Cost effective hydrogen evolution reaction (HER) catalyst without using precious metallic elements is a crucial demand for environment-benign energy production. Molybdenum sulfide is one of the promising candidates for such purpose, particularly in acidic condition, but its catalytic performance is inherently limited by the sparse catalytic edge sites and poor electrical conductivity. We report synthesis and HER catalysis of hybrid catalysts composed of amorphous molybdenum sulfide (MoSx) layer directly bound at vertical N-doped carbon nanotube (NCNT) forest surface. Owing to the high wettability of N-doped graphitic surface and electrostatic attraction between thiomolybdate precursor anion and N-doped sites, ∼2 nm scale thick amorphous MoSx layers are specifically deposited at NCNT surface under low-temperature wet chemical process. The synergistic effect from the dense catalytic sites at amorphous MoSx surface and fluent charge transport along NCNT forest attains the excellent HER catalysis with onset overpotential as low as ∼75 mV and small potential of 110 mV for 10 mA/cm(2) current density, which is the highest HER activity of molybdenum sulfide-based catalyst ever reported thus far.

Outstanding pristine properties of carbon nanotubes and graphene have limited the scope for real-life applications without precise controllability of the material structures and properties. This invited article to celebrate the 25th anniversary of Advanced Materials reviews the current research status in the chemical modification/doping of carbon nanotubes and graphene and their relevant applications with optimized structures and properties. A broad aspect of specific correlations between chemical modification/doping schemes of the graphitic carbons with their novel tunable material properties is summarized. An overview of the practical benefits from chemical modification/doping, including the controllability of electronic energy level, charge carrier density, surface energy and surface reactivity for diverse advanced applications is presented, namely flexible electronics/optoelectronics, energy conversion/storage, nanocomposites, and environmental remediation, with a particular emphasis on their optimized interfacial structures and properties. Future research direction is also proposed to surpass existing technological bottlenecks and realize idealized graphitic carbon applications.

Assembly of graphene into functional macroscopic objects, such as fi lms, [ 1 ] sheets, [ 2 ] fi bers, [ 3 ] foams, [ 4,5 ] and other complex architectures, [ 6 ] is of enormous research interest. How to attain desired structures in a cost effective and manufacturable manner is crucial for energy harvest/storage, catalysis, sensors and so on. Unlike fullerene or carbon nanotubes, whose assembly generally relies on weak van der Walls force or chemical modifi cation, two-dimensional graphene may straightforwardly exploit strong interlayer π -π stacking. Unfortunately, such a strong and directional interaction frequently results in graphitic stacking with minimal surface area. [ 7,8 ] Gelation is a straightforward route to macroscopic functional materials from graphene. Taking advantage of high electrical conductivity, large surface area, and soft hydrated character, graphene gel possesses enormous potentials for supercapacitor electrode, [9][10][11][12] catalytic support, [ 13,14 ] cell growth scaffold [ 15 ] and so on. [ 16,17 ] To date, several graphene gelation principles have been developed, including reduction of graphene oxide (GO) dispersion, [ 9,10,18 ] fl ow directed interfacial assembly [ 19 ] and template assembly. [ 20 ] Nevertheless, arbitrary large scale production of optimized porous structures via minimal processing steps remains formidable technological challenge.We present a surprisingly simple and versatile graphene gelation principle capable of three-dimensional shape engineering of micrometer thick hydrogels without any practical size limit. Simple immersion of arbitrary shaped Zn objects in aqueous GO dispersion spontaneously generates graphene hydrogel fi lms at Zn surfaces. This site specifi c gelation enables a wide range controllability of three-dimensional gel structures in porous morphology as well as macroscopic object scale according to customized purposes. Signifi cantly, this gelation principle has been exploited for high rate, large capacity supercapacitor electrodes. In general, fast charging/discharging rate (or power density) is hardly compatible with large areal capacity [21][22][23] (or energy density) for energy devices. While thin supercapacitor electrodes with facile electrolyte transports are favorable for high rate capacity, thick electrodes are desired for large areal capacity. [24][25][26] In this work, three-dimensional controllability of graphene gel morphology optimized the aqueous electrolyte transport within suffi ciently thick gel structures. Consequently, fundamental challenge to attain large areal capacity without sacrifi cing rate capability is successfully addressed.Synthetic scheme of graphene hydrogel is presented in Figure 1 a. While Zn foils are immersed in mild acidic dispersion of GO, black graphene hydrogels spontaneously grow at Zn surface. The grown gel thickness is roughly tunable with immersion time. Typically, one hour deposition produced 78-μ m-thick gel fi lms in 10 −3 M hydrochlorid acid (HCl) containing GO dispersion (Supporting information, Fig...