A Comparative Electrochemical Behaviour Study and Analytical Detection of the p-Nitrophenol Using Silver Solid Amalgam, Mercury, and Silver Electrodes

This work reports a comparative electrochemical behaviour study and p-nitrophenol analytical detection using silver solid amalgam, hanging dropping mercury, and silver electrodes. For this, square wave voltammetry was employed, where the analytical responses and the redox mechanisms could be compared for reduction processes of 4-nitrophenol by analysis of the voltammetric responses. The analytical performance of the electrode was evaluated and detection and quantification limits, recovery percentages, repeatability, and reproducibility for the silver solid amalgam and hanging dropping mercury electrodes presented similar values; the results presented for the silver electrode indicated worse analytical parameters than the other electrodes. The results indicate that the silver solid amalgam electrode can be considered a suitable tool and an interesting alternative for the analytical determination of 4-nitrophenol, as well as for the determination of other biological and environmentally interesting compounds that present analytical responses on mercury surfaces

Enhancing activity in a nanostructured BiVO₄ photoanode with a coating of microporous Al₂O₃

Nanostructured semiconductor photoanodes play an important role in solar fuel generation, and the design of the semiconductor − aqueous electrolyte interface can be crucial in enhancing the energy conversion efficiency. We have investigated the effects on photoelectrochemical oxygen evolution for monoclinic nanostructured BiVO4 films uncoated and coated with microporous sol-gel Al2O3 “over-layers”. Variation of the thickness of the Al2O3 coating (formed by surface sol-gel deposition and annealing at 435 °C) led to a reduction of pseudo-capacitance and allowed optimization of the quantum efficiency. Exploration of the photocurrent enhancement as a function of applied potential reveals two distinct potential domains/mechanisms: (i) a low bias region enhancement effect (assigned to a lowering of the rate of external recombination of electrons with oxygen) and (ii) a high bias region of enhancement (assigned to higher charge carrier mobility due to less trapping in surface states).</p

Photoanodes on titanium substrates:one-step deposited BiVO₄ versus two-step nano-V₂O₅ films impregnated with Bi^₃+

One-step deposition of photoelectrochemically active BiVO4 (monoclinic) from a polyethylene glycol (PEG300) precursor paint onto titanium substrates is demonstrated to lead to more complex multioxide phase films. Photocurrents in 0.5 M Na2SO4 remain relatively low when compared to those reported on tin-doped indium oxide (ITO) substrates, possibly due to the effect of detrimental underlying titanium oxide phases or mixed phases. For comparison, the one-step deposition is demonstrated also for the direct formation of V2O5 nanocrystalline films, which also exhibited low photoelectrochemical activity. Impregnation of nanocrystalline V2O5 with aqueous Bi3+ is shown to cause substantial recrystallization with formation of much more photoactive BiVO4. In particular, on low-temperature (high surface area) nano-V2O5 (400 °C) and after further mild annealing at 400 °C much improved photoelectrochemical water oxidation activity (ca. 0.3 mA cm−2 at 1.0 V vs Ag/AgCl (KCl (3 M) at 0.1-W cm−2 xenon lamp radiation) is observed. This opens up a new mild temperature two-step route for BiVO4 photocatalysts on practical titanium substrates.</p

Residual Energy Harvesting from Light Transients Using Hematite as an Intrinsic Photocapacitor in a Symmetrical Cell

Hematite as a sustainable photoabsorber material offers a band gap close to 2 eV and photoanode characteristics, but usually requires additional catalysts to enhance surface redox chemistry during steady state light energy harvesting for water splitting. Here, for a highly doped hematite film, sufficient intrinsic photocapacitor behavior is reported for the conversion of light transients into energy. Residual energy is harvested in a symmetric architecture with two opposing mesoporous hematite films on conductive glass. Transient light energy harvesting is shown to occur without the need for water splitting

Vacuum-annealing induces sub-surface redox-states in surfactant-structured α-Fe₂O₃ photoanodes prepared by ink-jet printing

Transparent nano-structured hematite (α-Fe2O3) films of approximately 550 nm thickness on tin-doped indium oxide (ITO) have been obtained conveniently by ink-jet printing of a Fe(NO3)3/Brij® O10 precursor ink and subsequent annealing at 500 °C in air. When illuminated with a blue LED (λ = 455 nm, ca. 100 mW cm−2), the hematite films exhibited photocurrents of up to 70 μA cm−2 at 0.4 V vs. SCE in 0.1 M NaOH electrolyte. Thermal annealing in vacuum at 500 °C for 2 h increased photocurrents more than three times to 230 μA cm−2 in agreement with previous literature reports for pure hematite materials. These results suggest that a simple ink-jetting process with surfactants is viable. The effects of vacuum-annealing on the photoelectrical properties of α-Fe2O3 films are discussed in terms of a sub-surface state templating hypothesis based on data gathered from photo-transients, field emission scanning electron microscopy, X-ray photoelectron spectroscopy analysis, X-ray diffraction, photocurrent spectra, and cyclic voltammetry

Enhancing activity in a nanostructured BiVO₄ photoanode with a coating of microporous Al₂O₃

Nanostructured semiconductor photoanodes play an important role in solar fuel generation, and the design of the semiconductor − aqueous electrolyte interface can be crucial in enhancing the energy conversion efficiency. We have investigated the effects on photoelectrochemical oxygen evolution for monoclinic nanostructured BiVO4 films uncoated and coated with microporous sol-gel Al2O3 “over-layers”. Variation of the thickness of the Al2O3 coating (formed by surface sol-gel deposition and annealing at 435 °C) led to a reduction of pseudo-capacitance and allowed optimization of the quantum efficiency. Exploration of the photocurrent enhancement as a function of applied potential reveals two distinct potential domains/mechanisms: (i) a low bias region enhancement effect (assigned to a lowering of the rate of external recombination of electrons with oxygen) and (ii) a high bias region of enhancement (assigned to higher charge carrier mobility due to less trapping in surface states).</p

Nucleation and growth of tin-zinc electrodeposits on a polycrystalline platinum electrode in tartaric acid

Current transients measurements and scanning electron microscopy were used to characterize the electrocrystallization process and morphology of tin-zinc alloys electrodeposited on Pt, in the absence and in the presence of tartaric acid. The model of Scharifker and Hills was used to analyze the current transients and it revealed that Sn-Zn electrocrystallization process in the presence of tartrate, under the studied conditions, is governed by three-dimensional progressive nucleation controlled by diffusion. In the absence of the complexant, the results indicated that nucleation process changes from instantaneous to progressive when the deposition potential becomes more negative, or when the incorporation of zinc occured to the deposit. The microscopic results showed deposits with two layers with different morphologies and is also influenced by deposition potential