I. Abstract of the Paper’s Core Research

This study prepares a pure‑water‑based Ti₃C₂Tₓ MXene aerosol ink and, leveraging the confinement effect of aerosol microdroplets, achieves simultaneous nanosheet curling and oriented alignment. We systematically investigate the influence of liquid flow rate and substrate wettability on nanosheet morphology, and perform detailed microstructural characterization of the electrodes along with electrochemical testing of energy‑storage devices. The key findings are as follows:

In-situ curling formation mechanism under microdroplet confinement

Atomized MXene microdroplets, constrained by the sheath gas, form parallel liquid streams; Marangoni convection within the droplets drives the flakes to migrate toward the edges. Solvent evaporation generates Laplace pressure, inducing spontaneous curling of the MXene and yielding a tubular porous structure. Single-layer printing enables loose stacking, with a BET surface area of 25.92 m²/g—2.3 times that of the vacuum‑filtered membrane sample.

Quasi-conical parallel liquid flow enables oriented lamellar arrangement.

Adjacent droplets give rise to multiple sets of tiny meniscus–three-phase contact lines, while unidirectional surface stress guides the MXene fibers to align neatly along the printing trajectory. Consequently, the interlayer spacing in the resulting film expands to 1.33 nm, significantly shortening the ion diffusion path.

The process window is precisely controllable.

At a sheath‑gas-to‑carrier‑gas focusing ratio of FR = 1.5, material overflow is minimized, and the printed layer thickness exhibits linear growth over 90 printing cycles. On plasma‑treated hydrophilic PET substrates, the lower layer shows reduced curling, while the upper droplet contact angle increases and the curled structure becomes more pronounced, enabling hierarchical control of pore morphology.

High-Performance Planar Micro-Supercapacitors

Aerosol direct-writing of 200-μm-wide interdigitated electrodes yields a post‑optimization capacitance of 34.87 mF·cm⁻² and an energy density of 1.744 μWh·cm⁻²; even after a 90° bend, the device retains a capacitance of 28.17 mF·cm⁻², with a capacity retention of 90% over 50 cycles, demonstrating excellent flexibility and mechanical robustness.

Gentle, additive-free throughout the entire process.

MXene is dispersed solely in pure water, without surfactants or binders; it can be printed at room temperature and atmospheric pressure. On a flexible PET substrate, it exhibits no thermal damage, and the resulting thin film remains intact after being bent a hundred times without cracking or delamination.

II. Complete Aerosol Preparation Process for Curved, Oriented MXene Electrodes

1) The LiF–HCl system etches the Ti₃AlC₂ MAX phase, and ultrasonic exfoliation yields few-layer MXene nanosheets; a 10 mg/mL ink is prepared in pure water without any additives.

2) Air plasma treatment of PET film enhances surface hydrophilicity;

3) Aerosol equipment employs ultrasonic atomization, with nitrogen serving as both the carrier gas and sheath gas; the focusing ratio is fixed at 1.5, the printing speed is 10 mm/s, and the nozzle–substrate distance is 5 mm.

4) Multi-layer cyclic stacking is used to print interdigitated patterns; as the solvent in each layer evaporates naturally, the confined microdroplets spontaneously self‑assemble into curled, oriented MXene films.

5) A planar micro-supercapacitor was assembled by coating a PVA/H₂SO₄ gel electrolyte.

6) Comprehensive electrochemical characterization, including SEM, BET, cyclic voltammetry, and galvanostatic charge–discharge measurements.

III. Core Advantages of the Three‑Five Aerosol Process (Comparison with Inkjet, Vacuum Filtration, and Screen Printing)

Precise in-situ microstructure control

The formation of lamellar curling and oriented alignment is achieved simultaneously, eliminating the need for etching or template‑based pore creation; this enables the one‑step fabrication of highly porous electrodes, thereby simplifying device‑fabrication processes.

Micrometer-scale maskless digital patterning

CAD‑customized interdigitated and arrayed energy‑storage electrodes with controllable line widths, ideal for rapid prototyping and iterative design of multi‑specification microcapacitors.

