Huajun Zheng

Three-dimensional NiCo2O4@NiWO4 core–shell nanowire arrays for high performance supercapacitors

Hierarchical NiCo2O4@NiWO4 core–shell nanowire arrays supported on nickel foam have been synthesized via a facile hydrothermal route coupled with a post-thermal treatment. The hydrothermally synthesized NiCo2O4 nanowire arrays serve as the scaffold for anchoring the NiWO4 nanosheets. When evaluated as binder-free electrodes for supercapacitors, the optimized NiCo2O4@NiWO4 hybrid electrode demonstrates remarkable electrochemical performance with a high specific capacitance of 1384 F g−1 at a current density of 1 A g−1 and superior cycling stability (87.6% retention over 6000 cycles at a current density of 5 A g−1). In addition, an asymmetric supercapacitor (ASC) based on the optimized NiCo2O4@NiWO4 electrode and activated carbon is assembled with 6 M KOH as the electrolyte. The as-fabricated ASC device can achieve a maximum high energy density of 41.5 W h kg−1 at a power density of 760 W kg−1. The excellent supercapacitive performance could be ascribed to the unique core–shell architecture and the synergistic effect from the NiCo2O4 nanowires and the ultrathin NiWO4 nanosheets.

Hierarchically structured WO3–CNT@TiO2NS composites with enhanced photocatalytic activity

A novel hierarchically structured WO3–CNT@TiO2NS composite was prepared by the combination of solvothermal and liquid-phase chemistry deposition techniques. The obtained composite has a highly rough and porous structure with WO3 nanoparticles distributed uniformly on the surface. The photocatalytic performance was tested by photocatalytic degradation of methylene blue. It is indicated that the WO3–CNT@TiO2NS composite shows more remarkable improvement of the photocatalytic performance than that of the CNT@TiO2NS. In particular, the presence of 15 wt% WO3 enables reaching the highest photocatalytic activity, which is 4 times that of CNT@TiO2NS. The enhanced photocatalytic properties are mainly attributed to the more efficient photogenerated carrier separation, enhanced light absorption as well as the higher adsorption ability. It is suggested that WO3 deposition is a promising way to enhance the photocatalytic activity of a TiO2-based photocatalyst.

Etching treatment of vertical WO3 nanoplates as a photoanode for enhanced photoelectrochemical performance

Vertically grown WO3 nanoplates (WO3NP) were successfully fabricated by a one-step hydrothermal process using citric acid as a structure directing agent. An innovative etching method was developed to obtain increased surface voids, active crystal facets and surface groups simultaneously, which led to a remarkably improved photocurrent density of ∼1.2 mA cm−2 at 1.23 V vs. RHE, compared to 0.97 mA cm−2 of pristine WO3. Incident photon to current efficiency (IPCE) measurements also displayed a substantive increase of photoresponse in the intrinsic absorption range. Interestingly, a lower onset potential can be obtained after etching which is caused by the change of conduction and valence band positions. Moreover, the photoelectrocatalytic activity of WO3 for degrading methylene blue (MB) was also evaluated. This effective design could provide a promising method to enhance the efficiency of photoelectrochemical performance based on WO3 photoanodes.

Carbon quantum dot sensitized Pt@Bi2WO6/FTO electrodes for enhanced photoelectro-catalytic activity of methanol oxidation

Carbon quantum dot sensitized Pt@Bi2WO6/FTO electrodes (simplified as CQDs-Pt@Bi2WO6/FTO) were successfully prepared by loading platinum particles onto Bi2WO6 nanoplates via a photo-deposition method and sensitized carbon quantum dots (CQDs) via a dip-coating method. The photoelectro-catalytic properties of the Pt@Bi2WO6/FTO and CQDs-Pt@Bi2WO6/FTO electrodes for methanol oxidation were investigated. The results indicated that the CQDs-Pt@Bi2WO6/FTO electrode shows higher photoelectro-catalytic activity and better stability than that of the Pt@Bi2WO6/FTO electrode. The higher photoelectro-catalytic performance for methanol oxidation was attributed due to the special synergetic effects between the photocatalytic and electrocatalytic process under solar light irradiation. More importantly, the introduction of CQDs broaden the photoresponse range of the Bi2WO6 material and improves the mobility of the photocarriers. Meanwhile, the doped CQDs act as preferential adsorption sites for the intermediate carbonaceous species during methanol oxidation. This not only alleviates CO poisoning towards the Pt particles, but also improves the efficiency of methanol oxidation by constructing a new type of CQDs-Pt electrocatalyst. The composite material, which combines the dual function of photocatalysis and electrocatalysis will be a promising candidate for new photoelectro-catalytic fuel cells.