Although direct methanol fuel cell offers high energy use efficiency and low pollution emission, the lack of suitable electrode materials poses a great challenge to its commercial application. ...Herein, a facile and scalable approach is developed to fabricate a hybrid electrocatalyst consisting of strongly coupled worm‐shape Pt nanocrystals and nitrogen‐doped low‐defect graphene (N‐LDG) sheets. Interestingly, it is found that the formation of Pt nanoworms (NWs) is induced by the N atoms in the high‐quality carbon matrix, which also allows the integration of their respective structural advantages and leads to a strong synergetic coupling effect. As a result, the obtained Pt NW/N‐LDG catalyst exhibits an extremely high mass activity of 1283.1 mA mg−1 toward methanol oxidation reaction, accompanied by reliable long‐term stability and good antipoisoning ability, which are dramatically enhanced as compared with conventional Pt nanoparticle catalysts dispersed on undoped LDG, reduced graphene oxide, and commercial carbon black supports.
The growth of Pt nanoworms on nitrogen‐doped low‐defect graphene is achieved by a combined CVD, heat treatment, and solvothermal method. Owing to the prominent structural features including large surface areas, well‐preserved pristine graphene structure, presence of catalytically active N atoms, and interconnected worm‐shape Pt configuration, the resulting hybrid is endowed with exceptional electrochemical properties toward methanol oxidation reaction.
The practical recycling of carbon dioxide (CO2) by the electrochemical reduction route requires an active, stable, and affordable catalyst system. Although noble metals such as gold and silver have ...been demonstrated to reduce CO2 into carbon monoxide (CO) efficiently, they suffer from poor durability and scarcity. Here we report three-dimensional (3D) graphene foam incorporated with nitrogen defects as a metal-free catalyst for CO2 reduction. The nitrogen-doped 3D graphene foam requires negligible onset overpotential (−0.19 V) for CO formation, and it exhibits superior activity over Au and Ag, achieving similar maximum Faradaic efficiency for CO production (∼85%) at a lower overpotential (−0.47 V) and better stability for at least 5 h. The dependence of catalytic activity on N-defect structures is unraveled by systematic experimental investigations. Indeed, the density functional theory calculations confirm pyridinic N as the most active site for CO2 reduction, consistent with experimental results.
The challenge in the electrosynthesis of fuels from CO2 is to achieve durable and active performance with cost-effective catalysts. Here, we report that carbon nanotubes (CNTs), doped with nitrogen ...to form resident electron-rich defects, can act as highly efficient and, more importantly, stable catalysts for the conversion of CO2 to CO. The unprecedented overpotential (−0.18 V) and selectivity (80%) observed on nitrogen-doped CNTs (NCNTs) are attributed to their unique features to facilitate the reaction, including (i) high electrical conductivity, (ii) preferable catalytic sites (pyridinic N defects), and (iii) low free energy for CO2 activation and high barrier for hydrogen evolution. Indeed, DFT calculations show a low free energy barrier for the potential-limiting step to form key intermediate COOH as well as strong binding energy of adsorbed COOH and weak binding energy for the adsorbed CO. The highest selective site toward CO production is pyridinic N, and the NCNT-based electrodes exhibit no degradation over 10 h of continuous operation, suggesting the structural stability of the electrode.
Two‐dimensional (2D) atomic layers such as graphene, and metal chalcogenides have recently attracted tremendous attention due to their unique properties and potential applications. Unfortunately, in ...most cases, the free‐standing nanosheets easily re‐stack due to their van der Waals forces, and lose the advantages of their separated atomic layer state. Here, a bottom‐up approach is developed to build three‐dimensional (3D) architectures by 2D nanosheets such as MoS2 and graphene oxide nanosheets as building blocks, the thin nature of which can be well retained. After simply chemical reduction, the resulting 3D MoS2‐graphene architectures possess high surface area, porous structure, thin walls and high electrical conductivity. Such unique features are favorable for the rapid diffusions of both lithium ions and electrons during lithium storage. As a consequence, MoS2‐graphene electrodes exhibit high reversible capacity of ≈1200 mAh g−1, with very good cycling performance. Moreover, such a simple and low‐cost assembly protocol can provide a new pathway for the large‐scale production of various functional 3D architectures for energy storage and conversions.
A bottom‐up approach is developed to build 3D architectures by 2D nanosheets such as MoS2 and graphene oxide nanosheets as building blocks. The resulting 3D architectures possess favorable diffusion kinetics for both lithium and electrons, leading to excellent electrochemical performance. Such a simple and low‐cost assembly protocol will provide a new pathway for the large‐scale production of various functional 3D architectures for energy storage and conversions.
