With the advancement of technology, electronic devices are increasingly demanding lightweight, high‑efficiency, and customizable energy‑storage solutions. From smartwatches to drones, and from wearables to intelligent sensors, the miniaturization of energy storage has become a key focus in scientific and technological research. Among numerous emerging materials, MXene has emerged as a rising star, thanks to its exceptional electrical conductivity, capacitance, and tunable properties. Nevertheless, efficiently, stably, and precisely integrating MXene into micrometer‑scale manufacturing processes remains a significant challenge.

Recent research published in Small Methods has pioneered a stable Ti₃C₂Tₓ MXene ink formulation and, combined with aerosol jet printing (AJP), enabled the fabrication of high‑resolution, high‑performance microsupercapacitors, opening new avenues for applications in microelectronics, energy storage, and beyond.

MXene

1. Basic Introduction to MXene

MXenes are a class of materials composed of two-dimensional transition metal carbides, nitrides, or carbonitrides, featuring a layered structure, such as Ti₃C₂Tₓ.

Composition: Primarily composed of elements such as Ti and C, it is obtained by removing “bulk” elements (e.g., Al) from MAX-phase materials via a specialized chemical process, yielding ultrathin two-dimensional layers.

Features:

High electrical conductivity: Similar to metals, making it suitable for use as an electrode material.

High specific surface area: provides a large number of active sites.

Excellent mechanical flexibility: facilitates the preparation of thin films.

Tunable surface functional groups (Tₓ): influence the material’s electrochemical performance and stability.

2. Working Principle of MXene

Conduction mechanism: The metallic carbide layers in the layered structure exhibit extremely high electron mobility, enabling efficient current conduction.

Energy storage: In supercapacitors, surface functional groups on MXene—such as carboxyl and hydroxyl groups—can effectively store positive and negative ions during charge–discharge cycles, enabling rapid charge–discharge kinetics. This makes MXene an ideal electrode material, offering both high capacitance and high efficiency.

Why is a stable MXene ink necessary?

1. Viscous Challenges and Stability Issues

易氧化：MXene材料极易在空气中氧化，从而影响导电性和储能性能。

Poor rheological properties: The viscosity of conventional MXene solutions is unstable, making it difficult to meet the requirements of printing processes.

Storage challenges: Once oxidized or precipitated, the ink’s performance degrades sharply, making long-term storage difficult.

2. Limitations of the Current Solution

Using complex additives or organic solvents (such as NMP and DMSO) can introduce toxicity and environmental concerns.

Drying at high temperatures may damage the MXene structure, resulting in a loss of controllability at high resolution.

3. Breakthroughs of this work

Through meticulous formulation, the research team has developed an MXene ink with exceptional chemical and physical stability. While maintaining optimal rheological properties, this ink significantly extends its shelf life, minimizes oxidation, and ensures consistent performance and high print quality during aerosol jet printing.

The Working Principle and Advantages of Aerosol Jet Printing (AJP)

1. Aerosol Jet Printing (AJP) technology

Process summary: The ink is atomized into a fine aerosol and carried by a gas stream onto the substrate surface, forming delicate lines and patterns.

Extremely high resolution: down to the 1-micrometer level, meeting the demands of modern microelectronic manufacturing.

Advantages:

Non-contact: Does not damage the substrate.

High precision: facilitates the fabrication of micron-scale structures.

Multi-layer application: can be sprayed multiple times to adjust the thickness.

Suitable for a variety of rigid or flexible substrates.

2. Specific Work Process

Preparation of metal nanoparticles (such as gold) as a conductive underlayer

The conductive layer is cured through heat treatment.

Prepare the subsequent MXene ink.

Using aerosol jet printing, precise deposition is achieved onto the conductive substrate, forming the electrode.

Suspension and multilayer stacking give rise to miniature supercapacitors.

3. Why choose aerosol jet printing (AJP)?

High-Resolution Manufacturing

Suitable for complex geometric structures in microelectronics.

Precisely control the probability of the wet–dry interface to prevent material waste.

It can be prepared on a variety of substrates, such as ceramics and plastics.

Why choose MXene plus aerosol jet printing (AJP) technology?

High Performance: High Capacitance, Fast Charge–Discharge, Long Cycle Life

High-Resolution Manufacturing: Micron-Level Precision Control

Simple process: suitable for large-scale, low-cost production.

