Effect of C doping on the structural and electronic properties of LiFePO_4:A first-principles investigation

Using first-principles calculations within the generalized gradient approximation （GGA） ＋U framework, we inves- tigate the effect of C doping on the structural and electronic properties of LiFePO4. The calculated formation energies indicate that C doped at O sites is energetically favoured, and that C dopants prefer to occupy 03 sites. The band gap of the C doped material is much narrow than that of the undoped one, indicating better electro- conductive properties. To maintain charge balance, the valence of the Fe nearest to C appears as Fe3＋, and it will be helpful to the hopping of electrons.

Regulation of hydrogen evolution performance of titanium oxide-carbon composites at high current density with a Ti-O hybrid orbital

Rational design and controllable synthesis of practical electrodes with high sta bility and activity at high current density for a hydrogen evolution reaction(HER)are critical for renewable and sustainable energy conversion.However,high-performance TiO_(2)-based electrocatalysts for HER are quite limited,and the cat alytic active centers still remain elusive.Herein,a simple strategy is demonstrated for the synthesis of TiO_(2)-carbon composite(TiO_(2)/C)with high HER performance and stability.The remarkable HER performance of TiO_(2)/C can be ascribed to the doping of carbon atoms,which leads to stronger hybridization of Ti 3d and O 2p orbitals,thus substantially improving the electrocatalytic efficiency.This study elucidates that the hydrogen evolution activity of oxide electrocatalysts can be largely improved by regulating their electronic structures by doping carbon atoms and also provides an effective strategy for designing heterostructured electro catalysts with high catalytic activity and stability at high current density for HER.

DFT study for combined influence of C-doping and external electric field on electronic structure and optical properties of TiO_(2)(001)surface

The electron structure and optical properties of C-TiO_(2)(001)surface under external electric field were studied by DFT method.After carbon doping,a new impurity level is introduced in the bandgap region of TiO_(2)(001)surface,and leads to the decrease of band gap,contributing to the shift of optical absorption to the visible region.When external electric field is applied across the C-TiO_(2)(001)surface,the band gap is further reduced with the increase of the electric field intensity from 0.1 eV to 0.5 eV.The electric field over 0.5 eV induces the electronic polarization.The spin-up bands show a gap,while spin-down electrons correspond to a metallic state.The energy gap of spin-up band decreases with increasing the electric field from 0.7 eV to 1.0 eV.The optical absorption of C-TiO_(2)(001)shifts to long wavelength compared with pure TiO_(2)(001).The electric filed make the optical absorption red-shift further,and the shift increases with an increase of the electric field,especially in the range of 0.7 eV-1.0 eV.The results show that the combined effect of carbon doping and electric field can enhance the photocatalytic activity of TiO_(2)(001)surface in visible region.

Carbon-doping-induced negative differential resistance in armchair phosphorene nanoribbons

By using a combined method of density functional theory and non-equilibrium Green＇s function formalism,we investigate the electronic transport properties of carbon-doped armchair phosphorene nanoribbons（APNRs）.The results show that C atom doping can strongly affect the electronic transport properties of the APNR and change it from semiconductor to metal.Meanwhile,obvious negative differential resistance（NDR） behaviors are obtained by tuning the doping position and concentration.In particular,with reducing doping concentration,NDR peak position can enter into m V bias range.These results provide a theoretical support to design the related nanodevice by tuning the doping position and concentration in the APNRs.

Hollow hydrangea-like nitrogen-doped NiO/Ni/carbon composites as lightweight and highly efficient electromagnetic wave absorbers

Hierarchical hollow-structured magnetic–dielectric materials are considered to be promising and competitive functional absorbers for microwave absorption(MA).Herein,a hierarchical hollow hydrangea multicomponent metal oxides/metal-carbon was designed and successfully produced via a facile self-assembly method and calcination process.Adequate magnetic NiO and Ni nanoparticles were suspended within the hollow hydrangea-like nitrogen-doped carbon matrix(HH N-NiO/Ni/C),constructing a unique hierarchical hollow structured multicomponent magnetic–dielectric MA composite.The annealing temperature and oxidation time were carefully regulated to investigate the complex permittivity and permeability.HH N-NiO/Ni/C delivers exceptional MA properties with maximum reflection loss of–45.8 dB at 1.7 mm thickness and displays a wide effective absorption frequency range of 5.6 GHz.The superior MA performance can be attributed to the following aspects:(1)The hierarchical hollow multicomponent structure offers plentiful of heterojunction interfaces triggering interfacial polarization;(2)nitrogen doped-carbon(N-C)facilitates the conductive loss by the unique electron migration path in the graphitized C and NiO/Ni;(3)magnetic NiO/Ni nanoparticles homogeneously dispersed within N-C form extensive C skeleton and strengthen the magnetic response ability;(4)hierarchical hollow wrinkled structures possess a large interspace and heterogeneous interface improving polarization loss and enhancing multireflection process and the unique structure satisfies magnetic and dielectric loss simultaneously resulting from synergistic effects of different components within the composites.