Have you ever imagined a future where smartphones can be folded like paper and smartwatches are printed directly onto clothing? Such innovations would be impossible without graphene—a two-dimensional carbon material often hailed as the “king of materials.” However, conventional graphene‑based printing inks typically rely on surfactants or polymers as dispersants. These additives must be removed through high‑temperature post‑processing, which limits their use on heat‑sensitive substrates and hinders the development of diverse flexible electronic devices.

Recent breakthrough: Chinese and Israeli scientists have developed a new type of graphene ink! By using polypropylene carbonate (PPC) as a dispersant and pairing it with a low‑surface‑tension solvent, high‑performance microsupercapacitors can be printed directly onto paper with a mild annealing process at just 220°C. Coupled with aerosol jet printing (AJP) technology, this approach enables intricate circuits to be effortlessly “brought to life” on paper.

Working principle

1. What is graphene liquid-phase exfoliation (LPE) technology?

Liquid-phase exfoliation (LPE) is a simple, cost-effective method for the large-scale production of high-quality graphene. It employs acoustic vibrations or shear forces to exfoliate bulk graphite flakes into monolayer or few-layer graphene, which is then dispersed into a stable suspension.

2. Why was polypropylene carbonate (PPC) chosen as the dispersant?

• Low decomposition temperature: The thermal decomposition temperature of PPC is below 200°C, which means it can be removed at a lower temperature, thereby avoiding degradation of graphene’s properties.
• Enhancing dispersibility and stability: PPC molecules exhibit excellent compatibility and adsorption capabilities, promoting the uniform dispersion of graphene and preventing agglomeration.
• Environmentally friendly and biodegradable: PPC is a biodegradable polymer, making it more eco‑friendly and aligning with the trend toward green manufacturing.
• Easy removal: After printing, heating to 220°C allows the removal of the PPC, yielding a pure, highly conductive graphene network.

3. The Core of Aerosol Jet Printing (AJP) Technology

• Spray atomization: Ultrasonic vibrations atomize the ink into tiny particles, forming an aerosol.
• Precise positioning: Using a high-pressure carrier gas, the aerosol is directed onto the substrate surface, forming fine, precise lines.
• In-situ fabrication: No molds or etching processes are required; electronic circuits are directly “drawn” onto the object’s surface.
• Significant advantages: high resolution, minimal material waste, easy operation, and compatibility with a wide range of flexible substrates.

4. Preparation Procedure

• Dissolve PPC using low‑surface‑tension solvents such as tetrahydrofuran and ethyl acetate.
• Graphite is added, and ultrasonic agitation is used to exfoliate it, yielding a graphene suspension.
• Stable graphene/PPC powder was obtained through centrifugation and filtration.
• Redisperse the powder to formulate an ink suitable for aerosol spraying.
• Using an aerosol jet printing device, ink is sprayed onto various substrates—such as paper, plastic, and glass—for high-precision printing.
• Finally, the sample is heated at low temperature to remove the PPC, yielding a highly conductive graphene conductive network with strong adhesion.

Scope of Application

1. Flexible Electronics and Sensors

• Wearable devices: sensors printed directly onto fabric that monitor heart rate and body temperature in real time.
• Transparent electrode: Used in foldable smartphones, with a bend‑resistance of over 100,000 cycles (Fig. 6f).
• Paper-based electronic tags: low-cost RFID tags that drive logistics intelligence.

2. Micro-supercapacitors (MSCs)

• High areal capacitance: 324 μF/cm² (at 5 mV/s), outperforming comparable light‑annealed devices.
• Cycle life: After 10,000 charge–discharge cycles, the capacity retention is 99.4%.
• Mechanical Flexibility: At a bending radius of 6 mm, the capacitance exhibits virtually no attenuation.
• Application scenarios: Providing embedded energy storage for flexible electronics, such as electronic skin and smart packaging.

3. Environmental Protection and Mass Production

• Green materials: PPC is synthesized from carbon dioxide and is biodegradable; THF solvent exhibits low toxicity.
• Roll-to-roll (R2R) production: Aerosol printing speeds of up to 10 m/min, suitable for industrial-scale manufacturing.

Technological Advantages

1. Low-temperature processing to protect heat-sensitive materials

Conventional graphene inks typically require sintering at temperatures above 300°C, which limits the choice of materials and substrates. In contrast, this technology can remove PPC at just 220°C, making it compatible with virtually all heat‑sensitive substrates, such as paper, plastics, and textiles.

2. Excellent adhesion and flexibility

Through low-temperature sintering, a uniform, continuous, and robust conductive network is formed, ensuring the device’s mechanical stability and durability under repeated bending.