Broad application potential: applicable across fields, from microelectronics to flexible electronics.

The future is promising: materials are continuously optimized, equipment is constantly upgraded, and the prospects are vast.

Application Prospects

1.

Microelectronic devices: such as smart patches and wearable devices

Microsensors: Power supply for temperature and humidity, gas, and pressure sensors

Smart Labels and IoT Devices: Enabling Thin, Integrated Energy Solutions

Flexible Electronics: Bendable and Rollable Energy Storage Devices

2.

Micro‑energy storage: advancing toward miniaturization, complex architectures, and multifunctionality.

Large-scale flexible manufacturing: leveraging roll-to-roll printing to enable low-cost, large-area production.

Integrated Intelligent Systems: Achieving the convergence of energy, sensing, and processing to advance the development of smart electronics.

Development of Novel MXene Materials: Optimizing Conductivity, Capacity, and Stability to Expand Application Frontiers

Environmental protection and sustainable development: non-toxic, easy to prepare, and aligned with the principles of green manufacturing.

Image and Text Guide

Figure 1. Schematic illustration of aerosol jet printing (AJP) of MXene supercapacitors on polyimide. 1) Gold nanoparticle ink was prepared based on our previous work. 2) The gold ink was aerosol jet printed onto a polyimide substrate. 3) The printed gold was annealed at 350°C. 4) Ti3C2Tx MXene ink was prepared. 5) The MXene ink was aerosol jet printed atop the annealed gold current collector. 6) The supercapacitors were annealed in an Ar/N2 atmosphere at 250°C for 2 hours.

Figure 2. Material and Ink Properties.

Figure 3. High-resolution printing and electrical characterization of printed MXene. a) Optical images of complex structures printed on a sapphire substrate, demonstrating the high‑resolution printability of MXene ink and the capability of aerosol jet printing (AJP) to fabricate small‑scale, intricate features. b, c) High‑magnification micrographs of complex structures printed on a sapphire substrate, corresponding to the structures shown in (a). d) Optical image of MXene ink printed onto an alumina tube with an inner diameter of 1 cm, highlighting the conformal printing capability of aerosol jet printing (AJP). e) Schematic of transmission line measurement (TLM) performed on a glass substrate, illustrating different numbers of printing passes (1, 2, and 3) of MXene ink, along with gold contact pad lengths of 2, 3, 4, 5, and 6 mm. f) Cross‑sectional scanning electron microscope images of three successive prints on a silicon substrate. g) Profile analysis of MXene ink printed once, twice, and three times on a glass substrate, showing variations in thickness. h) I–V curves for three‑layer printed MXene ink. i) Plot of resistance versus channel length for the printed TLM structure. j) Electrical conductivity and resistivity as functions of the number of printing layers, demonstrating the influence of layer count on electrical performance.

Figure 4. Electrochemical performance of Ti3C2Tx supercapacitors printed in a NaClO4/PC organic electrolyte. a) Comparison of cyclic voltammetry (CV) curves at a scan rate of 100 mV s−1 for one-, two-, and three-layer printed electrodes. The three-layer MXene supercapacitor exhibits a larger CV area. b) Comparison of galvanostatic charge–discharge (GCD) curves at a current of 150 μA for one-, two-, and three-layer printed electrodes. c) Area capacitance calculated from GCD curves of the three-electrode configuration at various currents. d) Cyclic stability of a three-layer aerosol jet‑printed (AJP) MXene supercapacitor over 10,000 cycles at a current of 150 μA. Insets show GCD curves at different cycle numbers, illustrating the device’s capacitive behavior. e) Nyquist plots of the three-layer MXene supercapacitor before and after 10,000 GCD cycles at a current of 150 μA. f) CV curves of the three-layer MXene supercapacitor at a scan rate of 100 mV s−1 under different potential windows of 0.4, 0.6, 0.8, 1, 1.2, 1.4, 1.6, 1.8, and 2 V, used to optimize the operating potential window. g) Area capacitance values derived from the CV curves across different voltage windows. h) Cyclic voltammetry curves at a potential window of 1.6 V with scan rates of 5, 10, 20, 40, 50, 80, and 100 mV s−1. i) Galvanostatic charge–discharge curves at a potential window of 1.6 V and currents of 10, 20, 40, 60, 80, 100, and 150 μA, demonstrating how expanding the voltage window enhances supercapacitor performance.

