Sputtered Stainless Steel on Silicon Photoanode for Stable Seawater Splitting in Photoelectrochemical Flow Cell

Photoelectrochemical(PEC)seawater splitting is a promising method for the direct utilization of solar energy and abundant seawater resources for hydrogen production.Photoelectrodes are susceptible to various ions in seawater and complicated competitive reactions,resulting in the failure of photoelectrodes.This paper proposes the design and fabrication of diff erent sputtered stainless steel(SS)fi lms deposited on silicon photoanodes,completely isolating the electrolytes and semiconductor substrate.Upon coupling with the PEC flow cell,the back-illuminated photoanode coated with 316 SS cocatalyst achieves stable operation for 70 h in natural seawater with a highly alkaline KOH(30 wt.%,7.64 mol/L)electrolyte due to the remarkable protection eff ect of the substrate from stainless steel,while the PEC seawater splitting system achieves a record hydrogen production rate of 600μmol/(h·cm^(2)).An appropriate Ni/Fe ratio in the SS ensures remarkable oxygen evolution activity,while chromic oxide ensures the effective anticorrosion effect by adjusting the microenvironment of the photoanodes.Moreover,fabricating PEC flow cells with photoanodes coated with SS cocatalysts are a viable strategy for PEC seawater splitting.

Enhanced electrocatalytic activity of iron amino porphyrins using a flow cell for reduction of CO_(2) to CO

The flexibility of molecular catalysts is highly coveted for the electrochemical reduction of carbon dioxide(CO_(2)) to carbon monoxide(CO) in both homogeneous and heterogeneous systems.While the electrocatalytic activity of molecular catalysts has been widely studied in H-cells;their less studied capabilities in more efficient flow cell reactors have the potential to rival that of heterogeneous catalysts.In this work,a comparative study of amino functionalized iron-tetraphenylporphyrins(amino-Fe-TPPs) immobilized onto carbonaceous materials in both H-cells and flow cells was conducted to selectively reduce CO_(2) to CO.In a flow cell set up operating in alkaline media,the resulting hybrid catalyst exhibits 87% faradaic efficiency(FE) with extraordinary current density(j) of 119 mA/cm^(2) and turnover frequency(TOF) of 14 s^(-1) at-1.0 V vs.RHE.This remarkable catalytic activity was achieved through thoughtful combination of molecular and flow cell design that provides an effective strategy for future immobilized heterogeneous approaches toward CO_(2) reduction reactions(CO_(2) RRs).

Lithium slurry flow cell,a promising device for the future energy storage

Lithium slurry flow cell(LSFC)is a novel energy storage device that combines the concept of both lithium ion batteries(LIBs)and flow batteries(FBs).Although it is hoped to inherit the advantages of both LIBs and FBs,such as high energy density,ease of fabrication,environmental friendly,independent energy and power density,to name but a few.While unfortunately,it still has many challenges to overcome before it becoming the future star in energy storage area.Here in this paper,we briefly recall its history and try to illustrate the main issues that hindering its research as well as application.As a typical interdisciplinary product,LSFC is definitely a promising candidate for large scale energy storage application,while obviously it still has a long way to go.

Rapid and controllable in-situ self-assembly of main-group metal nanofilms for highly efficient CO_(2)electroreduction to liquid fuel in flow cells

The electrocatalytic reduction of CO_(2)is a promising pathway to generate renewable fuels and chemicals.However,its advancement is impeded by the absence of electrocatalysts with both high selectivity and stability.Here,we present a scalable in-situ thermal evaporation technique for synthesizing series of Bi,In,and Sn nanofilms on carbon felt(CF)substrates with a high-aspect-ratio structure.The resulting main-group metal nanofilms exhibit a homogeneously distributed and highly exposed catalyst surface with ample active sites,thereby promoting mass transport and ad-/desorption of reaction intermediates.Benefiting from the unique fractal morphology,the Bi nanofilms deposited on CF exhibit optimal catalytic activities for CO_(2)electroreduction among the designed metal nanofilms electrodes,with the highest Faradaic efficiency of 96.9%for formate production at−1.3 V vs.reversible hydrogen electrode(RHE)in H-cell.Under an industrially relevant current density of 221.4 mA·cm−2 in flow cells,the Bi nanofilms retain a high Faradaic efficiency of 81.7%at−1.1 V(vs.RHE)and a good long-term stability for formate production.Furthermore,a techno-economic analysis(TEA)model shows the potential commercial viability of electrocatalytic CO_(2)conversion into formate using the Bi nanofilms catalyst.Our results offer a green and convenient approach for in-situ fabrication of stable and inexpensive thin-film catalysts with a fractal structure applicable to various industrial settings.

