The dawn of MXene duo: revolutionizing perovskite solar cells with MXenes through computational and experimental methods

Integrating MXene into perovskite solar cells (PSCs) has heralded a new era of efficient and stable photovoltaic devices owing to their supreme electrical conductivity, excellent carrier mobility, adjustable surface functional groups, excellent transparency and superior mechanical properties. This review provides a comprehensive overview of the experimental and computational techniques employed in the synthesis, characterization, coating techniques and performance optimization of MXene additive in electrodes, hole transport layer (HTL), electron transport layer (ETL) and perovskite photoactive layer of the perovskite solar cells (PSCs). Experimentally, the synthesis of MXene involves various methods, such as selective etching of MAX phases and subsequent delamination. At the same time, characterization techniques encompass X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, which elucidate the structural and chemical properties of MXene. Experimental strategies for fabricating PSCs involving MXene include interfacial engineering, charge transport enhancement, and stability improvement. On the computational front, density functional theory calculations, drift-diffusion modelling, and finite element analysis are utilized to understand MXene's electronic structure, its interface with perovskite, and the transport mechanisms within the devices. This review serves as a roadmap for researchers to leverage a diverse array of experimental and computational methods in harnessing the potential of MXene for advanced PSCs.

Spiral gas-solid two-phase flow continuous mechanochemical synthesis of salophen complexes and catalytic thermal decomposition of ammonium perchlorate

Although mechanochemistry is increasingly becoming an alternative to traditional chemical synthesis, highly efficient continuous mechanochemical synthesis techniques are still rare. In this work, a novel spiral gas-solid two-phase flow (S-GSF) synthesis technique for the mechanochemical synthesis of salophen complexes has been reported, which is an approach for continuous synthesis based solely on airflow impacting the reaction. The synthesis of salophen-Br-Cu was used as a model reaction to optimize the reaction conditions, and three other salophen complexes, namely, salophen-Br-Co, salophen-Br-Ni, and salophen-Br-Zn were synthesized on this basis. The structure and thermal stability of the obtained products were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, UV-vis spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, and differential thermal analysis (DTA). The results showed that these complexes can be obtained continuously at a rate close to 4 g min-1, and the corresponding space-time yield is close to 1.2 × 105 kg m-3 day-1. In addition, DTA was used to analyze the catalytic performance of the complex for ammonium perchlorate (AP). The results showed that compared to the conditions for pure AP, salophen-Br-Co and salophen-Br-Cu could significantly reduce the high-temperature decomposition of AP pyrolysis to 77.0 and 102.1 °C, respectively. According to the method of Kissinger calculations, the Ea of AP decomposition decreased from 217.3 kJ mol-1 to 131.0 and 118.5 kJ mol-1, respectively. The TG data at different heating rates were analyzed using two isoconversion methods, i.e. Flynne-Walle-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS). The activation energies of AP, AP + 10 wt% salophen-Br-Co, and AP + 10 wt% salophen-Br-Cu were calculated. When the conversion degree (α) is between 0.1 and 0.9, the Ea values obtained from the two isoconversion methods are similar and exhibit certain matching. These two isoconversion methods also confirm Kissinger's calculations.

MXene-Embedded Porous Carbon-Based Cu2O Nanocomposites for Non-Enzymatic Glucose Sensors

This work explores the use of MXene-embedded porous carbon-based Cu2O nanocomposite (Cu2O/M/AC) as a sensing material for the electrochemical sensing of glucose. The composite was prepared using the coprecipitation method and further analyzed for its morphological and structural characteristics. The highly porous scaffold of activated (porous) carbon facilitated the incorporation of MXene and copper oxide inside the pores and also acted as a medium for charge transfer. In the Cu2O/M/AC composite, MXene and Cu2O influence the sensing parameters, which were confirmed using electrochemical techniques such as cyclic voltammetry, electrochemical impedance spectroscopy, and amperometric analysis. The prepared composite shows two sets of linear ranges for glucose with a limit of detection (LOD) of 1.96 μM. The linear range was found to be 0.004 to 13.3 mM and 15.3 to 28.4 mM, with sensitivity values of 430.3 and 240.5 μA mM-1 cm-2, respectively. These materials suggest that the prepared Cu2O/M/AC nanocomposite can be utilized as a sensing material for non-enzymatic glucose sensors.

