Publications

"While conventional cleaning to remove the coating from plasma chamber walls becomes essential to reproduce the desired materials on the target substrate for widespread applications, an attention towards wall-deposited materials is scarce. Recycling those waste materials to value-added product is of great importance for sustainable progress of our modern society. Herein, we investigated the materials deposited on the wall of plasma chamber, explored their promising features and compared them with conventionally grown materials. A mixture of ZnO and α-Fe2O3 (ZF) exposed to high energy plasma was collected from the wall (ZF-W) and also from the substrate (ZF-S) to check the feasibility of providing same quality products. With same lattice constant of hematite, magnetite and zinc ferrites, ZF-W differs from ZF-S in coercivity, saturation magnetization, ferromagnetic stoichiometry and defects. In addition, degradation of Methyl Blue (MB) dye in ZF-W without use of any external light sources are comparable, more stable and durable in comparison to ZF-S. The slight differences obtained in the property-performances between ZF-W and ZF-S are attributed to the cationic arrangement and the oxygen vacancy defects present in the structure. The study reflects the potentiality of ZF-W as a promising active material for wastewater treatment just as one can use ZF-S. These findings clearly depict that the unused products with altered intrinsic properties obtained after plasma treatment has similar or even better potential to its actual targeted product and thus can be utilized properly thereby saving cost and time and, hence generates an unexplored direction for the materials science community."

"The controlled assembly of 2D materials into well-defined 3D architectures is a potential route to realise the unique thermal, electrical and mechanical properties on the macroscale. The traditional freeze-casting route for processing such aerogels is generally restricted to aqueously dispersed flakes, typically of graphene oxide (GO), which brings restrictions in its electrical properties. It is known that graphene oxide can help to stabilise graphene nanoplatelets (GNP) in a colloidal dispersion. Hence, we report a versatile aqueous processing route that uses this ability to produce rGO-GNP composites into lamellar aerogels via unidirectional freeze-casting. In order to optimise the properites of the aerogel, GO-GNP dispersions were partially reduced by L-ascorbic acid prior to freeze-casting for tuning the carbon and oxygen (C/O) ratio. The aerogels were heat treated afterwards to fully reduce the GO. The chemical reduction time was found to control the microstructure of the resultings aeorgels and tune their properties. An optimal partial reduction time of 35 mins led to an aerogel with compressive modulus of 0.51 ± 0.06 Mpa at a density of 23.2 ± 0.7 mg/cm3 and an electrical conductivity of 42.3 S/m at a density of 20.8 ± 0.8 mg/cm3 was achieved with partial reduction of 60 mins."

"Suitable electrothermal materials with high heating rates at low electric power are highly desirable for de-icing and thermal management applications. Herein, 3D epoxy resin/Ti3C2Tx MXene composites are synthesized and shown to be promising candidates for electrothermal heaters where the MXene serves as a nanoheater and the epoxy resin spreads the heat. An unidirectional freeze-casting technique was used to prepare an anisotropic Ti3C2Tx aerogel in which epoxy resin was then vacuum infiltrated and cured. The resulting composite showed an excellent Joule heating performance over repeated heating-cooling cycles. A steady-state temperature of 123 °C was obtained by applying a low voltage of 2 V with 5.1 A current and giving a total power output of 6.1 W/cm2. Such epoxy/MXene aerogel composites, prepared by a simple and cost-effective manner, are anticipated as a potential alternative to the traditional metal-based and nanocarbon-based electrothermal materials."

"Conventional 3D printing of graphene requires either a complex formulation of the ink with large quantities of polymers or essential post-processing steps such as freeze drying to allow printability. Here we present a graphene capillary suspension (GCS) containing 16.67 wt% graphene nanoparticles in aqueous suspension with 3.97 wt% carboxymethyl cellulose (CMC) as a stabiliser and a small quantity of the immiscible liquid octanol. This is shown to have the appropriate rheological properties for 3D printing, which is demonstrated through the fabrication of a simple lattice structure by direct writing and air drying at room temperature. The printed structure has a porosity of 81%, is robust for handling with a compression strength of 1.3 MPa and has an electrical conductivity of 250 S m⁻¹. After heat treatment at 350 °C conductivity is 2370 S m⁻¹ but the strength reduces to 0.4 MPa. X-Ray tomography of the internal architecture after printing shows the formation of the capillary suspension eliminates ordering of the 2D materials during extrusion through the printer nozzle. Thus capillary suspensions can be used to direct write graphene 3D structures without the necessity of complicated drying steps or burn-out of large quantities of polymer additions, facilitating shape retention and property control as compared to current 2D material ink formulations used for 3D printing."

