Laminar Flow Fuel Cell Research Articles

Effects of Bridge-Shaped Microchannel Geometry on the Performance of a Micro Laminar Flow Fuel Cell.

A laminar flow micro fuel cell comprising of bridge-shaped microchannel is investigated to find out the effects of the cross-section shape of the microchannel on the performance. A parametric study is performed by varying the heights and widths of the channel and bridge shape. Nine different microchannel cross-section shapes are evaluated to find effective microchannel cross-sections by combining three bridge shapes with three channel shapes. A three-dimensional fully coupled numerical model is used to calculate the fuel cell’s performance. Navier-Stokes, convection and diffusion, and Butler-Volmer equations are implemented using the numerical model. A narrow channel with a wide bridge shape shows the best performance among the tested nine cross-sectional shapes, which is increased by about 78% compared to the square channel with the square bridge shape.

A three-dimensional numerical model of a micro laminar flow fuel cell with a bridge-shaped microchannel cross-section

The operation of a laminar flow fuel cell (LFFC) involves complex interplay between various mass and electrochemical transport processes. Hence, to better design and more accurately predict performance, we developed a fully-coupled 3D numerical model that includes all the transport processes and electrochemical phenomena. Specifically, the model is based on the equations for the mass, momentum, species, and charge balances along with Butler–Volmer equations for electrode kinetics. The developed model was in excellent agreement with experimental data on a micro laminar flow fuel cell (μLFFC) with a bridge-shaped microchannel cross-section. Then, we used the model for a parametric study evaluating the influence of different operational and geometrical parameters (bridge aspect ratio, reactant flow rates, oxidant concentration) on the fuel cell performance (peak power density, fuel crossover, crossover current, power losses). The observed correlations were explained on the basis of mass and electrochemical transport phenomena, e.g., the behavior of the depletion zones at the fuel–oxidant and reactant–electrode interfaces. Based on these results, we recommend further design considerations for LFFCs. Although, the model was specifically developed for a particular μLFFC configuration, the computational model can be used to design and predict behavior of a wide variety of LFFC configurations.

Electronic modification of Pt via Ti and Se as tolerant cathodes in air-breathing methanol microfluidic fuel cells

We reported herein on the use of tolerant cathode catalysts such as carbon supported Pt(x)Ti(y) and/or Pt(x)Se(y) nanomaterials in an air-breathing methanol microfluidic fuel cell. In order to show the improvement of mixed-reactant fuel cell (MRFC) performances obtained with the developed tolerant catalysts, a classical Pt/C nanomaterial was used for comparison. Using 5 M methanol concentration in a situation where the fuel crossover is 100% (MRFC-mixed reactant fuel cell application), the maximum power density of the fuel cell with a Pt/C cathodic catalyst decreased by 80% in comparison with what is observed in the laminar flow fuel cell (LFFC) configuration. With Pt(x)Ti(y)/C and Pt(x)Se(y)/C cathode nanomaterials, the performance loss was only 55% and 20%, respectively. The evaluation of the tolerant cathode catalysts in an air-breathing microfluidic fuel cell suggests the development of a novel nanometric system that will not be size restricted. These interesting results are the consequence of the high methanol tolerance of these advanced electrocatalysts via surface electronic modification of Pt. Herein we used X-ray photoelectron and in situ FTIR spectroscopies to investigate the origin of the high methanol tolerance on modified Pt catalysts.

Tailoring nanostructured catalysts for electrochemical energy conversion systems

AbstractThis review covers topics related to the synthesis of nanoparticles, the anodic and cathodic electrochemical reactions and low temperature electrochemical energy devices. The thermodynamic aspects of nucleation and growth of nanoparticles are discussed. Different methods of chemical synthesis such as w/o microemulsion, Bönnemann, polyol and carbonyl are presented. How the electrochemical reactions take place on the surface of the catalytic nanoparticles and the importance of the substrate is put in evidence. The use of nanomaterials in low temperature energy devices such as H2/O2 polymer electrolyte or proton exchange membrane fuel cell (PEMFC) and micro-direct methanol fuel cell (μDMFC), as well as recent progress and durability, is discussed. Special attention is given to the novel laminar flow fuel cell (LFFC). This review starts with the genesis of catalytic nanoparticles, continues with the surface electrochemical reactions that occur on them, and finally it discusses their application in electrochemical energy devices such as low temperature fuel cells or Li-air batteries.

