When eutectic composites meet photoelectrochemistry – Highly stable and efficient UV–visible hybrid photoanodes

Charge transport channel and nonmetallic plasmon synergistically augment surface reaction kinetics and charge separation for efficient photoelectrochemical hydrogen evolution of CdS/TiN-sensitized Fe2V4O13 photoanode

Achieving simultaneous enhancement in the light energy utilization efficiency, bulk charge carrier separation and surface charge carrier injection efficiency as well as the surface reaction kinetics of water oxidation is a formidable challenge for photoanodes in photoelectrochemical (PEC) water splitting hydrogen generation. Herein, nanoparticle-assembled flower-like CdS spheres and nonmetallic plasmonic TiN nanoparticles are exploited to successively sensitize Fe2V4O13 nanoporous film (NPF) photoanode for achieving efficient PEC hydrogen evolution. The sensitization of TiN and CdS simultaneously integrates type-II band structure, surface plasmon resonance and Schottky junction into Fe2V4O13 NPF photoanode, synergistically achieving simultaneous enhancement in the light energy utilization efficiency, bulk charge carrier separation efficiency, surface reaction kinetics of water oxidation and surface charge carrier injection efficiency. As a result, the highest charge separation and injection efficiencies of CdS/TiN-sensitized Fe2V4O13 NPF photoanode are respectively increased by 25.5 and 1.96 times to those of bare Fe2V4O13 NPF photoanode. Furthermore, the designed and constructed CdS/TiN-sensitized Fe2V4O13 NPF photoanode exhibits substantially boosted unbiased solar-light-driven PEC hydrogen evolution ability with a photocurrent density of 2.12 mA/cm2, which is two orders of magnitude (662 times) higher than that of the unsensitized Fe2V4O13 NPF photoanode. The findings in this work provide a novel and promising strategy to design and construct high-performance Fe2V4O13-based nonmetallic plasmonic photoanodes for potential application in PEC hydrogen evolution.

Durability of SrTiO3-TiO2 eutectic composite as a photoanode for photoelectrochemical water splitting

The idea of employing sunlight - a virtually inexhaustible source of energy - to catalyze various chemical reactions or generate electrical current is intensively studied nowadays. Here, we describe a method for testing photoelectrochemical (PEC) stability developed using the example of photoanodes from an SrTiO3-TiO2 eutectic composite. Eutectic composite stability measurements were carried out in long-term cycles: 0.5, 1, 2, 5, 10, 20 and 50 h of constant electrode operation (total of 88.5 h). After each cycle, cyclic voltammetry, electrochemical impedance spectroscopy, reflectance, roughness, SEM/EDS microstructure analysis and the content of Sr and Ti ions in the applied electrolyte solution were examined. The initial value of the photocurrent density was 1.95 mA cm-2 at a potential of 1.5 V vs. Ag/AgCl in a pH 2 electrolyte environment and under 6 suns of illumination it increased almost four times, reaching 7.22 mA cm-2 after a total of 88.5 h of PEC stability cycles. Due to the better catalytic properties of TiO2, this phase degrades faster, causing an increase in the roughness of the electrode surface. At the same time, reflectance of the photoanode active layer dropped from around 35% to 15%. The investigated method of PEC material testing can be applied in areas beyond photoelectrochemical water splitting, such as chemistry, photovoltaics, sensing and others.

Reduced Self-Aggregation and Improved Stability of Silica-Coated Fe3O4/Ag SERS-Active Nanotags Functionalized With 2-Mercaptoethanesulfonate

Nanocomposites combining magnetic and plasmonic properties are very attractive within the field of surface-enhanced Raman scattering (SERS) spectroscopy. Applications presented so far take advantage of not only the cooperation of both components but also synergy (enhanced properties), leading to multi-approach analysis. While many methods were proposed to synthesize such plasmonic-magnetic nanoparticles, the issue of their collective magnetic behavior, inducing irreversible self-aggregation, has not been addressed yet. Thus, here we present a simple and fast method to overcome this problem, employing 2-mercaptoethanesulfonate (MES) ions as both a SERS tag and primer molecules in the silica-coating process of the previously fabricated Fe3O4/Ag nanocomposite. The use of MES favored the formation of silica-coated nanomaterial comprised of well-dispersed small clusters of Fe3O4/Ag nanoparticles. Furthermore, adsorbed MES molecules provided a reliable SERS response, which was successfully detected after magnetic assembly of the Fe3O4/Ag@MES@SiO2 on the surface of the banknote. Improved chemical stability after coating with a silica layer was also found when the nanocomposite was exposed to suspension of yeast cells. This work reports on the application of 2-mercaptoethanesulfonate not only providing a photostable SERS signal due to a non-aromatic Raman reporter but also acting as a silica-coating primer and a factor responsible for a substantial reduction of the self-aggregation of the plasmonic-magnetic nanocomposite. Additionally, here obtained Fe3O4/Ag@MES@SiO2 SERS nanotags showed the potential as security labels for the authentication purposes, retaining its original SERS performance after deposition on the banknote.

Construction of Ag-modified TiO2/ZnO heterojunction nanotree arrays with superior photocatalytic and photoelectrochemical properties

The work involves the preparation of TiO₂/ZnO heterojunction nanotree arrays by a three-step: hydrothermal, sol–gel, and secondary hydrothermal method, and then modification of Ag quantum dots (QDs).