Nitrogen and Oxygen Co-Doped Porous Hard Carbon Nanospheres with Core-Shell Architecture as Anode Materials for Superior Potassium-Ion Storage.

The investigation of carbonaceous-based anode materials will promote the fast application of low-cost potassium-ion batteries (PIBs). Here a nitrogen and oxygen co-doped yolk-shell carbon sphere (NO-YS-CS) is constructed as anode material for K-ion storage. The novel architecture, featuring with developed porous structure and high surface specific area, is beneficial to achieving excellent electrochemical kinetics behavior and great electrode stability from buffering the large volume expansion. Furthermore, the N/O heteroatoms co-doping can not only boost the adsorption and intercalation ability of K-ion but also increase the electron transfer capability. It is also demonstrated by experimental results and DFT calculations that K-ion insertion/extraction proceeds through both intercalation and surface capacitive adsorption mechanisms. As expected, the NO-YS-CS electrodes show high initial charge capacity of 473.7 mAh g-1 at 20 mA g-1 , ultralong cycling life over 2500 cycles with the retention of 85.8% at 500 mA g-1 , and superior rate performance (183.3 mAh g-1 at 1.0 A g-1 ). The K-ion full cell, with a high energy density of 271.4 Wh kg-1 and an excellent cyclic stability over 500 cycles, is successfully fabricated with K2 Fe[Fe(CN)6 ] cathode. This work will provide new insight on the synthesis and mechanism understanding of high-performance hard carbon anode for PIBs.

Electrochemical Exfoliation of Two-Dimensional Phosphorene Sheets and its Energy Application.

Recently, single or few-layer phosphorene has attracted intense attention due to its exceptional physicochemical properties. To this end, mass production of high-quality phosphorene nanosheets with specific functionalities represents a pivotal factor for the basic academic studies and practical applications. Among the current synthetic methods, electrochemical exfoliation of black phosphorous is one of the most hopeful ways for mass-production of phosphorene sheets owing to the uncomplicated apparatus, low cost as well as significant efficiency. Especially, regulating the electrochemical parameters not only induces adjustable phosphorene characteristics but also enables them a promising candidate in energy applications. In this Review, a concise and crucial studies of the recent and most representative developments in this domain was introduced, including the relationship between exfoliation philosophy, internal mechanisms, processing techniques, and multiple applications of phosphorene. At the end, a summary discussion and future perspectives is also provided.

Stabilizing a Lithium Metal Battery by an In Situ Li2S-modified Interfacial Layer via Amorphous-Sulfide Composite Solid Electrolyte.

A novel strategy has been proposed to produce in situ Li2S at the interfacial layer between lithium anode and the solid electrolyte, by using an amorphous-sulfide-LiTFSI-poly(vinylidene difluoride) (PVDF) composite solid electrolyte (SLCSE). Besides retarding the decomposition of PVDF in CSE, the Li2S-modified interfacial layer (SMIL) also improves the wettability between lithium metal and SLCSE which in turn optimizes the lithium deposition process. Our density functional theory calculation results reveal that the migration energy barrier of Li passing through SMIL is much lower than that of Li passing through LiF-modified interfacial layer (FMIL) formed from the decomposition of PVDF. The as-prepared SLCSE shows a Li ionic transference number of 0.44 and Li ion conductivity of 3.42 × 10-4 S/cm at room temperature, and the Li||SLCSE||LiFePO4 cell exhibits an outstanding rate performance with a capacity of 153, 144, 131, and 101 mAh/g at a current density of 0.05, 0.10, 0.25, and 0.50 mA/cm2, respectively.

Confinement of Pt NPs by hollow-porous-carbon-spheres via pore regulation with promoted activity and durability in the hydrogen evolution reaction.

Electrochemical water splitting is a promising method to generate pollution-free and sustainable hydrogen energy. However, the specific activity and durability of noble metal catalysts is the main hindrance to the hydrogen evolution reaction. Based on the continuous pore regulation of hollow porous carbon spheres (N-HPCSs) by hexadecyl trimethyl ammonium bromide, the 6.21 wt% Pt/N-HPCSs exhibited good dispersibility, according to a low overpotential of 45 mV (10 mA cm-2/1 M KOH). Its mass activity was 4 times that of the commercial 20 wt% Pt/C at -0.07 V (vs. RHE) potential. We analyse that the excellent activity is due to the interaction between Pt nanoparticles and N-HPCSs so that the electron density around the Pt atoms increases, which is beneficial for H2O to obtain electrons and transform into Had. Meanwhile the sea urchin-like structure of N-HPCSs facilitates the desorption of H2. Furthermore, the overpotential showed no obvious decrease in the long-term durability test, which should be attributed to the confinement of Pt nanoparticles by the well-defined pores in N-HPCSs to avoid the aggregation of Pt nanoparticles during long-term testing.

