Oxidized Laser-Induced Graphene for Efficient Oxygen Electrocatalysis

Unveiling the oxidation mechanisms of octa-penta graphene: a multidimensional exploration from first-principles to machine learning

Octa-penta graphene (OPG), a novel carbon allotrope characterized by its distinctive arrangement of pentagonal and octagonal rings, has garnered considerable attention due to its exceptional structure and functional properties. This study systematically investigates the oxidation mechanisms of OPG and elucidates the oxygen migration patterns on the OPG monolayer through first-principles calculations and machine-learning-based molecular dynamics (MLMD) simulations. Specifically, the oxidation processes on OPG-L and OPG-Z involve exothermic chemisorption, where oxygen molecules dissociate at the surfaces, forming stable epoxy groups. Notably, OPG-Z requires higher initial activation energy, reflecting the variable energy demands across different surfaces. The most energetically favorable adsorption sites for an oxygen atom on OPG-L and OPG-Z are the L8-5-2 site and the Z8-5-1 site, respectively, confirmed by their low adsorption energies and optimal bond configurations. Furthermore, the integrated-crystal orbital Hamilton population (ICOHP) and Bader charge analyses provide insights into the physical mechanisms of oxygen atom adsorption. Importantly, we found that oxidation also impacts the electronic properties of OPG, with OPG-L retaining its metallic characteristics post-oxygen adsorption, whereas OPG-Z undergoes a transformation from a metallic to a semiconducting state due to the introduction of oxygen. Oxygen migration on the OPG monolayer involves breaking and reforming of C-O bonds, with varying stability across adsorption sites and limited migration along the basal plane. MLMD simulations corroborate these migration patterns, offering detailed migration trajectories consistent with theoretical predictions. These findings enhance the understanding of oxygen migration dynamics on OPG, facilitate its experimental validations, and highlight its potential as a novel 2D material for applications in batteries, heat-resistant materials, and oxidation-resistant coatings.

Simplifying the Incorporation of Laser-Induced Graphene into Microfluidic Devices

Laser-induced graphene (LIG) electrodes have many attractive properties that make them promising platforms for many electrochemical applications. However, their fabrication is currently limited to a small number of substrates, with the most widely used being polyimide. Incorporating LIG electrodes into microfluidic devices is challenging because it requires transfer onto other substrates compatible with microfluidics. Transferring LIG electrodes to other substrates has been demonstrated, but it requires complicated mechanical procedures that impact electrode performance. Here, a simple transfer process has been developed that maintains the structural and electrochemical integrity of the LIG electrodes. The transferred LIG electrodes were characterized using morphological and electrochemical techniques, revealing comparable performance to nontransferred LIG in both surface-sensitive and surface-insensitive redox processes. The transferred electrodes were then incorporated into a microfluidic device, and their performance as a sensing platform was verified using the detection of dopamine in the presence of uric acid and ascorbic acid. This simple and versatile method of integrating LIG electrodes into microfluidic systems offers many opportunities for future applications.

One-Step Laser-Guided Fabrication of 3D Self-Assembled Graphene Micro-Rolls

Laser-induced graphene (LIG) has been systematically investigated and employed because of the spartan laser synthesis and functional three dimensional (3D) foam-like structures. However, thermally induced deformation during laser processing is generally undesirable and, therefore, strictly suppressed. This work introduces a novel laser-guided self-assembly approach integrated into the fabrication of LIG to generate multiscale 3D graphene foam structures in a single step. Leveraging the photothermal effects of laser ablation on polyimide films, we achieve concurrent LIG production and self-assembly, enabling the transformation of two dimensional films into 3D micro-rolls. The process is finely tuned through interface modification and optimized laser parameters, allowing precise control over the geometry of the resulting structures. Systematic investigations reveal that varying laser power and line spacing effectively adjust the diameters of the LIG micro-rolls. Characterization indicates that the LIG micro-rolls can be fabricated with very large curvature and limited internal space, enhancing the potential for microscale applications. Furthermore, our laser strategy facilitates the creation of symmetric, asymmetric, and double-tube micro-rolls, underscoring its design flexibility. This work highlights the potential of the laser-guided self-assembly strategy in graphene nanomaterials and miniaturized applications, which has been exemplarily verified through the LIG micro-roll supercapacitors.

Engineering p-Orbital States via Molecular Modules in All-Organic Electrocatalysts toward Direct Water Oxidation

Oxygen evolution reaction (OER) is an indispensable anode reaction for sustainable hydrogen production from water electrolysis, yet overreliance on metal-based catalysts featured with vibrant d-electrons. It still has notable gap between metal-free and metal-based electrocatalysts, due to lacking accurate and efficient p-band regulation methods on non-metal atoms. Herein, a molecular modularization strategy is proposed for fine-tuning the p-orbital states of series metal-free covalent organic frameworks (COFs) for realizing OER performance beyond benchmark precious metal catalysts. Optimized combination of benzodioxazole/benzodiimide-based building blocks achieves an impressive applied potential of 1.670 ± 0.004 V versus reversible hydrogen electrode (RHE) and 1.735 ± 0.006 V versus RHE to deliver enhanced current densities of 0.5 and 1.0 A cm-2, respectively. Moreover, it holds a notable charge transfer amount (stands for a long service life) within operation period that outperforms all reported metal-free electrocatalysts. Operando differential electrochemical mass spectrometry (DEMS) with isotope labeling identifies the adsorbate evolution mechanism (AEM). A variety of spectroscopic techniques and density functional theory (DFT) calculations reveal that the p-band center of these catalysts can be shifted stepwise to optimize the oxygen intermediate adsorption and lower the reaction energy barrier. This work provides a novel perspective for enhancing the electrocatalytic performance of metal-free COFs.

A surface modified laser-induced graphene based flexible biosensor for multiplexed sweat analysis

The growing popularity of electrochemical sensors featuring non-invasive biosensing technologies has generated significant enthusiasm for continuous monitoring of bodily fluid biomarkers, potentially aiding in the early detection of health issues in individuals. However, detection of multiple biomarkers in complex biofluids often necessitates a high-density array which creates a challenge in achieving cost-effective fabrication methods. To overcome this constraint, this work reports the fabrication of an electrochemical sensor utilizing a NiO-Ti3C2Tx MXene-modified flexible laser-induced graphene (LIG) electrode for the separate and concurrent analysis of ascorbic acid (AA), dopamine (DA), and uric acid (UA) in human sweat and also addresses the deficiencies in the existing state of the art by offering a cost-efficient and high-performance sensor that mitigates the degrading constraints of conventional LIG electrodes. Cyclic voltammetry and differential pulse voltammetry measurements reveals that the electrochemical properties of the modified electrode, attain a low detection limit and great sensitivity for the target biomarkers. The NiO-Ti3C2Tx/LIG sensor demonstrated enhanced electrocatalytic activity for the oxidation of ascorbic acid, dopamine, and uric acid, and proved useful for analysing these biomarkers in synthetic sweat samples. Under the optimized conditions, the LOD values were estimated to be 16, 1.97 and 0.78 μM for AA, DA and UA, respectively. The developed high-efficiency sensor holds significant promise for applications in flexible and wearable electronics for health monitoring.

