band gap can be absorbed by the photoanode, creating electron-hole pairs. The electron-hole pairs are split by the electric field in the space-charge region between the semiconductor and the electrolyte. The electrons move to the cathode through an external circuit. At the cathode, H+ ions from electrolyte are reduced to form hydrogen gas. At the photoanode, holes moves to the interface of semiconductor/electrolyte and oxidize OH- to produce oxygen gas via a four-electron process. The electrolyte allows H+ and OH- ions migrate and reach the proper electrode.

This complex process requires a comprehensive design matching of the various components of the PEC. In order to understand and optimize the charge transfer processes between these components, it is the great challenge to study the materials under realistic conditions or named as operando conditions. Which specific materials we are currently working on is described here. How we obtain electronic structure information during catalyst performance is described here.