Non-Epitaxial Growth of Transition Metal Oxide Crystalline Nanorods on Laser-Induced Graphene.

Graphene-based nanomaterials are very promising for wearable and flexible electronics because of their unique electrical and mechanical properties. However, their difficult chemical synthesis has limited wide-spread commercial adoption. In particular, energy storage devices such as micro-supercapacitors require a porous morphology for large specific surface area and patterning such as interdigitated designs, which traditionally requires multiple complex fabrication steps. Laser-induced graphene (LIG) is a recently developed method that solves this problem by simultaneously generating and patterning porous graphene electrodes. Laser irradiation of a polyimide (PI) substrate selectively transforms the PI into graphene. This method shows promise to fabricate miniaturized energy storage devices at low cost and on a flexible substrate. However, the capacitance of LIG micro-supercapacitors needs to be improved by developing novel charge storage mechanisms compatible with LIG electrodes. Typically, energy storage mechanisms are classified as either electrochemical double-layer capacitance (EDLC) or pseudocapacitance. EDLC is enhanced by facile adsorption of electrolyte ions on the electrode material. Therefore, light weight carbon-based materials such as activated carbon, carbon nanotubes, graphene and their different combinations are suitable for EDLC but ultimately their performance is limited by their specific surface area. Pseudocapacitance allows further charge to be stored beyond the limitations imposed by the electrode’s surface area utilizing redox reactions of the electrode material with the electrolyte ions. There has been extensive interest in enhancing pseudocapacitance using various redox reactions between electrode materials such as transition metal oxides, conducting polymers and electrolyte ions. Carbon-based large-scale supercapacitors have been reported with improved performance by adding redox species, which can undergo redox reactions with the carbon-based electrodes, to the electrolyte. Reports on micro-supercapacitors using redox electrolytes have been limited to electrodes fabricated by complex multi-step fabrication processes. Here, we report graphene micro-supercapacitors fabricated by one-step laser scribing with enhanced capacitance utilizing a redox electrolyte. Hydroquinone (HQ) is a promising candidate as a redox additive in the electrolyte owing to its double charge transfer mechanism i.e. loss of 2H+ and 2e- during the charging process, which results in benzoquinone (BQ). Similarly, BQ is reduced to HQ by gaining 2H+ and 2e- during discharging. HQ (0.5 mol/L) was added to the aqueous H2SO4 (1 mol/L) electrolyte, which was deposited onto interdigitated LIG electrodes. The laser parameters were optimized to achieve LIG with a fibrous morphology. Fig.1a shows a scanning electron microscope (SEM) image of the cross-section of the fibrous LIG on PI. The addition of HQ as a redox-active additive enhanced specific capacitance approximately 5 times compared to devices without the HQ additive. The unmodified H2SO4 electrolyte exhibited an areal capacitance of 0.8 mF/cm2. Addition of HQ raised the total capacitance to 3.9 mF/cm2 as calculated from the area under the cyclic voltammetry curve in Fig.1b. Cyclic voltammetry of the device with HQ electrolyte showed very strong peaks due to oxidation and reduction of HQ and BQ as shown in Fig. 1b. A typical cyclic voltammetry graph with rectangular shape due to EDLC was observed in H2SO4 at 10 mV/s scan rate. It remained stable even at a high scan rate of 1000 mV/s as shown in Fig.1c-d. These results demonstrate the conductive nature of the engraved graphene and facile adsorption of the H+ ions. The device was further tested at higher scan rates after the introduction of HQ (10-1000 mV/s as shown in Fig.1e-f. The redox peaks were found very stable at higher scan rates and their peak values move towards extreme potentials at higher scan rates. To further investigate the motion of electrolyte ions within the pores of the fibrous graphene, electrochemical impedance spectroscopy (EIS) was performed with and without HQ in H2SO4 (see Fig.1g-j). A semi circle at low frequencies was observed (see Fig.1j), which indicates only 3 Ω charge-transfer resistance owing to facile motion of the electrolyte ions. In conclusion, we report a facile method to increase the capacitance of micro-supercapacitors with laser-induced graphene electrodes. The method only requires the addition of one redox-active component to the electrolyte. Combined with the one-step fabrication and patterning of graphene by LIG, this method shows promise for low-cost flexible energy storage devices. Figure 1

Stable and durable laser-induced graphene patterns embedded in polymer substrates

Double-layer stretchable composite conductive graphene-hydrogel with wide-range linear sensing and thermal-humidity management for health monitoring

Wearable devices with integrated alarm functions play a vital role in daily life and can help people prevent potential hazards. Although many wearable sensors have been extensively studied and proposed to monitor various physiological signals, most of them are needed to integrate with the external alarm elements to realize warning, such as light-emitting diodes and buzzers, resulting in the system complexity and poor flexibility. In this paper, an integrated sensing and warning multifunctional device based on the mechanical and thermal effect of porous graphene is proposed on a bilayer asymmetrical pattern of laser-induced graphene (LIG). Compared with the strain sensor with nonpatterned LIG, the mechanical performance is greatly improved with the highest gauge factor value of up to 950 for the strain sensor with mesh-patterned LIG. On the contrary, the heating performance of the heater with nonpatterned LIG is better than that with mesh-patterned LIG. Combining the performance differences of different LIG patterns, the integrated wearable device with a bilayer asymmetrical LIG pattern is demonstrated. It can generate enough heating energy to warn the person when the detected signal meets the threshold condition measured in real time by the ultrasensitive strain sensor. This work will provide a new way to construct an integrated wearable device for realizing multifunctional applications. This integrated multifunctional device shows great potential toward the applications in healthcare monitoring and timely warning.