Transforming liquid flow fuel cells to controllable reactors for highlyefficient oxidation of 5-hydroxymethylfurfural to 2, 5-furandicarboxylic acid at low temperature

Highly-efficient oxidation of 5-hydroxymethylfurtural(HMF) to 2,5-furandicarboxylic acid(FDCA) at low temperature with air as the oxidant is still challenging.Herein,inspired by the respirato ry electron transport chain(ETC) of living cells mediated by electron carriers,we constructed artificial ETCs and transformed liquid flow fuel cells(LFFCs) to flexible reactors for efficient oxidation of HMF to produce FDCA under mild conditions.This LFFC reactor employed an electrodeposition modified nickel foam as an anode to promote HMF oxidation and(VO_(2))_(2)SO_(4) as a cathode electron carrier to facilitate the electron transfer to air.The reaction rate could be easily controlled by selecting the anode catalyst,adjusting the external loading and changing the cathodic electron carrier or oxidants.A maximal power density of 44.9 mW cm^(-2) at room temperature was achieved,while for FDCA production,short-circuit condition was preferred to achieve quick transfer of electrons.For a single batch operation with 0.1 M initial HMF,FDCA yield reached 97.1%.By fed-batch operation,FDCA concentration reached 144.5 g L^(-1) with a total yield of 96%.Ni^(2+)/Ni^(3+) redox couple was the active species mediating the electron transfer,while both experimental and DFT calculation results indicated that HMFCA pathway was the preferred reaction mechanism.

Analysis of temperature distribution in PV-integrated electrochemical flow cells

Photovoltaic(PV)-integrated flow cells for electrochemical energy conversion and storage underwent a huge development.The advantages of this type of integrated flow cell system include the simultaneous storage of solar energy into chemicals that can be readily utilized for generating electricity.However,most studies overlook the practical challenges arising from the inherent heat exposure and consequent overheating of the reactor under the sun.This work aims to predict the temperature profiles across PV-integrated electrochemical flow cells under light exposure conditions by introducing a computational fluid dynamics–based method.Furthermore,we discuss the effects of the flow channel block architecture on the temperature profile to provide insights and guidelines for the effective remedy of overheating.

Water flooding behavior in flow cells for ammonia production via electrocatalytic nitrogen reduction

The green production of ammonia,in an electrochemical flow cell under ambient conditions,is a promising way to replace the energy-intensive Haber-Bosch process.In the operation of this flow cell with an alkaline electrolyte,water is produced at the anode but also required as an essential reactant at the cathode for nitrogen reduction.Hence,water from the anode is expected to diffuse through the membrane to the cathode to compensate for the water needed for nitrogen reduction.Excessive water permeation,however,tends to increase the possibility of water flooding,which would not only create a large barrier for nitrogen delivery and availability,but also lead to severe hydrogen evolution as side reaction,and thus significantly lower the ammonia production rate and Faradaic efficiency.In this work,the water flooding phenomenon in flow cells for ammonia production via electrocatalytic nitrogen reduction is verified via the visualization approach and the electrochemical cell performance.In addition,the effects of the nitrogen flow rate,applied current density,and membrane thickness on the water crossover flux and ammonia production rate are comprehensively studied.The underlying mechanism of water transport through the membrane,including diffusion and electro-osmotic drag,is precisely examined and specified to provide more insight on water flooding behavior in the flow cell.

Lattice Boltzmann modeling of transport phenomena in fuel cells and flow batteries

Fuel cells and flow batteries are promising technologies to address climate change and air pollution problems. An understanding of the complex multiscale and multiphysics transport phenomena occurring in these electrochemical systems requires powerful numerical tools. Over the past decades, the lattice Boltzmann (LB) method has attracted broad interest in the computational fluid dynamics and the numerical heat transfer communities, primarily due to its kinetic nature making it appropriate for modeling complex multiphase transport phenomena. More importantly, the LB method fits well with parallel computing due to its locality feature, which is required for large-scale engineering applications. In this article, we review the LB method for gas-liquid two-phase flows, coupled fluid flow and mass transport in porous media, and particulate flows. Examples of applications are provided in fuel cells and flow batteries. Further developments of the LB method are also outlined.

