Three-dimensional Porous Graphene Research Articles

A smartphone-based electrochemical sensing platform for the portable and simultaneous determination of flavonoids in the pericarp of Citrus Reticulata

BackgroundThe efficient and timely determination of polymethoxylated flavones (PMFs, primarily nobiletin and tangeretin) and flavanone glycosides (primarily hesperidin) in Citri Reticulatae Pericarpium (CRP) is of paramount importance for the production of CRP and the evaluation of its efficacy. Conventional analytical methods including chromatography-based approaches commonly provide high sensitivity and selectivity, but require bulky equipment and complicated procedures performed by professional technicians and are thus inconvenient in practical applications. Therefore, there is a clear need for portable and miniaturised sensing platforms that can rapidly and simultaneously detect PMFs and hesperidin in CRP product. ResultsA state-of-the-art three-dimensional porous graphene electrode was first fabricated by direct laser scribing of a poly(ether-ether-ketone) (PEEK) film for electrocatalysis of nobiletin, tangeretin and hesperidin. Kinetic analysis was conducted to investigate the reaction mechanisms of these three flavonoids at such prepared PEEK-laser induced graphene (PEEK-LIG) electrodes. Since the as-prepared PEEK-LIG electrodes exhibited high electrocatalytic efficiency towards these three flavonoids, a portable electrochemical sensing platform assembled with a smartphone, a miniatured electrochemical workstation, and an integrated PEEK-LIG microchip was developed. Consequently, the developed portable electrochemical sensing platforms exhibited great sensitivity and low detection limits for both PMFs and hesperidin. More importantly, tests conducted on real CRP extract samples demonstrated that the developed portable electrochemical sensing platform exhibited high validity, high reliability, as well as excellent reproducibility. SignificanceThis is the inaugural report on the portable and simultaneous determination of PMFs and hesperidin in the pericarp of Citrus Reticulata, which may be utilised for differentiating CRP products. Furthermore, the portable and powerful electrochemical sensing platforms developed could also potentially be applied for a wide range of analytes, thanks to their simple and rapid fabrication and determination processes.

Laser Precise Synthesis of Oxidation-Free High-Entropy Alloy Nanoparticle Libraries.

High-entropy alloy nanoparticles (HEA-NPs) show exceptional properties and great potential as a new generation of functional materials, yet a universal and facile synthetic strategy in air toward nonoxidized and precisely controlled composition remains a huge challenge. Here we provide a laser scribing method to prepare single-phase solid solution HEA-NPs libraries in air with tunable composition at the atomic level, taking advantage of the laser-induced metastable thermodynamics and substrate-assisted confinement effect. The three-dimensional porous graphene substrate functions as a microreactor during the fast heating/cooling process, which is conductive to the generation of the pure alloy phase by effectively blocking the binding of oxygen and metals, but is also beneficial for realizing accurate composition control via microstructure confinement-endowed favorable vapor pressure. Furthermore, by combining an active learning approach based on an adaptive design strategy, we discover an optimal composition of quinary HEA-NP catalysts with an ultralow overpotential for Li-CO2 batteries. This method provides a simple, fast, and universal in-air route toward the controllable synthesis of HEA-NPs, potentially integrated with machine learning to accelerate the research on HEAs.

Binder-Free Three-Dimensional Porous Graphene Cathodes via Self-Assembly for High-Capacity Lithium-Oxygen Batteries.

The porous architectures of oxygen cathodes are highly desired for high-capacity lithium-oxygen batteries (LOBs) to support cathodic catalysts and provide accommodation for discharge products. However, controllable porosity is still a challenge for laminated cathodes with cathode materials and binders, since polymer binders usually shield the active sites of catalysts and block the pores of cathodes. In addition, polymer binders such as poly(vinylidene fluoride) (PVDF) are not stable under the nucleophilic attack of intermediate product superoxide radicals in the oxygen electrochemical environment. The parasitic reactions and blocking effect of binders deteriorate and then quickly shut down the operation of LOBs. Herein, the present work proposes a binder-free three-dimensional (3D) porous graphene (PG) cathode for LOBs, which is prepared by the self-assembly and the chemical reduction of GO with triblock copolymer soft templates (Pluronic F127). The interconnected mesoporous architecture of resultant 3D PG cathodes achieved an ultrahigh capacity of 10,300 mAh g-1 for LOBs. Further, the cathodic catalysts ruthenium (Ru) and manganese dioxide (MnO2) were, respectively, loaded onto the inner surface of PG cathodes to lower the polarization and enhance the cycling performance of LOBs. This work provides an effective way to fabricate free-standing 3D porous oxygen cathodes for high-performance LOBs.

