Jakob Heier

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Stable MXene Dough with Ultrahigh Solid Fraction and Excellent Redispersibility toward Efficient Solution Processing and Industrialization

Jakob Heier, Chi Zhang

Two-dimensional (2D) transition metal carbides, and/or nitrides, so-called MXenes, have triggered intensive research interests in applications ranging from electrochemical energy storage to electronics devices. Producing these functional devices by printing necessitates to match the rheological properties of MXene dispersions to the requirements of various solution processing techniques. In particular, for additive manufacturing such as extrusion-printing, MXene inks with high solid fraction are typically required, which is commonly achieved by tediously removing excessive free water (top-down route). Here, the study reports on a bottom-up route to reach a highly concentrated binary MXene-water blend, so-called MXene dough, by controlling the water admixture to freeze-dried MXene flakes by exposure to water mist. The existence of a critical threshold of MXene solid content (approximate to 60%), beyond which no dough is formed, or formed with compromised ductility is revealed. Such metallic MXene dough possesses high electrical conductivity, excellent oxidation stability, and can withstand a couple of months without apparent decay, providing that the MXene dough is properly stored at low-temperature with suppressed dehydration environment. Solution processing of the MXene dough into a micro-supercapacitor with gravimetric capacitance of 161.7 F g(-1) is demonstrated. The impressive chemical and physical stability/redispersibility of MXene dough indicate its great promise in future commercialization.

WILEY2023

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Functional Ink Formulation for Printing and Coating of Graphene and Other 2D Materials: Challenges and Solutions

Sina Abdolhosseinzadeh, Jakob Heier, Mohammad Jafarpour, Frank Nüesch

The properties of 2D materials are unparalleled when compared to their 3D counterparts; many of these properties are a consequence of their size reduction to only a couple of atomic layers. Metallic, semiconducting, and insulating types can be found and form a platform for a new generation of devices. Among the possible methods to utilize 2D materials, functional printing has emerged as a strong contender because inks can be directly formulated from dispersions obtained by liquid-phase exfoliation. Printed graphene-based devices are shifting from laboratory applications toward real-world and mass-producible systems going hand in hand with a good understanding of suitable exfoliation methods for the targeted type of ink. Such a clear picture does not yet exist for hexagonal boron nitride (h-BN), the transition metal dichalcogenides (TMDs), and black phosphorous (BP). Rather, reports of applications of these 2D materials in printed devices are scattered throughout the literature, not yet adding to a comprehensive and full understanding of the relevant parameters. This perspective starts with a summary of the most important features of inks from exfoliated graphene. For h-BN, the TMDs, and BP, the characteristic properties when exfoliated from solution and strategies to formulate inks are summarized.

WILEY2022

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Two-dimensional MXenes with their outstanding physical and chemical properties have been extensively used in numerous fields such as electrochemical energy storage, catalysis, and sensing. In these applications, high active surface area and facilitated diffusion of ions/atoms/molecules are crucial. While these features can be offered by porous films and structures, their fabrication at ambient conditions, especially with scalable methods such as printing and coating has proven to be quite challenging. Here, we have developed MXene inks containing a space-holder agent, based on which porous films with tunable porosities can be easily coated. The whole fabrication process lasts only a few minutes and is carried out at room temperature and pressure, making it suitable for continuous scalable production. Films with different porosities (up to 80 %) have been coated and used for the fabrication of solid-state microsupercapacitors with enhanced rate capability and improved capacitance (241 mF/cm(2)).

WILEY-V C H VERLAG GMBH2021

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