Microwave-Assisted Synthesis and Processing of Al-Doped, Ga-Doped, and Al, Ga Codoped ZnO for the Pursuit of Optimal Conductivity for Transparent Conducting Film Fabrication

This work reports the microwave-assisted fabrication of highly conducting Al-doped ZnO (AZO), Ga-doped ZnO (GZO), and Al, Ga codoped ZnO (AGZO) materials as cheaper earth abundant alternatives to indium tin oxide (ITO) for transparent conducting applications. All three doped ZnO powder samples were compressed into pellets, and their electrical properties were evaluated after the postsynthesis heat treatment. The heat treatment was performed by sintering the pellets at 600 °C in a reducing atmosphere using either conventional radiant annealing for 3 h or microwave annealing for 90 s. The Al and Ga dopant levels were systematically varied from 0.5 to 2.5 at. %, and it was found that the lowest resistivity values for the pelleted singly doped ZnO powders exist when the doping level is adjusted to 1.5 at. % for both AZO and GZO, giving resistivity values of 4.4 × 10–3 and 4.3 × 10–3 Ω·cm, respectively. The lowest resistivity of 5.6 × 10–4 Ω·cm was achieved for the pelleted codoped AGZO powder using the optimized Al and Ga dopant levels. Notably, this value is one magnitude lower than the best literature reported value for conventionally synthesized codoped AGZO powder. The resistivity values obtained for the pellets after radiant and microwave postsynthesis heat treatment are comparable, although the microwave heat treatment was performed only for 90 s, compared to 3 h for conventional radiant heat treatment. Hence, significant gains were made in the postannealing step by reducing time, cost, and energy required, benefiting our thrust for finding sustainable routes toward alternative low-cost transparent conducting oxides. As a proof of concept, transparent conducting thin films were fabricated via a simple aerosol-assisted deposition technique using our best conducting AGZO nanoparticles. The films exhibited a visible transmittance as good as 90% and a resistivity of 5.7 × 10–3 Ω·cm, which can compete with the existing high cost ITO films

Indium tin oxide nanowires manufactured via printing and laser irradiation

Metallic and semiconductor nanowires can provide dramatically increased electrical and optical properties in a wide range of fields, ranging from photovoltaics to sensors and catalysts. In this research, a rapid manufacturing process has been developed for printing indium tin oxide microparticles and converting them into nanowires. Microparticle indium tin oxide (ITO) inks were formulated and printed. These were then converted into hierarchical nanowire films via laser irradiation (980 nm, NIR) with raster speeds of 40 mm s−1 in air, much faster compared to traditional manufacturing processes. For a 4 cm2 film, only 40 s of processing were required. A full materials characterization was performed on the materials pre and post laser processing with the most probable conversion mechanism found to be a laser induced carbothermal reduction process. Microstructural, chemical, and crystallographic evidence of the laser induced carbothermal reduction process were derived from SEM, XRD, XPS and TEM analysis. Compared to conventionally heat-treated printed samples, laser processing was found to increase the conductivity of the printed ITO from 0.88% to 40.47% bulk conductivity. This research demonstrates the ability of printing and laser processing to form nanowires in a high-speed manufacturing context, thereby enabling the development of printed non-transparent ITO nanowire electronics and devices

The Pseudocapacitive Nature of CoFe 2 O 4 Thin Films

This is the author accepted manuscript. The final version is freely available from Elsevier via the DOI in this record.Nanostructured Cobalt ferrite (CoFe2O4) thin films are fabricated by aerosol-assisted chemical vapour deposition (AACVD) and studied for application in supercapacitors. XRD and Raman spectroscopic analysis confirms the formation of single phase CoFe2O4. SEM analysis shows that the thin film morphology consists of nanoparticles less than 100 nm in size that are sintered together to form larger dendrites raised from the substrate. The larger dendrites range from 0.5–1 μm in diameter and are uniformly distributed over the FTO substrate, providing a highly porous structure which is desired for supercapacitor electrodes. Three-electrode electrochemical measurements reveal that CoFe2O4 is pseudocapacitive and is highly conducting. Studies of CoFe2O4 thin films in two-electrode symmetric supercapacitor configuration show a capacitance of 540 μF cm−2 and a relaxation time constant of 174 ms. Around 80% of the capacitance is retained after 7000 charge-discharge cycles when a maximum charging voltage of 1 V was used, indicating that the pseudocapacitive processes in CoFe2O4 are highly reversible and that it exhibits excellent chemical stability in 1 M NaOH alkaline electrolyte solution. The results show that CoFe2O4 is a cheap and promising alternative pseudocapacitive material to replace the expensive pseudocapacitive materials.All authors acknowledge the support given by the members of ERL to successfully conduct this research. JS and KGUW acknowledge the support from UK EPSRC (EP/L017709/1). AAT contributed to the initial work of this investigation in 2011 when he was a member of the ERL team and working under the project funded by EPSRC EP/F057342/1. The authors acknowledge use of facilities within the Loughborough Materials Characterisation Centre (LMCC). We would also like to thank Patricia Cropper for her assistance in obtaining XPS measurements