Microwave-assisted hydrothermal synthesis of NiO/Co3O4 nanosheets decorated on three-dimensional porous graphene for supercapacitors

Electrode material is the key part of capacitor, which seriously affects the electrochemical performance of supercapacitor. NiO/Co3O4 nanosheets decorated on three-dimensional porous graphene (NiO/Co3O4/3DGN) have been prepared though a microwave-assisted hydrothermal method. It is found that NiO can affect the crystallinity and morphology of Co3O4 in the composites. The composites possess excellent electrochemical performance with the special capacity of 1303.9 F g−1 (at 1 A g−1). The assembled NiO/Co3O4/3DGN//AC asymmetric supercapacitor device achieved an energy density of 18.8 Wh kg−1 at a power density of 750.4 W kg−1 and maintained 92.7% of the initial capacitance after 10,000 cycles. The excellent capacitance and rate capability of the composites can be attributed to its unique structural features. The large surface area and the rich porosity provide more activate sites and facilitate the fast diffusion of electrolyte during the charge/discharge process. The direct contact between NiO/Co3O4 nanosheets and 3DGN ensures effective charge transport.

Ti3C2Tx/laser-induced graphene-based micro-droplet electrochemical sensing platform for rapid and sensitive detection of benomyl

The design and fabrication of high-performance electrode devices are highly important for the practical application of electrochemical sensors. In this study, flexible three-dimensional porous graphene electrode devices were first facilely fabricated using common laser ablation technique at room temperature. After then, hydrophilic two-dimensional MXene (Ti3C2Tx) nanosheet was decorated on the surface of the laser-induced graphene (LIG), resulting in disposable Ti3C2Tx/LIG electrode devices. After introducing Ti3C2Tx nanosheet, the electrochemical active area, electron transfer ability of LIG electrode device and its adsorption efficiency toward organic pesticide benomyl was significantly boosted. As a result, the fabricated Ti3C2Tx/LIG electrode device exhibited significantly enhanced electrocatalytic activity toward benomyl oxidation. Based on this, a novel and ultra-sensitive electrochemical platform for micro-droplet detection of benomyl was achieved in the range of 10 nM–6000 nM with detection sensitivity of 169.9 μA μM−1 cm−2 and detection limit of 5.8 nM. Considering the low-cost Ti3C2Tx/LIG electrode devices are rarely used for electrochemical analysis, we believed this research work will contribute to exploring the broader application of MXene/LIG electrode devices in the field of electrochemical sensing.

A three-dimensional hierarchical porous graphene aerogel as a fiber coating for headspace solid-phase microextraction: Enhancing the enrichment and detection of polychlorinated naphthalenes in fish

In this study, a novel three-dimensional hierarchical porous deep eutectic solvents-modified graphene aerogel (3D DES-GA) was synthesized for use as a solid-phase microextraction (SPME) fiber coating. The SPME fiber was characterized by its fluffy and hierarchical porous structure, uniform thickness, and rapid mass transfer capabilities. This fiber demonstrated a lifetime (≥160 uses) and excellent precision (with relative standard deviations of 2.4–6.6% for single fiber and 6.0–9.8% for fiber-to-fiber repeatability). The SPME fiber also exhibited remarkable extraction performance for polycyclic aromatic hydrocarbons and polychlorinated biphenyls, which are common persistent organic pollutants in environmental samples. When combined with gas chromatography-tandem mass spectrometry, the method allowed for high-efficiency extraction (enrichment factors ranging from 1225 to 4652 folds) and sensitive determination (limit of detection ranging from 0.010 to 0.056 pg g−1) of polychlorinated naphthalenes (PCNs) in complex samples. To validate this method, we applied it to the determination of four PCNs in five types of fish tissues. The results revealed the presence of 1-chloronaphthalene at concentrations of 7.0 ± 2.9–34.8 ± 2.1 pg g−1 and 1,4-dichloronaphthalene at concentrations of 6.0 ± 0.3–10.9 ± 1.4 pg g−1 in three fish species. Compared with reported sample pretreatment methods reported in the literature, this proposed headspace SPME method offers additional advantages, including simplicity of operation and reduced sample and organic solvent consumption.