Design rules for electrode arrangement in an air-breathing alkaline direct methanol laminar flow fuel cell

The influence of electrode length on performance is investigated in an air-breathing alkaline direct methanol laminar flow fuel cell (LFFC). Depletion of methanol at the electrode surface along the direction of flow hinders reaction kinetics and consequently also cell performance. Reducing the electrode length can decrease the influence of boundary layer depletion, and thereby, improve both the current and power densities. Here, the effect of boundary layer depletion was found to play a significant effect on performance within the first 18 mm of an electrode length. To further utilize the increased power densities provided by shorter electrode lengths, alternative electrode aspect ratios (electrode length-to-width) and electrode arrangements were explored experimentally. Furthermore, by fitting an empirical model based on experimentally obtained data, we demonstrate that a configuration comprised of a series of short electrodes and operated at low flow rates can achieve higher current and power outputs. The analysis of optimal electrode aspect ratio and electrode arrangements can also be applied to other microfluidic reactor designs in which reaction depletion boundary layers occur due to surface reactions.

Development of a Hydrogen-Powered Laminar Flow Fuel Cell

not Available.

Depth Averaged Analytic Solution for a Laminar Flow Fuel Cell with Electric Double Layer Effects

A comprehensive multidimensional analysis is presented for a laminar flow fuel cell with electric double layer (EDL) dependent kinetics in a planar microdevice. The EDL is described with the Stern model, and a generalized Frumkin--Butler--Volmer (gFBV) equation is used to describe the EDL dependent kinetics. The liquid electrolyte is modeled with the Poisson--Nernst--Planck (PNP) equations and the incompressible Navier--Stokes (NS) equations. For planar microchannel applications, the three-dimensional model is reduced to an in-plane depth averaged set of equations through an asymptotic analysis. The diffuse layers are resolved in the thin double layer limit through asymptotic matching by considering the Debye length to channel width ratio as a smallness parameter. This yields an outer problem for the bulk electrolyte and an inner problem for the anode and cathode diffuse regions. Fuel cell performance is then evaluated by introducing several specified local current density profiles. The resulting approximate analytic expressions, based on the proposed specified current density profiles, are validated against results from a numerical solution of the full in-plane PNP--NS--gFBV model, in which a priori current profile approximations are not required. We demonstrate that simple current density profiles yield physically unrealistic electrode potential distributions despite producing reasonably accurate overall device performance results. We also present an appropriate current density profile which yields accurate spatial distributions for the continuum fields and electrode potential distributions.

Role of the diffuse layer in acidic and alkaline fuel cells

A numerical model is developed to study electrolyte dependent kinetics in fuel cells. The model is based on the Poisson–Nernst–Planck (PNP) and generalized-Frumkin–Butler–Volmer (gFBV) equations, and is used to understand how the diffuse layer and ionic transport play a role in the performance difference between acidic and alkaline systems. The laminar flow fuel cell (LFFC) is used as the model fuel cell architecture to allow for the appropriate comparison of equivalent acidic and alkaline systems. We study the overall cell performance and individual electrode polarizations of acidic and alkaline fuel cells for both balanced and unbalanced electrode kinetics as well as in the presence of transport limitations. The results predict cell behavior based on electrolyte composition that strongly correlates with observed experimental results from literature and provides insight into the fundamental cause of these results. Specifically, it is found that the working ion concentration at the reaction plane plays a significant role in fuel cell performance including activation losses and the response to different kinetic rates at an individual electrode. The working ion and the electrode where its consumed are different for acidic and alkaline fuel cells. Therefore, we compare the role of the diffuse region in both acidic and alkaline fuel cells. From this we conclude that oxidant reduction at the cathode and slow fuel oxidation (such as alcohol oxidation) can be improved with an alkaline electrolyte.