Expanded MoSe2 Nanosheets Vertically Bonded on Reduced Graphene Oxide for Sodium and Potassium-Ion Storage.

The cost-efficient and plentiful Na and K resources motivate the research on ideal electrodes for sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs). Here, MoSe2 nanosheets perpendicularly anchored on reduced graphene oxide (rGO) are studied as an electrode for SIBs and PIBs. Not only does the graphene network serves as a nucleation substrate for suppressing the agglomeration of MoSe2 nanosheets to eliminate the electrode fracture but also facilitates the electrochemical kinetics process and provides a buffer zone to tolerate the large strain. An expanded interplanar spacing of 7.9 Å is conducive to fast alkaline ion diffusion, and the formed chemical bondings (C-Mo and C-O-Mo) promote the structure integrity and the charge transfer kinetics. Consequently, MoSe2@5%rGO exhibits a reversible specific capacity of 458.3 mAh·g-1 at 100 mA·g-1, great cyclability with a retention of 383.6 mAh·g-1 over 50 cycles, and excellent rate capability (251.3 mAh·g-1 at 5 A·g-1) for SIBs. For PIBs, a high first specific capacity of 365.5 mAh·g-1 at 100 mA·g-1 with a low capacity fading of 51.5 mAh·g-1 upon 50 cycles and satisfactory rate property are acquired for MoSe2@10%rGO composite. Ex situ measurements validate that the discharge products are Na2Se for SIBs and K5Se3 for PIBs, and robust chemical bonds boost the structure stability for Na- and K-ion storage. The full batteries are successfully fabricated to verify the practical feasibility of MoSe2@5%rGO composite.

Fe-Mn bimetallic oxides-catalyzed oxygen reduction reaction in alkaline direct methanol fuel cells.

Two Fe-Mn bimetallic oxides were synthesized through a facile solvothermal method without using any templates. Fe2O3/Mn2O3 is made up of Fe2O3 and Mn2O3 as confirmed via XRD. TEM and HRTEM observations show Fe2O3 nanoparticles uniformly dispersed on the Mn2O3 substrate and a distinct heterojunction boundary between Fe2O3 nanoparticles and Mn2O3 substrate. MnFe2O4 as a pure phase sample was also prepared and investigated in this study. The current densities in CV tests were normalized to their corresponding surface area to exclude the effect of their specific surface area. Direct methanol fuel cells (DMFCs) were equipped with bimetallic oxides as cathode catalyst, PtRu/C as the anode catalyst and PFM as the electrolyte film. CV and DMFC tests show that Fe2O3/Mn2O3(3 : 1) exhibits higher oxygen reduction reaction (ORR) activity than Fe2O3/Mn2O3(1 : 1), Fe2O3/Mn2O3(1 : 3), Fe2O3/Mn2O3(5 : 1) and MnFe2O4. The much superior catalytic performance is due to its larger surface area, the existence of numerous heterojunction interfaces and the synergistic effect between Fe2O3 and Mn2O3, which can provide numerous catalytic active sites, accelerate mass transfer, and increase ORR efficiency.

Quasi-zero-dimensional cobalt-doped CeO2 dots on Pd catalysts for alcohol electro-oxidation with enhanced poisoning-tolerance.

Deactivation of an anode catalyst resulting from the poisoning of COad-like intermediates is one of the major problems for methanol and ethanol electro-oxidation reactions (MOR & EOR), and remains a grand challenge towards achieving high performance for direct alcohol fuel cells (DAFCs). Herein, we report a new approach for the preparation of ultrafine cobalt-doped CeO2 dots (Co-CeO2, d = 3.6 nm), which can be an effective anti-poisoning promoter for Pd catalysts towards MOR and EOR in alkaline media. Compared to Pd/CeO2 and pure Pd, the hybrid Pd/Co-CeO2 nanocomposite catalyst exhibited a much enhanced activity and remarkable anti-poisoning ability for both MOR and EOR. The nanocomposite catalyst showed much higher mass activity (4×) than a state-of-the-art PtRu catalyst. The promotional mechanism was elucidated using extensive characterization and density-functional theory (DFT). A bifunctional effect of the Co-CeO2 dots was discovered to be due to (i) an enhanced electronic interaction between Co-CeO2 and Pd dots and (ii) the increased oxygen storage capacity of Co-CeO2 dots to facilitate the oxidation of COad. Therefore, the Pd/Co-CeO2 nanocomposite appears to be a promising catalyst for advanced DAFCs with low cost and high performance.