Graphene based materials have profoundly impacted research in nanotechnology, and this has significantly advanced biomedical, electronics, energy, and environmental applications. Laser-induced graphene (LIG) is made photothermally and has enabled a rapid route for graphene layers on polyimide surfaces. However, polysulfone (PSU), poly(ether sulfone) (PES), and polyphenylsulfone (PPSU) are highly used in numerous applications including medical, energy, and water treatment and they are critical components of polymer membranes. Here we show LIG fabrication on PSU, PES, and PPSU resulting in conformal sulfur-doped porous graphene embedded in polymer dense films or porous substrates using reagent- and solvent-free methods in a single step. We demonstrate the applicability as flexible electrodes with enhanced electrocatalytic hydrogen peroxide generation, as antifouling surfaces and as antimicrobial hybrid membrane-LIG porous filters. The properties and surface morphology of the conductive PSU-, PES-, and PPSU-LIG could be modulated using variable laser duty cycles. The LIG electrodes showed enhanced hydrogen peroxide generation compared to LIG made on polyimide, and showed exceptional biofilm resistance and potent antimicrobial killing effects when treated with Pseudomonas aeruginosa and mixed bacterial culture. The hybrid PES-LIG membrane-electrode ensured complete elimination of bacterial viability in the permeate (6 log reduction), in a flow-through filtration mode at a water flux of ∼500 L m-2 h-1 (2.5 V) and at ∼22 000 L m-2 h-1 (20 V). Due to the widespread use of PSU, PES, and PPSU in modern society, these functional PSU-, PES-, and PPSU-LIG surfaces have great potential to be incorporated into biomedical, electronic, energy and environmental devices and technologies.

Intelligent wearable devices based on laser-induced graphene (LIG) have attracted significant attention for human health monitoring. This paper proposed an innovative all-in-one design for preparing a self-powered smart insole using laser-induced MXene-composited graphene hybrid (LIG@MXene) from lignocellulose precursor. By incorporating MXene into the LIG, the composite achieved improved crystallinity and reduced defects, contributing to the electrical conductivity (17.2 Ω∙sq-1) and structural stability. The optimal laser processing parameters are 55% for laser power and 70 mms-1 for etching rate. The optimized LIG@MXene composite functions as a versatile platform for integrating triboelectric nanogenerator (TENG) with a high output power of 35 Vcm-2, supercapacitor with a superior areal capacitance of 71.4 mFcm-2 and the excellent cycling stability of 89.5% retention, Joule heater of the maximum heating temperature of 113°C at 5 V, and various flexible sensors for pressure, humidity and sweat composition with high sensitivity and linearity. In particular, the minimum L-tyrosine limit of detection in sweat is only 9.60 µM. These functional modules are embedded within an insole via a direct laser writing technology, which only emitted 9.10 kg CO2 eq during manufacturing. The direct laser-patterned synthesis of LIG@MXene composite represents a significant step forward in advancing smart wearable electronic devices.

Stretchable, ultrasensitive, and low-temperature NO2 sensors based on MoS2@rGO nanocomposites

Scalable fabrication of inkless, transfer-printed graphene-based textile microsupercapacitors with high rate capabilities

WITHDRAWN: The high-efficiency supercapacitor electrodes influencing laser-induced nanomaterials with Co-doped Nitrogen and Phosphorous

Laser-induced and KOH-activated 3D graphene: A flexible activated electrode fabricated via direct laser writing for in-plane micro-supercapacitors

Tongue pressure (TP) monitoring is essential for evaluating oral functions and improving elderly healthcare, particularly in addressing challenges related to chewing, swallowing, and speech. However, commercial balloon-based TP sensors have limitations in large footprints, small linear response ranges, and practical challenges in durability and replacement. Here, we introduce a novel TP sensor based on laser-induced graphene (LIG), fabricated through direct laser writing. This sensor is designed to provide a smaller footprint, higher linearity, enhanced durability, and simpler maintenance for advanced elderly healthcare. LIG patterns were generated on polyimide films by direct irradiation of ultraviolet (UV) nanosecond laser pulses and transferred onto biocompatible polydimethylsiloxane (PDMS) substrates. The sensor was encapsulated with an additional thin layer of PDMS to protect the oral environment. The fabricated TP sensor demonstrated exceptional sensitivity of 0.00594 kPa−1 across a wide pressure range (1–300 kPa), with rapid response times and long-term cyclic robustness. In-vivo tests validated its reliable and precise TP monitoring capability, proving its effectiveness in practical uses. Our approach paves a way for 3D-printed smart dentures for advanced elderly care while also offering broader applications in oral rehabilitation and biomechanical human-aid devices for general body pressure sensing.

