High performance BiFeO3 ferroelectric nanostructured photocathodes

Understanding the impact of Bi stoichiometry towards optimised BiFeO3 photocathodes: structure, morphology, defects and ferroelectricity

BiFeO3 thin films have been widely studied for photoelectrochemical water splitting applications because of its narrow bandgap and good ferroelectricity which can promote the separation of photo-generated charges. Bismuth is well known as a volatile element and excess bismuth is usually added into the precursor to compensate the loss of bismuth during heat treatment, but the amount of excess bismuth required and how excess bismuth will affect PEC performance have not been clearly studied. Herein, self-doped Bi1+x FeO3 thin films are prepared via simple chemical solution deposition method with excess bismuth from 0-30% in the precursor. The loss of bismuth after annealing is confirmed by EDX and XPS. Multiple factors were investigated and it was found that non-stoichiometric Bi resulted in changes of structure, morphology, defects, electronic properties and PEC performance. An enhanced photocurrent is observed in bismuth-rich BiFeO3 films, which can be ascribed to the larger grain size, decreased oxygen vacancies, lattice distortion and supported charge separation. Moreover, the photocathodic performance can be further enhance by ferroelectric poling. Our work indicates that deficient bismuth should be carefully avoided during heat treatment and moreover, a slight excess of Bi is beneficial for PEC performance. Therefore, we offer a simple way to enhance PEC performance of BiFeO3-based ferroelectric materials through careful control of their stoichiometry.

Effect of Morphology Modification of BiFeO3 on Photocatalytic Efficacy of P-g-C3N4/BiFeO3 Composites

This current study assessed the impacts of morphology adjustment of perovskite BiFeO3 (BFO) on the construction and photocatalytic activity of P-infused g-C3N4/U-BiFeO3 (U-BFO/PCN) heterostructured composite photocatalysts. Favorable formation of U-BFO/PCN composites was attained via urea-aided morphology-controlled hydrothermal synthesis of BFO followed by solvosonication-mediated fusion with already synthesized P-g-C3N4 to form U-BFO/PCN composites. The prepared bare and composite photocatalysts' morphological, textural, structural, optical, and photocatalytic performance were meticulously examined through various analytical characterization techniques and photodegradation of aqueous rhodamine B (RhB). Ellipsoids and flakes morphological structures were obtained for U-BFO and BFO, and their effects on the successful fabrication of the heterojunctions were also established. The U-BFO/PCN composite exhibits 99.2% efficiency within 20 min of visible-light irradiation, surpassing BFO/PCN (88.5%), PCN (66.8%), and U-BFO (26.1%). The pseudo-first-order kinetics of U-BFO/PCN composites is 2.41 × 10-1 min-1, equivalent to 2.2 times, 57 times, and 4.3 times of BFO/PCN (1.08 × 10-1 min-1), U-BFO, (4.20 × 10-3 min-1), and PCN, (5.60 × 10-2 min-1), respectively. The recyclability test demonstrates an outstanding photostability for U-BFO/PCN after four cyclic runs. This improved photocatalytic activity exhibited by the composites can be attributed to enhanced visible-light utilization and additional accessible active sites due to surface and electronic band modification of CN via P-doping and effective charge separation achieved via successful composites formation.

Controlled Porosity in Ferroelectric BaTiO3 Photoanodes

The use of ferroelectric polarization to promote electron-hole separation has emerged as a promising strategy to improve photocatalytic activity. Although ferroelectric thin films with planar geometry have been largely studied, nanostructured and porous ferroelectric thin films have not been commonly used in photo-electrocatalysis. The inclusion of porosity in ferroelectric thin films would enhance the surface area and reactivity, leading to a potential improvement of the photoelectrochemical (PEC) performance. Herein, the preparation of porous barium titanate (pBTO) thin films by a soft template-assisted sol-gel method is reported, and the control of porosity using different organic/inorganic ratios is verified by the combination of scanning electron microscopy and ellipsometry techniques. Using piezoresponse force microscopy, the switching of ferroelectric domains in pBTO thin films is observed, confirming that the ferroelectric polarization is still retained in the porous structures. In addition, the presence of porosity in pBTO thin films leads to a clear improvement of the PEC response. By electrochemical poling, we also demonstrated the tuning of the PEC performance of pBTO thin films via ferroelectric polarization. Our work offers a simple and low-cost approach to control the morphology optimization of ferroelectric thin films, which could open up the development of materials with great potential for PEC applications.

Screen-printed p–n BiOCl/BiFeO3 heterojunctions for efficient photocatalytic degradation of Rhodamine B

Colloidal-free screen-printed p–n BiOCl/BiFeO₃ heterojunctions are successfully synthesized to achieve photocatalytic degradation of Rhodamine B (RhB) using visible light (λ ≥ 400 nm). The crystalline structure of dense BiOCl nanosheets self-assembled with impressive aspect ratio atop BFO powders is confirmed by XRD, Raman and TEM measurements. Iron impurities inside these 10 ± 2 nm-thick BiOCl nanosheets increase visible light absorption. Fluorescent Rhodamine B (RhB) dye degradation is used to evaluate the photocatalytic performance of this unique heterojunction material. For optimal metal-enhanced RhB degradation, a few nanometers of platinum are deposited using the sputtering technique to act as a cocatalyst. This unique architecture yields an impressive 92% RhB degradation in only 150 min under visible light. Operating at near-neutral pH, the proposed approach also addresses the key issue of catalysis recovery, which remains one of the main drawbacks of current photocatalysis technologies.

We report a facile methodology to print colloid-free p–n BiOCl/BiFeO₃ heterojunctions for degradation of Rhodamine B. Thanks to dense interconnected networks of BiOCl nanosheets, a 92% degradation of rhodamine B is achieved under visible light.