All-Solution-Processed WO3/BiVO4 Core-Shell Nanorod Arrays for Highly Stable Photoanodes.

Tungsten oxide (WO3) and bismuth vanadate (BiVO4) are one of the most attractive combinations to construct an efficient heterojunction for photoelectrochemical (PEC) applications. Here, we report an all-solution-processed WO3/BiVO4 heteronanostructure photoanode with highly enhanced photoactivity and stability for sustainable energy production. The vertically aligned WO3 nanorods were synthesized on a fluorine-doped tin oxide/glass substrate by the hydrothermal method without a seed layer and BiVO4 was deposited by pulsed electrodeposition for conformal coating. Owing to the long diffusion lengths of charge carriers in the WO3 nanorods, the ability to absorb the wider range of wavelengths, and appropriate band-edge positions of the WO3/BiVO4 heterojunction for spontaneous PEC reaction, the optimum WO3/BiVO4 photoanode has a photocurrent density of 4.15 mA/cm2 at 1.23 V versus RHE and an incident-photon-to-current efficiency of 75.9% at 430 nm under front illumination, which are a double and quadruple those of pristine WO3 nanorod arrays, respectively. Our work suggests an environment-friendly and low-cost all-solution process route to synthesize high-quality photoelectrodes.

Nanostructured Na2Ti9O19 for Hybrid Sodium-Ion Capacitors with Excellent Rate Capability.

Herein, we report a new Na-insertion electrode material, Na2Ti9O19, as a potential candidate for Na-ion hybrid capacitors. We study the structural properties of nanostructured Na2Ti9O19, synthesized by a hydrothermal technique, upon electrochemical cycling vs Na. Average and local structures of Na2Ti9O19 are elucidated from neutron Rietveld refinement and pair distribution function (PDF), respectively, to investigate the initial discharge and charge events. Rietveld refinement reveals electrochemical cycling of Na2Ti9O19 is driven by single-phase solid solution reaction during (de)sodiation without any major structural deterioration, keeping the average structure intact. Unit cell volume and lattice evolution on discharge process is inherently related to TiO6 distortion and Na ion perturbations, while the PDF reveals the deviation in the local structure after sodiation. Raman spectroscopy and X-ray photoelectron spectroscopy studies further corroborate the average and local structural behavior derived from neutron diffraction measurements. Also, Na2Ti9O19 shows excellent Na-ion kinetics with a capacitve nature of 86% at 1.0 mV s-1, indicating that the material is a good anode candidate for a sodium-ion hybrid capacitor. A full cell hybrid Na-ion capacitor is fabricated by using Na2Ti9O19 as anode and activated porous carbon as cathode, which exhibits excellent electrochemical properties, with a maximum energy density of 54 Wh kg-1 and a maximum power density of 5 kW kg-1. Both structural insights and electrochemical investigation suggest that Na2Ti9O19 is a promising negative electrode for sodium-ion batteries and hybrid capacitors.

Recent Advances in Bismuth-Based Nanomaterials for Photoelectrochemical Water Splitting.

In recent years, bismuth-based nanomaterials have drawn considerable interest as potential candidates for photoelectrochemical (PEC) water splitting owing to their narrow band gaps, nontoxicity, and low costs. The unique electronic structure of bismuth-based materials with a well-dispersed valence band comprising Bi 6s and O 2p orbitals offers a suitable band gap to harvest visible light. This Review presents significant advancements in exploiting bismuth-based nanomaterials for solar water splitting. An overview of the different strategies employed and the new ideas adopted to improve the PEC performance of bismuth-based nanomaterials are discussed. Morphology control, the construction of heterojunctions, doping, and co-catalyst loading are several approaches that are implemented to improve the efficiency of solar water splitting. Key issues are identified and guidelines are suggested to rationalize the design of efficient bismuth-based materials for sunlight-driven water splitting.

Bi4TaO8Cl Nano-Photocatalyst: Influence of Local, Average, and Band Structure.

The average structure, local structure, and band structure of nanoparticles of photocatalyst Bi4TaO8Cl, an Aurivillius-Sillen layered material, has been studied by powder neutron Rietveld refinement, neutron pair distribution function technique, Raman scattering, and density functional theory calculations. A significant local structural deviation of nano-Bi4TaO8Cl was established in contrast to the local structure of bulk-Bi4TaO8Cl. Local structure was further supported by Raman scattering measurements. Through DFT calculations, we identify specific features in the electronic band structure that correlate lower secondary structural distortions in nano-Bi4TaO8Cl. Increased distortion of TaO6, decreased Ta-O-Ta bond angle, and increased octahedral tilt in the local structure of nano-Bi4TaO8Cl influence the band structure and the electron hole pair migration. Therefore, in addition to morphology and size, the local structure of a nanomaterial contributes to the photocatalytic performance. Trapping experiments confirm the role of superoxide radical in the photocatalysis mechanism of this material. Such studies help in developing new functional materials with better photocatalytic efficiency to address energy and environmental issues.

Photoluminescence tuning of Na1-xKxNdW2O8 (0.0 ≤ x ≤ 0.7) nanoparticles: synthesis, crystal structure and Raman study.

A series of Na1-xKxNdW2O8 (0.0 ≤ x ≤ 0.7) nanoparticles have been synthesized by an efficient glycothermal technique for the first time. SEM measurements confirmed the particle size ranges from 30-200 nm with ellipsoidal shaped morphology. Combined X-ray and neutron diffraction and Raman spectroscopy techniques were utilized in order to investigate the influence of K(+) ion substitution in NaNdW2O8. K(+) ion substitution in the crystal lattice introduced a change in the Nd-O bond length and the Nd-O-W bond angle of NaNdW2O8. The photoluminescence intensity increased up to the threshold composition x = 0.4. K(+) ion substitution resulted in blue shifted emission of NaNdW2O8. Size mismatch, the Nd-O-W angle and local disorder contributed to the observed difference in luminescence properties. Also, the chromaticity diagram for this blue emitting phosphor showed the possibility of tuning the emission by incorporation of K.