The scarcity and high cost of platinum-based electrocatalysts for the oxygen reduction reaction (ORR) has limited the commercial and scalable use of fuel cells. Heteroatom-doped nanocarbon materials ...have been demonstrated to be efficient alternative catalysts for ORR. Here, graphene quantum dots, synthesized from inexpensive and earth-abundant anthracite coal, were self-assembled on graphene by hydrothermal treatment to form hybrid nanoplatelets that were then codoped with nitrogen and boron by high-temperature annealing. This hybrid material combined the advantages of both components, such as abundant edges and doping sites, high electrical conductivity, and high surface area, which makes the resulting materials excellent oxygen reduction electrocatalysts with activity even higher than that of commercial Pt/C in alkaline media.
In this paper, we demonstrate that by simple laser induction, commercial polyimide films can be readily transformed into porous graphene for the fabrication of flexible, solid-state supercapacitors. ...Two different solid-state electrolyte supercapacitors are described, namely vertically stacked graphene supercapacitors and in-plane graphene microsupercapacitors, each with enhanced electrochemical performance, cyclability, and flexibility. Devices with a solid-state polymeric electrolyte exhibit areal capacitance of >9 mF/cm2 at a current density of 0.02 mA/cm2, more than twice that of conventional aqueous electrolytes. Moreover, laser induction on both sides of polyimide sheets enables the fabrication of vertically stacked supercapacitors to multiply its electrochemical performance while preserving device flexibility.
The cost effective synthesis and patterning of carbon nanomaterials is a challenge in electronic and energy storage devices. Here we report a one-step, scalable approach for producing and patterning ...porous graphene films with three-dimensional networks from commercial polymer films using a CO
infrared laser. The sp
-carbon atoms are photothermally converted to sp
-carbon atoms by pulsed laser irradiation. The resulting laser-induced graphene (LIG) exhibits high electrical conductivity. The LIG can be readily patterned to interdigitated electrodes for in-plane microsupercapacitors with specific capacitances of >4 mF cm
and power densities of ~9 mW cm
. Theoretical calculations partially suggest that enhanced capacitance may result from LIG's unusual ultra-polycrystalline lattice of pentagon-heptagon structures. Combined with the advantage of one-step processing of LIG in air from commercial polymer sheets, which would allow the employment of a roll-to-roll manufacturing process, this technique provides a rapid route to polymer-written electronic and energy storage devices.
Reduction of water to hydrogen through electrocatalysis holds great promise for clean energy, but its large-scale application relies on the development of inexpensive and efficient catalysts to ...replace precious platinum catalysts. Here we report an electrocatalyst for hydrogen generation based on very small amounts of cobalt dispersed as individual atoms on nitrogen-doped graphene. This catalyst is robust and highly active in aqueous media with very low overpotentials (30 mV). A variety of analytical techniques and electrochemical measurements suggest that the catalytically active sites are associated with the metal centres coordinated to nitrogen. This unusual atomic constitution of supported metals is suggestive of a new approach to preparing extremely efficient single-atom catalysts.
Many diseases are associated with oxidative stress, which occurs when the production of reactive oxygen species (ROS) overwhelms the scavenging ability of an organism. Here, we evaluated the carbon ...nanoparticle antioxidant properties of poly(ethylene glycolated) hydrophilic carbon clusters (PEG-HCCs) by electron paramagnetic resonance (EPR) spectroscopy, oxygen electrode, and spectrophotometric assays. These carbon nanoparticles have 1 equivalent of stable radical and showed superoxide (O ₂•⁻) dismutase-like properties yet were inert to nitric oxide (NO •) as well as peroxynitrite (ONOO ⁻). Thus, PEG-HCCs can act as selective antioxidants that do not require regeneration by enzymes. Our steady-state kinetic assay using KO ₂ and direct freeze-trap EPR to follow its decay removed the rate-limiting substrate provision, thus enabling determination of the remarkable intrinsic turnover numbers of O ₂•⁻ to O ₂ by PEG-HCCs at >20,000 s ⁻¹. The major products of this catalytic turnover are O ₂ and H ₂O ₂, making the PEG-HCCs a biomimetic superoxide dismutase.
