Core-shell particles of C-doped CdS and graphene: A noble metal-free approach for efficient photocatalytic H_(2) generation

To achieve efficient photocatalytic H_(2) generation from water using earth-abundant and cost-effective materials,a simple synthesis method for carbon-doped CdS particles wrapped with graphene(C-doped CdS@G)is reported.The doping effect and the application of graphene as cocatalyst for CdS is studied for photocatalytic H_(2) generation.The most active sample consists of CdS and graphene(CdS-0.15G)exhibits promising photocatalytic activity,producing 3.12 mmol g^-(1) h^-(1) of H_(2) under simulated solar light which is^4.6 times superior than pure CdS nanoparticles giving an apparent quantum efficiency(AQY)of 11.7%.The enhanced photocatalytic activity for H_(2) generation is associated to the narrowing of the bandgap,enhanced light absorption,fast interfacial charge transfer,and higher carrier density(N_(D))in C-doped CdS@G samples.This is achieved by C doping in CdS nanoparticles and the formation of a graphene shell over the C-doped CdS nanoparticles.After stability test,the spent catalysts sample was also characterized to investigate the nanostructure.

Morphology and Crystallinity-controlled Synthesis of Manganese Cobalt Oxide/Manganese Dioxides Hierarchical Nanostructures for High-Performance Supercapacitors

We demonstrate a novel preparative strategy for the well-controlled MnCo_2O_(4.5)@MnO_2 hierarchical nanostructures.Bothδ-MnO_2 nanosheets andα-MnO_2 nanorods can uniformly decorate the surface of MnCo_2O_(4.5)nanowires to form core-shell heterostructures.Detailed electrochemical characterization reveals that MnCo_2O_(4.5)@δ-MnO_2 pattern exhibits not only high specific capacitance of 357.5 F g^(-1)at a scan rate of 0.5 A g^(-1),but also good cycle stability(97%capacitance retention after 1000 cycles at a scan rate of 5 A g^(-1)),which make it have a promising application as a supercapacitor electrode material.

Unraveling the Role of Nitrogen-Doped Carbon Nanowires Incorporated with MnO_(2)Nanosheets as High Performance Cathode for Zinc-Ion Batteries

Manganese-based cathode materials are considered as a promising candidate for rechargeable aqueous zinc-ion batteries(ZIBs).Suffering from poor conductive and limited structure tolerance,various carbon matrix,especially N-doped carbon,were employed to incorporate with MnO_(2)for greatly promoted electrochemical performances.However,the related underlying mechanism is still unknown,which is unfavorable to guide the design of high performance electrode.Herein,by incorporating layered MnO_(2)with N-doped carbon nanowires,a free-standing cathode with hierarchical core-shell structure(denoted as MnO_(2)@NC)is prepared.Benefiting from the N-doped carbon and rational architecture,the MnO_(2)@NC electrode shows an enhanced specific capacity(325 mAh g^(−1)at 0.1 A g^(−1))and rate performance(90 mAh g^(−1)at 2 A g^(−1)),as well as improved cycling stability.Furthermore,the performance improvement mechanism of MnO_(2)incorporated by N-doped carbon is investigated by X-ray photoelectron spectroscopy(XPS),Raman spectrums and density functional theory(DFT)calculation.The N atom elongates the Mn-O bond and reduces the valence of Mn^(4+)ion in MnO_(2)crystal by delocalizing its electron clouds.Thus,the electrostatic repulsion will be weakened when Zn^(2+)/H^(+)insert into the host MnO_(2)lattices,which is profitable to more cation insertion and faster ion transfer kinetics for higher capacity and rate capability.This work elucidates a fundamental understanding of the functions of N-doped carbon in composite materials and shed light on a practical pathway to optimize other electrode materials.

