Solar-powered electrochemical production of hydrogen through water electrolysis is an active and important research endeavor. However, technologies and roadmaps for implementation of this process do ...not exist. In this perspective paper, we describe potential pathways for solar-hydrogen technologies into the marketplace in the form of photoelectrochemical or photovoltaic-driven electrolysis devices and systems. We detail technical approaches for device and system architectures, economic drivers, societal perceptions, political impacts, technological challenges, and research opportunities. Implementation scenarios are broken down into short-term and long-term markets, and a specific technology roadmap is defined. In the short term, the only plausible economical option will be photovoltaic-driven electrolysis systems for niche applications. In the long term, electrochemical solar-hydrogen technologies could be deployed more broadly in energy markets but will require advances in the technology, significant cost reductions, and/or policy changes. Ultimately, a transition to a society that significantly relies on solar-hydrogen technologies will benefit from continued creativity and influence from the scientific community.
Several application fields can benefit from solar-hydrogen technologies
via
specific short-term and long-term pathways.
Renewables challenge the management of energy supply and demand due to their intermittency. A promising solution is the direct conversion of the excess electrical energy into valuable chemicals in ...electrochemical reactors that are inexpensive, scalable, and compatible with irregular availability of electrical power. Membrane-less electrolyzers, deployed on a microfluidic platform, were recently shown to hold great promise for efficient electrolysis and cost-effective operation. The elimination of the membrane increases the reactor lifetime, reduces fabrication costs, and enables the deployment of liquid electrolytes with ionic conductivities that surpass those allowed by solid membranes. Here, we demonstrate a membrane-less architecture that enables unprecedented throughput by 3D printing a device that combines components such as the flow plates and the fluidic ports in a monolithic part, while at the same time, providing tight tolerances and smooth surfaces for precise flow conditioning. We show that inertial fluidic forces are effective even in millifluidic regimes and, therefore, are utilized to control the two-phase flows inside the device and prevent cross-contamination of the products. Simulations provide insight on governing fluid dynamics of coalescing bubbles and their rapid jumps away from the electrodes and help identify three key mechanisms for their fast and intriguing return towards the electrodes. Experiments and simulations are used to demonstrate the efficiency of the inertial separation mechanism in millichannels and at higher flow rates than in microchannels. We analyze the performance of the present device for two reactions: water splitting and the chlor-alkali process, and find product purities of more than 99% and Faradaic efficiencies of more than 90%. The present membrane-less reactor - containing more efficient catalysts - provides close to 40 times higher throughput than its microfluidic counterpart and paves the way for realization of cost-effective and scalable electrochemical stacks that meet the performance and price targets of the renewable energy sector.
Separation of electrolysis products using fluidic inertial forces in a 3D printed flow cell.
A non-intrusive method is presented for measuring different fluidic properties in a microfluidic chip by optically monitoring the flow of droplets. A neural network is used to extract the desired ...information from the images of the droplets. We demonstrate the method in two applications: measurement of the concentration of each component of a water/alcohol mixture, and measurement of the flow rate of the same mixture. A large number of droplet images are recorded and used to train deep neural networks (DNN) to predict the flow rate or the concentration. It is shown that this method can be used to quantify the concentrations of each component with a 0.5% accuracy and the flow rate with a resolution of 0.05 ml/h. The proposed method can in principle be used to measure other properties of the fluid such as surface tension and viscosity.
A simple and efficient synthesis of spirooxindole derivatives by one-pot, three-component reaction of isatins, malononitrile and different nucleophiles under catalyst-free condition in deep eutectic ...solvent is reported. A series of biological importance, spirooxindole derivatives were synthesized via a multicomponent reaction of isatin, or acenaphthoquinone, and malononitrile or cyanoacetic ester with 1,3-dicarbonyl compounds, naphtol and 4-hydroxycumarin in biodegradable choline chloride based deep eutectic solvent in good yields (50–95%). This green procedure has the advantages of higher yields, shorter reaction times, environmental friendliness, and easy work-up.
Display omitted
•First catalyst-free multicomponent reaction in deep eutectic solvent is explored.•The procedure gave good yields in lesser reaction times.•The biodegradable choline chloride based deep eutectic solvent was used in spirooxindole synthesis.•The developed low price deep eutectic solvents were applied as green media.
A finite element method is introduced to simulate surface tension dominated flow of two immiscible fluids featuring an enriched space for capturing both strong and weak pressure discontinuities. The ...proposed enriched finite element space is created utilizing the standard finite element shape functions. Discontinuities are captured by adding merely one additional degree of freedom per each node of the elements cut by the interface. Being local to the cut elements, these additional degrees of freedom are eliminated before assembling the global system of equations following a condensation procedure. The method is stabilized introducing a procedure for improving the conditioning of the enriched pressure contribution to the stiffness matrix in small-cut situations. An improved smoothing strategy based on an artificial diffusion equation is proposed to enhance the performance of the method on rather coarse meshes. A series of three-dimensional two-phase fluid flow benchmarks are solved to assess the performance of the method. Particular attention is paid to surface tension dominated cases. The method is verified by showing its accuracy in capturing strong pressure discontinuity at the interface of a spherical droplet as well as its capability in handling large pressure gradient discontinuity in a hydrostatic liquid–gas container. The method is further validated by simulating oscillations of a slightly disturbed spherical droplet. The mass conservation property of the method and the effect of the smoothing procedure on the result is assessed by simulating the oscillations of a prolate droplet. Ultimately, the method is tested in a more challenging setting by simulating the rising gas bubble inside a liquid domain.
•Stabilized pressure-enriched fixed-grid finite element method.•Accurate capturing of the discontinuity in the pressure and its gradient.•Condensation of the additional degrees of freedom.•Stabilization within the variational multi-scale framework.•Taylored for modeling the droplet dynamics.
