Advanced Healthcare MaterialsVolume 14, Issue 4 2570021 Inside Front CoverFree Access Transparent MXene Microelectrode Arrays for Multimodal Mapping of Neural Dynamics (Adv. Healthcare Mater. 4/2025) Sneha Shankar, Sneha ShankarSearch for more papers by this authorYuzhang Chen, Yuzhang ChenSearch for more papers by this authorSpencer Averbeck, Spencer AverbeckSearch for more papers by this authorQuincy Hendricks, Quincy HendricksSearch for more papers by this authorBrendan Murphy, Brendan MurphySearch for more papers by this authorBenjamin Ferleger, Benjamin FerlegerSearch for more papers by this authorNicolette Driscoll, Nicolette DriscollSearch for more papers by this authorMikhail Shekhirev, Mikhail ShekhirevSearch for more papers by this authorHajime Takano, Hajime TakanoSearch for more papers by this authorAndrew Richardson, Andrew RichardsonSearch for more papers by this authorYury Gogotsi, Yury GogotsiSearch for more papers by this authorFlavia Vitale, Flavia VitaleSearch for more papers by this author Sneha Shankar, Sneha ShankarSearch for more papers by this authorYuzhang Chen, Yuzhang ChenSearch for more papers by this authorSpencer Averbeck, Spencer AverbeckSearch for more papers by this authorQuincy Hendricks, Quincy HendricksSearch for more papers by this authorBrendan Murphy, Brendan MurphySearch for more papers by this authorBenjamin Ferleger, Benjamin FerlegerSearch for more papers by this authorNicolette Driscoll, Nicolette DriscollSearch for more papers by this authorMikhail Shekhirev, Mikhail ShekhirevSearch for more papers by this authorHajime Takano, Hajime TakanoSearch for more papers by this authorAndrew Richardson, Andrew RichardsonSearch for more papers by this authorYury Gogotsi, Yury GogotsiSearch for more papers by this authorFlavia Vitale, Flavia VitaleSearch for more papers by this author First published: 07 February 2025 https://doi.org/10.1002/adhm.202570021AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookxLinkedInRedditWechat Graphical Abstract Transparent Microelectrode Arrays The cover illustrates scalable and light artifact-resistant transparent neural microelectrode arrays based on thin, conductive films of Ti3C2Tx MXene. These arrays allow multimodal electrical and optical access to the brain for simultaneous electrophysiological recording of extracellular spiking activity, fluorescence imaging, and optogenetic stimulation in vivo. More details can be found in article 2402576 by Flavia Vitale and co-workers. Art by the team of Inmywork Studio (https://inmywork.com). Volume14, Issue4February 7, 20252570021 RelatedInformation

MXenes are promising passive components that enable lithium-sulfur batteries (LSBs) by effectively trapping lithium polysulfides (LiPSs) and facilitating surface-mediated redox reactions. Despite numerous studies highlighting the potential of MXenes in LSBs, there are no systematic studies of MXenes' composition influence on polysulfide adsorption, which is foundational to their applications in LSB. Here, a comprehensive investigation of LiPS adsorption on seven MXenes with varying chemistries (Ti2CTx, Ti3C2Tx, Ti3CNTx, Mo2TiC2Tx, V2CTx, Nb2CTx, and Nb4C3Tx), utilizing optical and analytical spectroscopic methods is performed. This work reports on the influence of polysulfide concentration, interaction time, and MXenes' chemistry (transition metal layer, carbide and carbonitride inner layer, surface terminations and structure) on the amount of adsorbed LiPSs and the adsorption mechanism. These findings reveal the formation of insoluble thiosulfate and polythionate complex species on the surfaces of all tested MXenes. Furthermore, the selective adsorption of lithium and sulfur, and the extent of conversion of the adsorbed species on MXenes varied based on their chemistry. For instance, Ti2CTx exhibits a strong tendency to adsorb lithium ions, while Mo2TiC2Tx is effective in trapping sulfur by forming long-chain polythionates. The latter demonstrates a significant conversion of intermediate polysulfides into low-order species. This study offers valuable guidance for the informed selection of MXenes in various functional components benefiting the future development of high-performance LSBs. The expansion of the MXene family prompted various independent studies aimed at exploring the potential use of different MXenes as passive components to enhance the performance of lithium-sulfur batteries. In this study, seven distinct MXenes, exhibiting variations in their material chemistry, are screened to evaluate their capability for polysulfide adsorption and elucidate the mechanisms underlying this adsorption. image