Modeling of Diffuse Charge Effects in a Microfluidic Based Laminar Flow Fuel Cell

A mathematical model for laminar flow fuel cells including electrical double layer and ion transport effects is developed. The model consists of the Poisson-Nernst-Plank equations and the modified Navier-Stokes equations to account for the advection of species in the downstream direction. The generalized Frumkin-Butler-Volmer equation is used for the fuel cell kinetics. The finite-volume method is used to develop a system of algebraic equations from the governing partial differential equations, and a numerical algorithm is developed to obtain the results. The accuracy of the 2-D numerical simulation is validated against published results using a 1-D analytical solution. Numerical results show that the concentration distributions for both the neutral species and ions change in both the cross-stream and streamwise directions. An especially interesting result is the change in positive ion concentration within the electrical double layer along the streamwise direction. A study on the importance of the electric body force in the momentum conservation equations is also presented. It is found that the flow results are only affected by the electric body force term at the start of the electrodes and has a negligible impact on device performance results. This model allows us to study both kinetically active (electrodes) and inactive (insulated wall) regions for a microfluidic fuel cell. The mathematical model and numerical simulation will be particularly useful in analyzing the complex behavior that occurs in laminar flow electrochemical devices where a minimum of two spatial dimensions must be considered and the electrical double layer and ion transport cannot be neglected.

Oxygen reduction reaction increased tolerance and fuel cell performance of Pt and Ru xSe y onto oxide–carbon composites

Pt and Ru x Se y nanoparticles were selectively deposited onto oxide sites of oxide–carbon composite substrates using the photo-deposition process and compared to conventional carbon support materials. The oxide was essentially anatase phase. Cyclic voltammetry and rotating disk electrode measurements for the oxygen reduction reaction (ORR) in formic acid containing-electrolyte showed a tolerance improvement for ORR of Pt supported on composite substrates. This positive substrate effect on platinum, turned out not to be favorable for Ru x Se y catalyst centers. On the other hand, the methanol tolerance for ORR was increased for both nanostructured materials supported on the oxide–carbon composite. Single H 2/O 2 fuel cell results were in agreement with half-cell electrochemical measurements on Pt, showing an improvement of the power density when using the oxide–carbon as substrate for the cathode. The composites were evaluated as cathode catalysts of an HCOOH laminar-flow fuel cell (LFFC) in which commercial Pd/C was used as an anode catalyst. The cathodes with Ru x Se y and Pt supported on TiO 2/C improved the specific power density by 15% and 24%, respectively, with respect to carbon as support.

Flow Rate Effect on Methanol Electro-oxidation in a Microfluidic Laminar Flow System

The effect of flow rate on the methanol electro-oxidation reaction in laminar flow was investigated using a direct methanol laminar flow fuel cell (LF-FC). A micro fuel cell was fabricated in polydimethylsiloxane using standard soft-lithography techniques. The electrochemical performance of methanol oxidation was characterized by anode polarization and electrochemical impedance spectroscopy analysis with and without sulfuric acid. The results show that in the absence of a sulfuric acid electrolyte (H2SO4) the methanol flow rate significantly influences methanol oxidation kinetics of the laminar flow direct methanol fuel cell. In the absence of H2SO4, it was found that the charge transfer resistance and onset potential of the methanol oxidation reaction significantly increases as the methanol flow rate increases. As a result, the anode current density of LF-FCs decreases at higher flow rates of methanol. However, this negative effect was reduced when a strong electrolyte, such as sulfuric acid, was mixed with the methanol solution.