Tandem Oxidation Activation of Carbon for Enhanced Electrochemical Synthesis of H2O2: Unveiling the Role of Quinone Groups and Their Operando Derivatives

Oxygen-doped carbon materials show great promise to catalyze two-electron oxygen reduction reaction (2e-ORR) for electrochemical synthesis of hydrogen peroxide (H2O2), but the identification of the active sites is the subject of ongoing debate. In this study, a tandem oxidation strategy is developed to activate carbon black for achieving highly efficient electrochemical synthesis of H2O2. Acetylene black (AB) is processed with O2 plasma and subsequent electrochemical oxidation, resulting in a remarkable selectivity of >96% over a wide potential range, and a record-setting high yield of >10 mol gcat -1 h-1 with good durability in gas diffusion electrode. Comprehensive characterizations and calculations revealed that the presence of abundant C═O groups at the edge sites positively correlated to and accounted for the excellent 2e-ORR performance. Notably, the edge hydroquinone group formed from quinone under operando conditions, which is overlooked in previous research, is identified as the most active catalytic site.

Laser-Induced Graphene on Novel Crosslinked Poly(dimethylsiloxane)/Triton X-100 Composites for Improving Mechanical, Electrical and Hydrophobic Properties

Laser-induced graphene (LIG) has become a highly promising material for flexible functional devices due to its robust mechanical stability, excellent electrical properties, and ease of fabrication. Most research has been focused on LIG production on rigid or flexible substrates, with an obvious gap in laser induction of graphene on elastic, stretchable substrates, which limits the scope of application of LIG in flexible electronics. We demonstrate laser induction of graphene on a novel, cross-linked poly(dimethylsiloxane) (PDMS)/Triton X-100 composite substrates. The effect of varying Triton content (1-30 wt.%) on the structural, thermal, surface, nanomechanical, and electrical properties of LIG was systematically studied. Physicochemical characterization confirmed the successful induction of LIG on the surface of PDMS/Triton composites. A higher content of Triton in the PDMS matrix improves the quality of LIG, increases stiffness and hydrophobicity, and somewhat decreases sheet resistance. Similar thermal properties and super-hydrophobicity were observed for LIG/PDMS/Triton materials as compared to their counterparts without LIG. Direct laser irradiation of graphene on the surface of PDMS/Triton composites results in the formation of extremely promising materials, which have great potential for use in flexible electronic devices.

Ruthenium Anchored Laser-Induced Graphene as Binder-Free and Free-Standing Electrode for Selective Electrosynthesis of Ammonia from Nitrate

Developing effective electrocatalysts for the nitrate reduction reaction (NO3RR) is a promising alternative to conventional industrial ammonia (NH3) synthesis. Herein, starting from a flexible laser-induced graphene (LIG) film with hierarchical and interconnected macroporous architecture, a binder-free and free-standing Ru-modified LIG electrode (Ru-LIG) is fabricated for electrocatalytic NO3RR via a facile electrodeposition method. The relationship between the laser-scribing parameters and the NO3RR performance of Ru-LIG electrodes is studied in-depth. At -0.59 VRHE, the Ru-LIG electrode exhibited the optimal and stable NO3RR performance (NH3 yield rate of 655.9 µg cm-2 h-1 with NH3 Faradaic efficiency of up to 93.7%) under a laser defocus setting of +2 mm and an applied laser power of 4.8 W, outperforming most of the reported NO3RR electrodes operated under similar conditions. The optimized laser-scribing parameters promoted the surface properties of LIG with increased graphitization degree and decreased charge-transfer resistance, leading to synergistically improved Ru electrodeposition with more exposed NO3RR active sites. This work not only provides a new insight to enhance the electrocatalytic NO3RR performance of LIG-based electrodes via the coordination with metal electrocatalysts as well as identification of the critical laser-scribing parameters but also will inspire the rational design of future advanced laser-induced electrocatalysts for NO3RR.

Rational Design of Earth-Abundant Catalysts toward Sustainability

Catalysis is crucial for clean energy, green chemistry, and environmental remediation, but traditional methods rely on expensive and scarce precious metals. This review addresses this challenge by highlighting the promise of earth-abundant catalysts and the recent advancements in their rational design. Innovative strategies such as physics-inspired descriptors, high-throughput computational techniques, and artificial intelligence (AI)-assisted design with machine learning (ML) are explored, moving beyond time-consuming trial-and-error approaches. Additionally, biomimicry, inspired by efficient enzymes in nature, offers valuable insights. This review systematically analyses these design strategies, providing a roadmap for developing high-performance catalysts from abundant elements. Clean energy applications (water splitting, fuel cells, batteries) and green chemistry (ammonia synthesis, CO2 reduction) are targeted while delving into the fundamental principles, biomimetic approaches, and current challenges in this field. The way to a more sustainable future is paved by overcoming catalyst scarcity through rational design.

Laser-Induced Graphene for Advanced Sensing: Comprehensive Review of Applications

Laser-induced graphene (LIG) and Laser-scribed graphene (LSG) are both advanced materials with significant potential in various applications, particularly in the field of sustainable sensors. The practical uses of LIG (LSG), which include gas detection, biological process monitoring, strain assessment, and environmental variable tracking, are thoroughly examined in this review paper. Its tunable characteristics distinguish LIG (LSG), which is developed from accurate laser beam modulation on polymeric substrates, and they are essential in advancing sensing technologies in many applications. The recent advances in LIG (LSG) applications include energy storage, biosensing, and electronics by steadily advancing efficiency and versatility. The remarkable flexibility of LIG (LSG) and its transformative potential in regard to sensor manufacturing and utilization are highlighted in this manuscript. Moreover, it thoroughly examines the various fabrication methods used in LIG (LSG) production, highlighting precision and adaptability. This review navigates the difficulties that are encountered in regard to implementing LIG sensors and looks ahead to future developments that will propel the industry forward. This paper provides a comprehensive summary of the latest research in LIG (LSG) and elucidates this innovative material's advanced and sustainable elements.