In the era of the internet of things, there exists a pressing need for technologies that meet the stringent demands of wearable, self-powered, and seamlessly integrated devices. Current approaches to developing MXene-based electrochemical sensors involve either rigid or opaque components, limiting their use in niche applications. This study investigates the potential of pristine Ti3C2Tx electrodes for flexible and transparent electrochemical sensing, achieved through an exploration of how material characteristics (flake size, flake orientation, film geometry, and uniformity) impact the electrochemical activity of the outer sphere redox probe ruthenium hexamine using cyclic voltammetry. The optimized electrode made of stacked large Ti3C2Tx flakes demonstrated excellent reproducibility and resistance to bending conditions, suggesting their use for reliable, robust, and flexible sensors. Reducing electrode thickness resulted in an amplified faradaic-to-capacitance signal, which is advantageous for this application. This led to the deposition of transparent thin Ti3C2Tx films, which maintained their best performance up to 73% transparency. These findings underscore its promise for high-performance, tailored sensors, marking a significant stride in advancing MXene utilization in next-generation electrochemical sensing technologies. The results encourage the analytical electrochemistry field to take advantage of the unique properties that pristine Ti3C2Tx electrodes can provide in sensing through more parametric studies.

Pseudocapacitors have the potential to achieve high energy and high power density simultaneously, a holy grail for electrochemical energy storage. MXene-based pseudocapacitors have made major progress in the last decade, achieving better energy and power density than carbon supercapacitors using the double-layer charge storage mechanism. However, one obstacle facing pseudocapacitors is their shorter lifetime. In MXene-based pseudocapacitors, which showed up to 500,000 cycles lifetime in aqueous electrolyte at room temperature, this concern is pronounced particularly at high temperatures due to the limited stability of the active material in aqueous solutions. This work shows that Ti 3 C 2 T x MXene electrodes in 5 M H 2 SO 4 possess excellent rate capabilities from -50 °C to 100 °C but also a sufficient lifetime at 70 °C when using a float test holding at -0.9 V vs. Hg/Hg 2 SO 4 . Post-mortem characterization using X-ray photoelectron spectroscopy and Raman spectroscopy showed negligible signs of oxidation in the bulk of the film. This work suggests sufficient stability of Ti 3 C 2 T x MXene as a negative electrode in protic aqueous electrolytes across a wide temperature range rooted in thermodynamics, making it promising for pseudocapacitor energy storage.

MAX phases, ternary transition metal carbides and nitrides, represent one of the largest families of layered materials. They also serve as precursors to MXenes, two-dimensional (2D) carbides and nitrides. The possibility of oxygen substitution in the carbon sublattice, forming oxycarbide MAX phases and MXenes, was recently reported using secondary ion mass spectrometry. However, while the effect of oxygen substitution on the properties of MXenes was investigated, little is known about its effect on the properties of MAX phases. Here, we explore the influence of process parameters (e.g., particle size, synthesis temperature, annealing time, etc.) and oxygen presence in the lattice on the oxidation resistance of Ti(3)AlC(2 )MAX phase powders. We show that X-ray diffraction measurements can identify oxygen substitution and assist in selecting MAX precursors to synthesize stable and highly conductive MXenes. Eliminating the substitutional oxygen from the MAX phase lattice increases the onset of oxidation by 400 degrees C, from approximately 490 to 890 degrees C. Finally, we discuss the impact of oxygen substitution in the MAX phases on the synthesis of MXenes and their resulting properties.

