Constructing Ionic Interfaces for Stable Electrochemical CO2 Reduction.

The electrochemical CO2 reduction reaction (CO2RR) has emerged as a promising approach for sustainable carbon cycling and valuable chemical production. Various methods and strategies have been explored to boost CO2RR performance. One of the most promising strategies includes the construction of stable ionic interfaces on metallic or molecular catalysts using organic or inorganic cations, which has demonstrated a significant improvement in catalytic performance. The stable ionic interface is instrumental in adjusting adsorption behavior, influencing reactive intermediates, facilitating mass transportation, and suppressing the hydrogen evolution reaction, particularly under acidic conditions. In this Perspective, we provide an overview of the recent advancements in building ionic interfaces in the electrocatalytic process and discuss the application of this strategy to improve the CO2RR performance of metallic and molecular catalysts. We aim to convey the future trends and opportunities in creating ionic interfaces to further enhance carbon utilization efficiency and the productivity of CO2RR products. The emphasis of this Perspective lies in the pivotal role of ionic interfaces in catalysis, providing a valuable reference for future research in this critical field.

Flash healing of laser-induced graphene.

The advancement of laser-induced graphene (LIG) technology has streamlined the fabrications of flexible graphene devices. However, the ultrafast kinetics triggered by laser irradiation generates intrinsic amorphous characteristics, leading to high resistivity and compromised performance in electronic devices. Healing graphene defects in specific patterns is technologically challenging by conventional methods. Herein, we report the rapid rectification of LIG's topological defects by flash Joule heating in milliseconds (referred to as F-LIG), whilst preserving its overall structure and porosity. The F-LIG exhibits a decreased ID/IG ratio from 0.84 - 0.33 and increased crystalline domain from Raman analysis, coupled with a 5-fold surge in conductivity. Pair distribution function and atomic-resolution imaging delineate a broader-range order of F-LIG with a shorter C-C bond of 1.425 Å. The improved crystallinity and conductivity of F-LIG with excellent flexibility enables its utilization in high-performance soft electronics and low-voltage disinfections. Notably, our F-LIG/polydimethylsiloxane strain sensor exhibits a gauge factor of 129.3 within 10% strain, which outperforms pristine LIG by 800%, showcasing significant potential for human-machine interfaces.

Laser-Induced Graphene-Based Sensors in Health Monitoring: Progress, Sensing Mechanisms, and Applications.

The rising global population and improved living standards have led to an alarming increase in non-communicable diseases, notably cardiovascular and chronic respiratory diseases, posing a severe threat to human health. Wearable sensing devices, utilizing micro-sensing technology for real-time monitoring, have emerged as promising tools for disease prevention. Among various sensing platforms, graphene-based sensors have shown exceptional performance in the field of micro-sensing. Laser-induced graphene (LIG) technology, a cost-effective and facile method for graphene preparation, has gained particular attention. By converting polymer films directly into patterned graphene materials at ambient temperature and pressure, LIG offers a convenient and environmentally friendly alternative to traditional methods, opening up innovative possibilities for electronic device fabrication. Integrating LIG-based sensors into health monitoring systems holds the potential to revolutionize health management. To commemorate the tenth anniversary of the discovery of LIG, this work provides a comprehensive overview of LIG's evolution and the progress of LIG-based sensors. Delving into the diverse sensing mechanisms of LIG-based sensors, recent research advances in the domain of health monitoring are explored. Furthermore, the opportunities and challenges associated with LIG-based sensors in health monitoring are briefly discussed.

Backbone Engineering of Polymeric Catalysts for High-Performance CO2 Reduction in Bipolar Membrane Zero-Gap Electrolyzer.

Bipolar membranes (BPMs) have emerged as a promising solution for mitigating CO2 losses, salt precipitation and high maintenance costs associated with the commonly used anion-exchange membrane electrode assembly for CO2 reduction reaction (CO2RR). However, the industrial implementation of BPM-based zero-gap electrolyzer is hampered by the poor CO2RR performance, largely attributed to the local acidic environment. Here, we report a backbone engineering strategy to improve the CO2RR performance of molecular catalysts in BPM-based zero-gap electrolyzers by covalently grafting cobalt tetraaminophthalocyanine onto a positively charged polyfluorene backbone (PF-CoTAPc). PF-CoTAPc shows a high acid tolerance in BPM electrode assembly (BPMEA), achieving a high FE of 82.6 % for CO at 100 mA/cm2 and a high CO2 utilization efficiency of 87.8 %. Notably, the CO2RR selectivity, carbon utilization efficiency and long-term stability of PF-CoTAPc in BPMEA outperform reported BPM systems. We attribute the enhancement to the stable cationic shield in the double layer and suppression of proton migration, ultimately inhibiting the undesired hydrogen evolution and improving the CO2RR selectivity. Techno-economic analysis shows the least energy consumption (957 kJ/mol) for the PF-CoTAPc catalyst in BPMEA. Our findings provide a viable strategy for designing efficient CO2RR catalysts in acidic environments.