Significance Mechanistic studies of nontoxic hydrophilic carbon cluster nanoparticles show that they are able to accomplish the direct conversion of superoxide to dioxygen and hydrogen peroxide. This is accomplished faster than in most single-active-site enzymes, and it is precisely what dioxygen-deficient tissue needs in the face of injury where reactive oxygen species, particularly superoxide, overwhelm the natural enzymes required to remove superoxide. We confirm here that the hydrophilic carbon clusters are unreactive toward nitric oxide radical, which is a potent vasodilator that also has an important role in neurotransmission and cytoprotection. The mechanistic results help to explain the preclinical efficacy of these carbon nanoparticles in mitigating the deleterious effects of superoxide on traumatized tissue.
A facile and cost-effective approach to the fabrication of a nanocomposite material of polyaniline (PANI) and graphene nanoribbons (GNRs) has been developed. The morphology of the composite was ...characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron microscopy, and X-ray diffraction analysis. The resulting composite has a high specific capacitance of 340 F/g and stable cycling performance with 90% capacitance retention over 4200 cycles. The high performance of the composite results from the synergistic combination of electrically conductive GNRs and highly capacitive PANI. The method developed here is practical for large-scale development of pseudocapacitor electrodes for energy storage.
There is great interest in renewable and sustainable energy research to develop low-cost, highly efficient, and stable electrocatalysts as alternatives to replace Pt-based catalysts for the hydrogen ...evolution reaction (HER). Though nanoparticles encapsulated in carbon shells have been widely used to improve the electrode performances in energy storage devices (e.g., lithium ion batteries), they have attracted less attention in energy-related electrocatalysis. Here we report the synthesis of nitrogen-enriched core–shell structured cobalt–carbon nanoparticles dispersed on graphene sheets and we investigate their HER performances in both acidic and basic media. These catalysts exhibit excellent durability and HER activities with onset overpotentials as low as ∼70 mV in both acidic (0.5 M H2SO4) and alkaline (0.1 M NaOH) electrolytes, and the overpotentials needed to deliver 10 mA cm–2 are determined to be 265 mV in acid and 337 mV in base, further demonstrating their potential to replace Pt-based catalysts. Control experiments reveal that the active sites for HER might come from the synergistic effects between the cobalt nanoparticles and nitrogen-doped carbon.
A composite material made of graphene nanoribbons and iron oxide nanoparticles provides a remarkable route to lithium‐ion battery anode with high specific capacity and cycle stability. At a rate of ...100 mA/g, the material exhibits a high discharge capacity of ~910 mAh/g after 134 cycles, which is >90% of the theoretical li‐ion storage capacity of iron oxide. Carbon black, carbon nanotubes, and graphene flakes have been employed by researchers to achieve conductivity and stability in lithium‐ion electrode materials. Herein, the use of graphene nanoribbons as a conductive platform on which iron oxide nanoparticles are formed combines the advantages of long carbon nanotubes and flat graphene surfaces. The high capacity over prolonged cycling achieved is due to the synergy between an electrically percolating networks of conductive graphene nanoribbons and the high lithium‐ion storage capability of iron oxide nanoparticles.
A facile and scalable synthesis route to a graphene nanoribbon (GNR)/Fe2O3 composite is developed as an anode material for lithium‐ion batteries. The unique structures of the GNRs with high electrical conductivity and the enhanced vacancy of the iron oxide nanoparticles leads to excellent electrochemical performance. The fabricated anode shows a reversible capacity of 1190 mAh/g and retains 910 mAh/g after 134 cycles with a high rate performance of 544 mAh/g at a rate of 2 A/g.
Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via ...burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp2-carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp2-carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites.
Bandgaps of photoluminescent graphene quantum dots (GQDs) synthesized from anthracite have been engineered by controlling the size of GQDs in two ways: either chemical oxidative treatment and ...separation by cross-flow ultrafiltration, or by a facile one-step chemical synthesis using successively higher temperatures to render smaller GQDs. Using these methods, GQDs were synthesized with tailored sizes and bandgaps. The GQDs emit light from blue-green (2.9 eV) to orange-red (2.05 eV), depending on size, functionalities and defects. These findings provide a deeper insight into the nature of coal-derived GQDs and demonstrate a scalable method for production of GQDs with the desired bandgaps.
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