Defect-rich Graphene Research Articles

In-situ observation of defects evolution of graphene nanoflakes in Pt/C catalyst for boosting ORR performance

The structural stability of supported metal nanoparticles determines the activity and longevity of heterogeneous catalysts. Unfortunately, the chemical/thermal working environment inevitably accelerates metal sintering to larger crystallites that leads to the degradation of catalytic performance. Here, we demonstrate that the distribution of defects in carbon support as an inherent parameter plays a crucial role in catalyst sintering. Based on in-situ transmission electron microscopy studies, the strong metal-support interaction between platinum (Pt) nanoparticles and defect-rich graphene nanoflakes largely suppresses metal sintering up to 700 °C. Particularly, the optimal carbon support can be achieved in the annealing process, in which the mass transfer and charge transport can be enhanced by accurately manipulating the distribution of defects in carbon matrix and graphitization degree. It is worth noting that the screened Pt/GNs-300 exhibits impressive oxygen reduction reaction performance with high half-wave potential (0.91 V), mass activity (108.1 A g–1Pt) and excellent stability. By its ascendancy in ORR, the Pt/GNs-300 exhibits a high open-circuit voltage of 1.41 V and a maximum power density of 198.6 mW cm−2 in Zn-air battery, implying its brilliant practicability. This work paves a pathway for achieving sinter-resistant metal-loaded catalysts in energy electrocatalysis.

Hydrogen spillover on Ni@Graphene enables robust and efficient catalytic hydrogenation of aqueous levulinic acid to γ-valerolactone

Hydrogenation of biomass-derived aqueous levulinic acid (LA) to produce γ-valerolactone (GVL) is a promising approach from biomass to sustainable platform chemicals. However, the practical application of this method is limited because aqueous LA is highly corrosive to metal-based hydrogenation catalyst in high-temperature hydrothermal environments. Herein, we encapsulated metallic Ni0 particles with a few layers of graphene using a hydrothermal carbon coating method to obtain Ni@FLG-600 catalyst, which exhibited efficient catalytic activity and excellent cycling stability for the hydrogenation of aqueous LA to GVL. The defect-rich graphene shell prevents the Ni0 from acid corrosion meanwhile selectively permits the passage of small H2 molecules. The resulted active H* on Ni0 spills over to the outer surface of graphene shell and reacts with LA. Remarkably, the amount of H* on graphene shell can be the descriptor of activity. This finding presents a new strategy for the fabrication of acid-resistant catalysts for aqueous biomass hydrogenation.

Cu/Fe3O4 heterogeneous nanospheres anchoring defect-rich graphene for effectively enhanced multi-band electromagnetic absorption

Nowadays, the practical application of electromagnetic absorbing materials required lightweight, high efficiency and especially broadband. Wherein, graphene-based electromagnetic absorbing materials had received extensive attention. The conventional design was to introduce magnetic particles onto graphene, but often lead to narrow bandwidth, hard to regulate, due to the lack of intrinsic coupling between magnetic particles and dielectric graphene. In principle, defect engineering could induce intrinsic ferromagnetism into graphene while increasing dielectric polarization loss, could be an effective means of expanding and regulating electromagnetic absorbing bands. Thus, in this paper, Cu/Fe3O4 heterogeneous nanospheres was constructed onsite defect-rich graphene to realize broadband electromagnetic absorbing modulation. The optimal RL value of Cu/Fe3O4/GE could reach −45.5 dB with obvious multi-band absorption, which was mainly attributed to the synergistic enhancement of defect-induced polarization loss, multiple interfacial polarization loss, as well as collaborative multipath magnetic loss. This work provides reference way for lightweight multi-band electromagnetic absorbing materials design.

Modified 3D Graphene for Sensing and Electrochemical Capacitor Applications.