A Pressure and Proximity Sensor Based on Laser-Induced Graphene

Smart wearable devices are extensively utilized across diverse domains due to their inherent advantages of flexibility, portability, and real-time monitoring. Among these, flexible sensors demonstrate exceptional pliability and malleability, making them a prominent focus in wearable electronics research. However, the implementation of flexible wearable sensors often entails intricate and time-consuming processes, leading to high costs, which hinder the advancement of the entire field. Here, we report a pressure and proximity sensor based on oxidized laser-induced graphene (oxidized LIG) as a dielectric layer sandwiched by patterned LIG electrodes, which is characterized by high speed and cost-effectiveness. It is found that in the low-frequency range of fewer than 0.1 kHz, the relative dielectric constant of the oxidized LIG layer reaches an order of magnitude of 104. The pressure mode of this bimodal capacitive sensor is capable of detecting pressures within the range of 1.34 Pa to 800 Pa, with a response time of several hundred milliseconds. The proximity mode involves the application of stimulation using an acrylic probe, which demonstrates a detection range from 0.05 mm to 37.8 mm. Additionally, it has a rapid response time of approximately 100 ms, ensuring consistent signal variations throughout both the approach and withdrawal phases. The sensor fabrication method proposed in this project effectively minimizes expenses and accelerates the preparation cycle through precise control of laser processing parameters to shape the electrode-dielectric layer-electrode within a single substrate material. Based on their exceptional combined performance, our pressure and proximity sensors exhibit significant potential in practical applications such as motion monitoring and distance detection.

Roles of Oxygen-Containing Functional Groups in Carbon for Electrocatalytic Two-Electron Oxygen Reduction Reaction

Recent years have witnessed great research interests in developing high-performance electrocatalysts for the two-electron (2e-) oxygen reduction reaction (ORR) that enables the sustainable and flexible synthesis of H2O2. Carbon-based electrocatalysts exhibit attractive catalytic performance for the 2e- ORR, where oxygen-containing functional groups (OFGs) play a decisive role. However, current understanding is far from adequate, and the contribution of OFGs to the catalytic performance remains controversial. Therefore, a critical overview on OFGs in carbon-based electrocatalysts toward the 2e- ORR is highly desirable. Herein, we go over the methods for constructing OFGs in carbon including chemical oxidation, electrochemical oxidation, and precursor inheritance. Then we review the roles of OFGs in activating carbon toward the 2e- ORR, focusing on the intrinsic activity of different OFGs and the interplay between OFGs and metal species or defects. At last, we discuss the reasons for inconsistencies among different studies, and personal perspectives on the future development in this field are provided. The results provide insights into the origin of high catalytic activity and selectivity of carbon-based electrocatalysts toward the 2e- ORR and would provide theoretical foundations for the future development in this 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.

Recent Advances in Laser-Induced Graphene-Based Materials for Energy Storage and Conversion

Laser-induced graphene (LIG) is a porous carbon nanomaterial that can be produced by irradiation of CO2 laser directly on the polymer substrate under ambient conditions. LIG has many merits over conventional graphene, such as simple and fast synthesis, tunable structure and composition, high surface area and porosity, excellent electrical and thermal conductivity, and good flexibility and stability. These properties make LIG a promising material for energy applications, such as supercapacitors, batteries, fuel cells, and solar cells. In this review, we highlight the recent advances of LIG in energy materials, covering the fabrication methods, performance enhancement strategies, and device integration of LIG-based electrodes and devices in the area of hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, zinc-air batteries, and supercapacitors. This comprehensive review examines the potential of LIG for future sustainable and efficient energy material development, highlighting its versatility and multifunctionality in energy conversion.

Synchronous Redox Reactions in Copper Oxalate Enable High-Capacity Anode for Proton Battery

Proton batteries are competitive due to their merits such as high safety, low cost, and fast kinetics. However, it is generally difficult for current studies of proton batteries to combine high capacity and high stability, while the research on proton storage mechanism and redox behavior is still in its infancy. Herein, the polyanionic layered copper oxalate is proposed as the anode for a high-capacity proton battery for the first time. The copper oxalate allows for reversible proton insertion/extraction through the layered space but also achieves high capacity through synchronous redox reactions of Cu2+ and C2O42-. During the discharge process, the bivalent Cu-ion is reduced, whereas the C═O of the oxalate group is partially converted to C-O. This synchronous behavior presents two units of charge transfer, enabling the embedding of two units of protons in the (110) crystal face. As a result, the copper oxalate anode demonstrates a high specific capacity of 226 mAh g-1 and maintains stable operation over 1000 cycles with a retention of 98%. This work offers new insights into the development of dual-redox electrode materials for high-capacity proton batteries.

Laser-induced transient conversion of rhodochrosite/polyimide into multifunctional MnO2/graphene electrodes for energy storage applications

Laser-induced graphene (LIG) has been extensively investigated for electrochemical energy storage due to its easy synthesis and highly conductive nature. However, the limited charge accumulation in LIG usually leads to significantly low energy densities. In this work, we report a novel strategy to directly transform natural rhodochrosite into ultrafine manganese dioxide (MnO2) nanoparticles (NPs) in the polyimide (PI) substrate for high-performance micro-supercapacitors (MSCs) and lithium-ion batteries (LIBs) through a scalable and cost-effective laser processing method. Specifically, laser treatment on rhodochrosite/polyimide precursors induces the thermal explosion, which splits rhodochrosite (10 μm) into MnO2 NPs (12-16 nm) on the carbon matrix of LIG due to the sputtering effect. Benefiting from largely exposed active sites from the ultrafine MnO2 and the synergetic effect from highly conductive LIG, the MnO2/LIG MSCs show a high specific capacitance of 544.0 F g-1 (154.3 mF cm-2; 14.16 F cm-3) at 3 A/g and 82.1% capacitance retention after 10,000 cycles at 5A/g, in contrast to pure LIG (<100 F g-1). Moreover, the MnO2/LIG-based LIBs show the highest reversible discharge capacity of ∼1097 mAh g-1 at 0.2 A/g and ∼ 866.4 mAh g-1 at 1.0 A/g. This study opens a new route for synthesizing novel LIG-based composites from natural minerals.

Laser-induced graphene on cross-linked sodium alginate

Laser-induced graphene (LIG) possesses desirable properties for numerous applications. However, LIG formation on biocompatible substrates is needed to further augment the integration of LIG-based technologies into nanobiotechnology. Here, LIG formation on cross-linked sodium alginate is reported. The LIG is systematically investigated, providing a comprehensive understanding of the physicochemical characteristics of the material. Raman spectroscopy, scanning electron microscopy with energy-dispersive x-ray analysis, x-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy techniques confirm the successful generation of oxidized graphene on the surface of cross-linked sodium alginate. The influence of laser parameters and the amount of crosslinker incorporated into the alginate substrate is explored, revealing that lower laser speed, higher resolution, and increased CaCl2content leads to LIG with lower electrical resistance. These findings could have significant implications for the fabrication of LIG on alginate with tailored conductive properties, but they could also play a guiding role for LIG formation on other biocompatible substrates.

