Ultrathin single-crystal PtSe2 nanosheets for high-efficiency O2 electroreduction to H2O2.

Electrochemical synthesis of H2O2via a two-electron oxygen reduction reaction (2e- ORR) has emerged as a promising alternative to the anthraquinone process. However, the strong competition from the 4e- pathway severely limits its activity and selectivity, especially for Pt-based catalysts. Herein, ultrathin single-crystal PtSe2 nanosheets were successfully prepared via an in situ selenization process using commercial Pt/C as a precursor, demonstrating an exclusive 2e- ORR pathway compared to the 4e- pathway of commercial Pt/C, delivering a high H2O2 selectivity over a wide pH range (>80%, up to 94.1%). Furthermore, in situ infrared spectroscopy results revealed Pt as an active center, accompanied by the key intermediate OOH* adsorption and HOOH formation.

Electrocatalytic two-electron oxygen reduction over nitrogen doped hollow carbon nanospheres.

The two-electron oxygen reduction reaction (2e- ORR) has become a hopeful alternative for production of hydrogen peroxide (H2O2), but its practical feasibility is hindered by the lack of efficient electrocatalysts to achieve high activity and selectivity. Herein, we successfully synthesized outstanding nitrogen doped hollow carbon nanospheres (NHCSs) for electrochemical production of H2O2. In 0.1 M KOH, NHCSs exhibit superior and sustained catalytic activity for the 2e- ORR with an unordinary selectivity of 96.6%. Impressively, such NHCSs manifest an ultrahigh H2O2 yield rate of 7.32 mol gcat.-1 h-1 and a high faradaic efficiency of 96.7% at 0.5 V in an H-cell system. Density functional theory calculations were performed to further reveal the catalytic mechanism involved.

Enhanced electrocatalytic performance of TiO2 nanoparticles by Pd doping toward ammonia synthesis under ambient conditions.

The traditional Haber-Bosch process in industry to produce NH3 leads to excessive CO2 emissions and a large amount of energy consumption. Ambient electrochemical N2 reduction is emerging as a green and sustainable alternative method to convert N2 to NH3, but is in sore need of efficient and stable electrocatalysts. Herein, we propose using Pd-doped TiO2 nanoparticles as a high-efficiency electrocatalyst to synthesize NH3 under ambient conditions. The Pd-TiO2 catalyst delivers a large NH3 yield (17.4 µg h-1 mgcat.-1) and a high faradaic efficiency (12.7%) at -0.50 V versus reversible hydrogen electrode in a neutral electrolyte, outperforming most Pd- and Ti-based electrocatalysts recently reported for N2 reduction. Most importantly, it also demonstrates extraordinary long-term electrochemical stability.

ZnO/CoS heterostructured nanoflake arrays vertically grown on Ni foam for high-rate supercapacitors.

Self-supported materials have been widely used in high-power energy storage devices due to the unique construction offering fast charge transfer from the active material to the conducting substrate. However, the electron conduction in the active material presents limitations on the overall performance of the electrode. In this work, we have fabricated hierarchical ZnO nanoflake arrays vertically grown on a nickel foam substrate and wrapped tightly by wrinkled porous CoS nanofilms (ZnO NFAs/CoS NFs) via a hydrothermal process and subsequent electrodeposition. Such an optimized ZnO NFAs/CoS NFs electrode exhibits an excellent specific capacitance of 1416 F g-1 at a current density of 1 A g-1, and remarkable cycling stability with 85.3% retention of the initial capacitance at 10 A g-1 after 5000 cycles. Additionally, density functional theory (DFT) calculations have been performed to further investigate the mechanism, proving the facilitated electron transfer from CoS to ZnO, giving rise to the superior electrochemical performance.

Ti2O3 Nanoparticles with Ti3+ Sites toward Efficient NH3 Electrosynthesis under Ambient Conditions.

Electrocatalytic nitrogen reduction reaction (NRR) enabled by introducing Ti3+ defect sites into TiO2 through a doping strategy has recently attracted widespread attention. However, the amount of Ti3+ ions is limited due to the low concentration of dopants. Herein, we propose Ti2O3 nanoparticles as a pure Ti3+ system that performs efficiently toward NH3 electrosynthesis under ambient conditions. This work has suggested that Ti3+ ions, as the main catalytically active sites, significantly increase the NRR activity. In an acidic electrolyte, Ti2O3 achieves extraordinary performance with a high NH3 yield and a Faradaic efficiency of 26.01 µg h-1 mg-1 cat. and 9.16%, respectively, which are superior to most titanium-based NRR catalysts recently reported. Significantly, it also demonstrates a stable NH3 yield in five consecutive cycles. Theoretical calculations uncovered that the enhanced electrocatalytic activity of Ti2O3 originated from Ti3+ active sites and significantly lowered the overpotential of the potential-determining step.

Enhanced Electrochemical H2O2 Production via Two-Electron Oxygen Reduction Enabled by Surface-Derived Amorphous Oxygen-Deficient TiO2-x.

