Solution-based Synthesis Approach Research Articles

Versatility of group VI layered metal chalcogenide thin films synthesized by solution-based deposition methods

This review summarizes major developments in various solution-based synthesis approaches and different applications such as supercapacitors, batteries, HER, and photocatalytic dye degradation of group VI layered metal dichalcogenide thin films.

Compositional and structural control in LLZO solid electrolytes.

Garnet-based solid-state electrolytes (SSEs) represent a promising class of materials for next-generation batteries with improved safety and performance. However, lack of control over the composition and crystal structure of the well-known Li7La3Zr2O12 (LLZO) garnet material has led to poor reproducibility with a wide range of ionic conductivities reported in the literature. In this study, the role of precursor homogeneity in controlling the compositional and structural evolution of Al-doped LLZO is explored. A novel solution-based synthesis approach is employed to demonstrate enhanced atomic-scale mixing of the starting materials in comparison to conventional solid-state preparation methods. Through this technique, it is shown that the stability and formation temperature of the highly conductive cubic phase is directly impacted by the spatial distribution of the doping element and reactant species in the precursor mixture. Precursor homogeneity was also an important factor in mitigating the formation of unwanted secondary impurities. These findings can be used to guide the synthesis of SSEs with reproducible material characteristics and enhanced electrolytic performance.

Synthesis of Electrospun NASICON Li1.5Al0.5Ge1.5(PO4)3 Solid Electrolyte Nanofibers by Control of Germanium Hydrolysis

We report the synthesis of ceramic Li1.5Al0.5Ge1.5(PO4)3 (LAGP) nanofibers by combining sol–gel and electrospinning techniques. A homogeneous and stable precursor solution based on chlorides was achieved by controlling Ge hydrolysis. Subsequent electrospinning and heat treatment resulted in highly porous nanostructured NASICON pellets. After a full chemical-physical characterization, various amounts of LAGP nanofibers were used as a filler to develop polyethylene oxide (PEO)-based composite electrolytes. The addition of 10% LAGP nanofibers has allowed doubling the ionic conductivity of the plain polymer electrolyte, by providing longer ion-conductive paths and reducing PEO crystallinity. These findings are promising towards developing solution-based synthesis approaches featuring Ge precursors. In addition, the achieved LAGP nanofibers proved to be a promising nanofiller candidate to develop composite electrolytes for next-generation solid-state batteries.

Performance evaluation of Au/p-CdTe/Cs2TiI6/n-TiO2/ITO solar cell using SCAPS-1D

Perovskite solar cells are a cheap and futuristic option for catering the single cell efficiency limit. Organic and in-organic Perovskite materials (ABX3) have excellent optical properties such as large absorption coefficient, tunable bandgap and solution based synthesis approach. This paper proposes a Perovskite solar cell with a power conversion efficiency (PCE) of 15.06%. The inorganic Cs2TiI6 double perovskite acts as an absorber layer with an optical band gap of 1.8 eV, CdTe as hole transport layer (HTL) and TiO2 as electron transport layer (ETL). This simple cell architecture may help to study and optimize the device parameters. The thickness of absorber material, ETL, HTL, bandgap of absorber material, interface defect density and temperature strongly influence the PCE of the device. The optimized thickness values for maximum PCE value are observed to be 0.01 μm for ETL, 4.33 μm for absorber layer and 2.75 μm for HTL. The temperature range for optimal device performance is around 270–280 K. Solar capacitance simulator (SCAPS-1D) has been used for calculations. The focus of the paper is to propose an environmental friendly non-toxic perovskite solar cell and to investigate optimized current, voltage and PCE characteristics of the device.

Performance enhancement of organic/Si solar cell using CNT embedded hole selective layer

In this work, we present a simple and solution-based synthesis approach to combine the virtues of PEDOT:PSS and carbon nanotube (CNT) by developing a composite film and their application as a hole selective layer (HSL) in organic-silicon hybrid heterojunction solar cell. The heterojunction solar cell with the optimised PEDOT: PSS-CNT HSL showed a notable open-circuit voltage (Voc) of 588.6 mV, short circuit current density (Jsc) of 25.3 mA/cm2 and fill factor (FF) of 60.79% yielding a photo-conversion efficiency (η) of 9.05%. The pristine PEDOT:PSS/Si device obtained an η of 6.2% with a Voc of 502 mV. The role of CNT in the charge transport mechanism and improving Voc was corroborated by employing various characterisation methods such as J-V, C-V, and electrochemical impedance spectroscopy. The composite layer induced a strong inversion layer in silicon and enhanced the device performance. The application of PEDOT:PSS-CNT composite film is not limited to c-Si solar cells, but can also be used to fabricate flexible organic and perovskite solar cells.