Ultrathin, Cationic Covalent Organic Nanosheets for Enhanced CO2 Electroreduction to Methanol.

Metalloporphyrins and metallophthalocyanines emerge as popular building blocks to develop covalent organic nanosheets (CONs) for CO2 reduction reaction (CO2 RR). However, existing CONs predominantly yield CO, posing a challenge in achieving efficient methanol production through multielectron reduction. Here, ultrathin, cationic, and cobalt-phthalocyanine-based CONs (iminium-CONs) are reported for electrochemical CO2 -to-CH3 OH conversion. The integration of quaternary iminium groups enables the formation of ultrathin morphology with uniformly anchored cobalt active sites, which are pivotal for facilitating rapid multielectron transfer. Moreover, the cationic iminium-CONs exhibit a lower activity for hydrogen evolution side reaction. Consequently, iminium-CONs manifest significantly enhanced selectivity for methanol production, as evidenced by a remarkable 711% and 270% improvement in methanol partial current density (jCH3OH ) compared to pristine CoTAPc and neutral imine-CONs, respectively. Under optimized conditions, iminium-CONs deliver a high jCH3OH of 91.7 mA cm-2 at -0.78 V in a flow cell. Further, iminium-CONs achieve a global methanol Faradaic efficiency (FECH3OH ) of 54% in a tandem device. Thanks to the single-site feature, the methanol is produced without the concurrent generation of other liquid byproducts. This work underscores the potential of cationic covalent organic nanosheets as a compelling platform for electrochemical six-electron reduction of CO2 to methanol.

In situ generation of highly localized chlorine by laser-induced graphene electrodes during electrochemical disinfection.

Laser-induced graphene (LIG) has gained popularity for electrochemical water disinfection due to its efficient antimicrobial activity when activated with low voltages. However, the antimicrobial mechanism of LIG electrodes is not yet fully understood. This study demonstrated an array of mechanisms working synergistically to inactivate bacteria during electrochemical treatment using LIG electrodes, including the generation of oxidants, changes in pH-specifically high alkalinity associated with the cathode, and electro-adsorption on the electrodes. All these mechanisms may contribute to the disinfection process when bacteria are close to the surface of the electrodes where inactivation was independent of the reactive chlorine species (RCS); however, RCS was likely responsible for the predominant cause of antibacterial effects in the bulk solution (i.e., ≥100 mL in our study). Furthermore, the concentration and diffusion kinetics of RCS in solution was voltage-dependent. At 6 V, RCS achieved a high concentration in water, while at 3 V, RCS was highly localized on the LIG surface but not measurable in water. Despite this, the LIG electrodes activated by 3 V achieved a 5.5-log reduction in Escherichia coli (E.coli) after 120-min electrolysis without detectable chlorine, chlorate, or perchlorate in the water, suggesting a promising system for efficient, energy-saving, and safe electro-disinfection.

Direct Synthesis of Ammonia from Nitrate on Amorphous Graphene with Near 100% Efficiency.

Ammonia is an indispensable commodity in the agricultural and pharmaceutical industries. Direct nitrate-to-ammonia electroreduction is a decentralized route yet challenged by competing side reactions. Most catalysts are metal-based, and metal-free catalysts with high nitrate-to-ammonia conversion activity are rarely reported. Herein, it is shown that amorphous graphene synthesized by laser induction and comprising strained and disordered pentagons, hexagons, and heptagons can electrocatalyze the eight-electron reduction of NO3 - to NH3 with a Faradaic efficiency of ≈100% and an ammonia production rate of 2859 µg cm-2 h-1 at -0.93 V versus reversible hydrogen electrode. X-ray pair-distribution function analysis and electron microscopy reveal the unique molecular features of amorphous graphene that facilitate NO3 - reduction. In situ Fourier transform infrared spectroscopy and theoretical calculations establish the critical role of these features in stabilizing the reaction intermediates via structural relaxation. The enhanced catalytic activity enables the implementation of flow electrolysis for the on-demand synthesis and release of ammonia with >70% selectivity, resulting in significantly increased yields and survival rates when applied to plant cultivation. The results of this study show significant promise for remediating nitrate-polluted water and completing the NOx cycle.

