Ya-Rong Zheng

Water Oxidation Electrocatalyzed by an Efficient Mn3O4/CoSe2 Nanocomposite

The design of efficient, cheap, and abundant oxygen evolution reaction (OER) catalysts is crucial to the development of sustainable energy sources for powering fuel cells. We describe here a novel Mn(3)O(4)/CoSe(2) hybrid which could be a promising candidate for such electrocatalysts. Possibly due to the synergetic chemical coupling effects between Mn(3)O(4) and CoSe(2), the constructed hybrid displayed superior OER catalytic performance relative to its parent CoSe(2)/DETA nanobelts. Notably, such earth-abundant cobalt (Co)-based catalyst afforded a current density of 10 mA cm(-2) at a small overpotential of ~0.45 V and a small Tafel slope down to 49 mV/decade, comparable to the best performance of the well-investigated cobalt oxides. Moreover, this Mn(3)O(4)/CoSe(2) hybrid shows good stability in 0.1 M KOH electrolyte, which is highly required to a promising OER electrocatalyst.

An efficient molybdenum disulfide/cobalt diselenide hybrid catalyst for electrochemical hydrogen generation

The electroreduction of water for sustainable hydrogen production is a critical component of several developing clean-energy technologies, such as water splitting and fuel cells. However, finding a cheap and efficient alternative catalyst to replace currently used platinum-based catalysts is still a prerequisite for the commercialization of these technologies. Here we report a robust and highly active catalyst for hydrogen evolution reaction that is constructed by in situ growth of molybdenum disulfide on the surface of cobalt diselenide. In acidic media, the molybdenum disulfide/cobalt diselenide catalyst exhibits fast hydrogen evolution kinetics with onset potential of −11 mV and Tafel slope of 36 mV per decade, which is the best among the non-noble metal hydrogen evolution catalysts and even approaches to the commercial platinum/carbon catalyst. The high hydrogen evolution activity of molybdenum disulfide/cobalt diselenide hybrid is likely due to the electrocatalytic synergistic effects between hydrogen evolution-active molybdenum disulfide and cobalt diselenide materials and the much increased catalytic sites.

Nitrogen-Doped Graphene Supported CoSe2 Nanobelt Composite Catalyst for Efficient Water Oxidation

The slow kinetics of the oxygen evolution reaction (OER) greatly hinders the large-scale production of hydrogen fuel from water splitting. Although many OER electrocatalysts have been developed to negotiate this difficult reaction, substantial progresses in the design of cheap, robust, and efficient catalysts are still required and have been considered a huge challenge. Here, we report a composite material consisting of CoSe2 nanobelts anchored on nitrogen-doped reduced graphene oxides (denoted as NG-CoSe2) as a highly efficient OER electrocatalyst. In 0.1 M KOH, the new NG-CoSe2 catalyst afforded a current density of 10 mA cm(-2) at a small overpotential of mere 0.366 V and a small Tafel slope of ∼40 mV/decade, comparing favorably with the state-of-the-art RuO2 catalyst. This NG-CoSe2 catalyst also presents better stability than that of RuO2 under harsh OER cycling conditions. Such good OER performance is comparable to the best literature results and the synergistic effect was found to boost the OER performance. These results raise the possibility for the development of effective and robust OER electrodes by using cheap and easily prepared NG-CoSe2 to replace the expensive commercial catalysts such as RuO2 and IrO2.

An Efficient CeO2/CoSe2 Nanobelt Composite for Electrochemical Water Oxidation

CeO2 /CoSe2 nanobelt composite for electrochemical water oxidation: A new CeO2 /CoSe2 nanobelt composite is developed as a highly effective water oxidation electrocatalyst by growing CeO2 nanoparticle CoSe2 nanobelts in situ via a simple polyol reduction route. The constructed hybrid catalyst shows extremely high oxgen evolution reaction (OER) activity, even beyond the state-of-the-art RuO2 catalyst in alkaline media.

Mixed-solution synthesis of sea urchin-like NiSe nanofiber assemblies as economical Pt-free catalysts for electrochemical H2 production

Nickel (Ni)-based nanomaterials have been intensively explored as promising noble-metal-free hydrogen evolution reaction (HER) electrocatalysts. Here, we report that uniform sea urchin-like NiSe nanofiber assemblies can be prepared on a large scale by a ternary mixed solvent strategy. The new NiSe exhibits very high HER activity in 0.5 M H2SO4, comparable to the best performance of the well-studied MoS2 catalysts. The Tafel slope of ∼64 mV per decade was observed for the sea urchin-like NiSe catalyst, suggesting that the Volmer–Heyrovsky HER mechanism presumably takes effect in the HER. Although the stability of such a NiSe nanofiber assembled nanostructure needs to be further improved, this study addresses the benefits and possibilities of using Ni-based chalcogenides to design high performance and low cost HER catalysts.

Super-elastic and fatigue resistant carbon material with lamellar multi-arch microstructure.