Less defective, nitrogen-doped 3-dimensional graphene (N3DG) and defect-rich, nitrogen-doped 3-dimensional graphene (N3DG-D) were made by the thermal CVD (Chemical Vapor Deposition) process via varying the carbon precursors and synthesis temperature. These modified 3D graphene materials were compared with pristine 3-dimensional graphene (P3DG), which has fewer defects and no nitrogen in its structure. The different types of graphene obtained were characterized for morphological, structural, and compositional assessment through Scanning Electron Microscopy (SEM), Raman Spectroscopy, and X-ray Photoelectron Spectroscopy (XPS) techniques. Electrodes were fabricated, and electrochemical characterizations were conducted to evaluate the suitability of the three types of graphene for heavy metal sensing (lead) and Electric Double-Layer Capacitor (EDLC) applications. Initially, the various electrodes were treated with a mixture of 2.5 mM Ruhex (Ru (NH3)6Cl3 and 25 mM KCl to confirm that all the electrodes underwent a reversible and diffusion-controlled electrochemical process. Defect-rich graphene (N3DG-D) revealed the highest current density, followed by pristine (P3DG) and less-defect graphene (N3DG). Further, the three types of graphene were subjected to a sensing test by square wave anodic stripping voltammetry (SWASV) for lead detection. The obtained preliminary results showed that the N3DG material provided a great lead-sensing capability, detecting as little as 1 µM of lead in a water solution. The suitability of the electrodes to be employed in an Electric Double-Layer Capacitor (EDLC) was also comparatively assessed. Electrochemical characterization using 1 M sodium sulfate electrolyte was conducted through cyclic voltammetry and galvanostatic charge-discharge studies. The voltammogram and the galvanostatic charge-discharge (GCD) curves of the three types of graphene confirmed their suitability to be used as EDLC. The N3DG electrode proved superior with a gravimetric capacitance of 6.1 mF/g, followed by P3DG and N3DG, exhibiting 1.74 mF/g and 0.32 mF/g, respectively, at a current density of 2 A/g.

Fe-doped densely stacked graphene for compact capacitive energy storage

Herein, we present iron oxide (α-Fe2O3) etching and simultaneous hydrothermal reduction approach to prepare densely stacked defect-rich graphene with abundant pseudocapacitive heteroatoms (18.1 wt% O and 1.2 wt% Fe). Electrochemical measurements were conducted in acidic (1 M H2SO4) and neutral (1 M Na2SO4) aqueous media. The Fe-doped densely stacked graphene (Fe-rGO) with a low specific surface area (32.9 m2 g−1) and high particle density (1.84 g cm−3) displayed high gravimetric and volumetric capacitances of 425 F g−1 and 780 F cm−3 at 0.25 A g−1, respectively, as well as outstanding rate performance (71 % capacitance retention at 20 A g−1 in 1 M H2SO4). Moreover, Fe-rGO exhibited high electrochemical and structural stability over 5000 cycles at 10 A g−1 without any loss in capacitance. An asymmetric supercapacitor (ASC) with Fe-rGO negative electrode and MnO2/PEDOT:PSS positive electrode was assembled with aqueous 1 M Na2SO4 electrolyte. The device exhibited 17.3 Wh kg−1 specific energy and a long cyclic stability (10,000 cycles at 1 A g−1). A practical application of the device was demonstrated by powering a light emitting diode.

Photocarrier relaxation and saturable absorption in defect-rich, direct chemical vapor deposition-grown graphene glass

Direct growth of large-area uniform graphene films on insulating materials could facilitate the applications of graphene in optoelectronic devices. The ultrafast photocarrier relaxation and saturable absorption of direct chemical vapor deposition-grown graphene glasses, with lots of defects, are studied by using femtosecond time-resolved pump–probe and Z-scan techniques at 800 nm. We find that both the relaxation times associated with hot carrier cooling and the hot phonon effect are greatly suppressed in these defect-rich graphene glasses, which further leads to the increase of both saturation intensity and anisotropy in transient optical response for graphene glasses as compared with defect-free graphene. And, both the suppression effect and saturation intensity increase with the thickness of graphene film. The dominance of defect-assisted carrier-acoustic phonon scattering (i.e., supercollision, the collision of a carrier with both an acoustic phonon and defects) in the cooling process of hot carriers is responsible for the suppression of relaxation time.

Super-oxidized “activated graphene” as 3D analogue of defect graphene oxide: Oxidation degree vs U(VI) sorption

Porous carbons are not favorable for sorption of heavy metals and radionuclides due to absence of suitable binding sites. In this study we explored the limits for surface oxidation of “activated graphene” (AG), porous carbon material with the specific surface area of ∼2700 m2/g produced by activation of reduced graphene oxide (GO). Set of “Super-Oxidized Activated Graphene” (SOAG) materials with high abundance of carboxylic groups on the surface were produced using “soft” oxidation. High degree of oxidation comparable to standard GO (C/O=2.3) was achieved while keeping 3D porous structure with specific surface area of ∼700–800 m2/. The decrease in surface area is related to the oxidation-driven collapse of mesopores while micropores showed higher stability. The increase in the oxidation degree of SOAG is found to result in progressively higher sorption of U(VI), mostly related to the increase in abundance of carboxylic groups. The SOAG demonstrated extraordinarily high sorption of U(VI) with the maximal capacity up to 5400 μmol/g, that is 8.4 – fold increase compared to non-oxidized precursor AG, ∼50 –fold increase compared to standard graphene oxide and twice higher than extremely defect-rich graphene oxide. The trends revealed here show a way to further increase sorption if similar oxidation degree is achieved with smaller sacrifice of surface area.

