Solar fuel production (Photoelectrocatalysis)
A promising sustainable solution for solar energy harvesting and utilization is artificial photosynthesis: the sunlight is used to split the water molecules and subsequently either reduce the CO2 producing methane and methanol, or evolve H2 molecules. We computationally design photoelectrocatalysts suitable for such application. Specifically, we study two main properties: the catalytic activity; and the materials ability to harvest light and create carriers that will be further used to activate the chemical reactions. Following similar approaches as for solar cell materials, we investigate the optical properties and band alignments. The primary difference here is that we align the band edge potentials with free energies of relevant reactions to estimate whether or not the excited carriers display the proper potentials to facilitate the reaction (promote charge transfer) from the thermodynamics viewpoint.
In particular, we predict the enhanced water splitting activity of recently synthesized two dimensional (2D) semiconducting materials MX2 (where M=Ti, Hf, Zr and X=S, Se, Te), hydrogenated silicene, stanene and phosphorene from the band edge alignment concept. The real catalytic mechanism of water dissociation is hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) which are needed to be envisaged together with the band edge alignment. A fundamental understanding of how to improve solar hydrogen production with such 2D materials is of great technological importance. We have performed a theoretical investigation [1, 2] in order to find the optimum photocatalytic activity of ultra-thin silicane and germanane with a series of functionalizing adatoms. HER and OER activity are determined from the surface-adsorbate interaction. This study can be an intuitive way to theoretically rationalize HER and OER activity for a series of functionalized different two-dimensional systems before performing the actual experiment in the laboratory. A comparative study of HER mechanism on WS2 and PtS2 monolayers has also been performed recently . The lightest 2D catalytic material has been found in the form of Boron monolayer based on our electronic structure calculations . We have also investigated a novel defect engineered g-C3N4 nanosheet produced by hydrogen treatment . On the basis of experimental as well as DFT calculations, it has been shown that the formation of two-coordinated nitrogen vacancy in g-C3N4 is responsible for the narrowed band gap and the enhancement in solar absorption. With improved optical absorption in the visible range, higher surface area, open pore structure, and lower rate of electron−hole recombination of the defective g-C3N4, it leads to higher photocatalytic activity as compared to pristine g-C3N4.
- Rationalizing Hydrogen and Oxygen Evolution Reaction Activity of Two-dimensional Hydrogenated Silicene and Germanene, C. Rupp, Sudip Chakraborty, J. Anversa, R. Baierle, R. Ahuja, ACS Appl. Mater. Interfaces, 8, 1536 (2016).
- The effect of impurities in ultra-thin hydrogenated silicene and germanene: A first principles study, C. Rupp, Sudip Chakraborty, R. Ahuja, R. Baierle, PhysChemChemPhys, 17, 22210 (2015).
- A Comparative Study of Hydrogen Evolution Reaction on WS2 and PtS2 pseudo-monolayer: Insight based on Density Functional Theory, S. H. Mir, Sudip Chakraborty, J. Warna, S. Narayan, P. C. Jha, P. K. Jha, R. Ahuja, Catalysis Science & Technology, 7, 687-692 (2017).
- Two-dimensional Boron: Lightest Catalyst for Hydrogen and Oxygen Evolution Reaction, S. Mir, Sudip Chakraborty, P. K. Jha, J. Warna, H. Soni, P. Jha, R. Ahuja, Applied Physics Letters, 109, 053903 (2016).
- Defect Engineered g-C3N4 for Efficient Visible Light Photocatalytic Hydrogen Production, Q. Tay, P. Kanhere, C. Ng, S. Chen, Sudip Chakraborty, A. Huan, T. Sum, R. Ahuja, and Z. Chen, Chemistry of Materials, 27, 4930 (2015).