Defect engineering on BiFeO_(3) through Na and V codoping for aqueous Na-ion capacitors

Sodium with low cost and high abundance is considered as a substitute element of lithium for batteries and supercapacitors,which need the appropriate host materials to accommodate the relatively large Na^(+) ions.Compared to Li^(+) storage,Na^(+) storage makes higher demands on the structural optimization of perovskite bismuth ferrite(BiFeO_(3)).We propose a novel strategy of defect engineering on BiFeO_(3) through Na and V codoping for high-efficiency Na^(+) storage,to reveal the roles of oxygen vacancies and V ions played in the enhanced electrochemical energy storage performances of Na-ion capacitors.The formation of the oxygen vacancies in the Na and V codoped BiFeO_(3)(denoted as NV-BFO),is promoted by Na doping and suppressed by V doping,which can be demonstrated by XPS and EPR spectra.By the first-principles calculations,the oxygen vacancies and V ions in NV-BFO are confirmed to substantially lower the Na^(+)migration energy barriers through the space and electric field effects,to effectively promote the Na^(+) transport in the crystals.Electrochemical kinetic analysis of the NV-BFO//NV-BFO capacitors indicates the dominant capacitive-controlled capacity,which depends on fast Na^(+) deintercalation-intercalation process in the NV-BFO electrode.The NV-BFO//NV-BFO capacitors open up a new avenue for developing highperformance Na-ion capacitors.

Functionalized periodic Au@MOFs nanoparticle arrays as biosensors for dual-channel detection through the complementary effect of SPR and diffraction peaks

A facile and low-cost method to prepare periodic Au@metal-organic framework （MOF） （MIL-100（Fe）） nanoparticle arrays was developed. The arrays were fabricated in situ using monolayer colloidal crystals as templates, followed by Au deposition on substrates, and annealing. MIL-100（Fe） coatings were applied on the nanospheres using a simple solvent thermal process. The prepared periodic Au@MIL-100（Fe） nanoparticle （NP） arrays were characterized by two peaks in the visible spectra. The first peak represented the surface plasmon resonance （SPR） of the Au nanospheres, and the other peak, or the diffraction peak originated from the periodic structure in the NP array. After modification with 3-aminophenylboronic acid hemisulfate （PBA）, the Au@MIL-100（Fe） NP arrays exhibited sensitive responses to different glucose concentrations with good selectivity. These responses could be due to the strong interaction between PBA and glucose molecules. The diffraction peak was sensitive at low glucose concentrations （less than 12 mM）, whereas the SPR peak rapidly responded at high concentrations. The peaks thus demonstrated satisfactory complementary sensitivity for glucose detection in different concentration regions. These results can be used to develop a dual-channel biosensor. We also created a standard diagram, which can be used to efficiently monitor blood glucose levels. The proposed strategy can be extended to develop different dual-channel sensors using Au@MIL-100（Fe） NP arrays agents. functionalized with different recognition