Multifunctional approach to improve water oxidation performance with MOF-based photoelectrodes

Metal-Organic Frameworks (MOFs) are a group of compounds with high porosity and diverse capabilities in photoelectrochemistry. The use of these compounds as photocatalysts and photoelectrodes is still a strong challenge due to bulk and surface recombination issues. To solve this problem, we applied a dual strategy to simultaneously enhance charge separation and catalytic activity in MIL-125-NH2 and UIO-66-NH2 MOF photocatalysts. Mesoporous TiO2 was used as electron-selective contact on the MOF surface (MOF/TiO2) to minimize bulk recombination. On the other hand, to increase the MOF catalytic activity for water oxidation, a well-matched Co3(PO4)2 (CoPi) co-catalyst (CoPi/MOF/TiO2) was used. The obtained results showed that CoPi and TiO2 were introduced in the MOF structure. The (CoPi/MOF/TiO2) photoelectrodes showed a photocurrent density 26 times higher compared to the reference MOF at 1.23 V vs. RHE for PEC water oxidation of artificial seawater, validating the developed strategy for further photocatalytic and photoelectrochemical applications.Funding for open access charge: CRUE-Universitat Jaume IWe acknowledge with appreciation the financial support from the University of Isfahan and Ministry of Science, Research and Technology Center for International Scientific Studies and Collaboration (CISSC). SG acknowledges the financial support from the Ministerio de Ciencia, Innovación y Universidades of Spain through funded project ENE2017-85087-C3-1-R

Copolymer‐templated nickel oxide for high‐efficiency mesoscopic perovskite solar cells in inverted architecture

Despite the outstanding role of mesoscopic structures on the efficiency and stability of perovskite solar cells (PSCs) in the regular (n–i–p) architecture, mesoscopic PSCs in inverted (p–i–n) architecture have rarely been reported. Herein, an efficient and stable mesoscopic NiOx (mp-NiOx) scaffold formed via a simple and low-cost triblock copolymer template-assisted strategy is employed, and this mp-NiOx film is utilized as a hole transport layer (HTL) in PSCs, for the first time. Promisingly, this approach allows the fabrication of homogenous, crack-free, and robust 150 nm thick mp-NiOx HTLs through a facile chemical approach. Such a high-quality templated mp-NiOx structure promotes the growth of the perovskite film yielding better surface coverage and enlarged grains. These desired structural and morphological features effectively translate into improved charge extraction, accelerated charge transportation, and suppressed trap-assisted recombination. Ultimately, a considerable efficiency of 20.2% is achieved with negligible hysteresis which is among the highest efficiencies for mp-NiOx based inverted PSCs so far. Moreover, mesoscopic devices indicate higher long-term stability under ambient conditions compared to planar devices. Overall, these results may set new benchmarks in terms of performance for mesoscopic inverted PSCs employing templated mp-NiOx films as highly efficient, stable, and easy fabricated HTLs

The Findings of Transcranial Doppler Ultrasonography in Patients with Ischemic Stroke

Background: Stroke is a multifactorial disorder, the most common cause being arterial occlusion. Transcranial Doppler Ultrasonography (TCD) is a common non-invasive method available for assessment the arterial blood flow of the brain. Objective: Assessment the hemodynamic parameters of cerebral arteries, using TCD device in patients suffering ischemic stroke. Materials and Methods: This descriptive cross-sectional study was conducted on patients with ischemic stroke in 2014 in Iran after being approved by ethics committee of Researches and Technology Vice-chancellorship of Guilan University of Medical Sciences. After obtaining informed consent, all patients underwent TCD. Demographic details and TCD findings were recorded. Data were analysed in SPSS software 21 using independent t-test, Chi-square, and Fisher's exact tests. The descriptive results were presented as mean ± SD and frequency. Results: A total of 102 patients (69 men and 33 women) with ischemic stroke and mean age of 63.72 ± 12.64 years participated in this study. Among 49.02% of patients at least one hemodynamic abnormality was diagnosed. Small Vessel Disease (SVD), extracranial stenosis (ECS) and intracranial stenosis (ICS) were found in 29.41%, 20.59% and 11.76% of patients respectively. Abnormal Pulsatility Index (PI), Peak Systolic Velocity (PSV) and Mean Blood Flow Velocity (Vm) were reported in 32.25%, 20.59% and 9.8% of them respectively. A significant relationship was found between PSV parameter and also presence of ECS and gender (p = 0.047). Moreover, SVD and abnormal PI were found significantly related to age (p = 0.002). Conclusion: TCD results showed almost half of the patients with ischemic stroke were found to have at least one hemodynamic abnormality

Photoelectrochemical water splitting with dual-photoelectrode tandem and parallel configurations: Enhancing light harvesting and carrier collection efficiencies

Photoelectrochemical (PEC) water splitting stands out as one of the most promising technologies to store solar energy into chemical bonds and decarbonize industry and transport. In the present study, we develop hetero- structured BiVO4/WO3 and TiO2/PANi photoanodes for water oxidation, aiming at maximizing their spectral activity and their light harvesting efficiency, rationalized by a detailed optical modeling of the PEC cell. Furthermore, we implement tandem and parallel dual-photoelectrode configurations to enhance the collection efficiency. Photocurrents of 1.68 and 2.29 mA/cm2 at 1.23 V vs RHE were obtained for tandem and parallel configurations, respectively, demonstrating an enhancement factor 4–6 for Tandem and Parallel cells

Hierarchical Ti-Based MOF with Embedded RuO2 Nanoparticles: a Highly Efficient Photoelectrode for Visible Light Water Oxidation

The Ti-based metal-organic framework (MOF) MIL-125-NH2 is one of the promising materials for solar water splitting because it contains a sensitizer and a catalytic center in a single structure. MIL-125-NH2 as many other MOFs has a microporous structure with pore diameters less than 2 nm. Compared with common MOFs, hierarchical mesoporous materials exhibit very large specific surface areas that facilitate diffusion of active species, accelerate subsequent surface reactions, and increase the bubble release rate by providing larger free spaces. Thus, the development of a facile method to create hierarchical porous MOFs with larger pore sizes remains a chemical challenge. Furthermore, MOF-type semiconducting materials usually have low activities in oxygen evolution reaction, and the presence of a suitable cocatalyst is needed to reduce the large O-2 overpotential. This study attempted to generate a hierarchical MIL-125-NH 2 MOF material with embedded RuO2 nanopartides as a highly efficient cocatalyst in a simple one-step process for use in efficient solar water oxidation. Different amounts of RuCl3 center dot H2O precursor salt were used simultaneously for creating hierarchical porosity in MIL-125-NH2 and for producing the assumed RuO2 cocatalyst. For comparison, a hydrochloric acid treatment was applied to generate hierarchical porosity in the MOF in the absence of ruthenium. The samples were characterized using high-resolution transmission electron microscopy (HRTEM), Brunauer-Emmett-Teller adsorption, powder X-ray diffraction, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. HRTEM gave evidence that in the ruthenium oxide-containing MIL-125-NH2 samples, tetragonal RuO2 nanoparticles are present. The materials were applied as photoelectrodes, and photoelectrochemical (PEC) water oxidation performance under visible light illumination was studied. The PEC water oxidation performance of the MIL-125-NH2 layer could be strikingly improved with a photocurrent density of about 10 times more than that of the pure MOF at 1.23 V versus reversible hydrogen electrode in artificial seawater, as a result of the hierarchical MOF structure and the presence of RuO2 as a cocatalyst. Furthermore, density functional theory calculations were performed to shed light on the electronic properties and the role of the RuO2 in the assumed hole transport