Structural and magnetic properties of highly Fe-doped ZnO nanoparticles synthesized by one-step solution plasma process

Among many preparation methods for the synthesis of Fe-doped ZnO nanoparticles which have been widely investigated due to versatile properties and potential applications in optoelectronics, photovoltaics, and spintronic devices, solution-based methods such as sol-gel, hydrothermal, and precipitation processes usually consume many reagents and involve numerous steps. In this study, we report a one-step synthesis of highly Fe-doped ZnO nanoparticles (NPs) by a solution plasma process (SPP) using FeCl2 and FeCl3 as precursors without any addition of chemicals. Breakdown of water bubbles caused by plasma discharge led to the formation of hydroxyl radicals, which reacted with the dissolved Zn2+ ions producing Zn(OH)2 that was indeed converted to ZnO through thermal dehydration. Meanwhile, Fe ions were incorporated into the host ZnO lattice during the synthesis process. Fe-doping levels in Zn1-xFexO NPs are easily controllable by changing the Fe precursor concentration and plasma discharging time. We achieved a high doping content (x = 0.14–0.46) within 30 min, which is difficult to achieve using traditional solution-based synthesis approaches. All the Fe-doped NPs exhibit ferromagnetic behavior, but the magnitude is strongly dependent on the Fe content and doping ratio of Fe2+ to Fe3+ ions, which are explained by the dominance and competition between the ferromagnetic and antiferromagnetic exchange interactions through the presence of mixed Fe2+ and Fe3+ ions. The observed optimal ratio of Fe2+ to Fe3+ for maximizing the magnetization is approximately 3:7. It is noteworthy that the magnetization of Fe-doped ZnO NPs can be simply controlled by manipulating the Fe content and composition of Fe2+ and Fe3+ ions achieved through the SPP. This result provides a platform for studying fundamental magnetic properties of TM-doped semiconductors for potential spintronic applications. Thus, the SPP has great potential as an alternative strategy for the synthesis of highly Fe-doped ZnO NPs, which can be expanded to the synthesis of other doped metal-oxide nanostructures for a broad range of research applications.

Ni-Fe-Based Nanostructures for Oxygen Evolution Reaction in Alkaline Media

Controlling morphology, composition, and crystalline phase of Ni-Fe-base nanostructures is of great interests in the development of nanocatalysts for improving the sluggish kinetics of oxygen evolution reaction (OER) in alkaline media. This work develops a scalable, solution-based synthesis approach based on thermal decomposition of organometallic complexes that enables manipulation of both the morphology and crystalline phase of the Ni-Fe nanocatalysts. Different design of morphologies including core-shell and alloy nanostructures are synthesized via either sequential or simultaneous injection. Using fine control of reaction kinetics, the resulting Ni-Fe-based nanostructures exhibit high uniformity with ultrafine size. These uniform nanostructures allow us to use transmission electron microscopy (TEM) including high resolution TEM and electron energy loss spectroscopy (EELS) for in-depth structural and electronic characterization of single particles. The quantitative analysis of the elemental distribution on individual particles using EELS not only matches well with that of the bulk measurement using inductively coupled plasma mass spectrometry but also reveals additional information for the composition of nanoparticles with uneven elemental distribution. Together with the x-ray methods including x-ray power diffraction, x-ray photoelectron emission spectroscopy, x-ray absorption spectroscopy on the bulk sample, we elucidate the morphology, composition, and structure of individual particles for each of these nanostructures in detail. Semi-quantitative analysis of the electronic structures using EELS on single particles agrees with the results from the x-ray techniques. We then evaluate the OER performance for these well-defined, Ni-Fe-based nanostructures and compare with Ni and Fe alone nanoparticles. Through this study we establish a fundamental understanding of morphological, compositional, and structural influences on the electrocatalytic activity of Ni-Fe-based nanocatalysts for OER and identify the best performed nanocatalysts to guide the design of future OER nanocatalysts for anion exchange membrane based electrocatalysis.

Highly Selective and Sensitive Methanol Sensor Using Rose-Like ZnO Microcube and MoO3 Micrograss-Based Composite

Rose-like ZnO microcube/MoO3 micrograss-based composite was synthesized via hydrothermal process followed by solution-based synthesis approach. The crystal structure, chemical state, morphology, and elemental analysis of the obtained rose-like composite were examined by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and energy dispersive X-ray spectrometer, respectively. The results indicated that rose-like ZnO microcube/MoO3 micrograss composite was obtained where ZnO microcube pistil and MoO3 micrograss petal were formed. Furthermore, volatile organic compounds sensing performance of the rose-like composite was examined, where sensors presented outstanding sensing performance toward methanol including high selectivity and sensitivity, low-optimal operating temperature as well as very stable response-recovery characteristics, and long-term stability. Such sensing performance can be ascribed to a combined effect of the unique rose-like structures and band formation between ZnO/MoO3 n–n heterojunction.