Strategic design and fabrication of MXenes-Ti_(3)CNCl_(2)@CoS_(2) core-shell nanostructure for high-efficiency hydrogen evolution

CoS_(2) is considered to be a promising electrocatalyst for hydrogen evolution reaction(HER).However,its further widespread applications are hampered by the unsatisfactory activity due to relatively high chemisorption energy for hydrogen atom.Herein,theoretical predictions of first-principles calculations reveal that the introduction of a Cl-terminated MXenes-Ti_(3)CNCl_(2) can significantly reduce the HER potential of CoS_(2)-based materials and the Ti_(3)CNCl_(2)@CoS_(2) core–shell nanostructure has Gibbs free energy of hydrogen adsorption(|ΔGH|)close to zero,much lower than that of the pristine CoS_(2) and Ti_(3)CNCl_(2).Inspired by the theoretical predictions,we have successfully fabricated a unique Ti_(3)CNCl_(2)@CoS_(2) core–shell nanostructure by ingeniously coupling CoS_(2) with a Cl-terminated MXenes-Ti_(3)CNCl_(2).Interface-charge transfer between CoS_(2) and Ti_(3)CNCl_(2) results in a higher degree of electronic localization and a formation of chemical bonding.Thus,the Ti_(3)CNCl_(2)@CoS_(2) core–shell nanostructure achieves a significant enhancement in HER activity compared to pristine CoS_(2) and Ti_(3)CNCl_(2).Theoretical calculations further confirm that the partial density of states of CoS_(2) after hybridization becomes more non-localized,and easier to interact with hydrogen ions,thus boosting HER performance.In this work,the success of oriented experimental fabrication of high-efficiency Ti_(3)CNCl_(2)@CoS_(2) electrocatalysts guided by theoretical predictions provides a powerful lead for the further strategic design and fabrication of efficient HER electrocatalysts.

WO_(3)@Fe_(2)O_(3) Core-Shell Heterojunction Photoanodes for Efficient Photoelectrochemical Water Splitting

Photoelectrochemical(PEC) hydrogen production from water splitting is a green technology to convert solar energy into renewable hydrogen fuel. The construction of host/guest architecture in semiconductor photoanodes has been proven to be an effective strategy to improve solar-to-fuel conversion efficiency. In this study, WO_(3)@Fe_(2)O_(3) core-shell nanoarray heterojunction photoanodes are synthesized from the in-situ decomposition of WO_(3)@Prussian blue(WO_(3)@PB) and then used as host/guest photoanodes for photoelectrochemical water splitting, during which Fe_(2)O_(3) serves as guest material to absorb visible solar light and WO_(3) can act as host scaffolds to collect electrons at the contact. The prepared WO_(3)@Fe_(2)O_(3) shows the enhanced photocurrent density of 1.26 m A cm^(-2)(under visible light) at 1.23 V. vs RHE and a superior IPEC of 24.4% at 350 nm, which is higher than that of WO_(3)@PB and pure WO_(3)(0.43 m A/cm^(-2) and 16.3%, 0.18 m A/cm^(-2) and 11.5%) respectively, owing to the efficient light-harvesting from Fe_(2)O_(3) and the enhanced electron-hole pairs separation from the formation of type-Ⅱ heterojunctions, and the direct and ordered charge transport channels from the one-dimensional(1D) WO_(3) nanoarray nanostructures. Therefore, this work provides an alternative insight into the construction of sustainable and cost-effective photoanodes to enhance the efficiency of the solar-driven water splitting.

Carbon nanofilm stabilized twisty V_(2)O_(3)nanorods with enhanced multiple polarization behavior for electromagnetic wave absorption application

Vanadium(V)oxides exhibit low electrical conductivity and poor polarization properties,especially in that V_(2)O_(3)has low stability and is easily oxidized to higher valence V oxides.To solve this problem,we herein provide a two-step strategy for the synthesis of carbon nanofilm stabilized twisty V_(2)O_(3)nanorods(V_(2)O_(3)@C),including a hydrothermal reaction and a controlled pyrolysis process.Conductivity tests and electron-spin resonance(ESR)spectra indicate that the coating of carbon nanofilm not only enhances the electrical conductivity but also generates abundant defects.The electromagnetic waves absorption(EMA)results suggest that V_(2)O_(3)@C exhibits excellent EMA performance at ultra-low thickness,where the effective absorption bandwidth gets to 7.21 GHz at 1.7 mm and the maximal absorption reaches–56 d B.Enhanced conductivity loss and improved multiple polarization relaxation were used to illustrate the absorbing mechanism of V_(2)O_(3)@C.This work provides new insights into the design of advanced nanocomposites for EMA applications.