Density functional theory study on the electronic properties of doped-cobalt oxide (CoO)

Cobalt oxide (CoO) has been widely studied for photocatalyst of water splitting and displaying a high-efficiency material. This paper reports a Density Functional Theory (DFT) study on the electronic properties of rock-salt CoO and analyzes effects of cations (Ni and Fe) and anions (N and F) dopants on the electronic properties. For this purpose, CASTEP software used for first principles plane-wave pseudo-potential calculations at different functional, i.e: GGA-PW91 and LDA. The electronic calculations of the CoO optimized structure showed a metallic structure if without considering spin-orbital interactions. After considering the spin-orbital interaction calculation, the CoO band structure possessed indirect and direct band gaps. The direct bandgap by GGA-PW91 calculation is 2.10 eV, it was agreed to the experimentally reported value of approximately 1.9-2.6 eV. Meanwhile, Ni, Fe, and F-doped CoO, demonstrating decreased CoO direct band gaps to 1.70 eV, 1.80 eV, and 1.73 eV, respectively. While N-doped CoO increased the CoO direct bandgap to 3.05 eV. All dopants shifted the conduction and valence bands position, where Ni-doped CoO band edges keep straddle to the redox potential of water splitting. Among other elements in this study, Ni is a more desirable dopant of CoO to enhance photoelectrochemical hydrogen production

Sintesis, pencirian spektroskopi dan sifat fotomangkin Rutenium(II) Bis(bipiridil)-2-(1H-pirazol-3-il)piridil

Kompleks Ru(II), [Ru(bpy)2(pypzH)](PF6)2 dengan bpy = 2,2’-bipiridil dan pypzH= 2-(1H-pirazol-3-il)piridin, telah berjaya disintesis dan dicirikan dengan teknik spektroskopi transformasi Fourier inframerah (FTIR), ultralembayung dan cahaya nampak (UV-Vis), resonans magnet nukleus (RMN), serta spektrometer jisim. Pengiraan dengan kaedah teori fungsi ketumpatan (DFT) dan DFT bersandar masa (TD) telah dijalankan untuk membangunkan struktur optimum dan elektronik kompleks Ru(II). Data yang diperoleh menunjukkan orbital molekul terisi dengan tenaga tertinggi (HOMO) disetempatkan pada logam Ru(II) dan ligan pypzH, manakala orbital molekul tidak terisi dengan tenaga terendah (LUMO) didapati tersebar secara menyeluruh pada kedua-dua struktur ligan bpy. Aktiviti fotomangkin kompleks telah diuji terhadap penguruaian pewarna tekstil bromotimol biru (BTB) disebabkan aktiviti foto [Ru(bpy)2(pypzH)](PF6)2 di bawah sinaran lampu xenon 450W (AM 1.5, penapis inframerah). Kadar dan tertib tindak balas foto-uraian BTB dikenal pasti dan dibincangkan bersama dengan mekanisma foto-uraian BTB

Kesan resonans plasmon aurum terhadap prestasi fotoelektrokimia fotokatod Cu2O

Dalam kajian ini, kesan lapisan Au di atas fotokatod kuprus oksida (Cu2O) terhadap tindak balas fotoelektrokimia telah diuji. Lapisan Cu2O dan Au ini telah disediakan di atas subtrak kaca stanum oksida terdop fluorin (FTO) dalam konfigurasi yang berlainan, melalui kaedah elektroendapan. Selepas itu, fotokatod ini dicirikan dengan mikroskopi elektron imbasan berpancaran medan (FESEM), spektroskopi ultra lembayung dan cahaya nampak (UV-Vis) dan analisis fotoelektrokimia. Daripada imej FESEM, lapisan Au telah berjaya diendapkan di atas substrak FTO dan permukaan Cu2O. Penyerapan plasmon Au pada julat cahaya nampak juga terbukti dan ia telah mempertingkatkan penggunaan cahaya nampak untuk tindak balas fotoelektrokimia. Oleh itu, prestasi fotoelektrokimia fotokatod Cu2O berplasmon telah meningkat secara ketara. Di bawah sinaran suria simulasi A.M 1.5, fotokatod Cu2O terapit Au telah menjanakan ketumpatan fotoarus yang tertinggi, iaitu ~4 kali ganda peningkatan berbanding prestasi fotokatod Cu2O tulen