Ultrasensitive, Fast-Responsive, Directional Airflow Sensing by Bioinspired Suspended Graphene Fibers.

The development of high-performance miniaturized and flexible airflow sensors is essential to meet the need of emerging applications. Graphene-based airflow sensors are hampered by the sluggish response and recovery speed and low sensitivity. Here we employ laser-induced graphene (LIG) with poststructural biomimicry for fabricating high-performance, flexible airflow sensors, including cotton-like porous LIG, caterpillar fluff-like vertical LIG fiber, and Lepidoptera scale-like suspended LIG fiber (SLIGF) structures. The structural engineering changes the deformation behavior of LIGs under stress, among which the synchronous propagation of the scale-like structure of SLIGF is the most conducive to airflow sensing. The SLIGF achieves the shortest average response time of 0.5 s, the highest sensitivity of 0.11 s/m, and a record-low detection threshold of 0.0023 m/s, benchmarked against the state-of-the-art airflow sensors. Furthermore, we showcase the SLIGF airflow sensors in weather forecasting, health, and communications applications. Our study will help develop next-generation waterflow, sound, and motion sensors.

Touch IoT enabled by wireless self-sensing and haptic-reproducing electronic skin.

Tactile sensations are mainly transmitted to each other by physical touch. Wireless touch perception could be a revolution for us to interact with the world. Here, we report a wireless self-sensing and haptic-reproducing electronic skin (e-skin) to realize noncontact touch communications. A flexible self-sensing actuator was developed to provide an integrated function in both tactile sensing and haptic feedback. When this e-skin was dynamically pressed, the actuator generated an induced voltage as tactile information. Via wireless communication, another e-skin could receive this tactile data and run a synchronized haptic reproduction. Thus, touch could be wirelessly conveyed in bidirections between two users as a touch intercom. Furthermore, this e-skin could be connected with various smart devices to form a touch internet of things where one-to-one and one-to-multiple touch delivery could be realized. This wireless touch presents huge potentials in remote touch video, medical care/assistance, education, and many other applications.

Atomically Thin, Ionic-Covalent Organic Nanosheets for Stable, High-Performance Carbon Dioxide Electroreduction.

The incorporation of charged functional groups is effective to modulate the activity of molecular complexes for the CO2 reduction reaction (CO2 RR), yet long-term heterogeneous electrolysis is often hampered by catalyst leaching. Herein, an electrocatalyst of atomically thin, cobalt-porphyrin-based, ionic-covalent organic nanosheets (CoTAP-iCONs) is synthesized via a post-synthetic modification strategy for high-performance CO2 -to-CO conversion. The cationic quaternary ammonium groups not only enable the formation of monolayer nanosheets due to steric hindrance and electrostatic repulsion, but also facilitate the formation of a *COOH intermediate, as suggested by theoretical calculations. Consequently, CoTAP-iCONs exhibit higher CO2 RR activity than other cobalt-porphyrin-based structures: an 870% and 480% improvement of CO current densities compared to the monomer and neutral nanosheets, respectively. Additionally, the iCONs structure can accommodate the cationic moieties. In a flow cell, CoTAP-iCONs attain a very small onset overpotential of 40 mV and a stable total current density of 212 mA cm-2 with CO Faradaic efficiency of >95% at -0.6 V for 11 h. Further coupling the flow electrolyzer with commercial solar cells yields a solar-to-CO conversion efficiency of 13.89%. This work indicates that atom-thin, ionic nanosheets represent a promising structure for achieving both tailored activity and high stability.

Anomalous Self-Optimizing Microporous Graphene-Based Lithium-ion Battery Anode from Laser Activation of Small Organic Molecules.

Laser scribing technology is a straightforward technique to fabricate porous graphene, yet only conducted with polymeric precursors. Compared to polymers, molecular engineering of small organic molecules is much easier, which can be used to modify the graphene with tailored performance. Here we report the first employment of a laser to respectively transform small organic molecules, pentacene quinone and tetraazapentacene quinone (TAPQ), into graphene (P-LIG and N-LIG) as high-performance lithium-ion battery anodes. The TAPQ, as the N-fused molecular precursor, produces nitrogen-doped graphene. Both N-LIG and P-LIG exhibit significant self-enhancement of capacity upon cycling; the N-LIG anode delivers reversible capacities of 5863 mAh g-1 at 0.2 A g-1 and retains 1970 mAh g-1 at 2 A g-1 after another 500 cycles, which is the best performance for the graphene-type anode. Kinetics studies and structural characterizations verify that the surface- and diffusion-controlled processes are both progressively optimized, providing extra lithium storage upon cycling. It is also supported by small-angle X-ray scattering that the disordering level of micropores is increased upon cycling for N-LIG, corresponding to the enhancement of microporous level. Our work successfully develops a novel facile approach to fabricating heteroatom-doped microporous graphene exhibiting high performance and provides new insight into the lithium storage mechanism.