PurposeThe purpose of this paper is to identify the applications and contributions of blockchain technology in finance in general, and to identify areas where the technology can make a larger impact ...in payment systems.Design/methodology/approachThe authors do an exhaustive review of blockchain technology and cryptocurrency, and examine the successful applications of blockchain technology in several finance disciplines including cryptocurrency. The authors critically evaluate the technical studies on behaviors in cryptocurrency prices.FindingsCryptocurrency is the first successful application of blockchain technology and can be used as the main fuel of the global money transfer network.Research limitations/implicationsBlockchain is a revolutionary technology that can change the world with its convenience, transparency, accuracy and efficiency in speed and cost. The growth of blockchain usage in finance depends on further familiarization and trust gained by an increasing number of proven successful usage cases and testimonials as well as appropriate legislative changes.Originality/valueThis paper provides a comprehensive review of the contributions that blockchain technology has made and is expected to make in the field of finance with the aim of adding value to corporate executives, investors, policy makers and a general audience.
The conception of practical solar-hydrogen generators requires the implementation of engineering design principles that allow photo-electrochemical material systems to operate efficiently, ...continuously and stably over their lifetime. At the heart of these engineering aspects lie the mass transport of reactants, intermediates and products throughout the device. This review comprehensively covers these aspects and ties together all of the processes required for the efficient production of pure streams of solar-hydrogen. In order to do so, the article describes the fundamental physical processes that occur at different locations of a generalized device topology and presents the state-of-the-art advances in materials and engineering approaches to mitigate mass-transport challenges. Processes that take place in the light absorber and electrocatalyst components are only briefly described, while the main focus is given to mass transport processes in the boundary-layer and bulk liquid or solid electrolytes. Lastly, a perspective on how engineering approaches can enable more efficient solar-fuel generators is presented.
The conception of practical solar-hydrogen generators requires the implementation of engineering design principles that allow photo-electrochemical material systems to operate efficiently, continuously and stably over their lifetime.
•Customized Level-set/Enriched-FEM framework for moving contact-line problems.•Combination of the molecular kinetic and hydrodynamic models at the numerical level.•Level-set regularization strategy ...incorporating contact with a solid substrate.•Application of the surface tension on zero-thickness phase interface.•Accurate capturing of the contact-line dynamics in wetting problems.
A physically consistent approach is introduced to simulate dynamics of droplets in contact with solid substrates. The numerical method is developed by introducing the molecular–kinetic model within the framework of the level-set/enriched finite element method and including the theoretically resolved sub-elemental hydrodynamics. The level-set method is customized to comply fully with the model acquired for the moving contact-line. The consistency of the proposed method is verified by comparing the simulation results with the theoretical predictions. In order to further validate the method, the spreading of a droplet is numerically modeled and compared rigorously with the experimental data reported in the literature. The proposed method is also employed to capture the evolution of a droplet trapped in a conical pore. All test-cases are simulated on three-dimensional computational domains.
Display omitted
► We synthesized a novel ionic liquid with two catalytic functions. ► This dual task-specific ionic liquid provides WO42- and –SO3H species. ► The catalyst is efficient for oxidation ...of cyclohexene to adipic acid.
The sole industrial process which currently used for adipic acid production is nitric acid oxidation of either cyclohexanol or cyclohexanol/cyclohexanone mixture. Emission of greenhouse nitrous oxide (N2O) gas from this process strongly contributes to global warming, resulting in acid rain and ozone depletion. Herein, we report a catalytic application of a novel dual task-specific ionic liquid (an ionic liquid with two catalytic functions) for oxidation of cyclohexene to adipic acid using 30% hydrogen peroxide. The catalyst showed desirable activity toward oxidation of cyclohexene and some cyclic olefins to produce their corresponding dicarboxylic acids.
•Determining of rheological behavior and viscosities of sonicated starches during the ultrasound-assisted modification (UAM)•UAM mathematical and 3D computational flow dynamics simulation of various ...botanical starches.•Remarkable decrease of shear stress after sonication treatment.
The study aimed to optimize the ultrasonic-assisted modification (UAM) of corn and potato starch by assessing the influence of ultrasound geometry, power, and frequency on the fluid flow for sonicated starch to achieve porous starch with a higher degree of hydrolyzing by α-amylase. This assessment was conducted through mathematical modeling and 3D computational fluid dynamics (CFD) simulations. The ultrasonic pressure field is determined by the solution of the non-linear Westervelt equation in the frequency domain. Then, the obtained field is utilized to simulate the dissipated power and flow field characteristics. According to the results obtained from the Rapid Visco Analyzer (RVA), it was observed that the peak and final viscosity of hydrolyzed sonicated starch were less than hydrolyzed native starch. This decrease in viscosity indicates a breakdown of the starch structure, leading to a more fluid-like consistency. The shear rate and shear stress data are used for rheology modeling. The fluid's viscosity is represented based on three models of Herschel–Bulkley, Casson, and Power law (Ostwald–de Waele). The magnitude of yield shear stress at low shear rates, the shear-thinning behavior, and the nearly Newtonian fluid nature at high shear rates are extracted from the viscosity models. The surfaces of the starch granules were analyzed using scanning electron microscopy (SEM) revealed that sonication treatments caused damage, cracks, and porosity on the surfaces of the starch granules which were prone to amylolytic enzymes. This indicates that the structural integrity of the granules was compromised and facilitated enzyme penetration. This study proposes that ultrasonication can be utilized to produce damaged starch, which is susceptible to hydrolysis by α-amylase. This approach holds the potential for reducing enzyme consumption in various industries.
PDF