3. High Resolution and Flexibility

Aerosol jet printing (AJP) can achieve line widths at the micrometer scale, meeting the demands of high‑density circuitry, while the jetting process is easy to operate and environmentally friendly, generating zero waste.

4. Broad substrate compatibility

It supports printing on a wide range of substrates, from rigid glass to flexible paper and plastic, breaking free from material constraints and enabling applications across diverse scenarios.

Advantages of Aerosol Jet Printing (AJP) Technology

• High resolution: micron-level line width, meeting the demands of complex circuits.
• Low material waste: Precise jetting reduces material loss.
• Multi-substrate compatibility: Supports a variety of materials, including paper, plastic, and metal.
• Environmental protection and energy efficiency: gentle processing, low energy consumption, and zero pollution.
• Scalability: Digital and contactless, suitable for industrial automated production.

Aerosol jet printing (AJP) is not only a breakthrough in printing technology but also a key driver of digital manufacturing and green innovation. It will pave the way for lighter, more flexible, and personalized electronic devices of the future.

Image and Text Guide

Figure 1. Preparation of printable graphene ink using polypropylene carbonate (PPC). a, b Schematic illustration of liquid-phase exfoliation (LPE) for isolating graphene from graphite, with PPC serving as the dispersant. c Photograph showing the separation of graphene/PPC into a powder after LPE, recovered from the liquid medium. d Photograph of graphene ink prepared by redispersing the graphene/PPC powder. e Photograph of graphene micro-supercapacitor (MSC) electrodes deposited on paper via aerosol jet printing (AJP) technology.

Figure 2. Effect of solvent surface tension on ppc‑assisted LPE.

Figure 3. Computational analysis of graphene/PPC interactions. Intermolecular interaction maps for graphene and PPC fragment‑cluster models, based on Hirshfeld partitioning (IGMH), using the independent gradient model (δginter isosurface: 0.005). The color scale for equilateral facets is derived from the product of the electron density (ρ) and the sign of the second eigenvalue of the Hessian of the electron density (λ2). In the graphene/PPC model, the atomic contributions to all interatomic interactions (top panel) and intermolecular interactions (bottom panel) are mapped; the color scale for intermolecular interactions between graphene and PPC fragments reflects the balance of attractive and repulsive forces governing these interactions.

Figure 4. Characterization of graphene exfoliated using PPC. a Fourier-transform infrared spectra of graphene with and without PPC exfoliation. b Redispersion ratios of graphene prepared with and without PPC in THF and A0 solutions, determined using the exponential decay model described in Equation (2). The gray dashed line indicates the A0 value for the THF‑based, PPC‑exfoliated graphene solution. d Scanning electron microscopy image of graphene after PPC removal. e Raman spectrum of graphene (black) following PPC removal; the gray component corresponds to graphite removed during LPE. f, g Thickness (f) and lateral size distribution (g) of graphene on Si/SiO2 after PPC removal, as observed by atomic force microscopy.

Figure 5. Aerosol jet printing (AJP) of graphene/PPC ink. a Schematic illustration of aerosol jet printing (AJP) of graphene/PPC ink. b Optical microscopy images of graphene lines printed on Si/SiO2 substrates using nozzles with apertures of 300 μm and 150 μm, at different numbers of print passes. c Thickness and width of the printed lines after a single pass. d Line thickness as a function of the number of print passes. e Line thickness after annealing at 220 °C for 30 minutes to remove the PPC. f–h Graphene printed on various substrates: glass (f), plastic (g), and paper (h).

Figure 6. Printing graphene MSCs on paper. a) Photograph of a fork‑fingered graphene electrode printed on paper for fabricating an MSC. b, c) Cyclic voltammograms (CV) of the graphene MSC at scan rates ranging from 5 to 1000 mV s⁻¹. d) Specific capacitance (C) as a function of scan rate. e) Relative specific capacitance after 10,000 charge–discharge cycles; C₁ denotes the initial areal capacitance. f) Nyquist plots of the device with and without bending deformation. The inset in f shows a schematic of the bent device with a bending radius (r) of 6 mm. At a scan rate of 50 mV s⁻¹, CV curves are presented for both the bent and unbent configurations.

This paper demonstrates a high-performance graphene ink derived from polypropylene carbonate (PPC), enabling high-precision, low-temperature, and environmentally friendly printing of electronic circuits via aerosol jet printing (AJP). This approach provides robust technical support for the widespread adoption and large-scale deployment of flexible electronic devices. Looking ahead, there is good reason to believe that such technologies will usher in a new era of low-cost, green, efficient, and personalized electronics manufacturing.