Abstract
Photocatalytic water oxidation remains the bottleneck in many artificial photosynthesis devices. The efficiency of this challenging process is inherently linked to the thermodynamic and electronic properties of the chromophore and the water oxidation catalyst (WOC). Computational investigations can facilitate the search for favorable chromophore‐catalyst combinations. However, this remains a demanding task due to the requirements on the computational method that should be able to correctly describe different spin and oxidation states of the transition metal, the influence of solvation and the different rates of the charge transfer and water oxidation processes. To determine a suitable method with favorable cost/accuracy ratios, the full catalytic cycle of a molecular ruthenium based WOC is investigated using different computational methods, including density functional theory (DFT) with different functionals (GGA, Hybrid, Double Hybrid) as well as the semi‐empirical tight binding approach GFN‐xTB. A workflow with low computational cost is proposed that combines GFN‐xTB and DFT and provides reliable results. GFN‐xTB geometries and frequencies combined with single‐point DFT energies give free energy changes along the catalytic cycle that closely follow the full DFT results and show satisfactory agreement with experiment, while significantly decreasing the computational cost. This workflow allows for cost efficient determination of energetic, thermodynamic and dynamic properties of WOCs.
Highlights
Chemical fuels produced by solar energy have shown potential as a clean energy alternative to carbon-based fossil fuels
We propose a computationally efficient workflow that combines GFN-xTB calculations for geometries and frequencies and B3LYP for energies, which leads to accurate relative Gibbs free energies along the catalytic cycle
All geometry optimizations as well as the vibrational analysis were performed with the Amsterdam Density Functional (ADF) and Density Functional Tight-Binding (DFTB) engines of the Amsterdam Modeling Suite (AMS) program package.[41,42,43]
Summary
Chemical fuels produced by solar energy have shown potential as a clean energy alternative to carbon-based fossil fuels. In addition to the catalyst itself, the coupling of the WOC to a suitable photooxidative dye is challenging due to the different requirements for oxidation potentials and HOMO energies for the different catalytic steps that involve a number of oxidation states of the transition metal. The other possible pathway involves two 2[Ru(V) = O]+ forming the 1[Ru(IV)-O-O-Ru(IV)]2+ dimer through a radical coupling mechanism: this mechanism has been called interaction of two metal oxo species (I2M) or radical oxo coupling (ROC) in the literature.[32,33] This binuclear reaction pathway often shows higher turnover frequencies and lower overpotentials than the WNA pathway. We evaluate the different methods with respect to predicting the correct catalytic pathway
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