In situ growth of copper oxide on MXene by combustion method for electrochemical ammonia production from nitrate

The elimination of the nitrogen pollutant nitrate ions through the electrochemical synthesis of ammonia is an important and environment friendly strategy. Electrochemical nitrate reduction requires highly efficient, selective, and stable catalysts to convert nitrate to ammonia. In this work, a composite of copper oxide and MXene was synthesized using a combustion technique. As reported, nitrate ions are effectively adsorbed by CuxO (CuO & Cu2O) nanoparticles. Herein, MXene is an excellent assembly for anchoring CuxO on its layered surface because it has a strong support structure. Powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analyses show the presence of oxidation states of metal ions and the formation of CuxO nanofoam anchors on the surface of MXene (Ti3C2Tx). The optimized CuxO/Ti3C2Tx composite exhibits an improved nitrate reduction reaction. The electrochemical studies of CuxO/Ti3C2Tx show an interesting nitrate reduction reaction (NO3RR) with a current density of 162 mA cm-2. Further, CuxO/Ti3C2Tx shows an electrocatalytic activity with an ammonia production of 41 982 μg h-1 mcat-1 and its faradaic efficiency is 48% at -0.7 V vs. RHE. Thus, such performance by CuxO/Ti3C2Tx indicates a well-suitable candidate for nitrate ion conversion to ammonia.

In situ growth of copper-based energetic complexes on GO and an MXene to synergistically promote the thermal decomposition of ammonium perchlorate

In this work, using tri(5-aminotetrazolium)triazine (H3TATT) as an energetic ligand, two new energetic complexes (ECs), Cu(HTATT)(H2O)2 (EC-Cu1) and [Cu3(TATT)2(H2O)2]n (EC-Cu2), have been synthesized under hydrothermal conditions. Their crystal structures, thermal decomposition behaviors and specific heat capacities were determined respectively. In addition, two ECs were combined with GO (graphene oxide) and an MXene (Ti3C2TX) respectively by an in situ growth strategy to obtain four carbon nanomaterials/EC composites, which were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The effects of two ECs and four composites on the thermal decomposition of AP were studied by differential scanning calorimetry (DSC). Among them, the sample containing 8 wt% composite (GO/EC-Cu2) has the best promoting effect on AP, causing the high temperature decomposition peak to overlap with the low temperature decomposition peak of AP, reducing the decomposition peak temperature of AP from 443.6 °C to 308.9 °C, and the heat release is up to 4875 J g-1. Compared with ECs acting solely on AP, composite materials have stronger synergistic and promoting effects. This study provides a new example of the synthesis of carbon nanomaterial/EC composites and the improvement of the performance of AP-based solid propellants.

Gelatin-modified Mxene carbon aerogels for ammonium-perchlorate-catalyzed thermal decomposition

The assembly of 2D Ti3C2Tx nanosheets into 3D structures with orderable structure has great importance for their use as catalyst carriers. However, Ti3C2Tx nanosheets are prone to accumulate in aqueous solutions owing to the strong van der Waals forces between Ti3C2Tx nanosheet layers, degrading their chemical properties. Carbon aerogel (Ti3C2Tx/G/Co) with a 3D porous structure and cobalt as the active site was prepared by a simple co-assembly-freeze-drying-high-temperature carbonization method for application in catalysis of ammonium perchlorate.