Conventional electrode preparation techniques of supercapacitors such as tape‐casting or vacuum filtration often lead to the restacking or agglomeration of two‐dimensional (2D) materials. As a result, tortuous paths are created for the electrolyte ions and their adsorption onto the surfaces of the active materials can be prevented. Consequently, maintaining high rate performance whilst increasing the thickness of electrodes has been a challenge. Herein, a facile freeze‐assisted tape casting (FaTC) method is reported for the scalable fabrication of flexible MXene (Ti3C2Tx ) supercapacitor electrode films of up to 700 μm thickness, exhibiting homogeneous ice‐template microstructure composed of vertically aligned MXene walls within lamellar pores. The efficient ion transport created by the internal morphology allows for fast electrochemical charge‐discharge cycles and near thickness‐independent performance at up to 3,000 mV s‐1 for films of up to 300 μm in thickness. By increasing the scan rate from 20 to 10,000 mV s‐1, Ti3C2Tx films of 150 μm in thickness sustain 50 % of its specific capacitance (222.9 F g‐1). When the film thickness is doubled to 300 μm, its capacitance is still retained by 60 % (at 213.3 F g‐1) when the scan rate is increased from 20 to 3,000 mV s‐1, with a capacitance retention above 97.7 % for over 14,000 cycles at 10 A g‐1. They also showed a remarkably high gravimetric and areal power density of 150 kW kg‐1 at 1,000 A g‐1 and 667 mW cm‐2 at 4,444 mA cm‐2, respectively. FaTC has the potential to provide industry with a viable way to fabricate electrodes formed from 2D materials on a large scale, whilst providing promising performance for use in a wide range of applications, such as flexible electronics and wearable energy storage devices.

Electrochemical capacitors (best known as supercapacitors) are high‐performance energy storage devices featuring higher capacity than conventional capacitors and higher power densities than batteries, and are among the key enabling technologies of the clean energy future. This review focuses on performance enhancement of carbon‐based supercapacitors by doping other elements (heteroatoms) into the nanostructured carbon electrodes. The nanocarbon materials currently exist in all dimensionalities (from 0D quantum dots to 3D bulk materials) and show good stability and other properties in diverse electrode architectures. However, relatively low energy density and high manufacturing cost impede widespread commercial applications of nanocarbon‐based supercapacitors. Heteroatom doping into the carbon matrix is one of the most promising and versatile ways to enhance the device performance, yet the mechanisms of the doping effects still remain poorly understood. Here the effects of heteroatom doping by boron, nitrogen, sulfur, phosphorus, fluorine, chlorine, silicon, and functionalizing with oxygen on the elemental composition, structure, property, and performance relationships of nanocarbon electrodes are critically examined. The limitations of doping approaches are further discussed and guidelines for reporting the performance of heteroatom doped nanocarbon electrode‐based electrochemical capacitors are proposed. The current challenges and promising future directions for clean energy applications are discussed as well.

Enhancing the rate of decomposition or removal of organic dye by designing a novel nanostructures is the subject of intensive research for waste-water treatment from the textile and pharmaceutical industries. Despite radical progress to mitigate this challenge by iron-based nanostructures, enhancing their stability and dye adsorption performance are highly desirable. Herein, the present manuscript incorporates alkali cations into iron oxide nanoparticles (IONPs) to tailor its structural and magnetic properties and to magnify methyl blue (MB) removal/decomposition capability. The process automatically functionalizes the IONPs without any additional steps. The plausible mechanisms proposed for the IONPs incubated in alkali chloride and hydroxide solutions are based on the structural investigations and correlated with the removal/adsorption capabilities. The methyl blue adsorption kinetics by the incubated IONPs is elucidated by the pseudo second-order reaction model. Not only the functional groups of -OH and -Cl attached to the surface of NPs, the present investigation reveals that the presence of alkali cations also significantly influences the MB adsorption kinetics and correlates with the cation content.

Poor cycling stability and mechanistic controversies have hindered the wider application of rechargeable aqueous Zn-MnO2 batteries. Herein, we provide direct evidence of the importance of Mn2+ in this type battery by using a bespoke cell. Without pre-addition of Mn2+, the cell exhibits an abnormal discharge-charge profile, meaning it functions as a primary battery. By adjusting the Mn2+ content in the electrolyte, the cell recovers its charging ability, via electrodeposition of MnO2. Additionally, a dynamic pH variation has been observed during the discharge-charge process, with a precipitation of Zn4(OH)6(SO4)· 5H2O buffering the pH of the electrolyte. Contrary to the conventional Zn2+ intercalation mechanism, MnO2 is first converted into MnOOH, which reverts to MnO2 via disproportionation, resulting in the dissolution of Mn2+. The charging process occurs by the electrodeposition of MnO2, thus improving the reversibility through the availability of Mn2+ ions in the solution.

