In suit growth of CuSe nanoparticles on MXene (Ti3C2) nanosheets as an efficient counter electrode for quantum dot-sensitized solar cells

Investigation and development of photocathodes using polyaniline Encapsulated Ti3C2Tx MXene nanosheets for dye-sensitized solar cells

In the current study, polyaniline (PANI) modified two-dimensional Ti3C2Tx MXene composites (PANI-Ti3C2Tx) are exploited as photocathodes in dye-sensitized solar cells (DSSCs). The study revealed that incorporating PANI into Ti3C2Tx improved the material's electrochemical properties, owing to the presence of amino groups in PANI that enhanced the material's electrical conductivity and thereby facilitated more rapid ion transport. In addition, PANI enhanced the surface wettability of Ti3C2Tx, resulting in an increase in the number of electroactive sites. The presence of PANI molecules in the interlayer and on the surface of Ti3C2Tx was confirmed through X-ray diffraction (XRD), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX), and X-ray photoelectron spectroscopy (XPS). Subsequently, electrochemical analysis of the PANI-Ti3C2Tx photocathode or counter electrode (CE) revealed a commendable electrocatalytic activity with the iodide/triiodide electrolyte, a favourable charge transfer kinetics, and a charge transfer resistance as low as platinum. Additionally, at AM 1.5G, the performance of the DSSC constructed using the thermally decomposed Pt-CE was 8.3% when subjected to simulated 1 sun light, whereas the efficiency of the DSSC constructed using the as-prepared composite material was 6.9% under corresponding conditions. PANI-Ti3C2Tx as the photocathode (CE) in a DSSC showed a higher power conversion efficiency (PCE) improvement than PANI CE and Ti3C2Tx CE DSSCs, emphasizing its potent catalytic activity and quick mass transport of electron capability. By capitalizing on the conductivity and electrocatalytic property of the two components, the as-fabricated PANI-Ti3C2Tx photocathode significantly increased the overall PCE of DSSCs. Furthermore, the DSSC utilizing the PANI-Ti3C2Tx CE demonstrated exceptional reproducibility and stability. This underscores its consistently high performance and significant resistance to corrosion in the iodide/triiodide redox electrolyte environment. Overall, these findings show that the PANI-Ti3C2Tx composite has the potential to be a competitive alternative to platinum-based CE materials for the development of DSSCs with exceptional performance.

Dendritic-like MXene quantum dots@CuNi as an efficient peroxidase candidate for colorimetric determination of glyphosate

Oxidized MXene quantum dots@CuNi bimetal (MQDs@CuNi) were firstly prepared through a simple hydrothermal method. Compared to the controlled samples, MQDs@CuNi1:1 showed the highest peroxidase-like activity. The catalytic mechanism of MQDs@CuNi1:1 was investigated using a steady-state fluorescence analysis, which showed that MQDs@CuNi1:1 efficiently decomposes H2O2 and produces highly reactive hydroxyl radicals (OH). Furthermore, theoretical calculations showed that the remarkable catalytic activity of MQDs@CuNi1:1 originates from the interaction between CuNi bimetal and MQDs to promote the activation and decomposition of H2O2, making it easier to combine with the hydrogen at the end of 3,3',5,5'-Tetramethylbenzidine (TMB). Accordingly, a sensitive colorimetric sensor is proposed to detect glyphosate (Glyp), displaying a low detection limit of 1.13 µM. The work will provide a new way for the development of high-performance nanozyme and demonstrate potential applicability for the determination of pesticide residues in environment.

MXenes for Energy Harvesting

Energy harvesting modules play an increasingly important role in the development of autonomous self-powered microelectronic devices. MXenes (i.e., 2D transition metal carbide/nitride) have recently emerged as promising candidates for energy applications due to their excellent electronic conductivity, large specific surface area, and tunable properties. Herein, a perspective on using MXenes to harvest energy from various sources in the environment is presented. First, the characteristics of MXenes that facilitate energy capturing are systematically introduced and the preparation strategies of MXenes and their derived nanostructures tailored toward such applications are summarized. Subsequently, the harvesting mechanism of different energy sources (e.g., solar energy, thermoelectric energy, triboelectric energy, piezoelectric energy, salinity-gradient energy, electrokinetic energy, ultrasound energy, and humidity energy) are discussed. Then, the recent progress of MXene-based nanostructures in energy harvesting, as well as their applications, is introduced. Finally, opinions on the existing challenges and future directions of MXene-based nanostructure for energy harvesting are presented.

