Huixiang Ang

Ultrathin S-doped MoSe2 nanosheets for efficient hydrogen evolution

We report the synthesis of ultrathin S-doped MoSe2 nanosheets demonstrating enhanced HER catalysis with a low onset overpotential of 90 mV and a Tafel slope of 58 mV per decade. We attribute the improved catalytic effects to the proliferation of unsaturated HER active sites in MoSe2 resulting from S-doping.

Binder-free graphene foams for O2 electrodes of Li-O2 batteries.

We report a novel method to prepare bind-free graphene foams as O2 electrodes for Li-O2 batteries. The graphene foams are synthesized by electrochemical leavening of the graphite papers, followed by annealing in inert gas to control the amount of structural defects in the graphene foams. It was found that the structural defects were detrimental to the processes of the ORR and OER in Li-O2 batteries. The round-trip efficiencies and the cycling stabilities of the graphene foams were undermined by the structural defects. For example, the as-prepared graphene foam with a high defect level (ID/IG = 0.71) depicted a round-trip efficiency of only 0.51 and a 20(th)-cycle discharge capacity of only 340 mA h g(-1) at a current density of 100 mA g(-1). By contrast, the graphene foam electrode annealed at 800 °C with ID/IG = 0.07 delivered a round-trip efficiency of up to 80% with a stable discharge voltage at ~2.8 V and a stable charge voltage below 3.8 V for 20 cycles. According to the analysis on the electrodes after 20 cycles, the structural defects led to the quickened decay of the graphene foams and boosted the formation of side products.

Hydrophilic Nitrogen and Sulfur Co‐doped Molybdenum Carbide Nanosheets for Electrochemical Hydrogen Evolution

Nitrogen and sulfur dual-doped Mo2 C nanosheets provide low operating potential (-86 mV for driving 10 mA cm(-2) of current density). Co-doping of N and S heteroatoms can improve the wetting property of the Mo2C electrocatalyst in aqueous solution and induce synergistic effects via σ-donation and π-back donation with hydronium cation.

3D Hierarchical Porous Mo2C for Efficient Hydrogen Evolution

Porous electrocatalyst for hydrogen production. 3D hierarchical porous molybdenum carbide provides a low operating potential (97 mV at 10 mA cm(-2) ). These beneficial textures of large specific surface area (302 m(2) g(-1) ) and hierarchical porous architecture containing dominant pore size distribution peak at 11 Å in width can provide large surface active sites and facilitate proton mass transport.

Compressed hydrogen gas-induced synthesis of Au–Pt core–shell nanoparticle chains towards high-performance catalysts for Li–O2 batteries

Herein we reported a green synthetic route for the preparation of Au–Pt core–shell nanoparticle chains in a two-step route without the use of any surfactants. In the synthesis, compressed hydrogen was used as a reducing reagent, which also promoted the assembly of particle chains. The as-prepared monodispersed gold nanoparticles were manipulated by dipoles to form chain-like nanostructures under high pressure; meanwhile, in situ epitaxial growth of Pt shell on gold nanochains occurred, leading to the formation of Au–Pt core–shell nanoparticle chains. The resulting bimetallic Au–Pt core–shell chains showed excellent catalytic activity as cathodes in lithium oxygen batteries with a low charge–discharge over potential and outstanding cycle performance because of its clean catalytic surface, interconnected nanostructure, which provided a good electron path and innate synergistic effect.

