A scanning photoelectrochemical microscopy (SPECM) technique is applied to rapidly screening the photoelectrochemical (PEC) activities of cobalt (Co)-incorporated bismuth vanadate (BiVO4) photocatalyst arrays with varying Co concentrations on conducting FTO and Ti substrates. The SPECM screening study is successfully utilized to determine an optimal Co concentration of 6% to improve the photocatalytic performance of BiVO4. Subsequently, pristine and Co-doped BiVO4 thin film photoanodes are fabricated by spin-coating/drop-casting methods with optimal precursor concentrations of Co, Bi, and V to validate the results of SPECM. Structural characterization by X-ray diffraction shows that 6% Co-BiVO4 contains a photocatalytically active scheelite-monoclinic phase of BiVO4. Scanning electron microscopy images and EDAX show that 6% Co is partly incorporated into the BiVO4 lattice and the remaining accumulates on the surface in the form of cobalt oxide, which is further evidenced by X-ray photoelectron spectroscopy (XPS) and Raman studies. Co-doped BiVO4 thin film photoanode prepared by spin-coating method exhibits similar remarkable PEC response with ∼150% increase in photocurrent density at 1.0 V vs RHE with respect to the pristine BiVO4 photoanode. Additionally, such photoanode exhibits a cathodic shift of ∼200 mV in the onset of water oxidation photocurrent. The Mott–Schottky analysis confirms an increase in charge carrier density of Co-doped BiVO4 photoanode. Thus, the enhanced water splitting performance by Co is attributed to largely due to (1) enhancement in water oxidation kinetics via formation of cobalt oxide (Co3O4) on the surface of BiVO4, and partially due to (2) enrichment in electronic conductivity of BiVO4 in the presence of Co. An unbiased Z-scheme solar water splitting system is demonstrated at the end of this work by combining an optimized Co-doped BiVO4/WO3 photoanode with a CuO/CuBi2O4 photocathode in a two-electrode configuration.

Au nanoparticles (NPs) have interesting optical properties, such as local field enhancement for improving light absorption and Raman scattering cross-section of an organic chromophore, and catalytic properties of improving the kinetics of redox reactions involved in clean energy transformations. Real-time electrochemical measurements of catalytic Au NPs would help resolve their local structure–function relationship, which can further provide insights into developing an optimal catalytic condition. It is extremely challenging to resolve the electrochemical events of electrocatalytic Au NPs at a single-particle level using conventional ensemble averaging methods. Here, we present a light-scattering-based spectroelectrochemistry analysis of single catalytic Au NPs at a transparent planar electrode and ultramicroelectrode (UME) with combined methods of electrochemistry and dark-field light scattering (DFS). Hydrazine oxidation reaction is used as a model system to characterize the catalytic characteristics of single Au NPs. Real-time light-scattering responses of Au NPs to surface adsorbates, Au oxide formation, double-layer charging, and nitrogen bubble formation upon hydrazine oxidation are investigated for both ensemble and single Au NPs. Such a light-scattering response to catalytic hydrazine oxidation at single Au NPs is highly sensitive to Au NP sizes. The DFS study of single Au NPs shows a minor decrease in the light-scattering signal in the low overpotential region because of the double-layer charging in the absence of hydrazine and the surface adsorbates N2H3 in the presence of hydrazine. A significant decrease in the DFS signal of Au NPs upon Au oxidation in the high-overpotential region can be obtained in the absence of hydrazine. Such an oxide-induced light-scattering signal loss effect can be weakened in the presence of hydrazine and completely eliminated in the presence of >50 mM hydrazine. Strong light scattering can be obtained because of nitrogen bubble formation on the Au NP surface. Theoretical modeling with COMSOL Multiphysics is applied to support the abovementioned conclusions.

The direct liquid injection chemical vapor deposition (DLI-CVD) method is used to grow pristine and molybdenum (Mo)-doped monoclinic scheelite phase bismuth vanadate (BVO) photoelectrodes. Superior photoelectrochemical (PEC) performance is achieved with ∼200 ± 50 nm thick pristine and 8 at. % Mo-doped BVO films grown at 550 °C. Photocurrent densities as high as ∼1.65 and 3.25 mA/cm2 are obtained for pristine and optimum 8% Mo-doped BVO electrodes, respectively, at 1.23 V vs reversible hydrogen electrode (RHE) under visible light AM 1.5G (100 mW/cm2) in 0.5 M phosphate buffer electrolyte in the presence of 0.1 M Na2SO3 hole scavenger. Somewhat lower photocurrent densities of ∼1.5 and 2.4 mA/cm2 are obtained for pristine and optimum 8% Mo-doped BVO electrodes, respectively, in the absence of Na2SO3. Onset potential values as low as ∼0.1 and 0.3 V vs RHE are achieved with pristine and Mo-doped BVO films for sulfite and water oxidation, respectively. The increased photocurrent density with Mo doping is attributed to enhanced charge carrier density and film conductivity as confirmed by PEC and Mott–Schottky analyses. Because of the dense high quality polycrystalline structure, the DLI-CVD fabricated Mo-doped BVO electrodes exhibit substantial stability under water and sulfite oxidation conditions without any protective layer and/or oxygen evolution cocatalysts. Scanning electrochemical microscopy (SECM) studies confirm the low porosity of Mo:BVO films and production of oxygen in a local area of Mo:BVO electrode under light illumination.

Photoelectrochemical (PEC) hydrogen generation is a promising solar energy harvesting technique to address the concerns about the ongoing energy crisis. Antimony selenide (Sb2Se3) with van der Waals‐bonded quasi‐1D (Q1D) nanoribbons, for instance, (Sb4Se6)n, has attracted considerable interest as a light absorber with Earth‐abundant elements, suitable bandgap, and a desired sunlight absorption coefficient. By tuning its anisotropic growth behavior, it is possible to achieve Sb2Se3 films with nanostructured morphologies that can improve the light absorption and photogenerated charge carrier separation, eventually boosting the PEC water‐splitting performance. Herein, high‐quality Sb2Se3 films with nanorod (NR) array surface morphologies are synthesized by a low‐cost, high‐yield, and scalable close‐spaced sublimation technique. By sputtering a nonprecious and scalable crystalline molybdenum sulfide (MoS2) film as a cocatalyst and a protective layer on Sb2Se3 NR arrays, the fabricated core–shell structured MoS2/Sb2Se3 NR PEC devices can achieve a photocurrent density as high as −10 mA cm−2 at 0 VRHE in a buffered near‐neutral solution (pH 6.5) under a standard simulated air mass 1.5 solar illumination. The scalable manufacturing of nanostructured MoS2/Sb2Se3 NR array thin‐film photocathode electrodes for efficient PEC water splitting to generate solar fuel is demonstrated.

Chitosan-coated silica nanocapsules with a double-shelled structure were crafted using Pluronic F127 as the template via the interfacial condensation approach. The shell of these nanocapsules was composed of an inner layer of silica and an outer layer of chitosan, which was designed for sustained release of vanillin. The average size of nanocapsules was proved to be approximately 37 nm, which could be tunable by varying the usage of chitosan. Significantly, these double-shelled nanocapsules possessed enhanced encapsulation efficiency of 95.5% for vanillin and showed sustained release behaviors. Thermal gravimetric results indicated that the double-shelled structure could endow capsules with improved thermal stability. All of these make them promising candidates for sustained release of small volatile molecules in the industrial field.