RESUMO

Electrochemical cells for direct conversion of solar energy to electricity (or hydrogen) are one of the most sustainable solutions to meet the increasing worldwide energy demands. In this report, a novel and highly-efficient ternary heterojunction-structured Bi4O7/Bi3.33(VO4)2O2/Bi46V8O89 photoelectrode is presented. It is demonstrated that the combination of an inversion layer, induced by holes (or electrons) at the interface of the semiconducting Bi3.33(VO4)2O2 and Bi46V8O89 components, and the rectifying contact between the Bi4O7 and Bi3.33(VO4)2O2 phases acting afterward as a conventional p-n junction, creates an adjustable virtual p-n-p or n-p-n junction due to self-polarization in the ion-conducting Bi46V8O89 constituent. This design approach led to anodic and cathodic photocurrent densities of + 38.41 mA cm-2 (+ 0.76 VRHE) and- 2.48 mA cm-2 (0 VRHE), respectively. Accordingly, first, this heterojunction can be used either as photoanode or as photocathode with great performance for artificial photosynthesis, noting, second, that the anodic response reveals exceptionally high: more than 300% superior to excellent values previously reported in the literature.

Assuntos

Técnicas Eletroquímicas/métodos , Fotossíntese/fisiologia , Eletricidade , Eletrodos , Processos Fotoquímicos , Energia Solar , Luz Solar

RESUMO

The dependence of frequency and applied magnetic field in the magnetoelectric effect (ME) of the composites 0.68Pb(Mg1/3Nb2/3)-0.32PbTiO3/CoFe2O4 (PMN-PT/CFO) and 0.68Pb(Mg1/3Nb2/3)-0.32PbTiO3/NiFe2O4 (PMN-PT/NFO) are investigated. The results for PMN-PT/CFO composite, show a hysteretic behavior for the ME coefficient, at low temperatures (5 K), for frequencies higher than 1000 Hz. Contrasting with these results, the ME coefficient for the PMN-PT/NFO shows a well-known peak-peak related with the magnetostriction coefficient. Based on energy levels of stabilization for each ferromagnetic phase, it was possible to explain the ME hysteretic distinct behavior of PMN-PT/CFO, because of the degeneracy in the energy levels, due to the spin-orbit coupling causing changes in the dynamic properties of the magnetoelastic interactions.

RESUMO

The microscopic origin of the ferroic and multiferroic properties of AlFeO3 have been carefully investigated. The maximum entropy method was applied to X-ray diffraction data and ab initio density functional theory calculations in order to obtain the electron density distributions and electric polarization. The study of chemical bonds shows that the bonds between Fe(3d) and O(2p) ions are anisotropic, leading to the configuration of shorter/longer and stronger/weaker bonds. This leads to electric polarization. Density of states calculations showed a magnetic polarization as a result of a weak ferromagnetic ordering. These results unambiguously show that AlFeO3 is a multiferroic material and exhibits a magnetoelectric coupling at room temperature, as has already been shown by experiments.