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Institute Solar Fuels


At the Institute for Solar Fuels we develop new materials and devices for the production of chemical fuels from cheap and abundant resources, such as water and CO2, using sunlight. Our current efforts are focused on photo-electrochemical water splitting. Towards this end, we develop deposition processes and synthesis routes for thin film and nanostructured semiconductors and catalysts, and we investigate the fundamental processes of charge generation, separation, and transfer in the bulk and at the interfaces of these materials. Of particular interest is the role of defects, which we aim to control by developing thermal treatments, passivation layers, and doping strategies. Our experimental toolbox includes a range of thin film deposition techniques, electrochemistry and photo-electrochemistry, time-resolved spectroscopy on fs – s time scales, and synchrotron-based methods under operando conditions.

News and Recent Publications

Electrolyte Selection Toward Efficient Photoelectrochemical Glycerol Oxidation on BiVO4

Glycerol, a by-product of biodiesel, can be converted into valuable chemicals using photoelectrochemical (PEC) devices, improving their economic viability. While much research has focused on photoelectrode materials and co-catalysts, the role of electrolytes in this process has been less studied. Our research investigates the impact of different acidic electrolytes on PEC glycerol oxidation using a nanoporous BiVO4 photoanode. We found that electrolyte composition significantly influences performance metrics like photocurrent, stability, and, to some extent, product selectivity. These findings underline the importance of electrolyte engineering in optimizing solar-driven biomass reforming.

Figure: ©HZB

Heejung Kong, Siddharth Gupta, Andrés F. Pérez-Torres, Christian Höhn, Peter Bogdanoff, Matthew T. Mayer, Roel van de Krol, Marco Favaro*, Fatwa Abdi*; Chem. Sci., just accepted; https://doi.org/10.1039/D4SC01651C


In situ and operando Raman spectroscopy of semiconducting photoelectrodes and devices for photoelectrochemistry

Photoelectrochemical (PEC) devices, which convert sunlight, water, and CO2 into fuels and valuable products, require advanced photoabsorber materials. Understanding interactions at the semiconductor/liquid interface is crucial for optimizing these materials. This perspective and technical paper highlights the use of operando Raman spectroscopy (RS) combined with electrochemical techniques to gain insights into photoelectrode behavior under working conditions. Despite challenges like low quantum efficiency and fluorescence, operando RS can reveal changes in photoabsorber structure and surface defects. It also aids in analyzing products from solar-driven biomass reforming. Our work discusses overcoming these challenges and introduces methods for real-time monitoring of PEC reactions, paving the way for improved photoelectrode design.

Figure: ©HZB

Marco Favaro*, Heejung Kong, Ronen Gottesman*; J. Phys. D: Appl. Phys. 2024, 57 103002; https://doi.org/10.1088/1361-6463/ad10d3

In situ investigation of ion exchange membranes reveals that ion transfer in hybrid liquid/gas electrolyzers is mediated by diffusion, not electromigration

Ion-exchange membranes (IEMs) are vital for devices like fuel cells and batteries, enabling selective ion transfer to sustain electrochemical processes. Understanding their molecular behavior is crucial for optimization. Traditionally, ion transfer is believed to occur through diffusion and electromigration. However, using in situ ambient pressure hard X-ray photoelectron spectroscopy combined with finite element analysis, we found that ion transport in IEMs at the liquid/gas interface is driven mainly by diffusion through ionized functional groups. Additionally, we detected unwanted polarization fields that negatively impact device performance. This study highlights the importance of in situ investigations to improve the efficiency of (photo)electrochemical devices.

Figure: ©HZB

Maryline Ralaiarisoa, Senapati Sri Krishnamurti, Wenqing Gu, Claudio Ampelli, Roel van de Krol, Fatwa F. Abdi, and Marco Favaro*; J. Mater. Chem. A 2023, 11, 13570-13587; https://doi.org/10.1039/D3TA02050A

Influence of Excess Charge on Water Adsorption on the BiVO4(010) Surface

Our study explores how water interacts with a molybdenum-doped BiVO4 surface, combining computational models and experimental techniques. We discovered that water splits into hydrogen and oxygen on this surface, changing its electronic structure. By comparing photoemission spectroscopy data with theoretical calculations, we found that this process stabilizes small electron polarons, which are localized charges that affect the material's properties. Our findings highlight how defects and dopants on oxide surfaces influence their reactivity with water, offering insights into designing better materials for applications like photocatalysis and sensors.

Figure: ©HZB

Wennie Wang, Marco Favaro, Emily Chen, Lena Trotochaud, Hendrik Bluhm, Kyoung-Shin Choi, Roel van de Krol, David E. Starr, and Giulia Galli; J. Am. Chem. Soc. 2022, 144, 37, 17173–17185; https://doi.org/10.1021/jacs.2c07501



Spectroscopic analysis with tender X-rays: SpAnTeX, a new AP-HAXPES end-station at BESSY II

We introduce a new facility at BESSY II for in situ spectroscopic analysis with tender X-rays, called SpAnTeX. This setup features a state-of-the-art electron spectrometer that performs efficiently under gas pressures up to 30 mbar and photon energies from 200 eV to 10 keV. It can capture photoelectron spatial distribution with high resolution and conduct time-resolved studies. An example experiment demonstrates its use with the dip-and-pull technique, highlighting its electrochemical capabilities. The end-station supports various interface investigations, including solid/liquid and solid/gas, making it versatile for advanced materials research.

Figure: ©HZB

Marco Favaro*, Pip C.J. Clark, Micheal J. Sear, Martin Johansson, Sven Maehl, Roel van de Krol, David E. Starr*; Surf. Sci. 2021, 713, 121903; https://doi.org/10.1016/j.susc.2021.121903