Graphene (G) and atomic layers of hexagonal boron nitride (h-BN) are complementary two-dimensional materials, structurally very similar but with vastly different electronic properties. Recent studies ...indicate that h-BN atomic layers would be excellent dielectric layers to complement graphene electronics. Graphene on h-BN has been realized via peeling of layers from bulk material to create G/h-BN stacks. Considering that both these layers can be independently grown via chemical vapor deposition (CVD) of their precursors on metal substrates, it is feasible that these can be sequentially grown on substrates to create the G/h-BN stacked layers useful for applications. Here we demonstrate the direct CVD growth of h-BN on highly oriented pyrolytic graphite and on mechanically exfoliated graphene, as well as the large area growth of G/h-BN stacks, consisting of few layers of graphene and h-BN, via a two-step CVD process. The G/h-BN film is uniform and continuous and could be transferred onto different substrates for further characterization and device fabrication.
An efficient hydrothermal approach is demonstrated to fabricate a series of graphene‐network‐backboned hybrid architectures such as MoS2/graphene and FeOx/graphene, showing high specific surface ...area, porous structure, and continuous graphene networks. Such unique architectures exhibit a high reversible capacity (about 1100 mA h g−1) for lithium ion batteries. High‐rate capabilities of full charge to discharge in 25–45 s with a long cycle life (1500 cycles) are achieved at different rates.
Although lithium ion batteries have gained commercial success owing to their high energy density, they lack suitable electrodes capable of rapid charging and discharging to enable a high power ...density critical for broad applications. Here, we demonstrate a simple bottom-up approach toward single crystalline vanadium oxide (VO2) ribbons with graphene layers. The unique structure of VO2-graphene ribbons thus provides the right combination of electrode properties and could enable the design of high-power lithium ion batteries. As a consequence, a high reversible capacity and ultrafast charging and discharging capability is achieved with these ribbons as cathodes for lithium storage. A full charge or discharge is capable in 20 s. More remarkably, the resulting electrodes retain more than 90% of the initial capacity after cycling more than 1000 times at an ultrahigh rate of 190C, providing the best reported rate performance for cathodes in lithium ion batteries to date.
Micrometer‐sized electrochemical capacitors have recently attracted attention due to their possible applications in micro‐electronic devices. Here, a new approach to large‐scale fabrication of ...high‐capacitance, two‐dimensional MoS2 film‐based micro‐supercapacitors is demonstrated via simple and low‐cost spray painting of MoS2 nanosheets on Si/SiO2 chip and subsequent laser patterning. The obtained micro‐supercapacitors are well defined by ten interdigitated electrodes (five electrodes per polarity) with 4.5 mm length, 820 μm wide for each electrode, 200 μm spacing between two electrodes and the thickness of electrode is ∼0.45 μm. The optimum MoS2‐based micro‐supercapacitor exhibits excellent electrochemical performance for energy storage with aqueous electrolytes, with a high area capacitance of 8 mF cm−2 (volumetric capacitance of 178 F cm−3) and excellent cyclic performance, superior to reported graphene‐based micro‐supercapacitors. This strategy could provide a good opportunity to develop various micro‐/nanosized energy storage devices to satisfy the requirements of portable, flexible, and transparent micro‐electronic devices.
A new approach for large‐scale fabrication of 2D MoS2 film‐based micro‐supercapacitors is developed via a simple spray painting of MoS2 nanosheets and subsequent laser patterning of the deposited film. The optimized MoS2‐based micro‐supercapacitor exhibits excellent electrochemical performance for energy storage, with a high area capacitance of 8 mF cm−2 and excellent cyclic performance, superior to state of the art carbon‐based micro‐supercapacitors.
Hexagonal boron nitride is a two-dimensional layered material that can be stable at 1,500 °C in air and will not react with most chemicals. Here we demonstrate large-scale, ultrathin, ...oxidation-resistant coatings of high-quality hexagonal boron nitride layers with controlled thicknesses from double layers to bulk. We show that such ultrathin hexagonal boron nitride films are impervious to oxygen diffusion even at high temperatures and can serve as high-performance oxidation-resistant coatings for nickel up to 1,100 °C in oxidizing atmospheres. Furthermore, graphene layers coated with a few hexagonal boron nitride layers are also protected at similarly high temperatures. These hexagonal boron nitride atomic layer coatings, which can be synthesized via scalable chemical vapour deposition method down to only two layers, could be the thinnest coating ever shown to withstand such extreme environments and find applications as chemically stable high-temperature coatings.
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