Compatible with various flexible, heat-sensitive substrates.

The entire process is carried out at ambient temperature, with no high‑temperature sintering; PET, PI, and biodegradable films can all be directly formed without damaging the flexible substrate.

A highly porous structure enhances the energy storage limit.

Microdroplets confined within a tubular, loosely packed MXene structure enable rapid ion penetration, resulting in a substantial improvement over densely stacked thin-film capacitors.

The ink system is simple and free of impurities.

A water-based, binder-free ink that prevents additives from clogging pores, reduces internal electrical resistance, and delivers superior cycling stability.

IV. Five Core Technological Innovations of This Study

Innovation 1: Mechanism of Confined Curling and Forming of Aerosol Microdroplets

We propose aerosol droplets as miniature reaction chambers, leveraging Laplace pressure to induce the spontaneous curling of MXene nanosheets, thereby opening a new avenue for in situ structural modulation of two-dimensional materials.

Innovation 2: Quasi-conical Parallel Liquid Flow Directed Arrangement Technology

By leveraging the unidirectional stress generated at the triple‑phase contact line of multiple curved menisci, MXene nanosheets are aligned in an ordered fashion along the printing path, thereby addressing the challenge of disordered interlayer stacking.

Innovative Three-Stage Hierarchical Regulation Strategy for Base Wettability Gradient

By tuning the number of printing layers, the surface contact angle of the thin film can be controlled, yielding a gradient electrode with a dense bottom layer and a porous top layer, thereby balancing electrical contact with the conductive substrate and ion storage.

Innovative All‑in‑One Process for Additive‑Free Pure Water MXene Aerosols

Eliminate dispersants and binders, reduce electrode–electrolyte interfacial impedance, and extend the device’s cycle life.

Innovative 5‑in‑1 Additive Manufacturing Solution for Flexible Planar Microcapacitors

A single device enables direct writing of complete interdigitated energy‑storage electrodes, eliminating the need for lamination and transfer processes, thus enabling rapid, lightweight fabrication of wearable energy‑storage devices.

V. Current Industry Challenges and Corresponding Solutions

Challenge 1: Conventional MXene films exhibit tightly stacked layers with few pores, resulting in slow ion diffusion and low capacitance.

✅ Aerosol‑induced confinement of microdroplets triggers the curling of nanosheets, yielding a tubular porous architecture with a doubled specific surface area and a substantial increase in active sites.

Challenge 2: Existing processes cannot simultaneously achieve curling and oriented alignment, resulting in an uncontrollable microstructure.

✅ Parallel‑constraint liquid flow generates directional stress, enabling simultaneous curling and orientation control during molding without the need for secondary processing.

Challenge 3: Inkjet and screen-printing inks require large amounts of additives, and residual impurities increase internal resistance and degrade cycling performance.

✅ MXene ink with pure water and no additives; the printed films are pristine, and electrochemical stability is significantly enhanced.

Challenge 4: Vacuum filtration membranes can only be used to fabricate planar, continuous sheets and cannot be employed to pattern microelectrodes.

✅ Maskless direct-write of aerosols enables on-demand fabrication of micrometer-scale interdigitated electrode arrays, compatible with on-chip micro‑power sources.

Challenge 5: High-temperature forming processes damage flexible plastic substrates, limiting the application of wearable devices.

✅ All‑process atomization deposition at room temperature ensures that flexible substrates such as PET remain stable and do not deform.

VI. Future Diversified Industrial Application Scenarios

1 Flexible Wearable Micro Energy Storage Power Source

An integrated planar micro-supercapacitor for smart wristbands and sweat-sensing patches, ultra-thin and flexible.

2 On-chip micro-energy storage chips

MEMS sensors and miniature RF components are paired with on-chip capacitors to enable self-powered operation of the chip.

3 Flexible Electronic Skin Pressure-Sensing Energy Storage Unit

Integrated sensing–energy storage composite device, reducing the footprint of wearable devices.

4 Portable disposable electrochemical detection chip

A micro‑interdigital electrode‑integrated energy storage module enables rapid on-site detection without the need for an external power supply.