The MXene family has rapidly expanded since its discovery in 2011 to include nearly 50 unique MXenes, not accounting for solid solutions and diverse surface terminations. However, a question raised since their discovery has been: What is the effect of n? In other words, how does the number of layers affect the MXene properties? To date, no direct study of the impact of n has been conducted due to the lack of isoelemental MXene compositions spanning more than two n values. Herein, we report on a system of three MXenes with identical M-site chemistries, (Mo2/3V1/3)n+1CnTx (n = 1, 2, and 3), allowing for the study of MXene structure-property relationships across n, for the first time. Chemical analysis of the samples shows complete and partial ordering of the M-elements in the n = 2 and 3 samples, respectively. We show that sample stability gradually evolves as n is increased from 1 to 3, while electronic and electrochemical properties exhibit more significant changes in going from n = 1 to 2 than from n = 2 to 3.

Magnetic nanomaterials are sought to provide new functionalities for applications ranging from information processing and storage to energy generation and biomedical imaging. MXenes are a rapidly growing family of two-dimensional transition metal carbides and nitrides with versatile chemical and structural diversity, resulting in a variety of interesting electronic and optical properties. However, strategies for producing MXenes with tailored magnetic responses remain underdeveloped and challenging. Herein, we incorporate elemental Ni and Co into Ti3C2Tx MXene by mixing with dilute metal chloride solutions. We achieve a uniform distribution of Ni and Co, confirmed by X-ray fluorescence (XRF) mapping with nanometer resolution, with Ni and Co concentrations of approximately 2 and 7 at% relative to the Ti concentration. The magnetic susceptibility of these Ni- and Co-incorporated Ti3C2Tx MXenes is one to two orders of magnitude larger than pristine Ti3C2Tx, illustrating the potential for dilute metal incorporation to enhance linear magnetic responses at room temperature.

Transparent microelectrode arrays have proven useful in neural sensing, offering a clear interface for monitoring brain activity without compromising high spatial and temporal resolution. The current landscape of transparent electrode technology faces challenges in developing durable, highly transparent electrodes while maintaining low interface impedance and prioritizing scalable processing and fabrication methods. To address these limitations, we introduce artifact-resistant transparent MXene microelectrode arrays optimized for high spatiotemporal resolution recording of neural activity. With 60% transmittance at 550 nm, these arrays enable simultaneous imaging and electrophysiology for multimodal neural mapping. Electrochemical characterization shows low impedance of 563 ± 99 kΩ at 1 kHz and a charge storage capacity of 58 mC cm⁻² without chemical doping. In vivo experiments in rodent models demonstrate the transparent arrays' functionality and performance. In a rodent model of chemically-induced epileptiform activity, we tracked ictal wavefronts via calcium imaging while simultaneously recording seizure onset. In the rat barrel cortex, we recorded multi-unit activity across cortical depths, showing the feasibility of recording high-frequency electrophysiological activity. The transparency and optical absorption properties of Ti₃C₂Tx MXene microelectrodes enable high-quality recordings and simultaneous light-based stimulation and imaging without contamination from light-induced artifacts.

MXenes are a family of two-dimensional (2D) carbides and nitrides with extraordinary electrical, optical, chemical, and electrochemical properties. There is a perception that MXenes are unstable and degrade quickly, limiting potential applications and requiring specific storage conditions to last for a long time. It primarily comes from studies on delaminated MXenes flakes in dilute dispersions and samples from defective or non-stoichiometric precursors when MXene research was in its infancy. In the years since then, significant developments in synthesis, processing, and understanding of their chemistry have led to dramatic increases in the environmental stability of many MXenes, especially the widely studied Ti3C2Tx. However, previous studies focused primarily on MXene dispersion, while in the majority of applications, MXenes are processed into films soon after synthesis. Herein, we analyze Ti3C2Tx free-standing films aged from 4 to 10 years through structural and morphological characterization along with electrical conductivity measurements to reveal the effect, or lack thereof, of prolonged storage under ambient conditions. Further, we show that the decrease in electronic conductivity over time is caused mainly by water uptake by the hydrophilic surfaces of MXenes, which can be removed by vacuum annealing. As a result, the conductivity of the films can be partially or almost completely recovered.