Operability timescale of defect-engineered graphene

Defects in the lattice are of primal importance to tune graphene chemical, thermal and electronic properties. Electron-beam irradiation is an easy method to induce defects in graphene following pre-designed patterns, but no systematic study of the time evolution of the resulting defects is available. In this paper, the change over time of defected sites created in graphene with low-energy (≤20 keV) electron irradiation is studied both experimentally via micro-Raman spectroscopy for a period of 6×103 h and through molecular dynamics simulations. During the first 10 h, the structural defects are stable at the highest density value. Subsequently, the crystal partially reconstructs, eventually reaching a stable, less defected condition after more than one month. The simulations allow the rationalization of the processes at the atomic level and confirm that the irradiation induces composite clusters of defects of different nature rather than well-defined nanoholes as in the case of high-energy electrons. The presented results identify the timescale of the defects stability, thus establishing the operability timespan of engineerable defect-rich graphene devices with applications in nanoelectronics. Moreover, long-lasting chemical reactivity of the defective graphene is pointed out. This property can be exploited to functionalize graphene for sensing and energy storage applications.

Porous Graphene Produced by Carbothermal Shock for Green Electromagnetic Interference Shielding in Both Microwave and Terahertz Bands.

The prospect of graphene-based shielding materials in the form of fillers is limited by the cumbersome preparation of graphene. Herein, defect-tunable porous graphene prepared by carbothermal shock using low-value sucrose as a precursor is proposed as an effective shielding filler. The resultant porous graphene exhibits 32.5dB shielding efficiency (SE) and 2.5-18GHz effective bandwidth at a mass loading of 20 wt%, competing with the shielding performance of graphene fillers prepared by other methods. Particularly, defect-rich graphene synthesized by increasing voltage and prolonging time shows increased electromagnetic (EM) wave absorption, echoing the current concept of green shielding. In addition, the strategy of controlling the discharge conditions to improve the absorption by the shield is developed in the terahertz band. The average SE and reflection loss of the samples in the THz band (0.2-1.2THz) exhibit 40.7 and 15.9dB at filler loading of 5 wt%, respectively, achieving effective shielding and absorption of THz waves. This work paves a new way for low-cost preparation of graphene for EM interference shielding fillers. Meanwhile, it supplies a reference for the shielding research of the upcoming applications integrating multiple EM bands (such as sixth-generation based integrated sensing and communication).

Defect-rich graphene skin modified carbon felt as a highly enhanced electrode for vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) with high energy density, long cycle life, flexible design and rapid response have attracted great attention in large-scale energy storage applications. However, the low activity of traditional carbon felt electrodes severely limits its practical implementation. Herein, we report the fabrication of modified carbon felt (CF) by coating defect-rich graphene through chemical vapor deposition (CVD) and subsequent Ar plasma treatment as a highly improved electrode (denoted as Ar-GCF) for VRFB. The modification of defect-rich graphene skin can not only expose a large number of graphene edges as highly active sites, but also offers copious oxygen-containing functional groups to improve the electronic conductivity of Ar-GCF and accelerate the VO2+/VO2+ redox, which are demonstrated by both electrochemical measurements and spin-polarized density functional theory (DFT) calculations. As a result, the VRFB with Ar-GCF electrode exhibited an improved energy efficiency (EE) by 7.10% compared with that of VRFB using an unmodified CF electrode. Moreover, the Ar-GCF electrode showed excellent stability, with the charge transfer resistance (Rct) increased by merely 15.79% after 800 cycles, while the Rct of CF electrode increased by 102.40% after 600 cycles.

Preparation of super thin and defect rich graphene shell and its application for high performance supercapacitor electrode and novel ORR catalyst support

We report for the first time that zinc oxide (ZnO) can not only effectively catalyze the conversion of acetylene into graphene, but also greatly lower the growth temperature to only 400 °C. With this method, super thin and defect rich graphene shell (TD-GS) is successfully prepared for the first time using ZnO nanoparticles as both the catalyst and template. The growth of TD-GS is tracked and monitored and its growth mechanism is illustrated. The as-prepared TD-GS exhibits remarkable performance as electrode material for applications in supercapacitors or novel catalyst support for oxygen reduction reaction. We also demonstrate that by simply adjusting the growth conditions or process, new carbon structures, like opened TD-GS, TD-GS aerogel and even graphene tube can be facilely realized.