The advancement of microelectronic devices mandates the development of flexible energy storage systems to enable the fabrication of miniaturized and wearable electronics. Herein, a sustainable approach is demonstrated for tuning the electronic and electrochemical properties of hierarchically porous laser‐induced graphene (LIG) substrates. The methodology entails the electrochemical deposition of polyoxovanadate nanoclusters (K5(CH3CN)3[V12O32Cl] (= K5{V12}) onto the highly porous LIG matrix. The comprehensive characterization is integrated through micro‐Raman spectroscopy and in‐depth X‐ray photoelectron spectroscopy to elucidate the deposition mechanism and electronic properties of the fabricated electrode. The results indicate a significant correlation between the orientation of the deposited clusters and the non‐crystalline regions of the LIG structure. Additionally, the cluster deposition results in a reduction of grain boundary defects in the nano‐graphite lattice of LIG. The optimized electrode exhibits enhanced areal capacitance (CA) of 125 mF cm−2 at a current density of 0.1 mA cm−2, representing a fivefold improvement compared to the undoped LIG substrate. Furthermore, as a proof of concept, a flexible solid‐state symmetrical supercapacitor device, fabricated with a PVA‐H2SO4 gel electrolyte, demonstrates an areal capacitance of 24.92 mF cm−2 at current density of 0.1 mA cm−2 and exhibits exceptional cycling stability, enduring up to 5000 consecutive galvanostatic charge‐discharge cycles.

Direct light‐to‐work conversion enables remote actuation through a non‐contact manner, among which the photothermal Marangoni effect is significant for developing light‐driven robots because of the diversity of applicable photothermal materials and light sources, as well as the high energy conversion efficiency. However, the lack of nanotechnologies that enable flexible integration of advanced photothermal materials with actuators of complex configurations significantly restricts their practical applications. In this paper, laser‐induced graphene (LIG) tape is reported as stick‐on photothermal labels for developing light‐driven actuators based on the Marangoni effect. With the help of direct laser writing technology, graphene patterns with superior photothermal properties are prepared on the PI tape. The patterned LIG tape can be stuck on any desired objects and generates an asymmetric photothermal field under light irradiation, forming a photothermal Marangoni actuator. Additionally, the PI tape with LIG patterns can be folded into 3D origami actuators that permit photothermal Marangoni actuation including both translation and rotation. The graphene‐based photothermal Marangoni actuators feature biocompatibility, which is confirmed by MDA‐MB‐231 cells proliferation experiments. Owing to the excellent photothermal property of LIG patterns, the as‐produced photothermal actuators can be manipulated by a variety of light sources, holding great promise for developing light‐driven soft robots.

Laser-induced graphene (LIG) has emerged as a promising technique for fabricating porous graphene electrodes for many applications, including biosensors and medical devices. However, improving electrochemical properties of LIG hinges on not only understanding the kinetics and energetics governing the physicochemical process of lasing, but also the tunability of surface chemistry and morphology of the produced LIG. This talk reveals the spatiotemporal laser control for achieving different LIG morphology and atomic structures with demonstrations of seamless transitions between conductive networked LIG structures and insulating fibrous LIG morphologies. The effect of laser fluence and multi-pass lasing on LIG morphology and properties will be shown. In addition, molecular engineering of the polymer substrate is explored for controlling the chemical and physical properties of the produced LIG. Finally, the electrochemical detection of neurotransmitters in the nanomolar range will be demonstrated. Our results show that heteroatom doping of graphene is possible by including sulfur or fluorine atoms into the backbone of the polyimide synthesized by two-step polycondensation. Accordingly, both the surface hydrophobicity and sensing sensitivity are shown to depend on the heteroatom-doping content. Taken together, our work paves the way for scalable fabrication of functional graphene-based electrodes and coatings on polymers for flexible and wearable electronics, as well as implantable devices, such as neural probes.

Laser-induced graphene (LIG) has gained considerable attention recently due to its unique properties and potential applications. In this study, we investigated using LIG in polyimide (PI) as a material for antenna applications. The LIG-−PI composite material was prepared by a facile picosecond laser (1064 nm) irradiation process, which resulted in a conductive graphene network within the PI matrix. Furthermore, LIG formation was confirmed by Raman spectroscopy and sheet resistance measurements. Finally, a patch antenna from LIG with 2.45 GHz microwaves was simulated, produced and tested. These findings suggest that LIG−PI composites have great potential for use in high-frequency electronic devices and can provide a new avenue for the development of flexible and wearable electronics.