Recent Advances and Synergistic Effects of Non-Precious Carbon-Based Nanomaterials as ORR Electrocatalysts: A Review

The use of platinum-free (Pt) cathode electrocatalysts for oxygen reduction reactions (ORRs) has been significantly studied over the past decade, improving slow reaction mechanisms. For many significant energy conversion and storage technologies, including fuel cells and metal-air batteries, the ORR is a crucial process. These have motivated the development of highly active and long-lasting platinum-free electrocatalysts, which cost less than proton exchange membrane fuel cells (PEMFCs). Researchers have identified a novel, non-precious carbon-based electrocatalyst material as the most effective substitute for platinum (Pt) electrocatalysts. Rich sources, outstanding electrical conductivity, adaptable molecular structures, and environmental compatibility are just a few of its benefits. Additionally, the increased surface area and the simplicity of regulating its structure can significantly improve the electrocatalyst's reactive sites and mass transport. Other benefits include the use of heteroatoms and single or multiple metal atoms, which are capable of acting as extremely effective ORR electrocatalysts. The rapid innovations in non-precious carbon-based nanomaterials in the ORR electrocatalyst field are the main topics of this review. As a result, this review provides an overview of the basic ORR reaction and the mechanism of the active sites in non-precious carbon-based electrocatalysts. Further analysis of the development, performance, and evaluation of these systems is provided in more detail. Furthermore, the significance of doping is highlighted and discussed, which shows how researchers can enhance the properties of electrocatalysts. Finally, this review discusses the existing challenges and expectations for the development of highly efficient and inexpensive electrocatalysts that are linked to crucial technologies in this expanding field.

Stabilize Sodium Metal Anode by Integrated Patterning of Laser-Induced Graphene with Regulated Na Deposition Behavior

Metallic sodium is regarded as the most potential anode for sodium-ion batteries due to its high capacity and earth-abundancy. Nevertheless, uncontrolled Na dendrite growth and infinite volume change remain great challenges for developing high-performance sodium metal batteries. This work provides a simple and general approach to stabilize sodium metal anode (SMA) by constructing Sn nanoparticles-anchored laser-induced graphene on copper foil (Sn@LIG@Cu) consisting of Sn@LIG composite, polyimide (PI) columns, and Cu current collector. The Sn-based sodiophilic species effectively reduce the Na nucleation overpotential and regulate the dendrite Na-free deposition. While the flexible PI columns act as binder and buffer the volume variation of Na during cycling. Besides, the unique patterned structure provides continuous and rapid channels for ion transportation, promoting the Na+ transport kinetics. Therefore, the as-fabricated Sn@LIG@Cu electrode exhibits outstanding rate performance to 40 mA cm-2 and excellent cycling stability without dendrite growth, which is confirmed by in-situ optical microscopy observation. Moreover, the practical full cell based on such an anode displays a favorable rate capability of up to 10 C and cycling performance at 5 C for 600 cycles. This work thus demonstrates a facile, highly-efficient, and scalable approach to stabilize SMAs and can be extended to other battery systems.

Laser-Carbonization - A Powerful Tool for Micro-Fabrication of Patterned Electronic Carbons

Fabricating electronic devices from natural, renewable resources is a common goal in engineering and materials science. In this regard, carbon is of special significance due to its biocompatibility combined with electrical conductivity and electrochemical stability. In microelectronics, however, carbon's device application is often inhibited by tedious and expensive preparation processes and a lack of control over processing and material parameters. Laser-assisted carbonization is emerging as a tool for the precise and selective synthesis of functional carbon-based materials for flexible device applications. In contrast to conventional carbonization via in-furnace pyrolysis, laser-carbonization is induced photo-thermally and occurs on the time-scale of milliseconds. By careful selection of the precursors and process parameters, the properties of this so-called laser-patterned carbon (LP-C) such as porosity, surface polarity, functional groups, degree of graphitization, charge-carrier structure, etc. can be tuned. In this critical review, a common perspective is generated on laser-carbonization in the context of general carbonization strategies, fundamentals of laser-induced materials processing, and flexible electronic applications, like electrodes for sensors, electrocatalysts, energy storage, or antennas. An attempt is made to have equal emphasis on material processing and application aspects such that this emerging technology can be optimally positioned in the broader context of carbon-based microfabrication.

Feather-like Gold Nanostructures Anchored onto 3D Mesoporous Laser-Scribed Graphene: A Highly Sensitive Platform for Enzymeless Glucose Electrochemical Detection in Neutral Media

The authors present a novel sensing platform for a disposable electrochemical, non-enzymatic glucose sensor strip at physiological pH. The sensing material is based on dendritic gold nanostructures (AuNs) resembling feather branches, which are electrodeposited onto a laser-scribed 3D graphene electrode (LSGE). The LSGEs were fabricated via a one-step laser scribing process on a commercially available polyimide sheet. This study investigates several parameters that influence the morphology of the deposited Au nanostructures and the catalytic activity toward glucose electro-oxidation. The electrocatalytic activity of the AuNs-LSGE was evaluated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and amperometry and was compared to commercially available carbon electrodes prepared under the same electrodeposition conditions. The sensor demonstrated good stability and high selectivity of the amperometric response in the presence of interfering agents, such as ascorbic acid, when a Nafion membrane was applied over the electrode surface. The proposed sensing strategy offers a wide linear detection range, from 0.5 to 20 mM, which covers normal and elevated levels of glucose in the blood, with a detection limit of 0.21 mM. The AuNs-LSGE platform exhibits great potential for use as a disposable glucose sensor strip for point-of-care applications, including self-monitoring and food management. Its non-enzymatic features reduce dependence on enzymes, making it suitable for practical and cost-effective biosensing solutions.

Bioinspired and Bioderived Aqueous Electrocatalysis

The development of efficient and sustainable electrochemical systems able to provide clean-energy fuels and chemicals is one of the main current challenges of materials science and engineering. Over the last decades, significant advances have been made in the development of robust electrocatalysts for different reactions, with fundamental insights from both computational and experimental work. Some of the most promising systems in the literature are based on expensive and scarce platinum-group metals; however, natural enzymes show the highest per-site catalytic activities, while their active sites are based exclusively on earth-abundant metals. Additionally, natural biomass provides a valuable feedstock for producing advanced carbonaceous materials with porous hierarchical structures. Utilizing resources and design inspiration from nature can help create more sustainable and cost-effective strategies for manufacturing cost-effective, sustainable, and robust electrochemical materials and devices. This review spans from materials to device engineering; we initially discuss the design of carbon-based materials with bioinspired features (such as enzyme active sites), the utilization of biomass resources to construct tailored carbon materials, and their activity in aqueous electrocatalysis for water splitting, oxygen reduction, and CO2 reduction. We then delve in the applicability of bioinspired features in electrochemical devices, such as the engineering of bioinspired mass transport and electrode interfaces. Finally, we address remaining challenges, such as the stability of bioinspired active sites or the activity of metal-free carbon materials, and discuss new potential research directions that can open the gates to the implementation of bioinspired sustainable materials in electrochemical devices.