Figure 5. Electrochemical performance of the three-layer printed Ti3C2Tx supercapacitor in an aqueous H2SO4–PVA gel electrolyte. a) Cyclic voltammograms recorded at scan rates of 5, 10, 20, 40, 50, 80, and 100 mV s−1. b) Galvanostatic discharge curves measured at current densities of 10, 20, 40, 60, 80, 100, and 150 μA. c) EIS results obtained in the aqueous electrolyte. The inset shows an optical image of the MXene supercapacitor mounted on a polyimide substrate. d) Cycling stability of the aerosol-jet-printed MXene supercapacitor over 2,000 cycles at a current of 150 μA. The inset displays galvanostatic discharge curves highlighting the capacitance retention at different cycle numbers. e) Nyquist plots recorded every 200 galvanostatic discharge cycles, ranging from 200 to 1,800 cycles, providing insights into the electrochemical behavior in the aqueous electrolyte. f) Cyclic voltammograms acquired under various bending angles—0°, 45°, 60°, and 90°. The inset presents a photograph of the MXene supercapacitor on a polyimide substrate bent at 60°. g) Photograph of a 2×2 array of MXene supercapacitors configured as 2S2P, comprising three printed MXene layers. h) Cyclic voltammograms measured at a scan rate of 100 mV s−1 for various configurations, including two devices connected in series (2S), two devices connected in parallel (2P), and a 2×2 device array (2S2P). i) GCD curves corresponding to the same configurations (2S, 2P, and 2S2P) at a current of 150 μA. Figure 6. a) High-resolution optical image of an ultra-thin MXene (HR-MXene) capacitor mounted on a polyimide substrate. Magnified views of selected regions highlight uniform ink deposition and fine printing features. b) Profile measurement analysis along the finger-like structure of the ultra-thin capacitor shown in panel (a). The average thickness of the Au/MXene ultra-thin capacitor is 1.75 μm, with the gold current collector layer measuring 0.5 μm and the top MXene layer averaging 1.25 μm. The thickness distribution of the gold current collector layer is illustrated in Figure S16 (Supporting Information). c) Variation in line width along the printed fingers, corresponding to panel (b). Line-width measurements were conducted at a thickness of 0.5 μm, excluding the gold layer. d) Cyclic voltammograms of the HR-MXene ultra-thin capacitor at different scan rates. e) Galvanostatic discharge curves of the HR-MXene ultra-thin capacitor at varying current densities. f) Optical image of a high-resolution 22‑cell array, with magnified views of selected areas. g) Comparison of areal capacitance between this study’s aerosol-jet‑printed MXene thin capacitor and MXene39 previously reported in gel electrolytes, demonstrating the superior performance of the aerosol-jet‑printed MXene. h) Comparison of volumetric capacitance of this material with that of MXene39 produced via inkjet printing (IJP) in gel electrolytes, confirming higher C/V values for the aerosol-jet‑printed MXene. i) Comparison of areal capacitance of the aerosol-jet‑printed MXene with previously reported supercapacitors (SCs). j) Comparison of volumetric capacitance of the aerosol-jet‑printed MXene with previously reported SCs. EP-MX: extrusion-printed MXene; IJP-MP/PH1000: inkjet-printed MXene/PH1000; IJP-MX: inkjet-printed MXene; IJP-G: inkjet-printed graphene; SM-G/MX: spray-masked graphene/MXene; SC-G/MX: spray-coated graphene/MXene; SC-G/PEDOT: spray-coated graphene/PEDOT; SCLCMX/rG: spray-coated and laser-cut masked MXene/reduced graphene; IJP-EEG: inkjet-printed electrochemically exfoliated graphene; G-Q Dot: graphene quantum dots; SC-G: spray-coated graphene; SCLCMX: spray-coated and laser-cut masked MXene; ScM-MX: scraped MXene; Transparent-MX: transparent MXene.

This study not only addresses the challenges of MXene ink stability and printability but also highlights the tremendous potential of aerosol jet printing (AJP) in the fabrication of micro‑energy devices. As the technology continues to advance and its application domains expand, it is anticipated that, in the near future, micro‑supercapacitors will play a pivotal role in portable electronic devices, sensor networks, and miniature energy‑storage systems, driving the development of smart devices toward greater lightness, higher performance, and enhanced integration.