Advances in the synthesis and applications of 2D MXene-metal nanomaterials

MXenes, two-dimensional (2D) materials that consist of transition metal carbides, nitrides and/or carbonitrides, have recently attracted much attention in energy-related and biomedicine fields. These materials have substantial advantages over traditional carbon graphenes: they possess high conductivity, high strength, excellent chemical and mechanical stability, and superior hydrophilic properties. Furthermore, diverse functional groups such as -OH, -O, and -F located on the surface of MXenes aid the immobilization of numerous noble metal nanoparticles (NP). Therefore, 2D MXene composite materials have become an important and convenient option of being applied as support materials in many fields. In this review, the advances in the synthesis (including morphology studies, characterization, physicochemical properties) and applications of the currently known 2D MXene-metal (Pd, Ag, Au, and Cu) nanomaterials are summarized based on critical analysis of the literature in this field. Importantly, the current state of the art, challenges, and the potential for future research on broad applications of MXene-metal nanomaterials have been discussed.

Ultra-high performance humidity sensor enabled by a self-assembled CuO/Ti3C2T X MXene

An ultra-high performance humidity sensor based on a CuO/Ti3C2T X MXene has been investigated in this work. The moisture-sensitive material was fabricated by a self-assembly method. The morphology and nanostructure of the fabricated CuO/Ti3C2T X composites were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectra. The humidity sensing abilities of the CuO/Ti3C2T X sensor in the relative humidity (RH) range from 0% to 97% were studied. The results showed that the humidity sensor had a high sensitivity of 451 kΩ/% RH, short response time (0.5 s) and recovery time (1 s), a low hysteresis value, and good repeatability. The CuO/Ti3C2T X sensor exhibited remarkable properties in human respiration rate monitoring, finger non-contact sensing, and environmental detection. The moisture-sensitive mechanism of CuO/Ti3C2T X was discussed. The fabricated CuO/Ti3C2T X showed great potential in the application of moisture-sensitive materials for ultra-high-performance humidity sensors.

Collaborative Enhancement of Humidity Sensing Performance by KCl-Doped CuO/SnO2 p-n Heterostructures for Monitoring Human Activities

In this study, a high-performance humidity sensor based on KCl-doped CuO/SnO2 p-n heterostructures was fabricated by a ball milling-roasting method. The morphology and nanostructure of the fabricated KCl-CuO/SnO2 composite were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and nitrogen sorption analysis. The results showed that the humidity sensor had a high sensitivity of 194 kΩ/%RH, short response and recovery times of 1.0 and 1.5 s, a low hysteresis value, and good repeatability. The energy band structure and complex impedance spectrum of the KCl-CuO/SnO2 composite indicated that the excellent humidity sensing performance originated from the ionic conductivity of KCl, the formation of heterojunctions, the change in the Schottky barrier height, and the depletion of electronic depletion layers. The KCl-CuO/SnO2 sensor has great potential in respiratory monitoring, noncontact sensing of finger moisture, and environmental monitoring.

TiO2 NPs/h-BN: Preparation and catalytic activities of a novel AP catalyst

The thermal decomposition performance of an oxidizer directly determines the thrust and specific impulse properties of the solid propellant. Hexagonal boron nitride (h-BN) has the characteristics of high catalytic activity and good stability, which can improve the heat release and decomposition temperature of the oxidant, and then improve the energy performance of the propellant. In this study, a novel hybrid material TiO₂ NPs/h-BN was successfully prepared by in situ growth, and it was found that when 5 wt.% TiO₂ NPs/h-BN was added, the initial decomposition temperature of ammonium perchlorate (AP) decreased by 67.6°C. Due to the addition of TiO₂, the gap between the h-BN layers as well as the specific surface increased, which optimized its thermocatalytic performance, and it also proposed a catalytic mechanism for the thermal decomposition process of AP.

Application of MXenes in Perovskite Solar Cells: A Short Review

Application of MXene materials in perovskite solar cells (PSCs) has attracted considerable attention owing to their supreme electrical conductivity, excellent carrier mobility, adjustable surface functional groups, excellent transparency and superior mechanical properties. This article reviews the progress made so far in using Ti3C2Tx MXene materials in the building blocks of perovskite solar cells such as electrodes, hole transport layer (HTL), electron transport layer (ETL) and perovskite photoactive layer. Moreover, we provide an outlook on the exciting opportunities this recently developed field offers, and the challenges faced in effectively incorporating MXene materials in the building blocks of PSCs for better operational stability and enhanced performance.