Transient Solid-State Laser Activation of Indium for High-Performance Reduction of CO2 to Formate.

Deficiencies in understanding the local environment of active sites and limited synthetic skills challenge the delivery of industrially-relevant current densities with low overpotentials and high selectivity for CO2 reduction. Here, a transient laser induction of metal salts can stimulate extreme conditions and rapid kinetics to produce defect-rich indium nanoparticles (L-In) is reported. Atomic-resolution microscopy and X-ray absorption disclose the highly defective and undercoordinated local environment in L-In. In a flow cell, L-In shows a very small onset overpotential of ≈92 mV and delivers a current density of ≈360 mA cm-2 with a formate Faradaic efficiency of 98% at a low potential of -0.62 V versus RHE. The formation rate of formate reaches up to 6364.4 µmol h-1mgIn-1$mg_{{\rm{In}}}^{--1}$ , which is nearly 39 folds higher than that of commercial In (160.7 µmol h-1mgIn-1$mg_{{\rm{In}}}^{--1}$ ), outperforming most of the previous results that have been reported under KHCO3 environments. Density function theory calculations suggest that the defects facilitate the formation of *OCHO intermediate and stabilize the *HCOOH while inhibiting hydrogen adsorption. This study suggests that transient solid-state laser induction provides a facile and cost-effective approach to form ligand-free and defect-rich materials with tailored activities.

Transient, Implantable, Ultrathin Biofuel Cells Enabled by Laser-Induced Graphene and Gold Nanoparticles Composite.

Transient power sources with excellent biocompatibility and bioresorablility have attracted significant attention. Here, we report high-performance, transient glucose enzymatic biofuel cells (TEBFCs) based on the laser-induced graphene (LIG)/gold nanoparticles (Au NPs) composite electrodes. Such LIG electrodes can be easily fabricated from polyimide (PI) with an infrared CO2 laser and exhibit a low impedance (16 Ω). The resulted TEBFC yields a high open circuit potential (OCP) of 0.77 V and a maximum power density of 483.1 µW/cm2. The TEBFC not only exhibits a quick response time that enables reaching the maximum OCP within 1 min but also owns a long lifetime over 28 days in vitro. The excellent biocompatibility and transient performance from in vitro and in vivo tests allow long-term implantation of TEBFCs in rats for energy harvesting. The TEBFCs with advanced processing methods provide a promising power solution for transient electronics.

Molecular Engineering of Laser-Induced Graphene for Potential-Driven Broad-Spectrum Antimicrobial and Antiviral Applications.

Worldwide, countless deaths have been caused by the coronavirus disease 2019. In addition to the virus variants, an increasing number of fatal fungal infections have been reported, which further exacerbates the scenario. Therefore, the development of porous surfaces with both antiviral and antimicrobial capacities is of urgent need. Here, a cost-effective, nontoxic, and metal-free strategy is reported for the surface engineering of laser-induced graphene (LIG). The authors covalently engineer the surface potential of the LIG from -14 to ≈+35 mV (LIG+ ), enabling both high-efficiency antimicrobial and antiviral performance under mild conditions. Specifically, several candidate microorganisms of different types, including Escherichia coli, Streptomyces tenebrarius, and Candida albicans, are almost completely inactivated after 10-min solar irradiation. LIG+ also exhibits a strong antiviral effect against human coronaviruses: 99% HCoV-OC43 and 100% HCoV-229E inactivation are achieved after 20-min treatment. Such enhancement may also be observed against other types of pathogens that are heat-sensitive and oppositely charged. Besides, the covalent modification strategy alleviates the leaching problem, and the low cytotoxicity of LIG+ makes it advantageous. This study highlights the synergy of surface potential and photothermal effect in the inactivation of pathogens and it provides a direction for designing porous materials for airborne disease removal and water disinfection.

Highly Efficient and Rapid Inactivation of Coronavirus on Non-Metal Hydrophobic Laser-Induced Graphene in Mild Conditions.