Cellulose-Based Laser-Induced Graphene Devices for Electrochemical Monitoring of Bacterial Phenazine Production and Viability

As an easily disposable substrate with a microporous texture, paper is a well-suited, generic substrate to build analytical devices for studying bacteria. Using a multi-pass lasing process, cellulose-based laser-induced graphene (cLIG) with a sheet resistance of 43.7 ± 2.3 Ωsq-1 is developed and utilized in the fabrication of low-cost and environmentally-friendly paper sensor arrays. Two case studies with Pseudomonas aeruginosa and Escherichia coli demonstrate the practicality of the cLIG sensors for the electrochemical analysis of bacteria. The first study measures the time-dependent profile of phenazines released from both planktonic (up to 60 h) and on-chip-grown (up to 22 h) Pseudomonas aeruginosa cultures. While similarities do exist, marked differences in phenazine production are seen with cells grown directly on cLIG compared to the planktonic culture. Moreover, in planktonic cultures, pyocyanin levels increase early on and plateau around 20 h, while optical density measurements increase monotonically over the duration of testing. The second study monitors the viability and metabolic activity of Escherichia coli using a resazurin-based electrochemical assay. These results demonstrate the utility of cLIG paper sensors as an inexpensive and versatile platform for monitoring bacteria and could enable new opportunities in high-throughput antibiotic susceptibility testing, ecological studies, and biofilm studies.

Salt-Induced Doping and Templating of Laser-Induced Graphene Supercapacitors

The use of inexpensive and widely available CO₂ lasers to selectively irradiate polymer films and form a graphene foam, termed laser-induced graphene (LIG), has incited significant research attention. The simple and rapid nature of the approach and the high conductivity and porosity of LIG have motivated its widespread application in electrochemical energy storage devices such as batteries and supercapacitors. However, nearly all high-performance LIG-based supercapacitors reported to date are prepared from costly, petroleum-based polyimide (Kapton, PI). Herein, we demonstrate that incorporating microparticles of inexpensive, non-toxic, and widely abundant sodium salts such as NaCl and Na₂SO₄ into poly(furfuryl alcohol) (PFA) resins enables the formation of high-performance LIG. The embedded particles aid in carbonization and act as a template for pore formation. While increasing both the carbon yield and surface area of the electrodes, the salt also dopes the LIG formed with S or Cl. The combination of these effects results in a two- to four-order-of-magnitude increase in device areal capacitance, from 8 μF/cm² for PFA/no salt at 5 mV/s to up to 80 mF/cm² for some PFA/20% Na₂SO₄ samples at 0.05 mA/cm², significantly higher than that of PI-based devices and most other LIG precursors.

Laser induced graphanized microfluidic devices

With the advent of cyber-physical system-based automation and intelligence, the development of flexible and wearable devices has dramatically enhanced. Evidently, this has led to the thrust to realize standalone and sufficiently-self-powered miniaturized devices for a variety of sensing and monitoring applications. To this end, a range of aspects needs to be carefully and synergistically optimized. These include the choice of material, micro-reservoir to suitably place the analytes, integrable electrodes, detection mechanism, microprocessor/microcontroller architecture, signal-processing, software, etc. In this context, several researchers are working toward developing novel flexible devices having a micro-reservoir, both in flow-through and stationary phases, integrated with graphanized zones created by simple benchtop lasers. Various substrates, like different kinds of cloths, papers, and polymers, have been harnessed to develop laser-ablated graphene regions along with a micro-reservoir to aptly place various analytes to be sensed/monitored. Likewise, similar substrates have been utilized for energy harvesting by fuel cell or solar routes and supercapacitor-based energy storage. Overall, realization of a prototype is envisioned by integrating various sub-systems, including sensory, energy harvesting, energy storage, and IoT sub-systems, on a single mini-platform. In this work, the diversified work toward developing such prototypes will be showcased and current and future commercialization potential will be projected.

Highly Robust Laser-Induced Graphene (LIG) Ultrafiltration Membrane with a Stable Microporous Structure

Laser-induced graphene (LIG) materials have great potential in water treatment applications. Herein, we report the fabrication of a mechanically robust electroconductive LIG membrane with tailored separation properties for ultrafiltration (UF) applications. These LIG membranes are facilely fabricated by directly lasing poly(ether sulfone) (PES) membrane support. Control PES membranes were fabricated through a nonsolvent-induced phase separation (NIPS) technique. A major finding was that when PES UF membranes were treated with glycerol, the membrane porous structure remained almost unchanged upon drying, which also assisted with protecting the membrane's nanoscale features after lasing. Compared to the control PES membrane, the membrane fabricated with 8% laser power on the bottom layer of PES (PES (B)-LIG-HP) demonstrated 4 times higher flux (865 LMH) and 90.9% bovine serum albumin (BSA) rejection. Moreover, LIG membranes were found to be highly hydrophilic and exhibited excellent mechanical and chemical stability. Owing to their excellent permeance and separation efficiency, these highly robust electroconductive LIG membranes have a great potential to be used for designing functional membranes.

Surface Engineering of Laser-Induced Graphene Enables Long-Term Monitoring of On-Body Uric Acid and pH Simultaneously

Laser-induced graphene (LIG) suffers from serious decay in long-term biosensing, which greatly restricts its practical applications. Herein, we report a new strategy to engineer the LIG surface with Au clusters and chitosan sequentially to form a C-Au-LIG electrode with a superhydrophilic and highly conductive 3D graphene surface, which demonstrates superior performance and negligible decay in both long-term storage and practical usage in vitro and in vivo environments. Moreover, the C-Au-LIG electrode can be used for detecting uric acid (UA) and pH simultaneously from a single differential pulse voltammetry curve with low-detection limitation, high accuracy, and negligible interference with other sweat biomarkers. The integrated C-Au-LIG wearable biosensor was employed to continuously monitor the UA content in human sweat, which can well reflect the daily intake of purines for at least 10 days. Therefore, the C-Au-LIG electrode demonstrates significant application potential and provides inspiration for surface engineering of other biosensor materials and electrodes.

Asymmetric Activation of the Nitro Group over a Ag/Graphene Heterointerface to Boost Highly Selective Electrocatalytic Reduction of Nitrobenzene

The electrocatalytic reduction of nitrobenzene to aniline normally faces high overpotential and poor selectivity because of its six-electron redox nature. Herein, a Ag nanoparticles/laser-induced-graphene (LIG) heterointerface was fabricated on polyimide films and employed as an electrode material for an efficient nitrobenzene reduction reaction (NBRR) via a one-step laser direct writing technology. The first-principles calculations reveal that Ag/LIG shows the lowest activation barriers for the NBRR, which could be attributed to the optimum adsorption of the H atom realized by the appropriate interaction between Ag/LIG heterointerfaces and nitrobenzene. As a result, the overpotential of the NBRR is reduced by 217 mV after silver loading, and Ag/LIG shows a high aniline selectivity of 93%. Furthermore, an electrochemical reduction of nitrobenzene in tandem with an electrochemical oxidative polymerization of aniline was designed to serve as an alternative method to remove nitrobenzene from the aqueous solution. This strategy highlights the significance of heterointerfaces for efficient electrocatalysts, which may stimulate the development of novel electrocatalysts to boost the electrocatalytic activity.

