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How can theory help with rapid screening of promising photocatalysts in solvent?
JCAP scientists are developing novel theoretical methods to predict the effect that solvents have on material properties — and consequently the photoelectrochemical performance — inside solar-fuels generators.
Inside a working integrated device that uses solar energy to convert carbon dioxide and water into fuels, chemical reactions occur on solid-liquid interfaces, where the solid is a photocatalyst and the liquid is a solvent. The efficiency of these fuel forming and oxygen evolving reactions depends on several parameters, including the alignment of a photocatlyst’s electronic states with solvent’s redox potential. Since solvent can affect the band edge positions of photocatalytic materials, JCAP theorists are developing and testing continuum methods, which pave the way for rapid screening of new materials and their performance in solvents, rather than in a vacuum.
Image is reproduced from Ping, Y., Sundararaman, R. & Goddard, W. A. Solvation effects on the band edge positions of photocatalysts from first principles. Physical Chemistry Chemical Physics, DOI: 10.1093/C5CP05740J (2015). With permission of the PCCP Owner Societies.
Using correlations between solvation shift and the type of surface and solvent, researchers are able to suggest approaches to engineer the band positions of surfaces in aqueous and non-aqueous solutions.
Recent results from these studies have been published in a Physical Chemistry Chemical Physics article by Dr. Yuan Ping, Dr. Ravishankar Sundararaman, and Prof. William A. Goddard III, in which the new theoretical models were used to predict the solvation effects on well-studied surfaces of silicon, titanium oxide, iridium oxide, and tungsten oxide in water. The results were found to be in good agreement with more computationally intensive ab initio molecular dynamics results and experimental measurements.
JCAP has advanced the traditional continuum solvation models to include treatment of ionic surfaces without the use of empirical parameters; however, many challenges still remain. Dr. Yuan Ping notes that it is “challenging to work with photocatalytic surfaces that have strong interactions with a solvent.” Certain materials can form chemical bonds with solvent molecules or develop surface defects as a result of interacting with a solvent. These cases require explicit consideration of the first layer of solvent to describe accurately these interactions and processes, and these calculations are under way.
The role that a solvent plays in interfacial energetics cannot be overstated. The novel computational method developed by Dr. Ravishankar Sundararaman and tested by Dr. Yuan Ping takes into account the electrostatic and van der Waals interactions with a solvent, allowing for accurate prediction of the shifts in the band edge position as large as 2 eV for materials that have an oxygen-deficient surface. The new method also shows how solvation effects differ for hydrophobic and hydrophilic materials. Possessing an accurate predictive knowledge of the correlation between solvation shifts, nature of the material surface, and the solvent, opens the door for in silico design of new efficient photoelectrochemical cells, where theory is used to examine many possible new combinations of photocatalysts and solvents.
- Written by X. Amashukeli
This work is performed by the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy (Award No. DE-SC0004993).
Publication
- Ping, Y., Sundararaman, R. & Goddard, W. A. Solvation effects on the band edge positions of photocatalysts from first principles. Physical Chemistry Chemical Physics, DOI: 10.1039/C5CP05740J(2015).