Construction of three-dimensional porous graphene with N,S co-doping in KOH-K2CO3 eutectic active molten salt system for supercapacitors

We prepared a three-dimensional porous graphene (3DPG) with N or/and S doping (N-3DPG, S-3DPG, NS-3DPG) in the KOH-K2CO3 eutectic active molten salt system. Graphene oxide, urea, and 3-mercaptopropionic acid are adopted as the 3DPG, nitrogen, and sulfur precursors, respectively. As a result, a continuous 3D network with dense cross-linked architecture is gained because the KOH-K2CO3 medium works as template to accelerate the conversion of GO to 3D architecture. A specific capacitance of 521 F/g is obtained for the NS-3DPG, which is much larger than that of 3DPG, N-3DPG, S-3DPG. A symmetric supercapacitor NS-3DPG||NS-3DPG delivers an energy density of 21.7 Wh/kg at a power density of 300 W/kg, and displays the capacitance retention ratio of 98.0 % after 10,000 cycles. An asymmetric supercapacitor 3DPG||NS-3DPG is assembled, which shows an energy density as high as 33.6 Wh/kg at a power density of 400 W/kg and little capacitance fading for 10,000 cycles. Outstanding supercapacitor performances of the 3DPG||NS-3DPG are attributed to its excellent 3D hierarchical porous structure and the synergistic effect of N,S co-doping.

Multi-scale experimental studies on mechanical properties of three-dimensional porous graphene cementitious composite

This study aimed to reveal the influence of 3D porous graphene on the cementitious composites from multiple scales. At the macro level, the 3D porous graphene could greatly improve the strength, elastic modulus, and crack resistance of the cementitious composite. At the micro level, the nanoindentation test indicated that the thickness of the interfacial transition zone (ITZ) could be reduced by adding 3D porous graphene, and the microcracks and pores could be lowered as well, which led to mechanical enhancement. Besides, statistical nanoindentation technique (SNT), X-ray diffraction (XRD), isothermal calorimetry, energy dispersive spectroscopy (EDS), and scanning electron microscope (SEM) evidenced that the 3D porous graphene could promote cement hydration and strengthen the elastic modulus and hardness of hydration products. Embedded in the hydration products, the 3D porous graphene could fill the cracks and pores and anchor the cement matrix at the micro-scale, which exhibited the reason for the positive effect caused by the 3D porous graphene at the macro-scale.

Enhancing supercapacitor performance through design optimization of laser-induced graphene and MWCNT coatings for flexible and portable energy storage

The field of supercapacitors consistently focuses on research and challenges to improve energy efficiency, capacitance, flexibility, and stability. Low-cost laser-induced graphene (LIG) offers a promising alternative to commercially available graphene for next-generation wearable and portable devices, thanks to its remarkable specific surface area, excellent mechanical flexibility, and exceptional electrical properties. We report on the development of LIG-based flexible supercapacitors with optimized geometries, which demonstrate high capacitance and energy density while maintaining flexibility and stability. Three-dimensional porous graphene films were synthesized, and devices with optimized parameters were fabricated and tested. One type of device utilized LIG, while two other types were fabricated on LIG by coating multi-walled carbon nanotubes (MWCNT) at varying concentrations. Characterization techniques, including scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, and voltammetry, were employed to analyze the fabricated devices. AFM analysis revealed a surface roughness of 2.03 µm for LIG due to laser treatment. SEM images displayed compact, dense, and porous surface morphology. XRD analysis confirmed the presence of graphene and graphene oxide, which was further supported by energy-dispersive X-ray spectroscopy (EDX) data. Raman spectroscopy indicated that the fabricated samples exhibited distinct D and G bands at 1362 cm–1 and 1579 cm–1, respectively. Cyclic voltammetry (CV) results showed that LIG's capacitance, power density, and energy density were 6.09 mF cm–2, 0.199 mW cm–2, and 3.38 µWh cm–2, respectively, at a current density of 0.2 mA cm–2. The LIG-MWCNT coated electrode exhibited a higher energy density of 6.05 µWh cm–2 and an areal-specific capacitance of 51.975 mF cm–2 compared to the LIG-based devices. The fabricated device has potential applications in smart electronics, nanorobotics, microelectromechanical systems (MEMS), and wearable and portable electronics.

