scholarly journals Ab Initio Studies of Bimetallic-Doped {0001} Hematite Surface for Enhanced Photoelectrochemical Water Splitting

Catalysts ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 940
Author(s):  
Joseph Simfukwe ◽  
Refilwe Edwin Mapasha ◽  
Artur Braun ◽  
Mmantsae Diale

First-principles calculations based on density functional theory (DFT) were carried out to study the energetic stability and electronic properties of a bimetallic-doped α-Fe2O3 photoanode surface with (Zn, Ti) and (Zn, Zr) pairs for enhanced PEC water splitting. The doped systems showed negative formation energies under both O-rich and Fe-rich conditions which make them thermodynamically stable and possible to be synthesised. It is found that in a bimetallic (Zn, Ti)-doped system, at a doping concentration of 4.20% of Ti, the bandgap decreases from 2.1 eV to 1.80 eV without the formation of impurity states in the bandgap. This is favourable for increased photon absorption and efficient movement of charges from the valance band maximum (VBM) to the conduction band minimum (CBM). In addition, the CBM becomes wavy and delocalised, suggesting a decrease in the charge carrier mass, enabling electron–holes to successfully diffuse to the surface, where they are needed for water oxidation. Interestingly, with single doping of Zr at the third layer (L3) of Fe atoms of the {0001} α-Fe2O3 surface, impurity levels do not appear in the bandgap, at both concentrations of 2.10% and 4.20%. Furthermore, at 2.10% doping concentration of α-Fe2O3 with Zr, CBM becomes delocalised, suggesting improved carrier mobility, while the bandgap is altered from 2.1 eV to 1.73 eV, allowing more light absorption in the visible region. Moreover, the photocatalytic activities of Zr-doped hematite could be improved further by codoping it with Zn because Zr is capable of increasing the conductivity of hematite by the substitution of Fe3+ with Zr4+, while Zn can foster the surface reaction and reduce quick recombination of the electron–hole pairs.

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Abdur Rauf ◽  
Muhammad Adil ◽  
Shabeer Ahmad Mian ◽  
Gul Rahman ◽  
Ejaz Ahmed ◽  
...  

AbstractHematite (Fe2O3) is one of the best candidates for photoelectrochemical water splitting due to its abundance and suitable bandgap. However, its efficiency is mostly impeded due to the intrinsically low conductivity and poor light absorption. In this study, we targeted this intrinsic behavior to investigate the thermodynamic stability, photoconductivity and optical properties of rhodium doped hematite using density functional theory. The calculated formation energy of pristine and rhodium doped hematite was − 4.47 eV and − 5.34 eV respectively, suggesting that the doped material is thermodynamically more stable. The DFT results established that the bandgap of doped hematite narrowed down to the lower edge (1.61 eV) in the visible region which enhanced the optical absorption and photoconductivity of the material. Moreover, doped hematite has the ability to absorb a broad spectrum (250–800) nm. The enhanced optical absorption boosted the photocurrent and incident photon to current efficiency. The calculated results also showed that the incorporation of rhodium in hematite induced a redshift in optical properties.


2015 ◽  
Vol 17 (4) ◽  
pp. 2634-2640 ◽  
Author(s):  
Joseph H. Montoya ◽  
Monica Garcia-Mota ◽  
Jens K. Nørskov ◽  
Aleksandra Vojvodic

Density functional theory results describing the theoretical electrocatalytic properties of perovskite oxides and oxynitrides suggest that the water splitting reaction will require cocatalysts due to high theoretical oxygen evolution and hydrogen evolution overpotentials.


Energies ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 150
Author(s):  
Yin-Pai Lin ◽  
Boris Polyakov ◽  
Edgars Butanovs ◽  
Aleksandr A. Popov ◽  
Maksim Sokolov ◽  
...  

Transition metal dichalcogenide (TMD) MoS2 and WS2 monolayers (MLs) deposited atop of crystalline zinc oxide (ZnO) and graphene-like ZnO (g-ZnO) substrates have been investigated by means of density functional theory (DFT) using PBE and GLLBSC exchange-correlation functionals. In this work, the electronic structure and optical properties of studied hybrid nanomaterials are described in view of the influence of ZnO substrates thickness on the MoS2@ZnO and WS2@ZnO two-dimensional (2D) nanocomposites. The thicker ZnO substrate not only triggers the decrease of the imaginary part of dielectric function relatively to more thinner g-ZnO but also results in the less accumulated charge density in the vicinity of the Mo and W atoms at the conduction band minimum. Based on the results of our calculations, we predict that MoS2 and WS2 monolayers placed at g-ZnO substrate yield essential enhancement of the photoabsorption in the visible region of solar spectra and, thus, can be used as a promising catalyst for photo-driven water splitting applications.


Author(s):  
Ahmad Ranjbar ◽  
Hossein Mirhosseini ◽  
Thomas D Küehne

Abstract We performed virtual materials screening to identify promising topological materials for photocatalytic water splitting under visible light irradiation. Topological compounds were screened based on band gap, band edge energy, and thermodynamics stability criteria. In addition, topological types for our final candidates were computed based on electronic structures calculated by means of hybrid density functional theory including exact Hartree-Fock exchange. Our final list contains materials which have band gaps between 1.0 eV and 2.7 eV in addition to band edge energies suitable for water oxidation and reduction. However, the topological types of these compounds calculated with the hybrid functional differ from those reported previously. To that end, we discuss the importance of computational methods for the calculation of atomic and electronic structures in materials screening processes.


2015 ◽  
Vol 17 (8) ◽  
pp. 5817-5825 ◽  
Author(s):  
Weiyan Guo ◽  
Yating Guo ◽  
Hao Dong ◽  
Xin Zhou

Se-doped and I-doped β-Ga2O3 are theoretically found to be promising photocatalysts for water splitting in the visible region.


MRS Advances ◽  
2018 ◽  
Vol 3 (13) ◽  
pp. 669-678 ◽  
Author(s):  
Joseph Simfukwe ◽  
Refilwe Edwin Mapasha ◽  
Artur Braun ◽  
Mmantsae Diale

ABSTRACTDensity 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.


Sign in / Sign up

Export Citation Format

Share Document