Synthesis, characterization and performance evaluation of three-layered photoanodes by introducing a blend of WO3 and Fe2O3 for dye degradation

A three-layered photoanode has been synthesized by the introduction of an additional layer of mixed WO3 and Fe2O3. A total of nine differently-packaged films were prepared by sol-gel method. The fabricated photoanodes were then successfully characterized by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). A comparative study was also done to differentiate the films fabricated with WO3, Fe2O3 and their mixture. Compact, columnar tree and shallow patterns were observed on the cross cleavage of the synthesized layers. These distinct patterns were associated with the growth of layers which consequently led to unique surface morphologies. An increase in photocurrent density was observed on the bicomponent film which has been linked to a high degree of surface roughness as well as improved internal porosity. Three-layered photoanodes, modified with an additional bicomponent layer of WO3:Fe2O3 established much higher photocurrent outputs compared to that of nanostructured WO3 or Fe2O3, regardless of the bicomponent layer arrangement. However, with the bicomponent layer on top and middle, the measured photocurrent soared more than three times as much compared to a slight increase observed when the bicomponent was placed on the bottom

Composite of titanium dioxide nanotube and cobalt sulfide for photoelectrochemical application

TiO2 nanotubes (NT) offer several advantages over other geometries for photoelectrochemical (PEC) applications. However, their performance in PEC water-splitting application has remained unsatisfactory due to its wide bandgap. To address this limitation, one approach is the incorporation of other materials as co-catalysts. Hence, in this study, a composite of TiO2 NT and cobalt sulfide (Cox Sy ) was successfully synthesized, and its potential as a photoelectrode for water molecules splitting was evaluated. The TiO2 NT was synthesized using electrochemical anodization of Ti foil, followed by annealing at 500 °C. Subsequently, Cox Sy was added to the TiO2 NT using hydrothermal method, and the composite was further annealed at 400 °C. Characterization technique, such as FESEM and XRD were employed to identify the morphological and phase structures, while UV-Vis reflectance spectroscopy was used for optical analysis. The efficiency of Cox Sy deposited on to TiO2 NT were evaluated by measuring the photocurrent generation. Remarkably, the sample of 60_Cox Sy /TiO2 NT exhibited photocurrent as high as 0.375 mA/ cm2 which is over sixfold higher than the bare TiO2 NT. The results reported in this study were higher than those reported previously

Hydrogen production from water splitting using TiO2 /CoS composite photocatalyst

Photocatalytic water splitting reaction has been considered an ideal method for hydrogen generation. In this study, a composite of TiO2 /CoS photocatalyst prepared by hydrothermal synthesis method assisted by ball milling crushing process was used. The TiO2 /CoS composites prepared with three variation compositions of 90/10, 80/20, and 70/30 were named M-10, M-20, and M-30, respectively. Field-emission scanning electron microscopy images showed that the morphologies of the composites were porous and uniform of nanospheres. The X-ray diffraction and energy dispersive spectroscopy analyses confirmed the presence of CoS in the composites. Ultraviolet–visible absorption characterization demonstrated the smallest bandgap value of approximately 2.72 eV presented by sample M-30 with the photocurrent density of 0.32 mA cm−2 at 0.9 V vs. Ag/AgCl. The presence of CoS in this study could increase the PC hydrogen generation of TiO2 by nearly 2.5 times. The composites forming a p-n heterojunction between TiO2 and CoS could prevent electron–hole recombination and increase the overall photoactivity of TiO2.

Experimental and theoretical study of Cu2 O photoelectrode and Cu2 O doped with Ag, Co, Ni and Zn metals for water splitting application

In the present study, cuprous oxide nanowire fabricated using wet chemical oxidation method was proven to produce high photoactive film for photoelectrochemical (PEC) water splitting. A relatively high photocurrent density of -5mA cm-2 at 0.6V vs Ag/AgCl was generated. The PEC performance is the reflection of intrinsic light absorption capacity at visible region which correspond to 2.0eV, an ideal band gap for PEC water splitting. Comparison with calculated data based on density functional theory using CASTEP shows that the band gap and light absorption capacity obtained from experimental work exhibited a close match. Hence, this study suggested that the preparation of Cu2 O thin film via wet chemical oxidation method obeyed the theoretical prediction. However, the Cu2 O is limited with poor stability in PEC condition attributed to the insufficient potential of its valence band to oxidize water. Therefore, an effort was directed to address the feasibility of shifting the valence band by modeling a doped Cu2 O with several dopants using DFT technique. The selected dopants were Ag, Co, Ni and Zn. Preliminary conclusion of this study indicated that doping could be used to tune the band gap of Cu2 O due to ionic radii of the dopant affected the shifting of band gap. In this study, Co showed more significant improvement of Cu2 O for photoelctrochemical water splitting process. However, to validate the simulation, further study should be carried out experimentally