MXenes are a large family of two-dimensional nanomaterials with diverse properties and potentials for electronic, photonic, energy storage, and other applications. Due to their hydrophilicity, MXenes capture water from the surrounding environment, which may lead to swelling and degradation of the assembled multi-layer films. Here we demonstrate that intercalation of N -methylformamide (NMF) leads to MXene films with improved stability at high temperatures and high humidity through host–guest hydrogen bonding. Due to strong interaction with MXene surface and occupation of the interlayer spacing, NMF mitigates intercalation of water and allows for better retention of electrical conductivity during prolonged use in hot and humid environments. Graphical abstract

Two-dimensional (2D) MXenes are a large family of materials with unique properties and numerous potential applications. They are typically produced by selective chemical etching of MAX phase precursors, which is a top-down approach allowing for scalable manufacturing. Multilayer MXenes are then further processed by chemical intercalation and delamination to produce a stable dispersion of 2D flakes in water. The current process of delamination requires multiple time-, energy-, and waste-intensive steps and still fails to delaminate some MXenes. Herein, we demonstrate a method of high-energy delamination called high-pressure homogenization (HPH) that combines high shear, cavitation forces, and impact forces to delaminate MXene without any post-process refinement steps or chemical intercalants. HPH-delaminated MXene can be made at scale with high throughput and yield with virtually no waste. We demonstrate the viability of this process by fabricating free-standing films with the material for use as electrodes for energy storage and as an effective antimicrobial coating where any residual lithium is undesirable. HPH-MXene electrodes demonstrated comparable capacitance to that of lithium-delaminated films with better rate capability. HPH-MXene films proved effective as antimicrobial coatings with over a two-log reduction in pathogenic microbes without the concern of chemical leaching by the coating. We anticipate that this method will decrease the cost of MXene manufacturing and be applicable to a variety MXenes, including those that cannot be currently delaminated via intercalation.

MXenes are two-dimensional (2D) transition metal carbides, nitrides, and carbonitrides typically synthesized from layered MAX-phase precursors. With over 50 experimentally reported MXenes and a near-infinite number of possible chemistries, MXenes make up the fastest-growing family of 2D materials. They offer a wide range of properties, which can be altered by their chemistry (M, X) and the number of metal layers in the structure, ranging from two in M2XTx to five in M5X4Tx. Only one M5X4 MXene, Mo4VC4, has been reported. Herein, we report the synthesis and characterization of two M5AX4 mixed transition metal MAX phases, Ti2.5Ta2.5AlC4 and Ti2.675Nb2.325AlC4, and their successful topochemical transformation into Ti2.5Ta2.5C4Tx and Ti2.675Nb2.325C4Tx MXenes. The resulting MXenes were delaminated into single-layer flakes, analyzed structurally, and characterized for their thermal and optical properties. This establishes a family of M5AX4 MAX phases and their corresponding MXenes. These materials were experimentally produced based on guidance from theoretical predictions, leading to more exciting applications for MXenes.

