Ultrafine niobium oxide nanocrystals/reduced graphene oxide (Nb2O5 NCs/rGO) was demonstrated as a promising anode material for sodium ion battery with high rate performance and high cycle durability. Nb2O5 NCs/rGO was synthesized by controllable hydrolysis of niobium ethoxide and followed by heat treatment at 450 °C in flowing forming gas. Transmission electron microscopy images showed that Nb2O5 NCs with average particle size of 3 nm were uniformly deposited on rGO sheets and voids among Nb2O5 NCs existed. The architecture of ultrafine Nb2O5 NCs anchored on a highly conductive rGO network can not only enhance charge transfer and buffer the volume change during sodiation/desodiation process but also provide more active surface area for sodium ion storage, resulting in superior rate and cycle performance. Ex situ XPS analysis revealed that the sodium ion storage mechanism in Nb2O5 could be accompanied by Nb(5+)/Nb(4+) redox reaction and the ultrafine Nb2O5 NCs provide more surface area to accomplish the redox reaction.

A solvothermal method is used to deposit Pt nanoparticles on anodized TiO2 nanotubes (T_NT). Surface characterization using SEM, EDX, and XRD indicates the formation of polycrystalline TiO2 nanotubes of 110 ± 10 nm diameter with Pt nanoparticle islands. The application of the T_NT/Pt photoanode has been examined toward simultaneous electrooxidation and photo(electro)oxidation of formic acid (HCOOH). Upon UV-vis photoillumination, the T_NT/Pt photoelectrode generates a current density of 72 mA/cm(2), which is significantly higher (∼39-fold) than that of the T_NT electrode (1.85 mA/cm(2)). This boosting in the overall current is attributable to the enhanced oxidation of formic acid at the T_NT/Pt-electrolyte interface. Further, a series of cyclic voltammetric (CV) responses, of which each anodic scan is switched to photoillumination at a certain applied bias (i.e., 0.2 V, 0.4 V, etc.), is used to identify the role of T_NT/Pt as a promoter for the photoelectrooxidation of formic acid and understand a carbon monoxide (CO)-free pathway. Chronoamperometric (j/t) measurements demonstrate the evidence of an external bias dependent variation in the time lag during the current stabilization. An analysis of the CV plots and j/t profiles suggests the existence of both the charge-transfer controlled process and the diffusion-controlled process during formic acid photoelectrooxidation.

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We report the hydrogen evolution reaction (HER) with molybdenum diselenide (MoSe2) and its reduced graphene oxide (rGO) hybrids synthesized by a microwave process followed by annealing at 400 °C. The content of GO was varied to understand its role in the electrocatalytic activities. Electrochemical performance of the as-synthesized and the annealed catalysts underscores (i) a requirement of catalytic activation of the as-synthesized samples, (ii) an apparent shift in the onset potential as a result of annealing, and (iii) striking changes in the Tafel slope as well as the overpotential. The results clearly reveal that partially crystalline plain MoSe2 is more elctroactive in comparison to its annealed counterpart, whereas annealing is advantageous to MoSe2/rGO. Improved HER performances of the annealed MoSe2/rGO hydrids arise from the synergistic effect between active MoSe2 and rGO of improved conductivity. The annealed hybrid of MoSe2 with rGO designated as MoSe2/rGO100_400 °C demonstrated an excellent HER activity with a small onset potential of −46 mV vs reversible hydrogen electrode, a smaller Tafel slope (61 mV/dec), and a reduced overpotential of 186 mV at −10 mA/cm2. As a result of a convenient synthetic process and the suitable electrocatalytic performance, this study would be beneficial to designing and fabricating other nanomaterials with/without a conductive support for their versatile applications.

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