Photoelectrocatalysis (PEC) is the art of making “chemical solar cells” - i.e. ones which harvest sunlight and use the energy to upgrade chemicals rather than delivering electricity. Also often called “artificial photosynthesis”, PEC combines the solar cell with electrocatalysis in order to direct as much as possible of the solar energy toward the target reaction. The archetypical reaction is water splitting (i.e. solar-driven electrolysis) to hydrogen and oxygen, but in recent years there is also a substantial interest in PEC-driven CO2 reduction where the target products (carbon monoxide, formic acid, ethylene and ethanol) are more valuable than hydrogen and which in theory could have as high efficiency as hydrogen.
However, in order to do any such reaction, the required working voltage of the PEC device must be at least 1.6 V and preferably closer to 1.8 V. In practice, this voltage requirement calls for a tandem solar harvesting device - i.e. one where two photons (one blue & one red) are captured in individually optimized absorbers, since a single-absorber device cannot produce sufficient voltage at reasonable current densities.
Figure 1 Tandem solar absorber configurations. From: B. Seger et al. Energy Environ. Sci. 7, pp. 2397 (2014)
In recent years, we have perfected the low-bandgap part of the tandem (absorbing the red photons), and now the quest is for the high-bandgap partner for the tandem, which will absorb the blue photons and yield a high working voltage (at least 1.1 V). Various thin-film material candidates are being investigated in a close collaboration with theory (DFT).
Photocatalysis (PC) is redox-catalysis, which is activated by light at room temperature. Many photocatalytic systems only work under UV light, but possess the ability to activate even quite stable species at room temperature. This makes PC a viable strategy for cleaning of air and water from low concentration pollutants - and even for sterilization (killing microbes). We work on PC with very concrete, technological applications in mind and we typically use our unique microreactor system for this work as it is a great benchmarking tool for PC.