Cathodic shift and improved photocurrent performance of cost-effective Fe2O3 photoanodes

We successfully fabricated cost-effective and efficient pulse electrodeposited Fe₂O₃ photoanodes for PEC water splitting application. Surface modifications of Fe₂O₃ by oxygen evolution catalysts like cobalt phosphate (Co–Pi), a monoclinic BiVO₄ or both showed cathodic/anodic shift in photocurrent with significantly improved photo-response.     

Crystalline-to-amorphous transformation of tantalum-containing oxides for a superior performance in unassisted photocatalytic water splitting

Crystalline tantalum-containing oxides are usually taken as the advanced photocatalysts for water splitting. How about the amorphous counterparts? In this work, a transformation of crystalline Na₂Ta₂O₆ (CNa₂Ta₂O₆) to amorphous TaO_x (Am-TaO_x) was achieved by a facial hydrothermal method. We proposed a transformation mechanism based on nucleation-dissolution -recrystallization and further intensified the influence of base concentration on the composition, crystallinity, and morphology (CCM) as confirmed by XRD, TEM, EDS. N₂-physisorption, Raman, IR, and XPS analysis. It is found that when comparing to the crystalline counterparts, amorphous samples possessed higher surface area, abundant surface hydration layers and H⁺ adsorption, showing an unassisted photocatalytic water splitting with a rate of 70 ± 7 μmol g^?1 h^?1, much larger than that of 15 ± 1 μmol g^?1h^?1 of CNa₂Ta₂O₆, 11 ± 1 μmol g^?1h^?1 of crystalline Ta₂O₅ (CTa₂O₅), 30±2 μmol g^?1h^?1 of mixture with crystalline Ta₂O₅ and amorphous Na_xTa_yO_z (CTa₂O₅/Am-Na_xTa_yO_z), and even 4.6 × 10^?4 μmol g^?1h^?1 for commercial TiO₂. This observation is beneficial from the short diffusion paths of amorphous state for charge carriers, amount of catalytic sites, and stronger reducing ability. These findings develop a novel and efficient pathway towards synthesizing the different CCM of tantalum-containing compounds under hydrothermal conditions and could open opportunities for further investigating the photocatalytic property of tantalum-containing materials.     

Hybrid photo-thermal sulfur-ammonia water splitting cycle: Thermodynamic analysis of the thermochemical steps

Solar driven hybrid sulfur-ammonia water splitting cycle (HySA) integrates a solar-photocatalytic hydrogen, H₂, production step (H₂ sub-cycle) with a high-temperature solar thermochemical oxygen, O₂, evolution step (O₂ sub-cycle), implementing efficient thermal energy storage as part of the cycle operation. Previous studies of the cycle omitted intermediate products, such as ammonium bisulfate, from the O₂ sub-cycle and, thus, neglected their potential impact on the cycle's chemistry. Also, there are discrepancies in reported literature for the thermodynamic properties of ammonium sulfate, (NH₄)₂SO_4, and ammonium bisulfate, NH₄HSO₄. In this study, thermal analysis experiments were conducted in order to determine the phase transition temperatures and enthalpies, and the heat capacity temperature dependence of the ammonium sulfate, (NH₄)₂SO_4, and ammonium bisulfate, NH₄HSO₄. Our experimentally determined values for these parameters agree well with the data reported in DIPPR Project 801 database. Moreover, an exploratory thermodynamic analyses was performed using AspenPlus^© and FactSage^©, that included all potential reaction products, in order to identify critical parameters for an optimum O₂ sub-cycle. A methodology is proposed and evaluated to mitigate AspenPlus^©'s deficiency to handle solid phase changes. The thermodynamic analyses demonstrate that the NH₄HSO₄ inclusion in the O₂ sub-cycle reduces the overall process energy requirements, and allows its use as an energy storage medium. Finally, we show that the use of molten salts, in combination with their interactions, significantly affects the efficiency and the operating conditions of the process, as well as the state of the mixtures.     

Further results on regular splittings and multisplittings

In this article a detailed study of the regularity of induced splitting from the two-stage and multisplitting iterative methods is made. We present sufficient conditions which guarantee that the induced splitting is still a regular one. Meanwhile, we have established two new comparison theorems for the induced splittings characterized by a monotone matrix. In addition, we have also applied these theorems to some concrete methods.     

TiO2/CeO2 core/shell heterojunction nanoarrays for highly efficient photoelectrochemical water splitting

In this paper, novel TiO₂/CeO₂ core/shell heterojunction nanorod (NR) arrays were synthesized as photoanode for photoelectrochemical (PEC) water splitting via a simple and facial two-step hydrothermal approach. This synthesis route can obtain different amount of CeO₂ nanoparticles by controlling the hydrothermal time and eventually achieve uniform TiO₂/CeO₂ core/shell nanostructures. The uniform TiO₂/CeO₂ core/shell heterojunction nanoarrays exhibit a markedly enhanced photocurrent density of 5.30 mA·cm^?2 compared to that of pristine TiO₂ NR 1.79 mA·cm^?2 at 1.23 V vs. RHE in 1 M KOH solution. The superior PEC performance of the TiO₂/CeO₂ core/shell heterojunction is primarily due to much enhanced visible light absorption and appropriate gradient energy gap structure. This work not only offers the synthesis route for the novel TiO₂/CeO₂ core/shell heterojunction, but also suggests that this new core/shell heterojunction has a great potential application for efficient PEC water splitting devices.     