Microscale fracture and creep analysis of 3D porous graphene-based cementitious material by nanoindentation test and energy-based method

As an exceptional nanomaterial, three-dimensional (3D) porous graphene possesses a promising capacity to enhance the performance of cementitious materials and reduce the usage of cement. However, the microscopic understanding of the fracture and creep behaviors of 3D porous graphene-based cementitious materials remains unclear. Here, we combine nanoindentation experiments and the energy-based method to investigate the microscale fracture and creep behaviors of both mortars and cement pastes. Specifically, we use the energy-based method to assess elastic modulus, hardness, fracture toughness, energy releasing rate, creep modulus, and creep characteristic time of cementitious materials containing 3D porous graphene. Our outcomes indicate that the additions of 3D porous graphene to both the mortar and cement paste improve their elastic behaviors. The fracture toughness and energy releasing rate reach the optimal values at 3D porous graphene content of 0.05 wt%. In addition, the presence of 3D porous graphene promotes the formation of high-density calcium silicate hydrate (C-S-H) and reduces the creeps in cementitious materials. Our findings provide insights into the performance of graphene-cementitious composites and represent a step forward toward the practical application of 3D porous graphene in concrete.

Improving the Corrosion Resistance of Zn-Rich Epoxy Coating with Three-Dimensional Porous Graphene

To improve the corrosion inhibition of zinc-rich epoxy (ZRE) composite coatings and shed light on the influence of the spatial structure of graphene fillers on the coatings’ performance, three-dimensional graphene (3DG) and a conventional graphene sheet (G) were used to modify the ZRE composite paint, respectively. The effect of introducing the 2D G fillers on the anti-corrosion behavior of ZRE was studied comprehensively, and its optimal content was determined to be 0.5 wt%. Interestingly, it was found that, comparing with 2D graphene sheets, the corrosion resistance of the ZRE coating could be enhanced more significantly with incorporating even less 3DG. With introducing only 0.1 wt% 3DG, the corrosion current intensity of the resulting 3DG/ZRE coating was reduced to be about 1/10 that of the G/ZRE coating with the same graphene content and 27% of that of the optimized G/ZRE. The corrosion products of the coating were analyzed with the XRD technique. The results indicated that, in contrast to neat ZRE coating, Zn5(CO3)2(OH)6 was absent from the corroded 3DG/ZRE coating, confirming its improved long-term anti-corrosion performance. The porous interconnected framework and high crystallinity of 3DG could contribute to not only its facilely mixing with epoxy resin, but also its effective incorporation into the conductive network of zinc micro-flakes, thus enhancing the corrosion resistance of its ZRE coating at a lower content. The innovative technology to improve the anti-corrosion performance of the ZRE coatings via using the 3D graphene fillers should be capable to be extended to other 2D fillers, such as MXenes.

Robust electrocatalysts decorated three-dimensional laser-induced graphene for selective alkaline OER and HER

Morphological and functional modifications allow graphene to be applied as promising electrode support for improved electrochemical cell performance. Typically, however, modification requires complicated steps with various organic additives, such as binders, which causes low electrochemical stability, especially under harsh pH conditions. Herein, we introduce self-supported and long-term stable water splitting electrodes based on nanoparticles (NPs) decoration on three-dimensional porous laser-induced graphene (3D-LIG). A binder-free, single-step electrochemical process homogeneously decorates the 3D-LIG electrodes with CuO and Pt NPs, referred to CuO-3D-LIG and Pt-3D-LIG electrodes, respectively. These electrodes are individually analyzed for enduring oxygen evolution (OER) and hydrogen evolution (HER) activities. The porous wrinkled morphology of the 3D-LIG offers a large surface area and facilitates electrolyte influx within channels. Whereas strongly anchored CuO and Pt NPs enable highly stable electrochemical performances of the CuO-3D-LIG and the Pt-3D-LIG electrodes. The corresponding OER and HER overpotentials at 10 mA cm−2 (η10) are observed at 251 mV and 455 mV. These electrodes offer excellent electrochemical robustness in operationally challenging alkaline conditions (1 M KOH, pH ∼ 14) for extensive periods. In addition, we confirm the workable electrostatic interactions NPs – graphene via Becke-3-parameter Lee–Yang–Parr (B3LYP) model with 6-31G (d,p) and Stuttgart-Dresden (SDD) basis, which is supposed to be responsible for electrochemical durability and high current density yield of CuO-3D-LIG and Pt-3D-LIG electrodes. This study offers one of a few experiments to utilize decorated 3D-LIG for both OER and HER processes, assuming their substantial industrial potential in overall water splitting.