The prevalence of COVID-19 has caused global dysfunction in terms of public health, sustainability, and socio-economy. While vaccination shows potential in containing the spread, the development of surfaces that effectively reduces virus transmission and infectivity is also imperative, especially amid the early stage of the pandemic. However, most virucidal surfaces are operated under harsh conditions, making them impractical or potentially unsafe for long-term use. Here, it is reported that laser-induced graphene (LIG) without any metal additives shows marvelous antiviral capacities for coronavirus. Under low solar irradiation, the virucidal efficacy of the hydrophobic LIG (HLIG) against HCoV-OC43 and HCoV-229E can achieve 97.5% and 95%, respectively. The photothermal effect and the hydrophobicity of the HLIG synergistically contribute to the superior inactivation capacity. The stable antiviral performance of HLIG enables its multiple uses, showing advantages in energy saving and environmental protection. This work discloses a potential method for antiviral applications and has implications for the future development of antiviral materials.

Laser-Engineered Graphene on Wood Enables Efficient Antibacterial, Anti-Salt-Fouling, and Lipophilic-Matter-Rejection Solar Evaporation.

Advances in solar steam generation have made a promise in mitigating the water scarcity problem. However, their practical use could be curtailed by the vaporized pollutants and the longevity limited by biofouling and salt-fouling that are often overlooked. Here, a flake of wood is reported to be engineered into a miniaturized solar water treatment device by a laser engraving process and demonstrates advantages over common solar systems. The device is structured to mimic the centralized water treatment plants, which contains a superhydrophilic graphene bottom layer for lipophilic organic matter rejection and antifouling, an intrinsic wood microchannels layer for water transport and thermal management, and a hydrophobic graphene top layer for solar-driven desalination while inhibiting salt deposition. The pore size of wood differentiates the water flux and hence the evaporation performance, and the balsa wood with a larger pore size possesses a higher evaporation rate of 1.6 ± 0.02 kg m-2 h-1 compared with pine wood. The hierarchical design achieves a solar energy conversion efficiency of 110% and a lipophilic organic matter removal efficiency of >90% and significantly improves longevity even at high salinity. This work illuminates a sustainable and cost-effective pathway for water treatment and shows potential for wastewater reuse.

Self-Reporting and Photothermally Enhanced Rapid Bacterial Killing on a Laser-Induced Graphene Mask.

Wearing face masks has been widely recommended to contain respiratory virus diseases, yet the improper use of masks poses a threat of jeopardizing the protection effect. We here identified the bacteria viability on common face masks and found that the majority of bacteria (90%) remain alive after 8 h. Using laser-induced graphene (LIG), the inhibition rate improves to ∼81%. Combined with the photothermal effect, 99.998% bacterial killing efficiency could be attained within 10 min. For aerosolized bacteria, LIG also showed superior antibacterial capacity. The LIG can be converted from a diversity of carbon precursors including biomaterials, which eases the supply stress and environmental pressure amid an outbreak. In addition, self-reporting of mask conditions is feasible using the moisture-induced electricity from gradient graphene. Our results improve the safe use of masks and benefit the environment.

Laser-Induced Graphene: En Route to Smart Sensing.

The discovery of laser-induced graphene (LIG) from polymers in 2014 has aroused much attention in recent years. A broad range of applications, including batteries, catalysis, sterilization, and separation, have been explored. The advantages of LIG technology over conventional graphene synthesis methods are conspicuous, which include designable patterning, environmental friendliness, tunable compositions, and controllable morphologies. In addition, LIG possesses high porosity, great flexibility, and mechanical robustness, and excellent electric and thermal conductivity. The patternable and printable manufacturing process and the advantageous properties of LIG illuminate a new pathway for developing miniaturized graphene devices. Its use in sensing applications has grown swiftly from a single detection component to an integrated smart detection system. In this minireview, we start with the introduction of synthetic efforts related to the fabrication of LIG sensors. Then, we highlight the achievement of LIG sensors for the detection of a diversity of stimuli with a focus on the design principle and working mechanism. Future development of the techniques toward in situ and smart detection of multiple stimuli in widespread applications will be discussed.

Covalently Grafting Cobalt Porphyrin onto Carbon Nanotubes for Efficient CO2 Electroreduction.

Molecular complexes with inexpensive transition-metal centers have drawn extensive attention, as they show a high selectivity in the electrochemical conversion of CO2 to CO. In this work, we propose a new strategy to covalently graft cobalt porphyrin onto the surface of a carbon nanotube by a substitution reaction at the metal center. Material characterization and electrochemical studies reveal that the porphyrin molecules are well dispersed at a high loading of 10 wt. %. As a result, the turnover frequency for CO formation is improved by a factor of three compared to traditional physically-mixed catalysts with the same cobalt content. This leads to an outstanding overall current density of 25.1 mA cm-2 and a Faradaic efficiency of 98.3 % at 490 mV overpotential with excellent long-term stability. This work provides an effective pathway for the improvement of the performance of electrocatalysts that could inspire rational design of molecular catalysts in the future.