Project Overview

This project explores the interaction of Cr-tetraphenylporphyrin (Cr-TPP) and Cr-TPPCl with KTaO3 (001) surfaces, optimizing photocatalytic water splitting for solar hydrogen production. Perovskite-based oxides exhibit unique electronic properties that enhance charge transfer and catalytic efficiency, making them promising candidates for sustainable energy applications.

Research Objectives

• Investigate charge transfer and separation mechanisms between Cr-TPP and KTaO3 in photocatalytic reactions.

• Examine Cr-TPP and Cr-TPPCl complexation on KTaO3 (001) slab models to determine favorable interaction energies.

• Conduct density functional theory (DFT) simulations to analyze electronic structures, charge distribution, and reaction feasibility.

Methodology & Computational Details

• DFT Calculations using Vienna Ab Initio Simulation Package (VASP).

• Exchange-Correlation Functional: Perdew-Burke-Ernzerhof (PBE) of Generalized Gradient Approximation (GGA).

• Cutoff Energy: 450 eV for plane-wave basis set.

• K-Point Mesh: 2 × 2 × 1 grid for Brillouin zone sampling.

• Ueff Parameter: 3 eV for Cr (3d transition metal) to account for on-site Coulomb interactions in Cr-TPP.

• Charge Transfer Analysis: Computed using VTST tools to assess charge redistribution trends.

Key Results & Findings

1. Structural & Energetic Stability of Cr-TPP on KTaO3

• Interaction energy analyses revealed higher stability when Cr-TPP is in flat orientation vs. tilted alignment.

• Structure E exhibited the most favorable interaction energy (-2.38 eV), while Structure A was least favorable (+1.80 eV).

• Figure 1: Coordination and interaction energy trends of Cr-TPP on KTaO3 (001).

2. Effect of Cl- Coordination in Cr-TPPCl

• Cl- insertion significantly influenced charge transfer and interaction energy.

• Highest interaction energy for Cr-TPPCl complexes was observed in Structure B1 (-1.99 eV).

• Charge transfer analysis confirmed enhanced charge redistribution in B1 vs. B, correlating with increased interaction energy.

• Figure 2: Impact of Cl- insertion on Cr-TPPCl interaction energy.

3. Charge Difference & Mechanistic Insights

• Charge transfer from Cr-TPP/Cr-TPPCl to KTaO3 was directly correlated with interaction energy variations.

• Surface reconstruction and oxidation states modulate complex stability and photocatalytic activity.

• Figure 3: Charge transfer analysis for critical structural cases.

Figure1: Results from DFT calculations showing the coordination of a Cr-tetraphenylporphyrin (Cr-TPP) on KTaO3[001]. The interaction energies (IE) between Cr(3+)-TPP with KTaO3[001] complexes are given in eV

Figure2: Results from DFT calculations showing the Cr-tetraphenylporphyrin chloride (Cr-TPPCl) on KTaO3[001]. The interaction energies (IE) between Cr(2+)-TPPCl with KTaO3[001] complexes are given in eV

Figure3: Charge Difference analyses for E, E1 and B, B1.

Conclusion & Impact

This research provides new insights into the interaction mechanisms of metalloporphyrins on perovskite oxide surfaces, supporting advanced material designs for photocatalysis. By optimizing Cr-TPP and Cr-TPPCl interactions on KTaO3, the findings contribute to the development of efficient solar-driven hydrogen production systems, a key step toward sustainable energy solutions.

Research Significance & Future Directions

• Optimizing perovskite-based catalysts for scalable photocatalytic hydrogen generation.

• Extending DFT-based charge transfer modeling to predict transition-metal complex interactions with different oxide surfaces.

• Investigating alternative transition metals (Mn, Fe, Co) in metalloporphyrins for solar-driven hydrogen production.

Funding & Acknowledgements

This research was supported by Mitsui Chemicals, Inc.-Carbon Neutral Research Center (MCI-CNRC) at the International Institute for Carbon-Neutral Energy Research (I2CNER), Kyushu University.