Stretchable strain sensor based on HfSe2/LIG composite with high sensitivity and good linearity within a wide range

Flexible strain sensors based on nanomaterials have sparked a lot of interest in the field of wearable smart electronics. Laser induced graphene (LIG) based sensors in particular stand out due to their straightforward fabrication procedure, three-dimensional porous structures, and exceptional electromechanical capabilities. Recent studies have focused on LIG composites, however, it is still difficult to achieve great sensitivity and excellent linearity in a wide linear working range. Herein, a strain sensor with high sensitivity and good linearity is prepared in this work, which was realized by carbonizing the polyimide film coated with HfSe2 to obtain three-dimensional porous graphene nanosheets decorated with HfSe2 (HfSe2/LIG). After being transferred to the flexible substrate of Ecoflex, it exhibits high stretchability, hydrophobicity and robustness, and obtains excellent electromechanical properties. The HfSe2/LIG strain sensor demonstrated high sensitivity (gauge factor, GF ≈ 46), a low detection limit (0.02%), good linearity (R2 = 0.99) in a large working range (up to 30%), and a quick response time (0.20 s). Additionally, it exhibits good stability and consistent behavior across a large number of strain/release test cycles (>3000 cycles). With these benefits, the sensor can be used to monitor various limb movements (including finger, wrist and neck movements) and minute artery activity, and can generate reliable signals. Therefore, the HfSe2/LIG-based sensor has enormous potential for use in wearable intelligent electronics and movement monitoring.

Highly sensitive photodetector based on laser-generated graphene with 3D heterogeneous multiscale porous structures

Graphene holds great promise in optoelectronics because of its high broadband light absorption across a wide range of wavelengths. Despite low optical absorption, various techniques have been devised to address this challenge. This study presents a new highly sensitive, photodetector based on three-dimensional (3D) porous graphene derived from fluorinated polyimide (fPI-3DPG). This material is produced via a laser photothermal process and features micro- and nanopore structures that increase the light absorbing area and support optically resonant structures. The resulting fPI-3DPG photodetectors display high photoresponsivity of 4.4 mA W−1 in the visible light range, an ultrahigh signal-to-noise ratio of ∼208, and a noise equivalent power of 0.54 × 10−11 W Hz−1/2. These photodetectors are also mechanically durable, surviving 10,000 cycles of bending and twisting. The laser photothermal method used in this study enables fast, cost effective production of wearable and flexible optical sensors for imaging and spectroscopy applications, making this 3D graphene a promising functional material for sensing technologies.

Solid-state, reagent-free and one-step laser-induced synthesis of graphene-supported metal nanocomposites from metal leaves and application to glucose sensing

The laser-induced method to prepare three-dimensional (3D) porous graphene has been widely used in many fields owing to its low-cost, easy operation, maskless patterning and ease of mass production. Metal nanoparticles are further introduced on the surface of 3D graphene to enhance its property. The existing methods, however, such as laser irradiation and electrodeposition of metal precursor solution, suffer from many shortcomings, including complicated procedure of metal precursor solution preparation, strict experimental control, and poor adhesion of metal nanoparticles. Herein, a solid-state, reagent-free, and one-step laser-induced strategy has been developed for the fabrication of metal nanoparticle modified-3D porous graphene nanocomposites. Commercial transfer metal leaves were covered on a polyimide film followed by direct laser irradiation to produce 3D graphene nanocomposites modified with metal nanoparticles. The proposed method is versatile and applicable to incorporate various metal nanoparticles including gold silver, platinum, palladium, and copper. Furthermore, the 3D graphene nanocomposites modified with AuAg alloy nanoparticles were successfully synthesized in both 21 Karat (K) and 18K gold leaves. Its electrochemical characterization demonstrated that the synthesized 3D graphene-AuAg alloy nanocomposites exhibited excellent electrocatalytic properties. Finally, we fabricated LIG-AuAg alloy nanocomposites as enzyme-free flexible sensors for glucose detection. The LIG-18K electrodes exhibited the superior glucose sensitivity of 1194 μA mM−1 cm−2 and low detection limits of 0.21 μM. The LIG-21K nanocomposite sensors showed two linear ranges from 1 μM to 1 mM and 2 mM–20 mM with good sensitivity. Furthermore, the flexible glucose sensor showed good stability, sensitivity, and ability to sense in blood plasma samples. The proposed one-step fabrication of reagent-free and metal alloy nanoparticles on LIG with excellent electrochemical performance opens up possibilities for diversifying potential applications of sensing, water treatment and electrocatalysis.