Effect of intermediate layer in photocurrent improvement of three-layer photoanodes using WO3 and Fe2O3

Sol–gel method was applied to synthesize WO3/Fe2O3 three-layer films in order to improve the generated photocurrent under UV–vis light irradiation. The films were deposited on FTO glass substrates through doctor bladding method. The samples were then calcined at 500 °C. The photocurrents of the synthesized photoanodes were evaluated by measuring the electric current and voltage under UV–vis light at room temperature. Scanning electron microscopy (SEM) revealed unique surface morphologies owing to the presence of the intermediate layers. At an applied potential of 1300 mV, the WO3\Fe2O3\WO3 and Fe2O3\WO3\Fe2O3 photoanodes exhibited photocurrent densities up to 0.1 mA/cm2 and 0.6 mA/cm2, respectively. It was found that porous films with easy accessibility to the inner surface reveal high photocurrents. The intermediate layer of WO3 demonstrated higher values of photocurrent due to roughness enhancement on the upper surface with columnar tree-growth particles. However, a compact state was observed on the cross section of Fe2O3 growth. A comparison was also drawn between the two and three-layer photoanodes using Fe2O3 andWO3. The films were characterized by XRD, SEM/EDX, and UV–vis irradiation to determine the photocurrent densities

Copper nanoparticles coating on FTO with improved adhesion using direct and pulse electrodeposition techniques from a simple copper sulphate solution

Copper (Cu) metal nanoparticles were deposited onto FTO glass using the electrodeposition method. The precursor used was CuSO4 ⋅5H2 O with Na2 SO4 as the inorganic additive. The formation of Cu was characterized using field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). This study investigated the impacts of the electrodeposition method (direct electrodeposition vs. pulse electrodeposition), voltages (-0.4 V and -0.8 V), electrodeposition time (60s to 900s) and pulse cycles (50 cycles to 300 cycles), and FTO etching (fixed to 20s etching) towards the morphology and adhesion of Cu deposited. The grain size and thickness of Cu deposited vary with deposition time and pulse cycles. The voltage of -0.4 V successfully deposits shiny, metallic brown Cu onto FTO glass. Meanwhile, the voltage of -0.8 V gives powdery brown Cu on the surface. In addition, compared to direct electrodeposition (DD), pulse electrodeposition (PD) provides a more compact and homogeneous coverage of Cu onto FTO glass. The tape-test results also indicate that FTO etching by electrolysis reduction can improve the adhesion strength between deposited thin Cu film and the FTO glass. This work demonstrates a facile electrodeposition technique with substrate etching as an effective deposition of Cu metal with the potential for application in a wide range of fields

3D Free-standing graphene: influence of etching solution and etching time on chemical vapor deposition on the graphene/nickel foam

Three-dimensional (3D) structures made of graphene sheets have been developed recently, and have resulted in the development of a new class of graphene materials known as 3D graphene materials. High-quality free-standing 3D graphene foam has been synthesized by chemical vapor deposition (CVD) on nickel foam followed by a chemical etching process to remove the nickel foam as a template. Field-emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), and Raman spectroscopy measurements were performed to investigate the morphologies, crystal phase, and the structure of nickel foam (NF), graphene/nickel foam (Gr/NF), and 3D graphene (3D Gr). In this study, the influence of etching solution and etching time on Gr/NF to produce free-standing 3D Gr was investigated. XRD spectroscopy showed that the mixed solutions of 1M FeCl3:1M HCl at 80 °C for 3 h can significantly remove the NF and no peaks of NF are observed, thus indicating a high crystal quality of 3D Gr was obtained. In addition, XRD spectroscopy revealed that by increasing the etching time beyond 3 h, the intensity of diffraction peaks decreases, thus degrading graphene quality. This research emphasizes the significance of proper selections of etching solution and etching time in removing the NF to maintain the characteristic, quality, and surface morphology of 3D Gr after the etching process