Insights on Thickness-Dependent Charge Transfer Efficiency Modulated by Ultrasonic Treatment in Hematite Photoanodes

Abstract

The comprehension of the solid−liquid interface associated with the poor charge carrier dynamic of hematite has prevented its commercial application as a photoanode in a photoelectrochemical cell. The development of a low-cost and scalable strategy to overcome such drawbacks is still being pursued by the scientific community. Here, a simple surface modification of hematite photoanode designed with different thicknesses was carried out by employing an ultrasonic treatment (UST) process. UST creates an inhomogeneous defect distribution based on the solid− liquid energetics. The thicker photoanodes (H-4h) showed that the mechanical process can contribute to removing unstable layers, creating favorable sites for oxygen evolution without compromise the solid−solid interface. The UST approach for H-2h has promoted surface states pinning and possibly increased the stress between hematite and FTO. The effects on thinner photoanodes (H-2h) can drastically create polarized states that enhance surface trapping states, reducing the photogenerated charge lifetime. The outcome findings reveal that the surface hydroxylation might be extremely dependent on the electrode thickness. This study indicates that the UST approach is an efficient tool to boost the performance of thicker photoanodes, as desired for practical applications. Thus, for thinner layers, the stress induced at the hematite−FTO interface can be aggravated by mechanical treatment overcoming the beneficial effects at the solid−liquid interface. In fact, hydroxylation conducted via the sonication process is highly recommended for designing thicker films.

Controlled Growth of a Highly Energetic, Less Electron-Dense Tetrahedral Fe3+ Phase on the Surface of α-Fe2O3 Nanoparticles toward Enhanced Optical, Magnetic, and Supercapacitive Performance

“…A higher precursor concentration enhances the nucleation rate and favors the formation of a more energetic tetrahedral phase as the areal ratio (A T /A O ) for 2p 3/2 and 2p 1/2 increases 1.5 and 4 times, respectively, in the A 4 compared to A 1 sample. On the other hand, a surface peak is associated with the Fe 3+ ion neighborhood surrounded by a lower electron density and needs greater energy to produce a photoelectron. , Figure a,b indicates that A 4 nanoparticles have rich lower electron surrounded Fe 3+ ions compared to A 1 as they increase from 8.7 to 22.2% for the A 1 and A 4 sample, respectively.…”

“…On the other hand, a surface peak is associated with the Fe 3+ ion neighborhood surrounded by a lower electron density and needs greater energy to produce a photoelectron. 51,52 Figure 5a,b indicates that A 4 nanoparticles have rich lower electron surrounded Fe 3+ ions compared to A 1 as they increase from 8.7 to 22.2% for the A 1 and A 4 sample, respectively.…”

The Influence of Magnetic Field and Nanoparticle Concentration on the Thin Film Colloidal Deposition Process of Magnetic Nanoparticles: The Search for High-Efficiency Hematite Photoanodes

“…For photoelectrochemical applications, the thickness of the film can be viewed as a crucial factor. Freitas et al [ 20 ] correlated the different thicknesses of hematite obtained by the hydrothermal method, demonstrating that the influence of surface modification promotes polarized states, improves surface trapping, and consequently decreases the lifetime of photogenerated charge. The APCVD method described by Gratzel et al [ 21 ] demonstrates the formation of films with varying thicknesses based on deposition time, as well as the effect of thickness on the low hematite diffusion length (5 nm).…”