Density functional theory study of Cu doped {0001} and {0112} surfaces of hematite for water splitting

Density Functional Theory (DFT) calculations study of Cu doped {0001} and {01-12} surfaces of hematite for enhanced water splitting have been carried out. The doping was restricted to planes in the vicinity of the surface, specifically from the top most layers to the third inner layer of Fe atoms. Thermodynamic stabilities were evaluated based on surface energies and formation energies. The evaluation of thermodynamic stabilities (negative formation energy values) shows that the systems are thermodynamically stable which suggest that they can be synthesized in the laboratory under favorable conditions. Doping on the top most layer yields the energetically most favorable structure. The calculated charge density difference plots showed the concentration of charge mainly at the top of the surface (termination region), and this charge depleted from the Cu atom to the surrounding Fe and O atoms. This phenomenon (concentration of charge at the top of the surface) is likely to reduce the distance moved by the charge carriers, decrease in charge recombination leading to facile transfer of charge to the adsorbate and, suggesting improved photoelectrochemical water oxidation activity of hematite. The analysis of electron electronic structure reveals that Cu doped surface systems does not only decrease the band gap but also leads to the correct conduction band alignment for direct water splitting without external bias voltage.Dr. Richard Andrew (formerly at University of Pretoria and now at University of Johannesburg) is acknowledged for his initial guidance in the DFT. Thanks to the Copperbelt University for funding under the staff development fellowship fund. Further gratitude goes to the University of Pretoria and the Center for High Performance Computing (CHPC), Research Institute in Cape Town, South Africa for the cluster resources. AB and MD acknowledges financial support from the Swiss South African Joint Research Programme project “Production of Liquid Solar Fuels from CO2 and water: Using Renewable Energy Resources” (IZLSZ2-149031). AB is grateful from the Swiss Nano Tera project SHINE (Solar Hydrogen Integrated Nano Electrolyzer, 20NA21-145936).The Copperbelt University for funding under the staff development fellowship fund. AB and MD acknowledges financial support from the Swiss South African Joint Research Programme project “Production of Liquid Solar Fuels from CO2 and water: Using Renewable Energy Resources” (IZLSZ2-149031). AB is grateful from the Swiss Nano Tera project SHINE (Solar Hydrogen Integrated Nano Electrolyzer, 20NA21-145936).https://www.cambridge.org/core/journals/mrs-advancesam2018Physic