Ti3C2T (x) MXene is emerging as the enabling material in a broad range of wearable and implantable medical technologies, thanks to its outstanding electrical, electrochemical, and optoelectronic properties, and its compatibility with high-throughput solution-based processing. While the prevalence of Ti3C2T (x) MXene in biomedical research, and in particular bioelectronics, has steadily increased, the long-term stability and degradation of Ti3C2T (x) MXene films have not yet been thoroughly investigated, limiting its use for chronic applications. Here, we investigate the stability of Ti3C2T (x) films and electrodes under environmental conditions that are relevant to medical and bioelectronic technologies: storage in ambient atmosphere (shelf-life), submersion in saline (akin to the in vivo environment), and storage in a desiccator (low-humidity). Furthermore, to evaluate the effect of the MXene deposition method and thickness on the film stability in the different conditions, we compare thin (25 nm), and thick (1.0 mu m) films and electrodes fabricated via spray-coating and blade-coating. Our findings indicate that film processing method and thickness play a significant role in determining the long-term performance of Ti3C2T (x) films and electrodes, with highly aligned, thick films from blade coating remarkably retaining their conductivity, electrochemical impedance, and morphological integrity even after 30 d in saline. Our extensive spectroscopic analysis reveals that the degradation of Ti3C2T (x) films in high-humidity environments is primarily driven by moisture intercalation, ingress, and film delamination, with evidence of only minimal to moderate oxidation.

Rigid, solid‐state components represent the current paradigm for electronic systems, but they lack post‐production reconfigurability and pose ever‐increasing challenges to efficient end‐of‐life recycling. Liquid electronics may overcome these limitations by offering flexible in‐the‐field redesign and separation at end‐of‐life via simple liquid phase chemistries. Up to now, preliminary work on liquid electronics has focused on liquid metal components, but these devices still require an encapsulating polymer and typically use alloys of rare elements like indium. Here, using the self‐assembly of jammed 2D titanium carbide (Ti 3 C 2 T x ) MXene nanoparticles at liquid–liquid interfaces, “all‐liquid” electrically conductive sheets, wires, and simple functional devices are described including electromechanical switches and photodetectors. These assemblies combine the high conductivity of MXene nanosheets with the controllable form and reconfigurability of structured liquids. Such configurations can have applications not only in electronics, but also in catalysis and microfluidics, especially in systems where the product and substrate have affinity for solvents of differing polarity.

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) possess a unique combination of properties, such as metallic conductivity combined with hydrophilicity and surface redox activity, that are important for energy storage, printed electronics, biomedical, catalytic and other applications. However, the use of many MXene chemistries beyond titanium carbides is limited by the cost of MAX phase precursors, which are usually produced from pure elements, involving expensive transition metals. Herein, we demonstrate a low-cost rapid aluminothermic combustion synthesis of MAX phases from an inexpensive oxide precursor, producing V 2 AlC in seconds, with low energy input. A reactor for self-propagating high-temperature synthesis (SHS) was designed and manufactured for this study. The V 2 CT x MXene produced from the SHS MAX is similar to MXene from conventional pressureless sintered MAX in terms of oxidation resistance, environmental stability, conductivity, and electrochemical performance, but has a larger flake size. This work demonstrates an alternative, low-cost and scalable approach to the synthesis of MAX phases and, subsequently, MXenes without sacrificing their properties.

Two-dimensional (2D) transition metal carbides and nitrides (MXenes) possess a unique combination of properties, such as metallic conductivity combined with hydrophilicity and surface redox activity, that are important for energy storage, printed electronics, biomedical, catalytic and other applications. However, the use of many MXene chemistries beyond titanium carbides is limited by the cost of MAX phase precursors, which are usually produced from pure elements, involving expensive transition metals. Herein, we demonstrate a low-cost rapid aluminothermic combustion synthesis of MAX phases from an inexpensive oxide precursor, producing V2AlC in seconds, with low energy input. A reactor for self-propagating high-temperature synthesis (SHS) was designed and manufactured for this study. The V2CTx MXene produced from the SHS MAX is similar to MXene from conventional pressureless sintered MAX in terms of oxidation resistance, environmental stability, conductivity, and electrochemical performance, but has a larger flake size. This work demonstrates an alternative, low-cost and scalable approach to the synthesis of MAX phases and, subsequently, MXenes without sacrificing their properties.