Adhesion behavior of endothelial progenitor cells to endothelial cells in simple shear flow

The adhesion of endothelial progenitor cells（EPCs） on endothelial cells（ECs） is one of the critical physiological processes for the regenesis of vascular vessels and the prevention of serious cardiovascular diseases.Here,the rolling and adhesion behavior of EPCs on ECs was studied numerically.A two-dimensional numerical model was developed based on the immersed boundary method for simulating the rolling and adhesion of cells in a channel flow.The binding force arising from the catch bond of a receptor and ligand pair was modeled with stochastic Monte Carlo method and Hookean spring model.The effect of tumor necrosis factor alpha（TNF-α） on the expression of the number of adhesion molecules in ECs was analyzed experimentally.A flow chamber system with CCD camera was set up to observe the top view of the rolling of EPCs on the substrate cultivated with ECs.Numerical results prove that the adhesion of EPC on ECs is closely related to membrane stiff-ness of the cell and shear rate of the flow.It also suggests that the adhesion force between EPC and EC by P-selectin glycoprotein ligand-1 only is not strong enough to bond the cell onto vessel walls unless contributions of other catch bond are considered.Experimental results demonstrate that TNF-α enhanced the expressions of VCAM,ICAM,P-selectin and E-selectin in ECs,which supports the numerical results that the rolling velocity of EPC on TNF-α treated EC substrate decreases obviously compared with its velocity on the untreated one.It is found that because the adhesion is affected by both the rolling velocity and the deformability of the cell,an optimal stiffness of EPC may exist at a given shear rate of flow for achieving maximum adhesion rates.

EXTRACTION KINETICS OF RARE EARTH（Ⅰ） A Constant Interfacial Cell with Laminar Flow

A technique was developed to study mass trans fer process and inter facial reaction in two phases system. This constant inter facial cell with a laminar flow was made into a cubic structure. The two fluids were continuously recycled and mixed. The concentration of each liquid could be monitored by two different methods. This kind of structure made both flows near the inter face flow parallel to the inter face. The inter face was smooth and steady. The mass trans fer rate could be judged by the linear velocity of the flows. The technique can be used for the analyses of the control step in both phases near the inter face in a diffusion control process. A preliminary hydrodynamics and mass trans fer study on the cell was presented, which ensures the distinguishing between a diffusion and a chemical reaction control process. A simplified mass transfer equation,N =0.5303D 1 /2* (Ci- Cb)* (V / B) 1/2, was achieved.

Novel Flow Field with Superhydrophobic Gas Channels Prepared by One-step Solvent-induced Crystallization for Micro Direct Methanol Fuel Cell

The CO2-induced capillary blocking in anode flow field is one of the key adverse factors to reduce the performance of a micro-direct methanol fuel cell(l DMFC). In order to solve this problem, new polycarbonate(PC) flow field plates with nested arrangement of hydrophilic fuel channels and superhydrophobic gas channels were designed,fabricated, and tested in this work. The gas channels were treated with solvent-induced crystallization using acetone solution. The superhydrophobicity with 160° water contact angle and 2° tilting angle was obtained on the PC substrates. A dummy cell using hydrogen peroxide decomposition reaction and a test loop were separately set up to evaluate the flow fields' performance. It was found that a 37 % pressure drop decrease can be obtained in the new serpentine flow field compared with that of the conventional one. The benefit of the new flow field to remove gas bubbles was also confirmed by an in situ visualization study on the dummy cell. Results show that the auxiliary superhydrophobic gas channels can speed up the discharge of the gas bubbles from the flow field, which will in turn improve the l DMFC performance.

Combined modeling of cell aggregation and adhesion mediated by receptor–ligand interactions under shear flow

Blood cell aggregation and adhesion to endothelial cells under shear flow are crucial to many biological processes such as thrombi formation, inflammatory cascade, and tumor metastasis, in which these cellular interactions are mainly mediated by the underlying receptor-ligand bindings. While theoretical modeling of aggregation dynamics and adhesion kinetics of interacting cells have been well studied separately, how to couple these two processes remains unclear. Here we develop a combined model that couples cellular aggregation dynamics and adhesion kinetics under shear flow. The impacts of shear rate （or shear stress） and molecular binding affinity were elucidated. This study provides a unified model where the action of a fluid flow drives cell aggregation and adhesion under the modulations of the mechanical shear flow and receptor-ligand interaction kinetics. It offers an insight into understanding the relevant biological processes and functions.