The electrochemical oxygen reduction reaction (ORR) is regarded as an attractive alternative to the anthraquinone process for sustainable and on-site hydrogen peroxide (H2O2) production. It is however hindered by low selectivity due to strong competition from the four-electron ORR and needs efficient catalysts to drive the 2e- ORR. Here, an acid oxidation strategy is proposed as an effective strategy to boost the 2e- ORR activity of metallic TiC via in-site generation of a surface amorphous oxygen-deficient TiO2-x layer. The resulting a-TiO2-x/TiC exhibits a low overpotential and high H2O2 selectivity (94.1% at 0.5 V vs reversible hydrogen electrode (RHE)), and it also demonstrates robust stability with a remarkable productivity of 7.19 mol gcat.-1 h-1 at 0.30 V vs RHE. The electrocatalytic mechanism of a-TiO2-x/TiC is further revealed by density functional theory calculations.

Preparation and characterization of flexible lithium iron phosphate/graphene/cellulose electrode for lithium ion batteries.

In this work, a free-standing flexible composite electrode was prepared by vacuum filtration method with LiFePO4, graphene and nanofibrillated cellulose (NFC). Compared with the pure LiFePO4 electrode, the resulting flexible composite (LiFePO4/graphene/NFC) electrode showed excellent mechanical flexibility, and possessed an enhanced initial discharge capacity of 151 mA h/g (0.1 C) and a good capacity retention rate with only 5% loss after 60 cycles due to suitable electrolyte wettability at the interface. Furthermore, the NFC and graphene formed a three-dimensional conductive framework, which provided high-speed electron conduction in the composite and reduced electrode polarization during charging-discharging processes. Moreover, the composite electrode could endure bending tests up to 1000 times, highlighting preferable mechanical strength and durability. These results demonstrated that the as-fabricated electrodes could be applied as flexible electrodes with an embedded power supply.

Easily fabricated and lightweight PPy/PDA/AgNW composites for excellent electromagnetic interference shielding.

Conductive polymer composites (CPCs) containing nanoscale conductive fillers have been widely studied for their potential use in various applications. In this paper, polypyrrole (PPy)/polydopamine (PDA)/silver nanowire (AgNW) composites with high electromagnetic interference (EMI) shielding performance, good adhesion ability and light weight are successfully fabricated via a simple in situ polymerization method followed by a mixture process. Benefiting from the intrinsic adhesion properties of PDA, the adhesion ability and mechanical properties of the PPy/PDA/AgNW composites are significantly improved. The incorporation of AgNWs endows the functionalized PPy with tunable electrical conductivity and enhanced EMI shielding effectiveness (SE). By adjusting the AgNW loading degree in the PPy/PDA/AgNW composites from 0 to 50 wt%, the electrical conductivity of the composites greatly increases from 0.01 to 1206.72 S cm-1, and the EMI SE of the composites changes from 6.5 to 48.4 dB accordingly (8.0-12.0 GHz, X-band). Moreover, due to the extremely low density of PPy, the PPy/PDA/AgNW (20 wt%) composites show a superior light weight of 0.28 g cm-3. In general, it can be concluded that the PPy/PDA/AgNW composites with tunable electrical conductivity, good adhesion properties and light weight can be used as excellent EMI shielding materials.

Paper-Based Inkjet-Printed Flexible Electronic Circuits.

Printed flexible electronics have been widely studied for their potential use in various applications. In this paper, a simple, low-cost method of fabricating flexible electronic circuits with high conductivity of 4.0 × 107 S·m-1 (about 70% of the conductivity of bulk copper) is demonstrated. Teslin paper substrate is treated with stannous chloride (SnCl2) colloidal solution to reduce the high ink absorption rate, and then the catalyst ink is inkjet-printed on its surface, followed by electroless deposition of copper at low temperature. In spite of the decrease in conductance to some extent, electronic circuits fabricated by this method can maintain function even under various folding angles or after repeated folding. This developed technology has great potential in a variety of applications, such as three-dimensional devices and disposable RFID tags.

Defect effects on the physical and electrochemical properties of nanoscale LiFe0.92PO4 and LiFe0.92PO4/C/graphene composites.

Nanoscale LiFe0.92PO4 and LiFe0.92PO4/C/graphene composites including defects as performance-improved cathode materials for lithium-ion batteries were prepared by a carbothermal reduction method. The physical and electrochemical properties of samples were characterized by means of X-ray diffraction, inductively coupled plasma optical emission spectrometry, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and electrochemical testing techniques. The results confirmed that defects existed within the nanoscale LiFe0.92PO4 lattice and had significant effects on improving the electrochemical properties of samples. The excellent graphene sheets covered on nanoparticles and formed a three-dimensional conductive network in nanoscale LiFe0.92PO4/C/graphene composites. The composites exhibited a discharge capacity of 90 mA h g(-1) at 10 C and capacity retention ratios of 98% after 100 cycles at various rates, implying outstanding high-rate capability and cycling stability.