A hematite photoelectrode grown on porous and conductive SnO₂ ceramics for solar-driven water splitting

Photoelectrochemical water splitting using solar energy is a highly promising technology to produce hydrogen as an environmentally friendly and renewable fuel with high-energy density. This approach requires the development of appropriate photoelectrode materials and substrates, which are low-cost and applicable for the fabrication of large area electrodes. In this work, hematite photoelectrodes are grown by aerosol assisted chemical vapour deposition (AA-CVD) onto highly-conductive and bulk porous SnO2 (Sb-doped) ceramic substrates. For such photoelectrodes, the photocurrent density of 2.8 mA cm-2 is achieved in aqueous 0.1 M NaOH under blue LED illumination (λ = 455 nm; 198 mW cm-2) at 1.23 V vs. RHE (reversible hydrogen electrode). This relatively good photoelectrochemical performance of the photoelectrode is achieved despite the simple fabrication process. Good performance is suggested to be related to the three-dimensional morphology of the porous ceramic substrate resulting in excellent light-driven charge carrier harvesting. The porosity of the ceramic substrate allows growth of the photoactive layer (SnO2-grains covered by hematite) to a depth of some micrometers, whereas the thickness of Fe2O3-coating on individual grains is only about 100–150 nm. This architecture of the photoactive layer assures a good light absorption and it creates favourable conditions for charge separation and transport.</p

Hematite photoelectrodes grown on porous CuO–Sb₂O₅–SnO₂ ceramics for photoelectrochemical water splitting

Photoelectrodes capable of cost-effective hydrogen production on a large scale, via photoelectrochemical water splitting under solar light, could offer an elegant solution to many current problems of humankind caused by over-reliance on fossil fuels and the resulting environmental pollution. The search and design of low-cost photoelectrode materials and substrates for practical applications are required. In this work, unmodified hematite photoanodes grown by metal-organic chemical vapor deposition (MO-CVD) onto CuO–Sb2O5–SnO2 ceramic substrates are reported. The deposition time of hematite precursor varied between 10 min, 60 min, and 90 min. The photoanode grown for 60 min exhibits the highest photocurrent density recorded at 1.23 V vs RHE (reversible hydrogen electrode): 4.79 mA/cm2 under blue light of Thorlabs LED M455L2 (455 nm), 0.41 mA/cm2 under the radiation of the real sun in Mexico, and 0.38 mA/cm2 under AM1.5G solar simulator conditions. The high porosity of CuO–Sb2O5–SnO2 ceramics permits the permeation of the hematite precursor into the substrate bulk, which results in 3D-growth of a thin Fe2O3-coating (50 nm or less) on conductive SnO2-grains in the ceramics to a depth of ca. 5 μm. The thick photocatalytic layer (SnO2-grains coated by hematite) of several micrometers assures a good light harvesting by the photoelectrode, while the nano-sized Fe2O3-films on conductive SnO2-grains is favorable for charge diffusion. This architecture of the photoelectrode results in good photoelectrochemical characteristics and is promising for further development.</p

INTRASPECIES PTEROMYS-TALLENNUSTEN (SCIURIDAE, MAMMALIA) TALVEN TURKIVÄRJEN VÄRITTÄMINEN MALLISSA

Peer reviewe

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

Brown bear attacks on humans : a worldwide perspective

The increasing trend of large carnivore attacks on humans not only raises human safety concerns but may also undermine large carnivore conservation efforts. Although rare, attacks by brown bears Ursus arctos are also on the rise and, although several studies have addressed this issue at local scales, information is lacking on a worldwide scale. Here, we investigated brown bear attacks (n = 664) on humans between 2000 and 2015 across most of the range inhabited by the species: North America (n = 183), Europe (n = 291), and East (n = 190). When the attacks occurred, half of the people were engaged in leisure activities and the main scenario was an encounter with a female with cubs. Attacks have increased significantly over time and were more frequent at high bear and low human population densities. There was no significant difference in the number of attacks between continents or between countries with different hunting practices. Understanding global patterns of bear attacks can help reduce dangerous encounters and, consequently, is crucial for informing wildlife managers and the public about appropriate measures to reduce this kind of conflicts in bear country.Peer reviewe

A hematite photoelectrode grown on porous and conductive SnO₂ ceramics for solar-driven water splitting

Photoelectrochemical water splitting using solar energy is a highly promising technology to produce hydrogen as an environmentally friendly and renewable fuel with high-energy density. This approach requires the development of appropriate photoelectrode materials and substrates, which are low-cost and applicable for the fabrication of large area electrodes. In this work, hematite photoelectrodes are grown by aerosol assisted chemical vapour deposition (AA-CVD) onto highly-conductive and bulk porous SnO2 (Sb-doped) ceramic substrates. For such photoelectrodes, the photocurrent density of 2.8 mA cm-2 is achieved in aqueous 0.1 M NaOH under blue LED illumination (λ = 455 nm; 198 mW cm-2) at 1.23 V vs. RHE (reversible hydrogen electrode). This relatively good photoelectrochemical performance of the photoelectrode is achieved despite the simple fabrication process. Good performance is suggested to be related to the three-dimensional morphology of the porous ceramic substrate resulting in excellent light-driven charge carrier harvesting. The porosity of the ceramic substrate allows growth of the photoactive layer (SnO2-grains covered by hematite) to a depth of some micrometers, whereas the thickness of Fe2O3-coating on individual grains is only about 100–150 nm. This architecture of the photoactive layer assures a good light absorption and it creates favourable conditions for charge separation and transport.</p

Analytical estimation of particle shape formation parameters in a plasma-chemical reactor

Analytical estimation of particle shape formation parameters in a plasma-chemical reactor implementing the process of thermochemical decomposition of liquid droplet agents (precursors) in the flow of a high-temperature gaseous heat-transfer medium was obtained. The basic factor which determines the process is the increase of concentration of a dissolved salt precursor component at the surface of a liquid particle due to solvent evaporation. According to the physical concept of the method of integral balance the diffusion process of concentration change is divided into two stages: the first stage is when the size of gradient layer does not reach the center of a spherical droplet and the second stage when the concentration at the center of a liquid droplet begins to change. The solutions for concentration fields were found for each stage using the method of integral balance taking into account the formation of salt precipitate when the concentration at the surface of the droplet reaches certain equilibrium value. The results of estimation of the influence of various reactor operation parameters and characteristics of initial solution (precursor) on the morphology of particles formed – mass fraction and localization of salt precipitate for various levels of evaporation

Analytical estimation of particle shape formation parameters in a plasma-chemical reactor

Analytical estimation of particle shape formation parameters in a plasma-chemical reactor implementing the process of thermochemical decomposition of liquid droplet agents (precursors) in the flow of a high-temperature gaseous heat-transfer medium was obtained. The basic factor which determines the process is the increase of concentration of a dissolved salt precursor component at the surface of a liquid particle due to solvent evaporation. According to the physical concept of the method of integral balance the diffusion process of concentration change is divided into two stages: the first stage is when the size of gradient layer does not reach the center of a spherical droplet and the second stage when the concentration at the center of a liquid droplet begins to change. The solutions for concentration fields were found for each stage using the method of integral balance taking into account the formation of salt precipitate when the concentration at the surface of the droplet reaches certain equilibrium value. The results of estimation of the influence of various reactor operation parameters and characteristics of initial solution (precursor) on the morphology of particles formed – mass fraction and localization of salt precipitate for various levels of evaporation