Chinmoy Bhattacharya

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.

Enhanced photovoltage in DSSCs: synergistic combination of a silver modified TiO2 photoanode and a low cost counter electrode

In this study, we have tailored both the active electrode with silver modified TiO2 (Ag–TiO2) as well as the counter electrode (CE) with Pt–reduced graphene oxide (Pt@RGO) nanocomposites to realize efficient and low cost devices. The synergistic combination of both modified electrodes leads to an improved light to electrical energy conversion with an overall efficiency of 8%. An increase in the photovoltage (VOC) of ∼16% (0.74 to 0.86 V) is achieved using Ag–TiO2 in comparison to the bare TiO2. This can be attributed to the shifting of the quasi-Fermi level of the TiO2 photoanode close to the conduction band in the presence of Ag nanoparticles (NPs) due to the formation of the Schottky barrier. On the other hand, the facile synthesis of Pt NPs on RGO nanosheets by a photo-reduction method without using chemical reducing or stabilizing agents demonstrates a higher efficiency than Pt as a CE due to the cooperation of the catalytic activity of Pt and the high electron conductivity of the RGO as a stable supporting material having more interfacial active sites. The quantity of Pt in the Pt@RGO nanocomposites is 10 times lower than in the Pt CE which reduces the cost and makes it viable for large scale commercial utilization.

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.