"2D transition metal carbides and nitrides (MXenes) have shown outstanding potential as electrode materials for energy storage applications due to a combination of metallic conductivity, wide interlayer spacing, and redox-active, metal oxide-like surfaces capable of exhibiting pseudocapacitive behavior. It is well known that 2D materials have a strong tendency to restack and aggregate, due to their strong van der Waals interactions, reducing their surface availability and inhibiting electrochemical performance. In order to overcome these problems, work has been done to assemble 2D materials into 3D porous macrostructures. Structuring 2D materials in 3D can prevent agglomeration, increase specific surface area and improve ion diffusion, whilst also adding chemical and mechanical stability. Although still in its infancy, a number of papers already show the potential of 3D MXene architectures for energy storage, but the impact of the processing parameters on the microstructure of the materials, and the influence this has on electrochemical properties is still yet to be fully quantified. In some situations the reproducibility of works is hindered by an oversight of parameters which can, directly or indirectly, influence the final architecture and its properties. This review compiles publications from 2011 up to 2019 about the research developments in 3D porous macrostructures using MXenes as building blocks, and assesses their application as battery and supercapacitor electrodes. Recommendations are also made for future works to achieve a better understanding and progress in the field."

"2D transition metal carbides and nitrides (MXenes) are electrochemically active materials capable of exhibiting pseudocapacitance. Multilayer MXenes are similar to graphite, but with larger interlayer spacing and surface functionalities which allow them to readily disperse in water and undergo a range of reactions without compromising their electrical conductivity. The large interlayer spacing enables MXenes to readily intercalate large ions, and form composites with materials such as graphene, metal oxides, transition metal dichalcogenides and silicon, with which they make electrodes able to deliver exceptional capacities at high power rates over thousands of cycles. Research into MXenes for energy storage has grown exponentially since 2011, and it is now necessary, especially for readers new to the field, to review progress made in more specific areas. This critical review will therefore analyse the progress made in developing MXene‐based batteries, focusing solely on anodes developed for metal‐ion batteries such as Li‐ion, Na‐ion and K‐ion."

"The rich elemental composition, surface chemistry, and outstanding electrical conductivity of MXenes make them a promising class of two-dimensional (2D) materials for electrochemical energy storage. To translate these properties into high performance devices, it is essential to develop fabrication strategies that allow MXenes to be assembled into electrodes with tunable architectures and investigate the effect of their pore structure on the capacitive performance. Here, we report on the fabrication of MXene aerogels with highly ordered lamellar structures by unidirectional freeze-casting of additive-free Ti3C2Tx aqueous suspensions. These structures can be subsequently processed into practical supercapacitor electrode films by pressing or calendering steps. This versatile processing route allows a wide control of film thickness, spacing within lamellae (to give electrolyte accessible sites), and densities (over 2 orders of magnitude) and hence gives control over the final properties. The as-prepared MXene aerogel with a density of 13 mg cm–3 achieves 380 F g–1 capacitance at 2 mV s–1 and 75 F g–1 at 50 mV s–1. The calendering of the MXene aerogel into a porous 60 μm thick film with a density of 434 mg cm–3 leads to a superior rate capability of 309 F g–1 at 50 mV s–1. In addition, the rolled electrodes present an improvement in volumetric capacitance of 104 times as compared to the as-prepared MXene aerogel. Finally, the outstanding cyclability of rolled electrodes strengthens their nomination for supercapacitor applications. In this paper we demonstrate the possibilities in tuning the porosity and the electrochemical properties of aerogels highlighting the importance of evaluating new and hybrid processing methods to develop energy storage applications. The simplicity and versatility of the developed fabrication strategy open opportunities for the utilization of MXene lamellae architectures in a wide range of applications requiring controlled porosity including catalysis, filtration, and water purification."

"Additive manufacturing (AM) technologies appear as a paradigm for scalable manufacture of electrochemical energy storage (EES) devices, where complex 3D architectures are typically required but are hard to achieve using conventional techniques. The combination of these technologies and innovative material formulations that maximize surface area accessibility and ion transport within electrodes while minimizing space are of growing interest. Herein, aqueous inks composed of atomically thin (1–3 nm) 2D Ti3C2Tx with large lateral size of about 8 µm possessing ideal viscoelastic properties are formulated for extrusion‐based 3D printing of freestanding, high specific surface area architectures to determine the viability of manufacturing energy storage devices. The 3D‐printed device achieves a high areal capacitance of 2.1 F cm−2 at 1.7 mA cm−2 and a gravimetric capacitance of 242.5 F g−1 at 0.2 A g−1 with a retention of above 90% capacitance for 10 000 cycles. It also exhibits a high energy density of 0.0244 mWh cm−2 and a power density of 0.64 mW cm−2 at 4.3 mA cm−2. It is anticipated that the sustainable printing and design approach developed in this work can be applied to fabricate high‐performance bespoke multiscale and multidimensional architectures of functional and structural materials for integrated devices in various applications."