Boundary element analysis of orthotropic delamination specimens with interface cracks

Abstract The boundary element method (BEM) with special crack-tip elements is used to obtain the stress intensity factors, K1 and K2, and the strain energy release rates of interface cracks in bilayer double cantilever beam (DCB) and end-loaded-split (ELS) specimens. The material system considered is one in which an orthotropic, transversely isotropic layer is bonded to another layer of equal thickness and made of the same material, but the latter being in the plane of transverse isotropy. The effects of the mechanical properties of the orthotropic material are characterized by the parameters, η1 and η2, which correspond to the purely imaginary roots of the characteristic equation for the material. Calibration results showing the variations of the normalized strain energy release rates with the geometry of the specimens are presented for a range of values of these material parameters. They show the same qualitative trends as for a completely homogeneous beam specimen. To provide a complete characterization of the near-tip fields of the interface crack, the phase angle ψ = tan−1 (K2/K1), which denotes the degree of the mode mixity there, is also obtained for each case. The results show that ψ generally attains a constant value when the ratio of the crack length to the layer thickness reaches a value of less than eight.

Platinum and Palladium Nanotubes Based on Genetically Engineered Elastin–Mimetic Fusion Protein-Fiber Templates: Synthesis and Application in Lithium-O2 Batteries

The coupling of proteins with self-assembly properties and proteins that are capable of recognizing and mineralizing specific inorganic species is a promising strategy for the synthesis of nanoscale materials with controllable morphology and functionality. Herein, GPG-AG3 protein fibers with both of these properties were constructed and served as templates for the synthesis of Pt and Pd nanotubes. The protein fibers of assembled GPG-AG3 were more than 10 μm long and had diameters of 20-50 nm. The as-synthesized Pt and Pd nanotubes were composed of dense layers of ~3-5 nm Pt and Pd nanoparticles. When tested as cathodes in lithium-O2 batteries, the porous Pt nanotubes showed low charge potentials of 3.8 V, with round-trip efficiencies of about 65% at a current density of 100 mA g(-1).

Fe-based metallopolymer nanowall-based composites for Li-O2 battery cathode

Metallopolymer nanowalls were prepared through a simple wet-chemical process using reduced graphene oxides as heterogeneous nucleation aids, which also help to form conductive electron paths. The nanowalls grow vertically on graphene surface with 100-200 nm in widths and ∼20 nm in thickness. The Fe-based metallopolymer nanowall-based electrode shows best performance as O2 cathode exhibiting high round-trip efficiencies and stable cycling performance among other transition metal containing metallopolymer counterparts. The electrode delivers discharge-charge capacities of 1000 mAh/g for 40 cycles and maintains round-trip efficiencies >78% at 50 mA/g. The 1(st)-cycle round-trip efficiencies are 79%, 72%, and 65% at current densities of 50, 200, and 400 mA/g, respectively. The NMR analysis of the Fe-based metallopolymer based electrode after 40 cycles reveals slow formation of the side products, CH3CO2Li and HCO2Li.

Using elastin protein to develop highly efficient air cathodes for lithium-O2 batteries

Transition metal-nitrogen/carbon (M-N/C, M = Fe, Co) catalysts are synthesized using environmentally friendly histidine-tag-rich elastin protein beads, metal sulfate and water soluble carbon nanotubes followed by post-annealing and acid leaching processes. The obtained catalysts are used as cathode materials in lithium-O2 batteries. It has been discovered that during discharge, Li2O2 nanoparticles first nucleate and grow around the bead-decorated CNT regions (M-N/C centres) and coat on the catalysts at a high degree of discharge. The Fe-N/C catalyst-based cathodes deliver a capacity of 12,441 mAh g(-1) at a current density of 100 mA g(-1). When they were cycled at a limited capacity of 800 mAh g(-1) at current densities of 200 or 400 mA g(-1), these cathodes showed stable charge voltages of ∼3.65 or 3.90 V, corresponding to energy efficiencies of ∼71.2 or 65.1%, respectively. These results are considerably superior to those of the cathodes based on bare annealed CNTs, which prove that the Fe-N/C catalysts developed here are promising for use in non-aqueous lithium-O2 battery cathodes.

Strain energy release rates of interface cracks in orthotropic layered beams

We present the results of a numerical (BEM) fracture mechanics analysis of orthotropic tri-layer beams with an interface crack and subjected to the loads as in DCB and ELS specimen set-ups