Electrodeposition of BiVO<inf>4</inf> with needle-like flower architecture for high performance photoelectrochemical splitting of water

Photoelectrochemical (PEC) water splitting is a green and sustainable approach capable of driving mass hydrogen production in the future. To realize this vision, development of a well-performing photoelectrode is highly demanded. In this comprehensive study, electrodeposition technique was applied for fabricating BiVO4 films by regulating the deposition time from 1 min until 9 min. Interestingly, the morphology, crystallinity, chemical structure, and optical properties of BiVO4 films depend strongly on the deposition time. It is found that BiVO4 layer deposited for 7 min with a cross-section thickness of around 321.1–326.5 nm showed the optimum performance, whereby the photocurrent reached up to ~0.32 mA/cm−2 at 1.23 V vs. RHE. The deposited BiVO4 represents tiny and long petals, similar to “needle” nanostructures, which is embedded closely into compact agglomerates. Such morphology enables the BiVO4 films to perform efficiently as photoanode in PEC cells. Besides, high crystallinity is detected from the sharp peaks of XRD and Raman analysis, as well as good light absorption capability that are the main contributors to the enhancement of PEC performance. In addition to the facile fabrication offered by electrodeposition method, the non-toxic attributes and the impressive PEC performance of the optimum BiVO4 layer could serve as an interesting option for other applications such as gas sensors, solar cells, degradation of pollutants and photocatalytic water splitting

Boosting photocatalytic activities of BiVO<inf>4</inf> by creation of g-C<inf>3</inf>N<inf>4</inf>/ZnO@BiVO<inf>4</inf> Heterojunction

© 2020 Elsevier Ltd BiVO4 has attracted great attention as a semiconductor for Photoelectrochemical (PEC) water splitting because of its low cost, good stability, and suitable band gap of 2.4 eV. In this research, the contribution of g-C3N4@ZnO on BiVO4 photoelectrochemical performance, light absorption, charge transportation, and morphology were investigated. Incorporation of g-C3N4/ZnO as underlying layer in heterojunction with BiVO4 boosted the photocurrent from ∼ 0.21 mA cm−2 for bare BiVO4 to 0.65 mA cm−2 for g-C3N4@ZnO/BiVO4 heterojunction composite structure at 1.23 V versus Ag/AgCl. The C and N elements derived from g-C3N4 on ZnO resulted in a tenacious interactions, lowered charge transfer resistance and increased light absorption of BiVO4. The high photoelectrochemical performance, together with good electrochemical impedance spectroscopy parameters and stability reveals g-C3N4/ZnO composite to be a suitable candidate in enhancing the performance of BiVO4 for PEC solar water splitting applications

Fabrication of exfoliated graphitic carbon nitride, (g-C<inf>3</inf>N<inf>4</inf>) thin film by methanolic dispersion

This paper reports the successful exfoliation of nanosheets from bulk g-C N by using urea as a precursor. The alteration from bulk g-C N powder, changed its semiconductor arrangements such as the optical absorption, chemical bonding, and topography images. A slow direct low thermal treatment (∼40 °C, 24 h) was proposed as a formation of a thinner layer by layer, complete and effective polymerization for an exfoliated g-C N . The photocurrent responses were more than two times higher for exfoliated g-C N compared with bulk g-C N , reaching ∼4.37 μA cm up to 10.21 μA cm at 1.23 vs. (Ag/AgCl). This fabrication method involved dispersing of the highly stable g-C N suspension onto FTO surface via spin coating, followed by a moderate post-annealing temperature at 350 °C. The monolayer g-C N act as a photoelectrode, responding to light and dark current, and maintained its own intrinsic n-types properties. The interaction of the C and N atom with molecules of methanol (CH OH) followed with vibration force (ultrasonication) produces the ultrafast drying and can transmit to disrupt the van der Waals forces within the g-C N structure. Therefore, due to the ability the good performance, the exfoliated g-C N can be envisioned as a potential application such as water splitting, solar cell, and environmental remediation. 3 4 3 4 3 4 3 4 3 4 3 4 3 4 3 3 4 3 4 −2 −