Since the first report on Ti 3 C 2 T x in 2011, the family of two-dimensional transition metal carbides, nitrides, and carbonitrides (MXenes) has increased substantially to include single and multi-element MXenes, with many more yet to be synthesized but predicted to possess attractive properties. To synthesize these elusive MXenes as well as to improve and scale up the manufacturing of known MXenes, a deeper mechanistic understanding of their synthesis processes is necessary, from the precursors to the etching–exfoliation and final intercalation–delamination steps. Here we examine computational modelling and in situ and ex situ characterization data to rationalize the reactivity and selectivity of MXenes towards various common etching and delamination methods. We discuss the effects of MAX phases, the predominant precursor, and other non-MAX layered materials on MXene synthesis and their resultant properties. Finally, we summarize the parameters behind successful (and unsuccessful) etching and delamination protocols. By highlighting the factors behind each step, we hope to guide the future development of MXenes with improved quality, yield and tunable properties.

Two-dimensional titanium carbide (Ti3C2TX ; MXene) is the most important member of the MXene family with attractive properties and applications in energy storage, electronics, medicine, and many others. A typical synthesis involves selective etching of a layered precursor (MAX phase), followed by intercalation with Li+ ions and delamination into individual flakes. Here, we demonstrate that, by adjusting the etching conditions, Ti3C2TX MXene can be delaminated with Na+ and K+. Since residual delamination agents are still present on the MXene surface after the delamination process, this protocol allows one to avoid adverse effects of Li+ and to improve the environmental stability of the films.

Despite the safety, low cost, and high theoretical capacity (820 mA h g-1) of Zn metal anodes, the prac-tical application of aqueous Zn metal batteries remains a critical challenge due to the Zn dendrite growth, corrosion, and hydrogen evolution reaction. Herein, we demonstrate the MXene ink hosting Zn metal anodes (MX@Zn) for high-performance and patternable Zn metal full batteries. The as-designed MX@Zn electrode is more facile and reversible than bare Zn and CC@Zn, as verified by better cyclic sta-bility and lower overpotentials of symmetric cells with the plating capacity of 0.05 mA h cm-2 at 0.1 mA cm-2 and of 1 mA h cm-2 at 1 mA cm-2. The MX@Zn | MnO2 full cells deliver a high specific capac-ity of 281.9 mA h g-1, 91.5% of the theoretical capacity, achieving 50% capacity retention from 60 mA g-1 to 300 mA g-1 and 79.7% of initial capacity after 200 cycles. Moreover, the patterned devices based on the MX@Zn electrode achieve high energy and power densities of 348.57 Wh kg-1 and 1556 W kg-1, respec-tively, along with a capacity retention of 64% and Coulombic efficiency of 99% over 500 cycles. The high performance of MX@Zn is attributed to the high electrical conductivity and hydrophilicity of MXene and rapid ion diffusion through the 3D interconnected porous channels.(c) 2022 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by ELSEVIER B.V. and Science Press. All rights reserved.

MXenes, a class of two-dimensional (2D) materials, are synthesized by etching MAX phase precursors to produce multilayer MXenes, where individual 2D sheets are held together by van der Waals forces. Typically, single 2D flakes of MXene are produced by chemical intercalation to delaminate multilayer MXenes, which is a time-intensive process that produces excess waste. In addition, intercalants affect the properties of MXenes. Many of them are toxic, limiting medical applications. Moreover, the process does not work for certain MXene chemistries, such as halogen-terminated MXenes produced by molten salt etching. This work demonstrates an alternative approach, shearing multilayer MXenes with a three-roll mill to produce single- and few-layer Ti3C2Tx flakes without chemical intercalants. The high shear produced Ti3C2Tx flakes showed a capacitance of 337 F g−1, comparable to flakes made with LiCl intercalation, in 3 M H2SO4. We generalize this approach by shear delamination of other MXenes.