Holey and Wrinkled Flash Graphene from Mixed Plastic Waste

High surface area varieties of graphene have captured significant attention, allowing for improved performance in a variety of applications. However, there are challenges facing the use of graphene in these applications since it is expensive and difficult to synthesize in bulk. Here, we leverage the capabilities of flash Joule heating to synthesize holey and wrinkled flash graphene (HWFG) in seconds from mixed plastic waste feedstocks, using in situ salt decomposition to produce and stabilize pore formation during the reaction. Surface areas as high as 874 m² g^-1 are obtained, with characteristics of micro-, meso-, and macroporosities. Raman spectroscopy confirms the wrinkled and turbostratic nature of the HWFG. We demonstrate HWFG applications in its use as a metal-free hydrogen evolution reaction electrocatalyst, with excellent stability, competitive overpotential, and Tafel slope; in a Li-metal battery anode allowing for stable and high discharge rates; and in a material with high gas adsorption. This represents an upcycle of mixed plastic waste, thereby affording a valuable route to address this pressing environmental pollutant concern.

Carbonaceous Oxygen Evolution Reaction Catalysts: From Defect and Doping-Induced Activity over Hybrid Compounds to Ordered Framework Structures

Oxygen evolution reaction (OER) is expected to be of great importance for the future energy conversion and storage in form of hydrogen by water electrolysis. Besides the traditional noble-metal or transition metal oxide-based catalysts, carbonaceous electrocatalysts are of great interest due to their huge structural and compositional variety and unrestricted abundance. This review provides a summary of recent advances in the field of carbon-based OER catalysts ranging from "pure" or unintentionally doped carbon allotropes over heteroatom-doped carbonaceous materials and carbon/transition metal compounds to metal oxide composites where the role of carbon is mainly assigned to be a conductive support. Furthermore, the review discusses the recent developments in the field of ordered carbon framework structures (metal organic framework and covalent organic framework structures) that potentially allow a rational design of heteroatom-doped 3D porous structures with defined composition and spatial arrangement of doping atoms to deepen the understanding on the OER mechanism on carbonaceous structures in the future. Besides introducing the structural and compositional origin of electrochemical activity, the review discusses the mechanism of the catalytic activity of carbonaceous materials, their stability under OER conditions, and potential synergistic effects in combination with metal (or metal oxide) co-catalysts.

Magnetically Aligned Ultrafine Cobalt Embedded 3D Porous Carbon Metamaterial by One-Step Ultrafast Laser Direct Writing

Spatial manipulation of nanoparticles (NPs) in a controlled manner is critical for the fabrication of 3D hybrid materials with unique functions. However, traditional fabrication methods such as electron-beam lithography and stereolithography are usually costly and time-consuming, precluding their production on a large scale. Herein, for the first time the ultrafast laser direct writing is combined with external magnetic field (MF) to massively produce graphene-coated ultrafine cobalt nanoparticles supported on 3D porous carbon using metal-organic framework crystals as precursors (5 × 5 cm2 with 10 s). The MF-confined picosecond laser scribing not only reduces the metal ions rapidly but also aligns the NPs in ultrafine and evenly distributed order (from 7.82 ± 2.37 to 3.80 ± 0.84 nm). ≈400% increment of N-Q species within N compositionis also found as the result of the special MF-induced laser plasma plume. (). The importance of MF is further exmined by electrochemical water-splitting tests. Significant overpotential improvements of 90 and 150 mV for oxygen evolution reaction and hydrogen evolution reaction are observed, respectively, owing to the MF-induced alignment of the NPs and controlled elemental compositions. This work provides a general bottom-up approach for the synthesis of metamaterials with high outputs yet a simple setup.

Inherent Surface Activation of Laser-Scribed Graphene Decorated with Au and Ag Nanoparticles: Simultaneous Electrochemical Behavior toward Uric Acid and Dopamine

Laser-scribed graphene electrodes (LSGEs) have attracted great attention for the development of electrochemical (bio)sensors due to their excellent electronic properties, large surface area, and high porosity, which enhances the electrons' transfer rate. An increasing active surface area and defect sites are the quickest way to amplify the electrochemical sensing attributes of the electrodes. Here, we have found that the activation procedure coupled to the electrodeposition of metal nanoparticles resulted in a significant amplification of the active area and the analytical performance. This preliminary study is supported by the demonstration of the simultaneous electrochemical sensing of dopamine (DA) and uric acid (UA) by the electrochemically activated LSGEs (LSGE*s). Furthermore, the electrodeposition of two different metal nanoparticles, gold (Au) and silver (Ag), was performed in multiple combinations on working and reference electrodes to investigate the enhancement in the electrochemical response of LSGE*s. Current enhancements of 32, 27, and 35% were observed from LSGE* with WE:Au/RE:LSG/CE:LSGE, WE:Au/RE:Au/CE:LSGE, and WE:Au/RE:Ag/CE:LSGE, compared to the same combinations of LSGEs without any surface activation. A homemade and practical potentiostat, KAUSTat, was used in these electrochemical depositions in this study. Among all of the combinations, the surface area was increased 1.6-, 2.0-, and 1.2-fold for WE:Au/RE:LSG/CE:LSGE, WE:Au/RE:Au/CE:LSGE, and WE:Au/RE:Ag/CE:LSGE prepared from LSGE*s, respectively. To evaluate the analytical performance, DA and UA were detected simultaneously in the presence of ascorbic acid. The LODs of DA and UA are calculated to be ∼0.8 and ∼0.6 μM, respectively. Hence, this study has the potential to open new insights into new surface activation strategies with a combination of one-step nanostructured metal depositions by a custom-made potentiostat. This novel strategy could be an excellent and straightforward method to enhance the electrochemical transducer sensitivity for various electrochemical sensing applications.

Carbon-based metal-free electrocatalysts: from oxygen reduction to multifunctional electrocatalysis

Since the discovery of N-doped carbon nanotubes as the first carbon-based metal-free electrocatalyst (C-MFEC) for oxygen reduction reaction (ORR) in 2009, C-MFECs have shown multifunctional electrocatalytic activities for many reactions beyond ORR, such as oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO₂RR), nitrogen reduction reaction (NRR), and hydrogen peroxide production reaction (H₂O₂PR). Consequently, C-MFECs have attracted a great deal of interest for various applications, including metal-air batteries, water splitting devices, regenerative fuel cells, solar cells, fuel and chemical production, water purification, to mention a few. By altering the electronic configuration and/or modulating their spin angular momentum, both heteroatom(s) doping and structural defects (e.g., atomic vacancy, edge) have been demonstrated to create catalytic active sites in the skeleton of graphitic carbon materials. Although certain C-MFECs have been made to be comparable to or even better than their counterparts based on noble metals, transition metals and/or their hybrids, further research and development are necessary in order to translate C-MFECs for practical applications. In this article, we present a timely and comprehensive, but critical, review on recent advancements in the field of C-MFECs within the past five years or so by discussing various types of electrocatalytic reactions catalyzed by C-MFECs. An emphasis is given to potential applications of C-MFECs for energy conversion and storage. The structure-property relationship for and mechanistic understanding of C-MFECs will also be discussed, along with the current challenges and future perspectives.

