Erik Kjeang

A microfluidic fuel cell with flow-through porous electrodes.

A microfluidic fuel cell architecture incorporating flow-through porous electrodes is demonstrated. The design is based on cross-flow of aqueous vanadium redox species through the electrodes into an orthogonally arranged co-laminar exit channel, where the waste solutions provide ionic charge transfer in a membraneless configuration. This flow-through architecture enables improved utilization of the three-dimensional active area inside the porous electrodes and provides enhanced rates of convective/diffusive transport without increasing the parasitic loss required to drive the flow. Prototype fuel cells are fabricated by rapid prototyping with total material cost estimated at 2 USD/unit. Improved performance as compared to previous microfluidic fuel cells is demonstrated, including power densities at room temperature up to 131 mW cm-2. In addition, high overall energy conversion efficiency is obtained through a combination of relatively high levels of fuel utilization and cell voltage. When operated at 1 microL min-1 flow rate, the fuel cell produced 20 mW cm-2 at 0.8 V combined with an active fuel utilization of 94%. Finally, we demonstrate in situ fuel and oxidant regeneration by running the flow-through architecture fuel cell in reverse.

Hydrogen Peroxide as an Oxidant for Microfluidic Fuel Cells

We demonstrate a microfluidic fuel cell incorporating hydrogen peroxide oxidant. Hydrogen peroxide (H 2 O 2 ) is available at high concentrations, is highly soluble and exhibits a high standard reduction potential. It also enables fuel cell operation where natural convection of air is limited or anaerobic conditions prevail, as in submersible and space applications. As fuel cell performance critically depends on both electrode and channel architecture, several different prototype cells are developed and results are compared. High-surface area electrodeposited platinum and palladium electrodes are evaluated both ex situ and in situ for the combination of direct H 2 O 2 reduction and oxygen reduction via the decomposition reaction. Oxygen gas bubbles produced at the fuel cell cathode introduce an unsteady two-phase flow component that, if not controlled, can perturb the co-laminar flow interface and reduce fuel cell performance. A grooved channel design is developed here that restricts gas bubble growth and transport to the vicinity of the cathodic active sites, enhancing the rate of oxygen reduction, and limiting crossover effects. The proof-of-concept microfluidic fuel cell produced power densities up to 30 mW cm -2 and a maximum current density of 150 mA cm -2 , when operated on 2 M H 2 O 2 oxidant together with formic acid-based fuel at room temperature.

A perspective on microfluidic biofuel cells

This review article presents how microfluidic technologies and biological materials are paired to assist in the development of low cost, green energy fuel cell systems. Miniaturized biological fuel cells, employing enzymes or microorganisms as biocatalysts in an environmentally benign configuration, can become an attractive candidate for small-scale power source applications such as biological sensors, implantable medical devices, and portable electronics. State-of-the-art biofuel cell technologies are reviewed with emphasis on microfabrication compatibility and microfluidic fuel cell designs. Integrated microfluidic biofuel cell prototypes are examined with comparisons of their performance achievements and fabrication methods. The technical challenges for further developments and the potential research opportunities for practical cell designs are discussed.

Mitigation of Chemical Membrane Degradation in Fuel Cells: Understanding the Effect of Cell Voltage and Iron Ion Redox Cycle

Chemical membrane degradation through the Fentons reaction is one of the main lifetime-limiting factors for polymer-electrolyte fuel cells. In this work, a comprehensive, transient membrane degradation model is developed to capture and elucidate the complex in situ degradation mechanism. A redox cycle of iron ions is discovered within the membrane electrolyte assembly, which sustains the Fe(II) concentration and results in the most severe chemical degradation at open circuit voltage. The cycle strength is critically reduced at lower cell voltages, which leads to an exponential decrease in Fe(II) concentration and associated membrane degradation rate. When the cell voltage is held below 0.7 V, a tenfold reduction in cumulative fluoride release is achieved, which suggests that intermediate cell voltage operation would efficiently mitigate chemical membrane degradation and extend the fuel cell lifetime.