Cryptographic techniques of strategic data splitting and secure information management

This publication presents techniques for classifying strategic information, namely financial figures which make it possible to determine the standing of an enterprise or an organisation. These techniques of classifying (hiding) strategic information will be presented based on their application to problems of securely storing data of special significance, i.e. cryptographic information sharing protocols. What will be innovative will be the use of cryptographic information sharing protocols in cognitive systems for data analysis. This class of systems will be discussed based on systems for the semantic analysis of ratio data used to analyse liquidity indicators.     

Hydrogen energy production using manganese/semiconductor system inspired by photosynthesis

Hydrogen is the most efficient and the cleanest fuel. Inspired by photosynthesis, which is able to catalyze water-splitting reaction to achieve energy storage on the large scale at room temperature and neutral pH in nature, artificial systems and technology have been increasing advanced and great progresses have been made over the past decades. The three-dimensional structure of photosystem II with oxygen-evolving activity has been determined at an atomic level, which provides a thorough image with the specific position of each atom in the Mn₄CaO₅ cluster. These advancements have significantly enhanced our understanding of the mechanisms of water splitting in photosynthesis and offered a unique opportunity for hydrogen fuel production. In this review, the recent efforts in the area of manganese/semiconductor system for hydrogen generation were summarized with examples and discussed to highlight the operation mechanisms of this kind of catalytic configuration. A robust PS II mimic containing manganese/semiconductor nanostructure to accomplish the photo water splitting chemistry was evaluated. The development, mechanism, and future improvement of the manganese/semiconductor system were presented. The manganese/semiconductor system is highly likely to offer novel technology for hydrogen energy production.     

Photoelectrochemical characteristics of CuO films with different electrodeposition time

This paper explores the effect of electrodeposition time on microstructure, optical, and photoelectrochemical properties of CuO films. CuO films were electrochemically deposited on tin-doped indium oxide (ITO) substrates using a Cu₂O electrodeposition method followed by annealing at 550 °C for 2 h. The electrochemical deposition was carried out at different times (300, 600, 1200, and 1800 s) utilizing a copper sulfate pentahydrate and lactic acid solution. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were used to perform phase and microstructure analysis. Photoluminescence (PL) studies confirmed an increase in emission intensities with increasing deposition time. In addition, a significant change was observed in photoelectrochemical properties of the film by varying the deposition time. The film deposited for 600 s showed a high photocurrent density of ?0.55 mA cm^?2 at ?0.5 V. Moreover, a lowest resistance from electrochemical impedance spectroscopy (EIS) was recorded for the films electrochemically deposited for 600 s.     

Efficient photoelectrochemical water splitting and impedance analysis of WO3−x nanoflake electrodes

Solar-powered water splitting with photoelectrochemical (PEC) devices is considered to be a promising method to simultaneously harvest and store solar energy at a large scale. Nanostructured semiconductors offer potential advantages in PEC application due to their large surface area and size-dependent properties, such as increased absorption coefficient, increased band-gap energy and reduced carrier-scattering rate. In this contribution, self-doped tungsten trioxide (WO_3?x) nanoflake arrays were synthesized via a new route which involves the dealloying of Fe–W amorphous alloy, thermal treatment in air and properly cathodic polarization. The effects of different cathodic polarization current leading to different x value in WO_3?x on the morphology, phase, and photoelectrochemical performance of the resultant samples were investigated. It was found that WO_3?x with the appropriate x value presents a dramatic photoelectrochemical current density of 8.7 mA cm^?2 in the presence of methanol as a hole scavenger, five folds larger than that of pristine WO₃ nanoflakes. UV–vis reflection spectra suggest that the light absorption spectrum range of WO_3?x extends from UV to visible light region. Electrochemical impedance spectroscopy disclosed that the unique nanoflake architecture and the surface defects offer improved light harvesting as well as efficient charge transportation.     

Photoelectrode nanomaterials for photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is among the most promising approaches for energy conversion due to its practical efficiency. Unfortunately, many works simply test typical cases without profound insight, and this does not lead us very far. Two concepts are usually neglected: (i) the rate-determining step is usually the electrocatalytic process conducting the water splitting, and thus, the interfacial reaction at the electrode surface can be practically more important that the absorption of photons by the semiconductors, and (ii) the architecture of nanomaterials can directly control both photon absorption and electrochemical catalysis. While narrating the importance of the first concept the primary focus of the present review focuses on the second concept to summarize the general effects of nanostructures on the PEC performance. The nano-architecture has a larger impact on the electrocatalytic properties of the photoelectrode rather than light harvesting capability, but this feature is usually neglected. In fact, designing a nano-architecture is a tuning process to balance a series of different processes, which are in competition in a complicated system, for optimizing the PEC performance. The most important task is to maximize the number of electrocatalytic sites and forming a more effective electrode/electrolyte interface while reducing the number of charge recombination centers. Nanostructuring is normally in favor of the former while unfavorably supporting the latter.