Improved photocatalytic activity of d-FeOOH by using H2O2 as an electron acceptor.

In this work, d-FeOOH nanoparticles were synthesized by a simple co-precipitation method and used as a photocatalyst in the presence of H2O2 for the oxidation of Rhodamine B (RhB) dye under artificial light. The d-FeOOH was characterized by powder X-ray diffraction, 57Fe M?ssbauer spectroscopy, N2 adsorption/desorption and UV?vis diffuse reflectance measurements. The d-FeOOH nanoparticles have high specific surface area (101 m2 g 1) and optical bandgap energy of 2.02 eV. Under artificial light, only 59% of RhB (100 mL; 20 mg L 1) was photocatalytically degraded by d-FeOOH in 60 min reaction. However, after adding H2O2, the photocatalytic activity of d-FeOOH was significantly improved, reaching 87% of dye removal. Tests using scavengers of reactive species and EPR analysis revealed that h+ and OH are the main species in this system. Based on the experimental results, the mechanism of RhB photodegradation in the presence of d-FeOOH and H2O2 was proposed. By this mechanism, the OH can be formed by direct water oxidation or by H2O2 reduction, as the electron transfer from the conduction band of d-FeOOH to H2O2 is thermodynamically favorable. Moreover, the H2O2 retards the electron-hole recombination in d-FeOOH, thus increasing its photocatalytic activity. Given its high efficiency for degrading RhB in water, d-FeOOH revealed to be a promising photocatalyst to be tested in the oxidation of emerging pollutants for the environmental decontamination

Enhanced photocatalytic hydrogen generation from water by Ni(OH)2 loaded on Ni-doped d-FeOOH nanoparticles obtained by one-step synthesis.

Ni(OH)2 loaded on Ni-doped d-FeOOH photocatalysts were prepared by a simple and low-cost one-step precipitation method. The effect of Ni(OH)2 nanoparticles and Ni2+ doping on the photocatalytic hydrogen production rates by d-FeOOH in aqueous suspension was investigated. The results showed that the photocatalytic H2-production activity of d-FeOOH was significantly enhanced by doping with Ni2+ ions and by loading Ni(OH)2 on its surface. The maximum H2-production was obtained for the sample with 20 wt% Ni, which provided 5746 mmol h 1 g 1. This high photocatalytic H2-production is due to the combined effects of Ni2+ doping and Ni(OH)2 loaded on the d-FeOOH surface. The Ni2+ doping increased the conductivity and charge transfer in d-FeOOH, whereas the Ni(OH)2 improved the charge separation in the d-FeOOH and, consequently, the photocatalytic H2-production activity

Bismuth vanadate photoelectrodes with high photovoltage behave as photoanode and photocathode in photoelectrochemical cells for water splitting.

Using dual-photoelectrode photoelectrochemical (PEC) devices based on earth-abundant metal oxides for unbiased water splitting is an attractive means of producing green H2 fuel, but is challenging, owing to low photovoltages generated by PEC cells. This problem can be solved by coupling n-type BiVO4 with n-type Bi4V2O11 to create a virtual p/n junction due to the formation of a hole-inversion layer at the semiconductor interface. Thus, photoelectrodes with high photovoltage outputs were synthesized. The photoelectrodes exhibited features of pand n-type semiconductors when illuminated under an applied bias, suggesting their use as photoanode and photocathode in a dual-photoelectrode PEC cell. This concept was proved by connecting a 1 mol% W-doped BiVO4/Bi4V2O11 photoanode with an undoped BiVO4/Bi4V2O11 photocathode, which produced a high photovoltage of 1.54 V, sufficient to drive standalone water splitting with 0.95% efficiency

High water oxidation performance of W-Doped BiVO4 photoanodes coupled to V2O5 rods as a photoabsorber and hole carrier.

Monoclinic BiVO4 is recognized as a promising photoanode for water oxidation, but its relatively wide bandgap energy (Eg ?2.5?eV) and poor charge transport limit the light absorption (?abs) and charge separation (?sep) efficiencies, thus resulting in low photocurrents. To solve these drawbacks, here the ?abs????sep product has been decoupled by combining W?doped BiVO4 and V2O5 rods (Eg ?2.1?eV) for simultaneously increasing the light harvesting and the charge separation in photoanodes under back?side illumination. In this strategy, V2O5 rods maximize the light absorption and hole transport throughout the W?BiVO4 film, making more holes to achieve the V2O5/W?BiVO4/H2O interface to trigger the water oxidation reaction with photocurrents as high as 6.6?mA?cm?2 at 1.23 VRHE after 2?h reaction. Notably, under back?side illumination, the W?BiVO4/V2O5 photoanode exhibited ?abs????sep of 74.5 and 93.0% at 0.5 and 1.23 VRHE, respectively, the highest values reported up to date for BiVO4?based photoelectrodes. This simple strategy brings us closer to develop efficient photoanodes for photoelectrochemical water splitting devices

Electrocatalytic performance of different cobalt molybdate structures for water oxidation in alkaline media.

Cobalt molybdates with different crystalline structures, i.e., ?, ?, and hydrated (H)-CoMoO4, were synthesized, and their electrocatalytic activities were thoroughly examined for catalyzing the oxygen evolution reaction (OER) in alkaline media. The material characteristics were associated with the electrocatalytic properties by evaluating the CoMoO4 crystal structures (XRD and Raman), morphologies (TEM), and electrochemical features (electrochemically active surface area, roughness factor, electrochemical impedance, Tafel analysis, and controlled-current electrolysis). These combined findings revealed that the electrocatalytic performance is greatly influenced by the crystalline structures of CoMoO4, following the order ?-CoMoO4 > H-CoMoO4 > ?-CoMoO4. The H-CoMoO4 catalysts crystallized in the triclinic space group, P[1 with combining macron] (#2), with Z = 4. On the other hand, the ?- and ?-CoMoO4 catalysts exhibited a monoclinic structure, C2/m (#12), with Z = 8. In the OER experiments, ?-CoMoO4 showed an overpotential of 0.43 ? 0.05 V compared to the 0.51 ? 0.05 V and 0.56 ? 0.04 V exhibited by the H-CoMoO4 and ?-CoMoO4 catalysts, respectively, to achieve 10 mA cm?2. All CoMoO4 structures displayed stability for at least 6 h at a controlled current density of 10 mA cm?2. Finally, computational simulations indicate that the coexistence of Co and Mo ions in edge-shared octahedral sites of ?-CoMoO4 may favor the interaction between the O atom of the water molecule and the metal adsorption sites due to its surface being electronically less dense than ?- and H-CoMoO4 surfaces, thus resulting in its higher performance for OER