Design of phase change composite with hierarchical energy-transfer pathway via laser-induced graphene for efficient energy storage, conversion, and utilization

To achieve efficient energy harvesting and utilization, phase change composites (PCCs) with high energy storage density, thermal conductivity, and photothermal conversion ability have always been a research focus. Herein, a three-dimensional (3D) porous laser-induced graphene supporting matrix with the plant leaf-mimetic network (PLMN) for loading phase change materials (PCMs) was fabricated by direct laser writing on polybenzoxazine resin (Poly(PH-ddm)). PLMN is designed to consist of laser-induced graphene (LIG) with both vein-like and mesophyll-like structures, the former one mainly responsible for efficient energy harvesting as well as fast heat flow transport and the latter one as the dominant part for high encapsulation of polyethylene glycol (PEG) PCM. The obtained plant leaf-mimetic composite (PLMC) exhibits a large latent heat of 162.3 J/g and high thermal conductivity of 1.18 W/m·K (391.67 % increment than pure PEG). PLMC also shows a high solar energy conversion efficiency of 84.1 %, which benefits from the well-designed PLMN structure as well as the thermal insulation effect of the resin layer. In addition, the resin layer provides mechanical support and flame-retardant function, ensuring the use safety of PLMC. The applications of PLMC for efficient utilization of solar energy and thermal management of electronics have been well-demonstrated. This work provides novel insights into the design and fabrication of PCCs with great potential in solar energy utilization and other thermal energy-related processes.

O-doping induced abundant active-sites in MoS2 nanosheets for propelling polysulfide conversion of Li-S batteries

The oxygen doped MoS2 nanosheets were in-situ grown into the three-dimensional (3D) porous graphene frameworks (O-MoS2/G) through a facile hydrothermal method, and then used to coat the commercial PP separators for Li-S batteries. The relatively low hydrothermal temperature should be a key factor for achieving the O-doped MoS2. The O dopants could expand and disturb interlayer structures of MoS2 to produce abundant active edge sites for adsorption and catalytic conversion of polysulfides. Moreover, the basal planes of MoS2 should be also activated by the O doping and exhibit enhanced chemical adsorption strength towards polysulfides for propelling electrochemical conversion. Owing to the synergistic effects of the 3D porous graphene frameworks and the inlaid O-MoS2 nanosheets, the Li-S cells with high S areal loading cathodes and O-MoS2/G@PP separators exhibit excellent electrochemical performances with a high specific capacity of 1141 mAh g−1 at the 1st cycle at 0.1 C, reversible capacities of 772 mAh g−1 at the 50th cycle at 0.2 C and 583 mAh g−1 at the 100th cycle at 0.5 C. These encouraging results provide that the heteroatom doping should be a promising approach to improve the adsorption and catalytic activity of MoS2 for propelling the polysulfide conversion in Li-S batteries.

Co2P nanowire arrays anchored on a 3D porous reduced graphene oxide matrix embedded in nickel foam for a high-efficiency hydrogen evolution reaction.

Regulating the structural and interfacial properties of transition metal phosphides (TMPs) by coupling carbon-based materials with large surface areas to enhance hydrogen evolution reaction (HER) performance presents significant progress for water splitting technology. Herein, we constructed a composite substrate of a three-dimensional porous graphene oxide matrix (3D-GO) embedded in nickel foam (NF) to grow a Co2P electrocatalyst. Well-defined gladiolus-like Co2P nanowire arrays tightly anchored on the substrate show enhanced electrochemical characteristics for the hydrogen evolution reaction (HER) based on the promoting roles of 3D porous reduced GO (3D-rGO) derived from 3D-GO, which promotes the dispersion of active components, improves the rate of electron transfer, and facilitates the transport of water molecules. As a result, the obtained Co2P@3D-rGO/NF electrode exhibits superior HER activity in 1.0 M KOH media, achieving overpotentials of 36.5 and 264.7 mV at current densities of 10 and 100 mA cm-2, respectively. The electrode also has a low Tafel slope of 55.5 mV dec-1, a large electrochemical surface area, and small charge-transfer resistance, further revealing its mechanism of high intrinsic activity. Moreover, the electrode exhibits excellent HER stability and durability without surface morphology and chemical state changes.