Microwave-assisted hydrothermal synthesis of copper selenides (Cu2-xSe) thin films for quantum dots-sensitized solar cells

In this work, copper selenide (Cu_2-xSe) thin films were grown on FTO conductive glass substrates using a facile microwave-assisted hydrothermal method. The effects of synthesis parameters such as precursor components and deposition time on the stoichiometry and morphology of the synthesized films were systematically investigated through different techniques including XRD, SEM, and AFM. In order to evaluate the electrochemical catalytic performance of the synthesized copper selenide in electrolyte containing the sulfide/polysulfide redox couple, we assembled liquid-junction quantum dots-sensitized solar cells (QDSSC) using the synthesized copper selenide thin films as counter electrodes and CdSe quantum dots-sensitized mesoporous TiO₂as photoanodes. Under the illumination of one Sun (100 mW cm^-2), the QDSSC assembled with the optimal copper selenide CEs (Cu:Se = 1:1) exhibited a power conversion efficiency of 2.07%, which is much higher than that of traditional Pt counter electrode (0.76%).

2D MXene: A Potential Candidate for Photovoltaic Cells? A Critical Review

The 2D transition metal carbides/nitrides (2D MXenes) are a versatile class of 2D materials for photovoltaic (PV) systems. The numerous advantages of MXenes, including their excellent metallic conductivity, high optical transmittance, solution processability, tunable work-function, and hydrophilicity, make them suitable for deployment in PV technology. This comprehensive review focuses on the synthesis methodologies and properties of MXenes and MXene-based materials for PV systems. Titanium carbide MXene (Ti3 C2 Tx ), a well-known member of the MXene family, has been studied in many PV applications. Herein, the effectiveness of Ti3 C2 Tx as an additive in different types of PV cells, and the synergetic impact of Ti3 C2 Tx as an interfacial material on the photovoltaic performance of PV cells, are systematically examined. Subsequently, the utilization of Ti3 C2 Tx as a transparent conductive electrode, and its influence on the stability of the PV cells, are discussed. This review also considers problems that emerged from previous studies, and provides guidelines for the further exploration of Ti3 C2 Tx and other members of the 2D MXene family in PV technology. This timely study is expected to provide comprehensive understanding of the current status of MXenes, and to set the direction for the future development in 2D material design and processing for PVs.

Hierarchical MXene/transition metal chalcogenide heterostructures for electrochemical energy storage and conversion

MXenes have gained rapidly increasing attention owing to their two-dimensional (2D) layered structures and unique mechanical and physicochemical properties. However, MXenes have some intrinsic limitations (e.g., the restacking tendency of the 2D structure) that hinder their practical applications. Transition metal chalcogenide (TMC) materials such as SnS, NiS, MoS₂, FeS₂, and NiSe₂ have attracted much interest for energy storage and conversion by virture of their earth-abundance, low costs, moderate overpotentials, and unique layered structures. Nonetheless, the intrinsic poor electronic conductivity and huge volume change of TMC materials during the alkali metal-ion intercalation/deintercalation process cause fast capacity fading and poor-rate and poor-cycling performances. Constructing heterostructures based on metallic conductive MXenes and highly electrochemically active TMCs is a promising and effective strategy to solve these problems and enhance the electrochemical performances. This review highlights and discusses the recent research development of MXenes and hierarchical MXene/TMC heterostructures, with a focus on the synthesis strategies, surface/heterointerface engineering, and potential applications for lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, supercapacitors, electrocatalysis, and photocatalysis. The critical challenges and perspectives of the future development of MXenes and hierarchical MXene/TMC heterostructures for electrochemical energy storage and conversion are forecasted.

MXene-Based Materials for Solar Cell Applications

MXenes are a class of two-dimensional nanomaterials with exceptional tailor-made properties, making them promising candidates for a wide variety of critical applications from energy systems, optics, electromagnetic interference shielding to those advanced sensors, and medical devices. Owing to its mechano-ceramic nature, MXenes have superior thermal, mechanical, and electrical properties. Recently, MXene-based materials are being extensively explored for solar cell applications wherein materials with superior sustainability, performance, and efficiency have been developed in demand to reduce the manufacturing cost of the present solar cell materials as well as enhance the productivity, efficiency, and performance of the MXene-based materials for solar energy harvesting. It is aimed in this review to study those MXenes employed in solar technologies, and in terms of the layout of the current paper, those 2D materials candidates used in solar cell applications are briefly reviewed and discussed, and then the fabrication methods are introduced. The key synthesis methods of MXenes, as well as the electrical, optical, and thermoelectric properties, are explained before those research efforts studying MXenes in solar cell materials are comprehensively discussed. It is believed that the use of MXene in solar technologies is in its infancy stage and many research efforts are yet to be performed on the current pitfalls to fill the existing voids.