CuInS2 quantum dots anchored onto the three-dimensional flexible self-supporting graphene oxide array with regulatable crystallinity and defect density for efficient photocatalytic synthesis of xylonic acid

Photocatalytic biorefinery is receiving increasing attention as a promising approach for biomass utilization. In this field, I-III-VI quantum dots have emerged as efficient photocatalysts with unique physical and chemical properties that stem from their quantum and size effects. To fully exploit the advantages of quantum dots, a three-dimensional flexible self-supporting material (CIS@FSM) is fabricated with the assistance of defect-rich graphene oxide (GO), which is employed as a supporter to trap the quantum dots and promote charge separation/migration. Under visible-light irradiation, a xylonic acid yield of 65.05 % is obtained and no obvious decline of the photocatalytic performance is observed after nine runs. Moreover, the photocatalytic performance of CIS@FSM can be tuned by modulating the crystallinity and defect density. The investigation of the mechanism of the xylonic acid production reveals the presence of all oxidation active species, with h+ playing the primary role. This work provides insights for semiconductor-based photocatalytic biorefinery.

Preparation of Super Thin and Defect Rich Graphene Shell and its Application for High Performance Supercapacitor Electrode and Novel Orr Catalyst Support

Preparation of Super Thin and Defect Rich Graphene Shell and its Application for High Performance Supercapacitor Electrode and Novel Orr Catalyst Support

Understanding of catalytic ROS generation from defect-rich graphene quantum-dots for therapeutic effects in tumor microenvironment

Owing to their low cost, high catalytic efficiency and biocompatibility, carbon-based metal-free catalysts (C-MFCs) have attracted intense interest for various applications, ranging from energy through environmental to biomedical technologies. While considerable effort and progress have been made in mechanistic understanding of C-MFCs for non-biomedical applications, their catalytic mechanism for therapeutic effects has rarely been investigated. In this study, defect-rich graphene quantum dots (GQDs) were developed as C-MFCs for efficient ROS generation, specifically in the H2O2-rich tumor microenvironment to cause multi-level damages of subcellular components (even in nuclei). While a desirable anti-cancer performance was achieved, the catalytic performance was found to strongly depend on the defect density. It is for the first time that the defect-induced catalytic generation of ROS by C-MFCs in the tumor microenvironment was demonstrated and the associated catalytic mechanism was elucidated. This work opens a new avenue for the development of safe and efficient catalytic nanomedicine.

Defect-rich graphene stabilized atomically dispersed Cu3 clusters with enhanced oxidase-like activity for antibacterial applications

Nanozyme has attracted great attention due to its diverse enzymatic catalytic activities. But there are still challenges in constructing novel nanozyme with robust catalytic activity. Here, we report an atomically dispersed and fully exposed Cu3 cluster stabilized on defect-rich nanodiamond-graphene hybrid support (Cu3/ND@G) with unique active adsorption sites, which benefit the adsorption and cleavage of O2, resulting in enhanced oxidase-like and antibacterial activity. The catalytic rate constant of Cu3/ND@G (Kcat = 1.474 × 10−1 s−1) is higher than those of previously reported copper single atom oxidase mimics (0.5 × 10−3 s−1) and even the commercial Pt/C mimics (1.01 × 10−2 s−1). DFT calculation revealed that the atomically dispersed Cu3 cluster as active center significantly improves the oxidase-like activity, attributing to the easy dissociation of O2 into reactive oxygen species (•OH). The atomically dispersed Cu3 cluster with an antibacterial rate of 100% in the NaAc buffer presents its potential application in the field of antibacterial materials.

Defective graphene nanosheets for drinking water purification: Adsorption mechanism, performance, and recovery

Defect-rich graphene oxide (dGO) was used as sorbent for organic contaminants of emerging concern in tap water, including drugs and dyes, and the performance compared to those of lower-defects graphene types. The role of holes and carbonyl- carboxylic groups on graphene nanosheets surface on the adsorption mechanism and efficiency was investigated. dGO showed enhanced adsorption capacity toward two fluoroquinolone antibiotics (ofloxacin, OFLOX, and ciprofloxacin, CIPRO) in tap water with a maximum capacity of 650 mg/g, compared to 204 mg/g for Hummers derived commercial GO (hGO) and 125 mg/g for less defected Brodie derived GO (bGO) for OFLOX. The role of defects on the selective adsorption of OFLOX was also modelled by MD simulations, highlighting a mechanism mainly driven by the shape complementarity between the graphene holes and the molecules. Adsorption isotherms revealed different adsorption model for dGO, with a Langmuir fitting for dGO and BET fitting for all the other investigated samples. The maximum adsorption capacity of dGO for OFLOX was about six times higher than that of Granular Activated Carbon (95 mg/g), the industrial adsorption standard technology. Finally, it was also demonstrated that dGO can be recovered from treated water by ultrafiltration, this preventing secondary contamination risks and enabling safe use of graphene nanosheets for water purification.