MATHEMATICAL MODELLING OF BUBBLE DRIVENFLOWS IN A NOVEL ALUMINUM ELECTROLYSIS CELL

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Mathematical simulation of gas induced bath flow in drained aluminum reduction cell

A mathematical model describing the bubble driven bath flow in a drained cell with a center sump was presented, which spanned the fluid around half an anode and was developed to simulate the flow fields. The calculated results show reasonable agreement with the experiment. Then the model was developed to a full cell model, and bath flow pattern in the whole cell was predicted and analyzed. The flow pattern variation with the changes of the ACD, anode slope, anode immersion depth and current density, especially the fluid secondary recirculation, was modeled. According to the results, side channel or slots feeding technique was recommended in such a drained cell.

Microfluidic-based single cell trapping using a combination of stagnation point flow and physical barrier

Single cell trapping in vitro by microfluidic device is an emerging approach for the study of the relationship between single cells and their dynamic biochemical microenvironments. In this paper, a hydrodynamic-based microfluidic device for single cell trapping is designed using a combination of stagnation point flow and physical barrier.The microfluidic device overcomes the weakness of the traditional ones, which have been only based upon either stagnation point flows or physical barriers, and can conveniently load dynamic biochemical signals to the trapped cell. In addition, it can connect with a programmable syringe pump and a microscope to constitute an integrated experimental system.It is experimentally verified that the microfluidic system can trap single cells in vitro even under flow disturbance and conveniently load biochemical signals to the trapped cell. The designed micro-device would provide a simple yet effective experimental platform for further study of the interactions between single cells and their microenvironments.

Air flow control based on optimal oxygen excess ratio in fuel cells for vehicles

Air flow control is one of the most important control methods for maintaining the stability and reliability of a fuel cell system, which can avoid oxygen starvation or oxygen saturation. The oxygen excess ratio （OER） is often used to indicate the air flow condition. Based on a fuel cell system model for vehicles, OER performance was analyzed for different stack currents and temperatures in this paper, and the results show that the optimal OER was affected weakly by the stack temperature. In order to ensure the system working in optimal OER, a control scheme that includes an optimal OER regulator and a fuzzy control was proposed. According to the stack current, a reference value of air flow rate was obtained with the optimal OER regulator and then the air compressor motor voltage was controlled with the fuzzy controller to adjust the air flow rate provided by the air compressor. Simulation results show that the control method has good dynamic and static characteristics.

COUPLED SIMULATION OF 3D ELECTRO-MAGNETO-FLOW FIELD IN HALL-HEROULT CELLS USING FINITE ELEMENT METHOD

Two full 3D steady mathematical models are developed by finite element method （FEM） to calcalate coupled physics fields. the electro-magnetic model is built and solved first and so is the fluid motion model with the acquired electromagnetic force as source body forces in Navier-Stokes equations. Effects caused by the ferromagnetic shell, busbar system around, and open boundary problem as well as inside induced current were considered in terms of the magnetic field. Furthermore, a new modeling method is found to set up solid models and then mesh them entirely with so-called structuralized grids, namely hex-mesh. Examples of 75kA prebaked cell with two kinds of busbar arrangements are presented. Results agree with those disclosed in the literature and confirm that the coupled simulation is valid. It is also concluded that the usage of these models facilitates the consistent analysis of the electric field to magnetic field and then flow motion to the greater extent, local distributions of current density and magnetic flux density are very much dependent on the cell structure, the steel shell is a shield to reduce the magnetic field and flow pattern is two dimensional in the main body of the metal pad.

Electrical Parameters Determination from Base Thickness Optimization in a Silicon Solar Cell under Influence of the Irradiation Energy Flow of Charged Particles

In this work, we study the characteristics I-V and P-V of a silicon solar cell as well as its fill factor, its electrical power from the optimum thickness obtained in the base under variation of the irradiation energy flow of charged particles. The recombination velocity at the junction corresponding to the maximum power point was also deduced.

Effect of electromagnetic force and anode gas on electrolyte flow in aluminum electrolysis cell

Based on the commercial computational fluid dynamics software CFX-4.3, electrolyte flow fields in a 156 kA pre-baked anode aluminum electrolysis cell were investigated in three different cases where the electrolyte melt was driven by different kinds of force, i.e. electromagnetic force only, the anode gas drag force only and both of the former two forces. The results show that when electromagnetic force was introduced only, most of the electrolyte moves horizontally; when anode gas drag force was introduced only, the electrolyte flows mainly around each anode with small circulation; when electromagnetic force and anode gas drag force were both introduced together, the structure of the electrolyte flow fields and the velocity of electrolyte are similar to that of the case where only anode gas drag force is used. The electrolyte flow fields are mainly determined by the anode gas drag force.