Advances in Porous Graphene and Scalable Wet-Spinning Fiber Assembly

ConspectusTwo-dimensional (2D) materials with astonishing properties and thickness dimensions are attractive for nanodevices and optoelectronics devices. Among them, 2D graphene─an atomically thin single layer with a strong covalently bonded sp2-hybridized hexagonal carbon network─has fascinating physicochemical properties. 2D graphene is at the tip of the iceberg of 2D materials. However, graphene is prone to self-restacking and agglomeration, deteriorating its properties. The introduction of porous structures to graphene sheets ameliorates their properties, e.g., increasing the surface area, providing ion transport channels, and enhancing the stability; thus, the performance of graphene-based materials is improved. Owing to their exciting properties, 2D holey graphene (HG) with nanoholes in its 2D basal plane and three-dimensional (3D) porous graphene with structural pores and interconnected architectures structural derivatives of graphene are promising for addressing the aforementioned challenges synergistically. Perforation in 2D graphene with tunable pore size, pore density, and uniformity is crucial for improving the performance of dense graphene. The unique pore structure and large exposed edges indicate the improved properties of porous graphene. Furthermore, macroscopically assembled one-dimensional (1D) fibrous electrodes of holey and porous graphene building blocks are promising, as they are lightweight, have high flexibility, and have strong wearability for future next-generation electronics.In this Account, we systematically highlight our efforts related to the conventional synthesis methodologies to recent emerging methods of “holey” or “porous” graphene/graphene oxide. First, we focus on the synthesis strategies and advances of 2D HG in-plane holes suitable for fast ion transport. Recent emerging synthesis methodologies are discussed for preparing 2D HG, which uses an environmentally benign approach with low toxicity compared to conventional etching methods, which frequently involve the use of hazardous or toxic oxidizing reagents, thereby causing severe environmental pollution. Second, compared with graphene, the 3D porous graphene comprises self-assembled graphene sheets (holey) containing structural macropores with a larger accessible surface area, high pore volume, and better flexibility, stability, and mechanical properties preferred for energy conversion and storage applications. Here, the recent progress and emerging synthesis approaches for 3D porous graphene-based nanomaterials are comprehensively discussed. Furthermore, the advantages of 2D HG and 3D porous graphene are discussed for water transport and electrochemical storage. Third, recent advances in the use of straightforward, large-scale wet-spinning processes to fabricate macroscopically assembled 1D fibrous electrodes with excellent mechanical flexibility and deformability using holey or porous graphene-based fibers (GFs) are described. Different approaches are discussed for preparing holey or porous GFs, such as wet-spinning assembly of holey graphene oxide (HGO), coagulant-assisted porous structures, and the post-activation process. Thus, the wet-spun holey or porous GFs are promising for miniaturized-based next-generation wearable electronic devices. Finally, we focus on the current status, fundamental understanding, future directions, and challenges of wet-spinning assemblies of holey/porous graphene-based nanomaterials for the next generation of wearable electronics.

Graphene aerogel loaded with CeO2 as a catalyst for selective catalytic reduction of NOx with NH3 at low temperature

NH3 selective catalytic reduction (NH3-SCR) has been a common method for eliminating nitrogen oxides (NOx) from the flue gas. The low-temperature denitrification has sparked widespread concern. Here, a CeO2/graphene aerogel (CeO2/GA) catalyst material was synthesized by a one-step hydrothermal method using a three-dimensional (3-D) porous graphene aerogel structure as a carrier for NH3-SCR at low-temperature. The presence of nanoparticle CeO2 inhibited agglomeration between graphene sheets, while the graphene aerogel as a carrier produced a porous structure and improved nanoparticle dispersal. The specific surface area of composite catalyst material was 178.68 m2/g. Catalysts with efficient charge transfer and abundant chemisorbed oxygen promoted redox reactions, more acidic sites were essential to improving catalytic activity. At 270 °C, the NOx conversion (94.9%) of this catalyst was 2.9 times higher than that of pure CeO2 and it demonstrated good N2 selectivity and catalytic stability.