Research of the SPECSY group

Electrochemistry is a field that is becoming increasingly important in a post-fossil, greenhouse-gas neutral energy system, mainly for energy storage in batteries or sustainable hydrogen production. Here, the interface between the solid and the electrolyte is decisive for the performance of the application. Understanding this interface in terms of structure, chemical composition, and energy level distribution allows to create high-performance devices. Controlling the composition of the top layer of a photoelectrochemical solar cell on a sub-nanometre level enabled us to create world-record solar water splitting cells.^1,2

However, the access to the interfacial properties - especially while immersed into the liquid electrolyte - on an atomistic level is challenging. Typical methods of surface science based on electrons only work to a limited degree - if at all - in liquid environments such as water. Therefore, our group uses the optical method reflection anisotropy spectroscopy (RAS), which is highly surface-sensitive, for probing solid-liquid interfaces. To derive an atomistic understanding from experimental spectra, this technique requires computational modelling, starting from an electronic structure model obtained with density functional theory.³

We combine experimental and computational spectroscopy in a single group, developing the methods necessary to study fundamental properties of electrochemical interfaces in batteries and solar fuel devices by means of RAS.

From a more general point of view, we are also thinking about other approaches, where (photo)electrochemistry could contribute in mitigating global warming. Here negative emissions, where CO₂ is captured from the atmosphere and the carbon transformed into an easily storable product, the carbon sink, is an exciting new field. The advantage of using photoelectrochemical methods, 'artificial photosynthesis', instead of methods relying on natural photosynthesis is the greatly reduced land footprint.⁴

Selected publications:

[1] Efficient Direct Solar-to-Hydrogen Conversion by In Situ Interface Transformation of a Tandem Structure, Nature Communications 6 (2015), p. 8286. doi:10.1038/ncomms9286.
[2] Monolithic Photoelectrochemical Device for 19% Direct Water Splitting, ACS Energy Letters 3(8) (2018), pp. 1795–1800. doi:10.1021/acsenergylett.8b00920.
[3] Water adsorption on the P-rich GaP(100) surface: Optical spectroscopy from first principles, New Journal of Physics 20(3) (2018), p. 033031. doi:10.1088/1367-2630/aaaf38.
[4] ESD Ideas: Photoelectrochemical carbon removal as negative emission technology, Earth System Dynamics 10(1) (2019), p. 1. doi:10.5194/esd-10-1-2019.
[5] Efficiency Gains for Thermally Coupled Solar Hydrogen Production in Extreme Cold, Energy & Environmental Science 14 (2021), p. 4410-4417. doi:10.1039/d1ee00650a.