Solution-based synthesis of carbon-hematite composite thin films for high-performance supercapacitor applications

Abstract

Mono-, Few-, and Multiple Layers of Copper Antimony Sulfide (CuSbS2): A Ternary Layered Sulfide

Layered materials with controlled thickness down to monolayer are being intensively investigated for unraveling and harnessing their dimension-dependent properties. Copper antimony sulfide (CuSbS2) is a ternary layered semiconductor material that has been considered as an absorber material in thin film solar cells due to its optimal band gap (∼1.5 eV) with high absorption coefficient of over >10(4) cm(-1). We have for the first time developed solution-based approaches for the synthesis of mono-, few-, and multiple layers of CuSbS2. These include a colloidal bottom-up approach for the synthesis of CuSbS2 nanoplates with thicknesses from six layers to several layers, and a hybrid bottom-up-top-down approach for the formation of CuSbS2 mesobelts. The latter can be exfoliated by Li-ion intercalation and sonication to obtain layers down to monolayer thickness. Time-dependent TEM studies provide important insights into the growth mechanism of mesobelts. At the initial stage the nanoplates grow laterally to form nanosheets as the primary structure, followed by their folding and attachment through homoepitaxy to form prolate-like secondary structures. Eventually, these prolate-like structures form mesocrystals by oriented attachment crystal growth. The changes in optical properties with layer thickness down to monolayers have been studied. In order to understand the thickness-dependent optical and electrical properties, we have calculated the electronic structures of mono- and multiple layers (bulk) of CuSbS2 using the hybrid functional method (HSE 06). We find that the monolayers exhibit noticeably different properties from the multilayered or the bulk system, with a markedly increased band gap that is, however, compromised by the presence of localized surface states. These localized states are predominantly composed of energetically favorable Sb pz states, which break off from the rest of the Sb p states that would otherwise be at the top of the gap. The developed solution-based synthesis approaches are versatile and can likely be extended to other complex layered sulfides.

Shape-Control and Electrocatalytic Activity-Enhancement of Pt-Based Bimetallic Nanocrystals

Due to the increasing worldwide energy demand and environ-mental concerns, the need for alternative energy sources is growing stronger, and platinum catalysts in fuel cells may help make the technologies a reality. However, the pursuit of highly active Pt-based electrocatalysts continues to be a challenge. Scientists developing electrocatalysts continue to focus on characterizing and directing the construction of nanocrystals and advancing their electrochemical applications. Although chemists have worked on Pt-based bimetallic (Pt-M) preparations in the past, more recent research shows that both shape-controlled Pt-M nanocrystals and the assembly of these nanocrystals into supercrystals are promising new directions. A solution-based synthesis approach is an effective technique for preparing crystallographic facet-directed nanocatalysts. This is aided by careful selection of the metal precursor, capping ligand, reducing agent, and solvent. Incorporating a secondary metal M into the Pt lattice and manipulating the crystal facets on the surface cooperatively alter the electrocatalytic behavior of these Pt-M bimetallic nanocrystals. Specifically, chemists have extensively studied the {111}- and {100}-terminated crystal facets because they show unique atomic arrangement on surfaces, exhibit different catalytic performance, and possess specific resistance to toxic adsorbed carbon monoxide (COads). For catalysts to have maximum efficiency, they need to have resistance to COads and other poisonous carbon-containing intermediates when the catalysts operate under harsh conditions. A necessary design to any synthesis is to clearly understand and utilize the role of each component in order to successfully induce shape-controlled growth. Since chemists began to understand Pt nanocrystal shape-dependent electrocatalytic activity, the main obstacles blocking proton exchange membrane fuel cells are anode poisoning, sluggish kinetics at the cathode, and low activity. In this Account, we discuss the basic concepts in preparation of Pt-M bimetallic nanocrystals, focusing on several immaculate examples of manipulation at the nanoscale. We briefly introduce the prospects for applying Pt-M nanocrystals as electrocatalysts based on the electronic and geometric standpoints. In addition, we discuss several key parameters in the solution-based synthesis approach commonly used to facilitate Pt-M nanocrystals, such as reaction temperature and time, the combination of organic amines and acids, gaseous adsorbates, anionic species, and solvent. Each example features various nanoscale morphologies, such as spheres, cubes, octahedrons, and tetrahedrons. Additionally, we outline and review the superior electrocatalytic performances of the recently developed high-index Pt-M nanostructures. Next, we give examples of the electrocatalytic capabilities from these shape-defined Pt-M architectures by highlighting significant accomplishments in specific systems. Then, using several typical cases, we summarize electrochemical evaluations on the Pt-based shape-/composition-dependent nanocatalysts toward reactions on both the anode and the cathode. Lastly, we provide an outlook of current challenges and promising directions for shape-controlled Pt-M bimetallic electrocatalysts.

Electrode materials for rechargeable lithium batteries

Miniaturization in electronics and rapid advances in portable devices demand lightweight, compact, high-energy density batteries. Lithium batteries offer several advantages such as higher cell voltage, higher energy density, and longer shelf life as compared to other rechargeable systems. Although the rocking-chair concept of utilizing insertion compounds as both cathode and anode hosts has made the rechargeable lithium batteries a commercial reality, cost and environmental considerations require the development of inexpensive electrode hosts such as manganese oxides for consumer applications. Innovative synthesis and processing procedures (including low-temperature, solution-based synthesis approaches to obtain amorphous and nanocrystalline oxide electrode hosts) play a key role in developing new as well as better-performing known electrode materials.