Two-stage confinement derived small-sized highly ordered L10-PtCoZn for effective oxygen reduction catalysis in PEM fuel cells.

Intermetallic ordered PtCo is effective for high oxygen reduction reaction (ORR) activity and stability. However, preparing small-sized, highly ordered PtM alloys is still challenging. Herein, we report a controlled two-stage confinement strategy, in which highly ordered PtCoZn/NC nanoparticles of 5.3 nm size were prepared in a scalable process. The contradiction between the high ordering degree with the small particle size as well as the atomic migration with the space confinement was well resolved. An outstanding PEMFC performance was achieved for L10-PtCoZn/NC with a high mass activity (MA) of 1.21 A/mgPt at 0.9 ViR-free, 80.1 % MA retention after 30 k cycles in H2-O2 operation, and a high mass-specific power density of 8.24 W mg-1Pt in H2-Air operation with a slight loss of cell voltage@0.8 A cm-2 of 28 mV after 30 k cycles. The high performance can be ascribed to the high Pt area exposure, the enhanced Pt-Co coupling, and the prevented agglomeration in the mesoporous carbon wall. Overall, this strategy may contribute to the commercialization of fuel cells.

Operando spectroscopies capturing surface reconstruction and interfacial electronic regulation by FeOOH@Fe2O3@Ni(OH)2 heterostructures for robust oxygen evolution reaction.

Developing high-performance and low-cost electrocatalysts for oxygen evolution reaction (OER) and understanding the phase evolution in the catalytic process are vital to improving the overall efficiency of electrochemical water splitting. Herein, a hybrid heterogeneous FeOOH@Fe2O3@Ni(OH)2 electrocatalyst with robust OER intrinsic activity and a low overpotential of 269 mV to obtain a current density of 100 mA cm-2 and a Tafel slope value of 60.15 mV dec-1 is effectively prepared. The dynamic surface evolution has been detected by in-situ Raman spectroscopy, which exposes that FeOOH@Fe2O3@Ni(OH)2 is reconstituted as Ni(Fe)OOH demonstrated as catalytically active species under high potential. X-ray photoelectron spectroscopy analysis indicates that partial electrons of Ni in the heterogeneous interface transfer to Fe. Furthermore, partial Fe doping of NiOOH under high potential accompanied by the oxidized Ni3+ with optimized d-orbit electronic configuration for nearly unity eg occupancy results in proper chemisorption bonding strength for oxygen reaction intermediates and is conducive to enhancing OER reaction kinetics. This work provides ideas that multicomponent heterostructure can adjust the electronic structure of iron and nickel to enhance the intrinsic activity of OER, which could help with the design and synthesis of high-performance OER catalysts used in energy storage and conversion.

Mesoporous hierarchical NiCoSe2-NiO composite self-supported on carbon nanoarrays as synergistic electrocatalyst for flexible lithium-sulfur batteries.

Lithium-sulfur batteries (LSBs) have enormous application potential in the flexible energy storage field due to their large theoretical specific capacities and high energy densities. However, lithium-sulfur batteries face a notorious shuttle effect problem. To address this challenge, this work reports a three-dimensional (3D) structure of binary transition metal selenides (B-TMSe) hierarchical composites (CC/NiCoSe2-NiO) on carbon cloth as a self-supporting sulfur host for flexible LSBs. According to the density functional theory (DFT) calculations, NiCoSe2can exert a synergetic effect of high affinity with Lithium polysulfides (LiPSs) and electrocatalytic activity to lower the adsorption energy barrier and accelerate the sluggish reaction kinetics of polysulfides. Consequently, the CC/NiCoSe2-NiO-based electrodes realize a large specific capacity of approximately 1363 mAh/g at a current density of 0.1C, excellent rate performance (454.66 mAh/g at 5C) and a reversible specific capacity of 978.9 mAh/g at 1C, along with impressive cycling stability with an attenuation rate of 0.038% per cycle for 1000 cycles. They also achieve a large reversible cycle capacity of 919.43 mAh/g at 0.2C even at a high sulfur loading (3.5 mg/cm2). With a lean electrolyte (E/S ratio 10 µL/mg) and a high sulfur loading of 2.65 mg/cm2, a large capacity of 934.1 mAh/g is retained after 150 cycles at 0.5C. The assembled pouch cells from S@CC/NiCoSe2-NiO electrodes show a high initial discharge capacity of 1039.5 mAh/g at 1C at a sulfur loading of 2.65 mg/cm2 and maintain strong stability under high twisting and buckling.

Role of the heterojunctions in In2O3-composite SnO2 nanorod sensors and their remarkable gas-sensing performance for NO(x) at room temperature.

Establishing heterostructures, as a good strategy to improve gas sensing performance, has been studied extensively. In this research, In2O3-composite SnO2 nanorod (ICTOs) heterostructures have been prepared via electrospinning, followed by calcination. It is found that In2O3 can improve the carrier density and oxygen deficiency of SnO2. In particular, the 3ICTO (Sn : In atom ratio of 25 : 0.3) nanorods with special particle distributions show an excellent sensing response towards different concentrations of NOx at room temperature. The highest sensing response is up to 8.98 for 100 ppm NOx with a fast response time of 4.67 s, which is over 11 times higher than that of pristine SnO2 nanorods at room temperature and the lowest detection limit is down to 0.1 ppm. More significantly, it presents good stability after 30 days for NOx of low concentration (0.1 ppm and 0.5 ppm). In addition, the rational band structure model combined with the surface depletion model which describe the NOx gas sensing mechanism of 3ICTO are presented. The 3ICTO nanorods may be promising in the application of gas sensors.