Topological Defect‐Rich Carbon as a Metal‐Free Cathode Catalyst for High‐Performance Li‐CO2 Batteries (Adv. Energy Mater. 30/2021)

Li–CO2 Batteries In article number 2101390, Dong Liu, Chuangang Hu, Liming Dai and co–workers develop topological defect–rich graphene based materials as high–performance metal–free cathodes in Li–CO2 batteries. The cathodes' sufficient and effective active sites for CO2 reduction/evolution facilitate the formation/decomposition of Li2CO3 during the discharging/charging process, resulting in unprecedented battery performance.

Intrinsic Defect-Rich Graphene Coupled Cobalt Phthalocyanine for Robust Electrochemical Reduction of Carbon Dioxide

Carbon-based matrix is known to exert a profound influence on the stability and activity of a supported molecular catalyst for electrochemical CO2 reduction reaction (eCO2RR), while regulating the interfacial π-π interaction by designing functional species on the carbon matrix has seldom been explored. Herein, promoted π electron transfer between a graphene substrate and cobalt phthalocyanine (CoPc) is achieved by introducing abundant intrinsic defects into graphene (DrGO), which not only generates more electrochemically active Co sites and leads to a positive shift of the Co2+/Co+ reduction potential but also enhances the CO2 chemical adsorption. Consequently, as compared to the defect-free counterpart rGO-CoPc, DrGO-CoPc could yield CO with a Faradaic efficiency (FECO) higher than 85% in a wide potential range from -0.53 to -0.88 V, and the largest FECO and partial CO current density (JCO) achieve 90.2% and 73.9 mA cm-2, respectively. More importantly, both FECO and JCO can be dramatically improved when conducting eCO2RR in an ionic liquid-based electrolyte, for which FECO is higher than 90.0% in a wide potential range of 600 mV, with the peak JCO of up to 113.6 mA cm-2 in an H-type cell. The excellent eCO2RR performance of DrGO-CoPc rates itself as one of the best immobilized molecular catalysts.

Regulating coordination number in atomically dispersed Pt species on defect-rich graphene for n-butane dehydrogenation reaction

Metal nanoparticle (NP), cluster and isolated metal atom (or single atom, SA) exhibit different catalytic performance in heterogeneous catalysis originating from their distinct nanostructures. To maximize atom efficiency and boost activity for catalysis, the construction of structure–performance relationship provides an effective way at the atomic level. Here, we successfully fabricate fully exposed Pt3 clusters on the defective nanodiamond@graphene (ND@G) by the assistance of atomically dispersed Sn promoters, and correlated the n-butane direct dehydrogenation (DDH) activity with the average coordination number (CN) of Pt-Pt bond in Pt NP, Pt3 cluster and Pt SA for fundamentally understanding structure (especially the sub-nano structure) effects on n-butane DDH reaction at the atomic level. The as-prepared fully exposed Pt3 cluster catalyst shows higher conversion (35.4%) and remarkable alkene selectivity (99.0%) for n-butane direct DDH reaction at 450 °C, compared to typical Pt NP and Pt SA catalysts supported on ND@G. Density functional theory calculation (DFT) reveal that the fully exposed Pt3 clusters possess favorable dehydrogenation activation barrier of n-butane and reasonable desorption barrier of butene in the DDH reaction.

Scalable solid-phase synthesis of defect-rich graphene for oxygen reduction electrocatalysis

Defect-engineered carbon materials have been emerged as promising electrocatalysts for oxygen reduction reaction (ORR) in metal-air batteries. Developing a facile strategy for the preparation of highly active nanocarbon electrocatalysts remains challenging. Herein, a low-cost and simple route is developed to synthesize defective graphene by pyrolyzing the mixture of glucose and carbon nitride. Molecular dynamics simulations reveal that the graphene formation is ascribed to two-dimensional layered feature of carbon nitride, and high compatibility of carbon nitride/glucose systems. Structural measurements suggest that the graphene possesses rich edge and topological defects. The graphene catalyst exhibits higher power density than commercial Pt/C catalyst in a primary Zn-air battery. Combining experimental results and theoretical thermodynamic analysis, it is identified that graphitic nitrogen-modified topological defects at carbon framework edges are responsible for the decent ORR performance. The strategy presented in this work can be can be scaled up readily to fabricate defective carbon materials.