Tuning Metal Elements in Open Frameworks for Efficient Oxygen Evolution and Oxygen Reduction Reaction Catalysts

Electrochemical methods are promising technical routes for future clean energy storage and conversion. Most of the electrochemical methods involve oxygen reactions. Unfavorable kinetics and sluggish reactions are the main challenges for these processes. We report here a facile synthesis of highly efficient oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts. The catalysts are synthesized through the fine-tuning of metal ions (M, specifically Co, Ni, Zn, and Cu) in Prussian blue analogues (PBAs) and thus termed as M-PBAs. The CoNi-PBA-2 catalyst shows the highest activity toward OER with an onset potential at 280 mV and a Tafel slope of 63 mV dec^-1. Zn-PBA catalysts demonstrate high selectivity in two-electron-transfer ORR. The H₂O₂ yield is as high as 88% at 0 V vs RHE. Density functional theory (DFT) calculations also confirm the high selectivity of Zn-PBA toward H₂O₂ in ORR.

Polyimide-Derived Carbon-Coated Li4Ti5O12 as High-Rate Anode Materials for Lithium Ion Batteries

Carbon-coated Li₄Ti₅O₁₂ (LTO) has been prepared using polyimide (PI) as a carbon source via the thermal imidization of polyamic acid (PAA) followed by a carbonization process. In this study, the PI with different structures based on pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) moieties have been synthesized. The effect of the PI structure on the electrochemical performance of the carbon-coated LTO has been investigated. The results indicate that the molecular arrangement of PI can be improved when the rigid p-PDA units are introduced into the PI backbone. The carbons derived from the p-PDA-based PI show a more regular graphite structure with fewer defects and higher conductivity. As a result, the carbon-coated LTO exhibits a better rate performance with a discharge capacity of 137.5 mAh/g at 20 C, which is almost 1.5 times larger than that of bare LTO (94.4 mAh/g).

Application of functionalized graphene in Li-O2 batteries

Li-O₂ batteries (LOB) are considered as one of the most promising energy storage devices using renewable electricity to power electric vehicles because of its exceptionally high energy density. Carbon materials have been widely employed in LOB for its light weight and facile availability. In particular, graphene is a suitable candidate due to its unique two-dimensional structure, high conductivities, large specific surface areas, and good stability at high charge potential. However, the intrinsic catalytic activity of graphene is insufficient for the sluggish kinetics of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in LOB. Therefore, various surface functionalization schemes for graphene have been developed to tailor the surface chemistry of graphene. In this review, the properties and performances of functionalized graphene cathodes are discussed from theoretical and experimental aspects, including heteroatomic doping, oxygen functional group modifications, and catalyst decoration. Heteroatomic doping breaks electric neutrality of sp² carbon of graphene, which forms electron-deficient or electron-rich sites. Oxygen functional groups mainly create defective edges on graphene oxides with C-O, C=O, and -COO-. Catalyst decoration is widely attempted by various transition and precious metal and metal oxides. These induced reactive sites usually improve the ORR and/or OER in LOB by manipulating the adsorption energies of O₂, LiO₂, Li₂O₂, and promoting electron transportation of cathode. In addition, functionalized graphene is used in anode and separators to prevent shuttle effect of redox mediators and suppress growth of Li dendrite.

Synergistic Modulation of Carbon-Based, Precious-Metal-Free Electrocatalysts for Oxygen Reduction Reaction

Developing alternatives to noble-metal-based catalysts toward the oxygen reduction reaction (ORR) process plays a key role in the application of low-temperature fuel cells. Carbon-based, precious-metal-free electrocatalysts are of great interest due to their low cost, abundant sources, active catalytic performance, and long-term stability. They are also supposed to feature intrinsically high activity and highly dense catalytic sites along with their sufficient exposure, high conductivity, and high chemical stability, as well as effective mass transfer pathways. In this Review, we focus on carbon-based, precious-metal-free nanocatalysts with synergistic modulation of active-site species and their exposure, mass transfer, and charge transport during the electrochemical process. With this knowledge, perspectives on synergistic modulation strategies are proposed to push forward the development of Pt-free ORR catalysts and the wide application of fuel cells.

Laser Synthesis and Microfabrication of Micro/Nanostructured Materials Toward Energy Conversion and Storage

Nanomaterials are known to exhibit a number of interesting physical and chemical properties for various applications, including energy conversion and storage, nanoscale electronics, sensors and actuators, photonics devices and even for biomedical purposes. In the past decade, laser as a synthetic technique and laser as a microfabrication technique facilitated nanomaterial preparation and nanostructure construction, including the laser processing-induced carbon and non-carbon nanomaterials, hierarchical structure construction, patterning, heteroatom doping, sputtering etching, and so on. The laser-induced nanomaterials and nanostructures have extended broad applications in electronic devices, such as light-thermal conversion, batteries, supercapacitors, sensor devices, actuators and electrocatalytic electrodes. Here, the recent developments in the laser synthesis of carbon-based and non-carbon-based nanomaterials are comprehensively summarized. An extensive overview on laser-enabled electronic devices for various applications is depicted. With the rapid progress made in the research on nanomaterial preparation through laser synthesis and laser microfabrication technologies, laser synthesis and microfabrication toward energy conversion and storage will undergo fast development.

Polyaramid-Based Flexible Antibacterial Coatings Fabricated Using Laser-Induced Carbonization and Copper Electroplating

A method for the fabrication of flexible electrical circuits on polyaramid substrates is presented based on laser-induced carbonization followed by copper electroplating. Locally carbonized flexible sheets of polyaramid (Nomex), by laser radiation, create rough and highly porous microstructures that show a higher degree of graphitization than thermally carbonized Nomex sheets. The found recipe for laser-induced carbonization creates conductivities of up to ∼45 S cm^-1, thereby exceeding that observed for thermally pyrolyzed materials (∼38 S cm^-1) and laser carbon derived from Kapton using the same laser wavelength (∼35 S cm^-1). The electrical conductivity of the carbonized tracks was further improved by electroplating with copper. To demonstrate the electrical performance, fabricated circuits were tested and improvement of the sheet resistance was determined. Copper films exhibit antimicrobial activity and were used to fabricate customized flexible antibacterial coatings. The integration of laser carbonization and electroplating technologies in a polyaramid substrate points to the development of customized circuit designs for smart textiles operating in high-temperature environments.