Comparative investigation of the performances of hematite nanoplates and nanograins in lithium-ion batteries.

In this work, we selectively prepared two samples with quite different nanocrystal shapes, i.e. nanoplates and nanograins but with almost identical surface areas to make a clear comparison of nanocrystal shapes on electrochemical performance. The electrochemical results indicate that the thinner hexagonal α-Fe2O3 nanoplates considerably enclosed by two larger (0001) basal surfaces exhibit higher capacity and stability than thicker α-Fe2O3 nanograins enclosed by a variety of crystal facets. During the conversion reaction, an orientated growth of porous nanostructure with orientated nanowalls as a stable framework is observed for the nanoplate, readily supplying a pathway for long and easy lithiation-delithiation cycling. The improved electrochemical performance of α-Fe2O3 nanoplates is surely related to the nanostructure with significantly stacked (0001) lattice planes along [0001] direction for orientated growth of γ-Fe2O3 nanodomains along one [111] direction.

Small-sized and contacting Pt-WC nanostructures on graphene as highly efficient anode catalysts for direct methanol fuel cells.

The synergistic effect between Pt and WC is beneficial for methanol electro-oxidation, and makes Pt-WC catalyst a promising anode candidate for the direct methanol fuel cell. This paper reports on the design and synthesis of small-sized and contacting Pt-WC nanostructures on graphene that bring the synergistic effect into full play. Firstly, DFT calculations show the existence of a strong covalent interaction between WC and graphene, which suggests great potential for anchoring WC on graphene with formation of small-sized, well-dispersed WC particles. The calculations also reveal that, when Pt attaches to the pre-existing WC/graphene hybrid, Pt particles preferentially grow on WC rather than graphene. Our experiments confirmed that highly disperse WC nanoparticles (ca. 5 nm) can indeed be anchored on graphene. Also, Pt particles 2-3 nm in size are well dispersed on WC/graphene hybrid and preferentially grow on WC grains, forming contacting Pt-WC nanostructures. These results are consistent with the theoretical findings. X-ray absorption fine structure spectroscopy further confirms the intimate contact between Pt and WC, and demonstrates that the presence of WC can facilitate the crystallinity of Pt particles. This new Pt-WC/graphene catalyst exhibits a high catalytic efficiency toward methanol oxidation, with a mass activity 1.98 and 4.52 times those of commercial PtRu/C and Pt/C catalysts, respectively.

Enhanced dispersion and durability of Pt nanoparticles on a thiolated CNT support.

High dispersion Pt nanoparticles supported on surface thiolation functional carbon nanotubes (SH-CNTs) is presented and electrochemical measurements confirm that the Pt/SH-CNTs catalyst shows good durability and excellent ORR activity.

Carbon-in-Al4C3 nanowire superstructures for field emitters.

As a kind of ionic (or salt-like) carbide, for Al(4)C(3), hardly any active functions have been found except for structure material purposes. However, considering the unique characteristic features of its crystal structure, we think Al(4)C(3) in fact might have huge potential for exhibiting active functionality on field-emission applications. Herein, we report the feasibility to approach such emitters by creating Al(4)C(3)-based nanowire superstructures. The conductive amorphous carbon (a-C) nanolayers are embedded quasi-periodically in Al(4)C(3) nanowire and generate essential electrical contact to the insulating Al(4)C(3). The superstructures acting as cold electron emitters display excellent field emission performance with the turn-on field as low as 0.65-1.3 V/µm and the threshold field down to 2.1-2.6 V/µm. We speculate that the emission characteristics, which are ever better than carbon nanotubes, are attributed to the unique crystal structure of Al(4)C(3) and the enhanced electrons transport in the nanowires due to the existence of a-C nanolayers. Such emitters are technologically useful, because they can be easily fabricated on large substrates, and the synthesis process is simple and broadly applicable. The findings conceptually provide new opportunities for the application of Al(4)C(3) ceramic material in vacuum microelectronic devices.

Hierarchical hollow Co9S8 microspheres: solvothermal synthesis, magnetic, electrochemical, and electrocatalytic properties.

A simple solvothermal route in a binary solution of triethylenetetramine (TETA) and deionized water (DIW) has been used to synthesize hierarchical hollow Co(9)S(8) microspheres with high surface area (80.38 m(2) g(-1)). An appropriate volume ratio of TETA:DIW has been found to be essential for the formation of hollow Co(9)S(8) microspheres. The magnetic study indicated that the Co(9)S(8) hollow microspheres are paramagnetic at high temperature and antiferromagnetic at low temperature. The oxygen reduction reaction experiments demonstrated that the onset potential of the Co(9)S(8) sample is 0.88 V, which is comparable to the value predicted for Co(9)S(8) (0.74 V) from the theoretical simulation. The discharge capability of Co(9)S(8) hollow microspheres as cathode materials for lithium ion batteries and their electrocatalytic activity for the oxygen reduction reaction (ORR) have been studied.