Harahari Mandal

Development of ternary iron vanadium oxide semiconductors for applications in photoelectrochemical water oxidation

Herein, we report the synthesis of Fe–V-oxides via the drop casting of metal precursor solutions in different proportions onto an indium tin oxide (ITO) coated glass followed by annealing in air at 500 °C for 3 h. UV-vis spectroscopy of the Fe–V-oxides indicates absorption due to ‘direct’ and ‘indirect’ band gaps, although Fe-oxide shows a direct band gap nature. Scanning electron microscopy-energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD) studies reveal different surface morphologies with variable crystalline phases for the Fe2O3, FeVO4, FeV2O4 and Fe2VO4 semiconductors. The photoelectrochemical (PEC) water oxidation reaction over the different materials reveals that the FeV2O4 semiconductor exhibits the maximum photocurrent of 0.18 mA cm−2 at an applied bias of +1.0 V (vs. Ag/AgCl) under the illumination of 100 mW cm−2 compared to the other Fe2O3, FeVO4 and Fe2VO4 semiconductors. Electrochemical impedance spectroscopic (Mott–Schottky) analysis confirms n-type semiconductivity for all the materials with highest donor density, in the order of 2.7 × 1020 cm−3, for the FeV2O4 thin film, and PL spectra are useful for measuring the separation efficiency of the photo-generated charge carriers. Chronoamperometric studies under constant illumination of the best semiconductor (FeV2O4) indicate the significant stability of the material, and photoelectrochemical action spectra demonstrate 22% incident photon to current conversion efficiency (IPCE) and 60% absorbed photon to current conversion efficiency (APCE).

Benign role of Bi on an electrodeposited Cu2O semiconductor towards photo-assisted H2 generation from water

In this paper we report a Bi modified Cu2O semiconductor (SC) for improved photoelectrochemical (PEC) hydrogen (H2) production from aqueous solution. For the first time, we found out that the PEC performance of SC thin films improve dramatically by ∼2 fold when Bi nanoparticles (BiNPs) are added in the form of a suspension or act as a matrix coated over ITO glass during electrodeposition of Cu2O. On the other hand, the addition of an optimized amount of Bi3+ ions (10 nM) in the deposition bath also facilitated the hydrogen evolution reaction over Cu2O. Maximum photocurrents for the Cu2O film developed from these three different conditions are: −5.2 mA cm−2 for ITO/BiNPfilm/Cu2O, −4.9 mA cm−2 for ITO/BiNPsus/Cu2O, and −3.7 mA cm−2 for ITO/Biion/Cu2O, whereas that for pure Cu2O on ITO appears as −2.6 mA cm−2. This is the highest reported photocurrent of Cu2O on any conducting glass substrates without employing any hydrogen evolution catalyst. SEM and XRD studies of the films indicate that the materials are composed of “cubic” crystallites of preferential (111) orientation, and their size varies from 18–26 nm. Addition of Bi modifies the band position with a decrease in the bandgap energy of Cu2O. Smaller charge-transfer resistance (Rct) and ohmic resistance (Rs) facilitate the H2 evolution reaction over the ITO/BiNPfilm/Cu2O film, whereas its lowest carrier density suggests minimum defect sites, i.e. better crystallinity of the film matrix.

Improvement of photocatalytic activity of surfactant modified In2O3 towards environmental remediation

The present paper describes photocatalytically active In2O3 thin films developed using a direct drop-cast method on F-doped tin oxide (FTO) coated glass substrates using 10 mM In(NO3)3 dissolved in ethylene glycol containing 0–0.0125 M Triton-X 100 (TX-100) surfactant and annealed in air at 600 °C to obtain the desired metal oxide. The absorption spectrum measured the direct band gap of the surfactant modified In2O3 as 3.48 eV along with an indirect gap of 2.69 eV indicating near visible absorptivity of the materials, which was established through linear sweep voltammetry under periodic UV-Vis and visible irradiation for oxidation of water and a sacrificial reagent, SO32−. The electrochemical impedance spectroscopic (Mott–Schottky) analysis confirms n-type semiconductivity for these materials. Addition of an optimized level of 0.01 M TX-100 surfactant to the precursor solution improves the photoelectrochemical performance of the film to 2.3 fold. The electrochemical action spectra indicate a maximum value of the incident photon to current conversion efficiency (IPCE) for the 0.01 M surfactant modified In2O3 of 28% and the corresponding absorbed photon to current conversion efficiency (APCE) of 40%. Addition of surfactant to the In3+ precursor solution results in uniformly distributed particle growth on the surface with better crystallinity.