5 Two-Dimensional Energy Storage Materials Laboratory R&D Platform

Rapidly tune the porosity and alignment of MXene, enabling low-cost screening of high-performance electrode formulations.

Image and Text Guide

Figure 1. Schematic diagram of the AJP process: from MXene ink to patterned printing.

The MXene dispersion, after being formulated into an ink, is atomized by an ultrasonic nebulizer (1.7 MHz) and carried by a nitrogen carrier gas into the print head. A coaxial sheath gas (nitrogen, 120 sccm) then focuses and confines the stream into a collimated jet, which is directed onto a plasma‑treated PET substrate to form patterns with a line width of 200 μm. The focusing ratio is FR = 1.5 (sheath gas: 120 sccm; carrier gas: 80 sccm), with a nozzle diameter of 300 μm, a stand-off distance of 5 mm, and a printing speed of 10 mm/s. After 90 printing cycles, the line width remains constant, while the film thickness increases linearly.

Figure 2. Cross-sectional morphology of MXene prepared by vacuum filtration control and AJP printing.

(a) SEM image of a densely stacked cross-section of Ti₃C₂Tₓ obtained via vacuum filtration, showing tightly packed layers; (b) The cross-section of the AJP‑printed pattern exhibits a multilayered laminar architecture, with orientation aligned along the nozzle‑travel direction; (c) A local magnification reveals curled tubular MXene nanosheets (indicated by dashed lines); (d) HRTEM measurements reveal a layer spacing of 1.33 nm in the curled MXene, larger than the 1.08 nm observed in the vacuum‑filtered membrane. The BET specific surface area increases from 11.26 m²/g for the densely stacked structure to 25.92 m²/g for the curled architecture.

Figure 3. Mechanism of MXene curling orientation under aerosol droplet confinement

(a) AJP aerosol streams deposit onto the substrate; (b) Microscale sheath‑gas confinement induces multiple quasi‑parallel droplet jets to form parallel liquid flows on the surface; (c) Multiple small meniscus‑type three‑phase contact lines (TCLs) develop between adjacent droplets, generating a quasi‑unidirectional surface tension Fγ and a Laplace pressure ΔP, which together align MXene nanosheets along the flow direction and curl them into tubular structures; (d) SEM image of the curled tubular architecture; (e, f) Comparison: during natural dewetting, the surface tension acts normal to the surface toward the sphere’s center, yielding only planar‑packed nanosheets.

Figure 4. Topographic differences on the printed cross-section and water contact angle

(a) SEM image of an MXene pattern cross-section, with the upper and lower regions delineated by red dashed lines; (b) Top magnification: droplets pinned at high curvature induce strong curling of the nanosheets; (c) Bottom magnification: on a hydrophilic PET substrate, MXene deposits in a nearly planar configuration with low curvature; (d) After five printing cycles, the film exhibits a water contact angle of 63.31°; (e) Following plasma treatment, the contact angle on the PET substrate decreases to 18.26°. The degree of curling varies with the number of deposition cycles and the surface wettability.

Figure 5. Physical appearance of the interdigitated electrode and its electrochemical performance.

(a) Printed curled MXene interdigitated microelectrodes: line width 200 μm, thickness 45 μm, gap 300 μm; fabricated via 90 printing cycles. The inset shows the MSC device after encapsulation with a PVA/H₂SO₄ gel electrolyte. (b) CV curves at various scan rates (5–50 mV/s) are approximately rectangular, indicating capacitive behavior. (c) GCD curves at different current densities (0.1–0.5 mA/cm²) exhibit near‑linear symmetry. (d) The Nyquist plot shows no distinct semicircle and a nearly vertical slope in the low‑frequency region, reflecting efficient charge transfer; the inset presents the equivalent circuit. After optimization, the device achieves an areal capacitance of 34.87 mF/cm² and an energy density of 1.744 μWh/cm², retaining 90% of its initial capacitance after 5,000 cycles and maintaining 28.17 mF/cm² even under 90° bending.