Enhanced electrochemical water splitting activity in annealed TiO2 nanoparticles of photoanode

In this paper, we present the electrochemical water splitting characteristics of TiO2/FTO electrodes via spin-coating method. By using thermal annealing approach, the TiO2 nanoparticle (P25) was modified with a more active photocatalyst. The annealed TiO2 nanoparticle-based photoanode in vacuum shows photocurrent density of 0.27 mA/cm2 and photoconversion efficiency of (η = 0.22%) at potential of 0.4 V (vs. RHE), which are higher than those of annealed TiO2 nanoparticle-based electrode in air. The improved photoelectrochemical property is attributed to high oxygen vacancy density with more active sides, while TiO2 nanoparticle was annealed in vacuum (∼10−1 torr) with oxide concentration conditions. From this finding, we propose that a thermal annealing process might serve as an approach for fabricating the photoanodes of TiO2-based materials consisting of much active photocatalyst

Influence of Oxygen Vacancy Density on the Polaronic Configuration in Rutile

Polaronic configurations that were introduced by oxygen vacancy in rutile TiO2 crystal have been studied by the DFT + U method. It is found that the building block of TiO6 will expand when extra electron is trapped in the central Ti atom as polaron. With manually adjusting the initial geometry of oxygen vacancy structure, a variety of polaronic configurations are obtained after variable-cell relaxation. By calculating different sizes of supercell model, it is found that the most stable configuration can be influenced by the density of oxygen vacancy. With increasing interaction between vacancies, the most stable polaronic configuration change from small polaronic configuration to mixed configuration.

Systematic derivation of a surface polarisation model for planar perovskite solar cells

Increasing evidence suggests that the presence of mobile ions in perovskite solar cells (PSCs) can cause a current–voltage curve hysteresis. Steady state and transient current–voltage characteristics of a planar metal halide CH3NH3PbI3PSC are analysed with a drift-diffusion model that accounts for both charge transport and ion vacancy motion. The high ion vacancy density within the perovskite layer gives rise to narrow Debye layers (typical width ~2 nm), adjacent to the interfaces with the transport layers, over which large drops in the electric potential occur and in which significant charge is stored. Large disparities between (I) the width of the Debye layers and that of the perovskite layer (~600 nm) and (II) the ion vacancy density and the charge carrier densities motivate an asymptotic approach to solving the model, while the stiffness of the equations renders standard solution methods unreliable. We derive a simplifiedsurface polarisationmodel in which the slow ion dynamics are replaced by interfacial (non-linear) capacitances at the perovskite interfaces. Favourable comparison is made between the results of the asymptotic approach and numerical solutions for a realistic cell over a wide range of operating conditions of practical interest.