A Brief Review of the Role of 2D Mxene Nanosheets toward Solar Cells Efficiency Improvement

This article discusses the application of two-dimensional metal MXenes in solar cells (SCs), which has attracted a lot of interest due to their outstanding transparency, metallic electrical conductivity, and mechanical characteristics. In addition, some application examples of MXenes as an electrode, additive, and electron/hole transport layer in perovskite solar cells are described individually, with essential research issues highlighted. Firstly, it is imperative to comprehend the conversion efficiency of solar cells and the difficulties of effectively incorporating metal MXenes into the building blocks of solar cells to improve stability and operational performance. Based on the analysis of new articles, several ideas have been generated to advance the exploration of the potential of MXene in SCs. In addition, research into other relevant MXene suitable in perovskite solar cells (PSCs) is required to enhance the relevant work. Therefore, we identify new perspectives to achieve solar cell power conversion efficiency with an excellent quality-cost ratio.

Antimony tin oxide/lead selenide composite as efficient counter electrode material for quantum dot-sensitized solar cells

Antimony tin oxide (ATO)/lead selenide (PbSe) composite was rationally designed and fabricated on fluorine doped tin oxide glass (FTO) for using as counter electrode (CE) of quantum dot sensitized solar cells (QDSSCs). The electrocatalytic activity of the CE is deeply investigated in the polysulfide electrolyte by employing the Tafel, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) of the symmetrical cells. The results confirm that the ATO/PbSe CE has better electrocatalytic activity and stability than that of PbSe CE obtained by pulse voltage electrodeposition (PVD). The enhanced electrocatalytic performance of ATO/PbSe CE can be attributed to its high specific surface area, excellent permeability, conductivity and interface connectivity, which provide more electrocatalytic active sites for the reduction of polysulfide species, as well as fast channels for ions diffusion and electron transport. As a result, the CdS QDSSCs and CdS/CdSe co-sensitized QDSSCs assembled by the ATO/PbSe CE exhibits better power conversion efficiency (η) of 1.72% and 5.59%, respectively than that of PbSe CE obtained by PVD. Furthermore, photovoltaic property of the ATO/PbSe CE in CdS/CdSe co-sensitized QDSSCs keeps stable for over 200 min. This present work provides a simple and effective strategy for the construction of high-performance CE materials of QDSSCs.

A covalent organic polymer-TiO2/Ti3C2 heterostructure as nonenzymatic biosensor for voltammetric detection of dopamine and uric acid

Heterostructures have potential to blend the advantages of each material, even exhibiting the evolutionary performance due to synergistic effects. Herein, covalent organic polymers (NUF) are integrated with a TiO₂/Ti₃C₂T_x nanocomposite (TiO₂/TiCT) to form TiO₂/TiCT-NUF heterojunctions as an enlarged nonenzymatic biosensor for dopamine (DA) and uric acid (UA). Detection is performed by differential pulse voltammetry (DPV). The TiO₂/TiCT/NUF exhibits high sensing activity with low detection limits of 0.2 and 0.18 nM (S/N = 3) in the concentration ranges from 0.002 to 100 μM and 0.001 to 60 μM for simultaneous determination of DA and UA, respectively. In addition, the TiO₂/TiCT/NUF provides good selectivity and reproducibility for DA and UA detection in urine and serum samples with recoveries of 98.4 to 100.9%. The proposed heterojunctions manifest an intriguing potential as a candidate of an electrochemical sensor for sole and simultaneous detection of DA and UA.

MXenes for Solar Cells

Application of two-dimensional MXene materials in photovoltaics has attracted increasing attention since the first report in 2018 due to their metallic electrical conductivity, high carrier mobility, excellent transparency, tunable work function and superior mechanical property. In this review, all developments and applications of the Ti3C2Tx MXene (here, it is noteworthy that there are still no reports on other MXenes' application in photovoltaics by far) as additive, electrode and hole/electron transport layer in solar cells are detailedly summarized, and meanwhile, the problems existing in the related studies are also discussed. In view of these problems, some suggestions are given for pushing exploration of the MXenes' application in solar cells. It is believed that this review can provide a comprehensive and deep understanding into the research status and, moreover, helps widen a new situation for the study of MXenes in photovoltaics.

Glucose-derived porous carbon as a highly efficient and low-cost counter electrode for quantum dot-sensitized solar cells

The power conversion efficiency of the QDSCs assembled with a CdS/CdSe sensitized TiO₂ photoanode and the C₉₀₀ CE is up to 5.61% under one sun illumination.