There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Hydrogen fuel is considered as the cleanest renewable resource and the primary alternative to fossil fuels for future energy supply. Sustainable hydrogen generation is the major prerequisite to realize future hydrogen economy. The electrocatalytic hydrogen evolution reaction (HER), as the vital step of water electrolysis to H2 production, has been the subject of extensive study over the past decades. In this comprehensive review, we first summarize the fundamentals of HER and review the recent state-of-the-art advances in the low-cost and high-performance catalysts based on noble and non-noble metals, as well as metal-free HER electrocatalysts. We systemically discuss the insights into the relationship among the catalytic activity, morphology, structure, composition, and synthetic method. Strategies for developing an effective catalyst, including increasing the intrinsic activity of active sites and/or increasing the number of active sites, are summarized and highlighted. Finally, the challenges, perspectives, and research directions of HER electrocatalysis are featured.

Recent Advances in Electrocatalytic Hydrogen Evolution Using Nanoparticles.

Hydrogen has been hailed as a clean and sustainable alternative to finite fossil fuels in many energy systems. Water splitting is an important method for hydrogen production in high purity and large quantities. To accelerate the hydrogen evolution reaction (HER) rate, it is highly necessary to develop high efficiency catalysts and to select a proper electrolyte. Herein, the performances of non-noble metal-based carbon composites under various pH values (acid, alkaline and neutral media) for HER in terms of catalyst synthesis, structure and molecular design are systematically discussed. A detailed analysis of the structure-activity-pH correlations in the HER process gives an insight on the origin of the pH-dependence for HER, and provide guidance for future HER mechanism studies on non-noble metal-based carbon composites. Furthermore, this Review gives a fresh impetus to rational design of high-performance noble-metal-free composites catalysts and guide researchers to employ the established electrocatalysts in proper water electrolysis technologies.

Non-Noble Metal-based Carbon Composites in Hydrogen Evolution Reaction: Fundamentals to Applications.

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Heterostructures for Electrochemical Hydrogen Evolution Reaction: A Review

Electrocatalysts for hydrogen evolution reaction

For increasing scalability and reducing cost, transition metal dichalcogenides-based electrocatalysts presently have been proposed as substitutes for noble metals to generate hydrogen, but these alternatives usually suffer from inferior performance. Here, a Ravenala leaf-like WxC@WS2 heterostructure is grown via carbonizing WS2 nanotubes, whose outer walls being partially unzipped along with the Wx C “leaf-valves” attached to the inner tubes during the carbonization process. This heterostructure exhibits a catalytic activity for hydrogen evolution reaction with low overpotential of 146 mV at 10 mA cm−2 and Tafel slope of 61 mV per decade, outperforming the performance of WS2 nanotubes and WxC counterparts under the same condition. Density functional theory calculations are performed to unravel the underlying mechanism, revealing that the charge distribution between WxC and WS2 plays a key role for promoting H atom adsorption and desorption kinetics simultaneously. This work not only provides a potential low-cost alternative for hydrogen generation but should be taken as a guide to optimize the catalyst structure and composition.

/pdf/interface-engineered-wxc-ws2-nanostructure-for-enhanced-3azf5l32z1.pdf

Interface Engineered WxC@WS2 Nanostructure for Enhanced Hydrogen Evolution Catalysis

Electrocatalytic hydrogen production at low overpotential is a promising route towards a clean and sustainable energy. Layered transition metal dichalcogenides (LTMDs) have attracted copious attention for their outstanding activities in hydrogen evolution reaction (HER). However, the horizontally laid nanosheets suffer from a paucity of active edge sites. Herein, we report the successful synthesis of vertical-oriented WS2 nanosheets through a hydrothermal method followed by a facile sulfurization process. Furthermore, the surface of synthesized WS2 nanosheets was decorated by ultrathin reduced graphene oxide (rGO) nanoplates. This is achieved for the first time by bringing the rGO on the surface of vertical-oriented WS2 nanosheets, which is conducive to rapid electron transport during the HER process. Significantly, the as-synthesized rGO/WS2 nanosheets exhibit improved HER activity as compared to the undecorated ones. It needs a low overpotential of only 229 mV vs. RHE to afford a current density of 10 mA cm(-2). We believe that this hybrid structure demonstrated remarkable HER activity brought about by a compatible synergism between rGO and WS2.

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A vertical-oriented WS2 nanosheet sensitized by graphene: an advanced electrocatalyst for hydrogen evolution reaction.

We report the controlled growth of highly ordered and well aligned one-dimensional tellurium nanostructure arrays via a one-step catalyst-free physical vapor deposition method. The density, size and fine structures of tellurium nanowires are systematically studied and optimized. Field emission measurement was performed to display notable dependence on nanostructure morphologies. The ordered nanowire array based field emitter has a turn-on field as low as 3.27 V μm−1 and a higher field enhancement factor of 3270. Our finding offers the possibility of controlling the growth of tellurium nanowire arrays and opens up new means for their potential applications in electronic devices and displays.

http://www.nanoctr.cn/hejun/keyanchengguo/201507/W020150811447018143016.pdf

Site-specific nucleation and controlled growth of a vertical tellurium nanowire array for high performance field emitters

We report for the first time the synthesis of single crystalline In2Te3 nanosheets. Te nanorods were first produced by controlling the reaction kinetics and then In2Te3 nanosheets nucleated at the body of Te nanorods in the presence of organic surfactant. The self-assembly and the certain directional growth process of In2Te3 on the body of Te nanorods resulted in an ordered nanostring-cluster which subsequently gave split In2Te3 nanosheets. The transformation can be attributed to the developed facets and organic surfactants which can greatly enlarge the lateral dimensions and produce nanosheets. The morphology evolution from nanorods to nanosheets is demonstrated with experimental evidence collected via SEM, TEM and XRD studies. The synthesis of nanorods/nanosheets will supply additional opportunities for the exploration of novel fundamental properties of telluride based chalcogenides materials. Initial hydrogen storage results pave the way for utilizing telluride-based nanostructures for gas storage and gas sensing properties. Also, the photoresponse properties of indium telluride offers good knowledge for the fabrication of nanoscale electronic and optoelectronic devices.

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Lianfeng Sun

Papers

Interface Engineered WxC@WS2 Nanostructure for Enhanced Hydrogen Evolution Catalysis

A vertical-oriented WS2 nanosheet sensitized by graphene: an advanced electrocatalyst for hydrogen evolution reaction.

Site-specific nucleation and controlled growth of a vertical tellurium nanowire array for high performance field emitters

Telluride-based nanorods and nanosheets: synthesis, evolution and properties