Low-density compressible materials enable various applications but are often hindered by structure-derived fatigue failure, weak elasticity with slow recovery speed and large energy dissipation. Here we demonstrate a carbon material with microstructure-derived super-elasticity and high fatigue resistance achieved by designing a hierarchical lamellar architecture composed of thousands of microscale arches that serve as elastic units. The obtained monolithic carbon material can rebound a steel ball in spring-like fashion with fast recovery speed (∼580 mm s−1), and demonstrates complete recovery and small energy dissipation (∼0.2) in each compress-release cycle, even under 90% strain. Particularly, the material can maintain structural integrity after more than 106 cycles at 20% strain and 2.5 × 105 cycles at 50% strain. This structural material, although constructed using an intrinsically brittle carbon constituent, is simultaneously super-elastic, highly compressible and fatigue resistant to a degree even greater than that of previously reported compressible foams mainly made from more robust constituents.

Scalable Template Synthesis of Resorcinol–Formaldehyde/Graphene Oxide Composite Aerogels with Tunable Densities and Mechanical Properties

Resorcinol-formaldehyde (RF) and graphene oxide (GO) aerogels have found a variety of applications owing to their excellent properties and remarkable flexibility. However, the macroscopic and controllable synthesis of their composite gels is still a great challenge. By using GO sheets as template skeletons and metal ions (Co(2+), Ni(2+), or Ca(2+)) as catalysts and linkers, the first low-temperature scalable strategy for the synthesis of a new kind of RF-GO composite gel with tunable densities and mechanical properties was developed. The aerogels can tolerate a strain as high as 80% and quickly recover their original morphology after the compression has been released. Owing to their high compressibility, the gels might find applications in various areas, for example, as adsorbents for the removal of dye pollutants and in oil-spill cleanup.

One-pot synthesis of hierarchical magnetite nanochain assemblies with complex building units and their application for water treatment

We report that unique hierarchical magnetite (Fe3O4) nanochain assemblies with complex flower-like nanostructures as secondary building blocks and smaller nanoparticles as primary building blocks can be prepared by a facile and surfactant-free one-pot approach using Fe(acac)3 as precursor in polyol solution. The resultant Fe3O4 nanochains possess superparamagnetic property, large saturation magnetization (82.1 emu/g), high Brunauer–Emmett–Teller (BET) specific surface area (43.5 m2 g−1), and also good water-dispersibility. Thanks to these wonderful intrinsic properties, the Fe3O4 nanochains exhibit excellent ability to remove an organic pollutant in waste water. For example, Congo red, a common azo-dye in textile industry, can be completely removed within 5 min at room temperature when the initial concentration of Congo red in solution was 100 mg/L. In addition, the Fe3O4 assembled tertiary chain-like structures can be recycled by a simple heat treatment, which keeps almost the same removal ability and a litter slower adsorption rate even used for the third time. Beyond as an adsorbent for water treatment, these Fe3O4 nanochain assemblies may be useful in other fields such as magnetic resonance imaging (MRI), and drug delivery based on their novel structures and intrinsic multi-functionalities.

Highly crystalline PtCu nanotubes with three dimensional molecular accessible and restructured surface for efficient catalysis

Direct methanol fuel cells (DMFCs) as candidates for dominant energy conversion devices based on the higher energy densities of liquid methanol show unique advantages over hydrogen-based fuel cells, such as cheapness and ease of storage and transportation. However, the fundamental challenges for electrochemical oxidation of methanol are the sluggish electro-oxidation kinetics and recovery of Pt surfaces to lower costs. Here, we report a mixed solvent strategy to prepare a highly active and durable class of electrocatalysts with connected single crystalline nanoparticles (NPs), forming an open architecture. Each single crystalline NP along PtCu nanotubes (NTs) can be considered as a highly active unit with specific facet and assembles along one-dimensional (1D) direction. The Pt1Cu1–AA NTs achieve a factor of 5.5 and 10.3 enhancement in mass activity (2252 mA mg−1) and specific activity (6.09 mA cm−2) for methanol oxidation reaction (MOR) relative to Pt/C catalysts, respectively. Moreover, after long-term stability tests, the activity of the NTs could be recovered via a simple potential cycling process (reactivation process) to the initial value or better. Thus this kind of catalysts would limit the costs to the initial investment and recovery and show potential possibility in real DMFC devices.

Phase-Selective Syntheses of Cobalt Telluride Nanofleeces for Efficient Oxygen Evolution Catalysts

Cobalt-based nanomaterials have been intensively explored as promising noble-metal-free oxygen evolution reaction (OER) electrocatalysts. Herein, we report phase-selective syntheses of novel hierarchical CoTe2 and CoTe nanofleeces for efficient OER catalysts. The CoTe2 nanofleeces exhibited excellent electrocatalytic activity and stablity for OER in alkaline media. The CoTe2 catalyst exhibited superior OER activity compared to the CoTe catalyst, which is comparable to the state-of-the-art RuO2 catalyst. Density functional theory calculations showed that the binding strength and lateral interaction of the reaction intermediates on CoTe2 and CoTe are essential for determining the overpotential required under different conditions. This study provides valuable insights for the rational design of noble-metal-free OER catalysts with high performance and low cost by use of Co-based chalcogenides.