Genuine Active Species Generated from Fe3 N Nanotube by Synergistic CoNi Doping for Boosted Oxygen Evolution Catalysis

The surface reconstruction of oxygen evolution reaction (OER) catalysts has been proven favorable for enhancing its catalytic activity. However, what is the active site and how to promote the active species generation remain unclear and are still under debate. Here, the in situ synthesis of CoNi incorporated Fe₃ N nanotubes (CoNi-Fe₃ N) on the iron foil through the anodization/electrodeposition/nitridation process for use of boosted OER catalysis is reported. The synergistic CoNi doping induces the lattice expansion and up shifts the d-band center of Fe₃ N, which enhances the adsorption of hydroxyl groups from electrolyte during the OER catalysis, facilitating the generation of active CoNi-FeOOH on the Fe₃ N nanotube surface. As a result of this OER-conditioned surface reconstruction, the optimized catalyst requires an overpotential of only 285 mV at a current density of 10 mA cm^-2 with a Tafel slope of 34 mV dec^-1 , outperforming commercial RuO₂ catalysts. Density functional theory (DFT) calculations further reveal that the Ni site in CoNi-FeOOH modulates the adsorption of OER intermediates and delivers a lower overpotential than those from Fe and Co sites, serving as the optimal active site for excellent OER performance.

Laminated Laser-Induced Graphene Composites

Laser-induced graphene (LIG) is a porous graphene foam generated by lasing carbon-based precursors. Compositing LIG expands the spectrum of applications for which the material may be used. Techniques for scale-up of LIG composites will be essential as the technology approaches commercialization. Roll-to-roll processing is of special interest, as precisely controlled patterning can be performed in conjunction with continuous formation of composites. Here, we demonstrate a simple lamination compositing method that is compatible with roll-to-roll processing and yields functional, patterned, and multilayered LIG composites with various thermoplastic films. Multiple lamination steps are used to encapsulate LIG within composites. We also demonstrate several applications for LIG that have been enabled by the lamination compositing technique. These include robust flexible electrodes generated through laminating copper foil strips into the LIG composite, LIG-based triboelectric nanogenerators to harvest waste mechanical energy, antimicrobial LIG composite bandages with varying hydrophobicity, and LIG puncture detectors.

Preserving nanoscale features in polymers during laser induced graphene formation using sequential infiltration synthesis

Direct lasing of polymeric membranes to form laser induced graphene (LIG) offers a scalable and potentially cheaper alternative for the fabrication of electrically conductive membranes. However, the high temperatures induced during lasing can deform the substrate polymer, altering existing micro- and nanosized features that are crucial for a membrane's performance. Here, we demonstrate how sequential infiltration synthesis (SIS) of alumina, a simple solvent-free process, stabilizes polyethersulfone (PES) membranes against deformation above the polymers' glass transition temperature, enabling the formation of LIG without any changes to the membrane's underlying pore structure. These membranes are shown to have comparable sheet resistance to carbon-nanotube-composite membranes. They are electrochemically stable and maintain their permeability after lasing, demonstrating their competitive performance as electrically conductive membranes. These results demonstrate the immense versatility of SIS for modifying materials when combined with laser induced graphitization for a variety of applications.

Robust Carbon-Stabilization of Few-Layer Black Phosphorus for Superior Oxygen Evolution Reaction

Few-layer exfoliated black phosphorus (Ex-BP) has attracted tremendous attention owing to its promising applications, including in electrocatalysis. However, it remains a challenge to directly use few-layer Ex-BP as oxygen-involved electrocatalyst because it is quite difficult to restrain structural degradation caused by spontaneous oxidation and keep it stable. Here, a robust carbon-stabilization strategy has been implemented to prepare carbon-coated Ex-BP/N-doped graphene nanosheet (Ex-BP/NGS@C) nanostructures at room temperature, which exhibit superior oxygen evolution reaction (OER) activity under alkaline conditions. Specifically, the as-synthesized Ex-BP/NGS@C hybrid presents a low overpotential of 257 mV at a current density of 10 mA cm−2 with a small Tafel slope of 52 mV dec−1 and shows high durability after long-term testing.

Airflow Enhanced Solar Evaporation Based on Janus Graphene Membranes with Stable Interfacial Floatability

Solar interfacial evaporation has been recognized as a versatile energy conversion protocol for cutting-edge applications such as water treatment and power generation (e.g., hydro voltaic effect). Recently, to enhance water evaporation rates, water temperature and evaporation area have been considered as essential ingredients, and thus photothermal materials and three-dimensional hierarchical structures have been developed to promote light-to-heat conversion efficiency and enhance interfacial evaporation. However, less attention has been paid to the airflow effect, because the interfacial floatability of photothermal membranes should be considered under air blast. Here, inspired from the stable interfacial floatability of lotus leaves, we report the airflow enhanced solar interfacial evaporation approach using a graphene-based Janus membrane. Laser-induced graphene (LIG) film was treated unilaterally by O₂ plasma, forming a LIG/oxidized LIG (LIG-O) Janus membrane with distinct wettability on two sides. Higher water evaporation rate of 1.512 kg m^-2 h^-1 is achieved. The high solar interfacial evaporation performance can be attributed to the two advantages: (i) the combination of microscale capillary water transporting and nanoscale light trapping; (ii) hydrophobic/hydrophilic Janus membrane for stable interfacial floatability under airflow. Our approach is feasible for developing high-performance solar interfacial evaporation devices for practical clean energy utilization.

Electronic Asymmetric Distribution of RhCu Bimetallic Nanocrystals for Enhancing Trifunctional Electrocatalysis

Developing efficient and durable multifunctional electrocatalysts for oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR) is of significant importance for many electrochemical energy devices, such as water electrolyzers, metal-air batteries, and fuel cells. Herein, the Rh-Cu alloy nanocrystals (NCs) are prepared with a simple wet-chemical approach. The tuning of morphology and the asymmetric electron distribution provide more efficient Rh-Cu bimetallic sites. Meanwhile, the incorporation of Cu into the Rh lattice could reduce the oxidation of Rh-Cu bimetallic sites and increase the catalytic stability. Under the tuning of the composition, the drastically enhanced electrocatalytic activities of HER, OER, and ORR are achieved in the Rh₆Cu₁ NCs with the cell voltage required to be as low as 1.55 V to accomplish an overall water splitting of 10 mA cm^-2 and a maximum power density of 142.58 mW cm^-2 for a zinc-air battery with good stability, representing the best trifunctional electrocatalysts for all we know. This work highlights the design and control of Rh-Cu NCs, which could be a potential alternative approach to trifunctional catalysis and further boosts the development of the bimetallic electrocatalysts in the energy conversion system.