Convective Heat Transfer in Microchannels of Noncircular Cross Sections: An Analytical Approach

Analytical solutions are presented for velocity and temperature distributions of laminar fully developed flow of Newtonian, constant property fluids in micro/minichannels of hyperelliptical and regular polygonal cross sections. The considered geometries cover several common shapes such as ellipse, rectangle, rectangle with round corners, rhombus, star-shape, and all regular polygons. The analysis is carried out under the conditions of constant axial wall heat flux with uniform peripheral heat flux at a given cross section. A linear least squares point matching technique is used to minimize the residual between the actual and the predicted values on the boundary of the channel. Hydrodynamic and thermal characteristics of the flow are derived; these include pressure drop and local and average Nusselt numbers. The proposed results are successfully verified with existing analytical and numerical solutions from the literature for a variety of cross sections. The present study provides analytical-based compact solutions for velocity and temperature fields that are essential for basic designs, parametric studies, and optimization analyses required for many thermofluidic applications. [DOI: 10.1115/1.4006207]

Modification of DIRECT for high-dimensional design problems

DIviding RECTangles (DIRECT), as a well-known derivative-free global optimization method, has been found to be effective and efficient for low-dimensional problems. When facing high-dimensional black-box problems, however, DIRECTs performance deteriorates. This work proposes a series of modifications to DIRECT for high-dimensional problems (dimensionality d>10). The principal idea is to increase the convergence speed by breaking its single initialization-to-convergence approach into several more intricate steps. Specifically, starting with the entire feasible area, the search domain will shrink gradually and adaptively to the region enclosing the potential optimum. Several stopping criteria have been introduced to avoid premature convergence. A diversification subroutine has also been developed to prevent the algorithm from being trapped in local minima. The proposed approach is benchmarked using nine standard high-dimensional test functions and one black-box engineering problem. All these tests show a significant efficiency improvement over the original DIRECT for high-dimensional design problems.

Microfluidic fuel cell systems

A microfluidic fuel cell is a microfabricated device that produces electrical power through electrochemical reactions involving a fuel and an oxidant. Microfluidic fuel cell systems exploit co-laminar flow on the microscale to separate the fuel and oxidant species, in contrast to conventional fuel cells employing an ion exchange membrane for this function. Since 2002 when the first microfluidic fuel cell was invented, many different fuels, oxidants, and architectures have been investigated conceptually and experimentally. In this mini-review article, recent advancements in the field of microfluidic fuel cell systems are documented, with particular emphasis on design, operation, and performance. The present microfluidic fuel cell systems are categorized by the fluidic phases of the fuel and oxidant streams, featuring gaseous/gaseous, liquid/gaseous, and liquid/liquid systems. The typical cell configurations and recent contributions in each category are analyzed. Key research challenges and opportunities are highlighted and recommendations for further work are provided.

Glycerol electro-oxidation in alkaline media using Pt and Pd catalysts electrodeposited on three-dimensional porous carbon electrodes

In this work, Pd and Pt electrocatalysts were electrodeposited on three-dimensional carbon paper and carbon nanofoam with the purpose of increasing the catalytic area to improve the glycerol electro-oxidation. SEM and cross-sectional SEM micrographs showed that Pd and Pt particles were well-distributed over the entire three-dimensional electrode surfaces. Commercial Pd/C and Pt/C catalysts deposited by the spray method were used for comparison, showing lower surface area (SA) utilization than those electrodeposited. The electrodeposition effectiveness to cover the electrode surfaces was evaluated by changes in overall SA and through the calculation of electrochemically active surface area (EASA) and specific surface area (SSA). Despite the larger EASA values found for Pd and Pt on nanofoam, Pt on paper showed the highest utilization of the surface area, obtaining an SSA of 58.1 m2 g−1. Moreover, the electrodeposition of Pd and Pt dramatically increased the EASA versus the geometrical area, improving this ratio 16 (Pd on paper), 151 (Pt on paper), 158 (Pd on nanofoam) and 277-fold (Pt on nanofoam). The electrodeposited porous Pt electrodes showed good activity for glycerol oxidation, exhibiting a more negative potential than Pd-based materials. However, for fuel cell applications operated at intermediate temperatures, Pd on carbon paper is the optimal candidate to be used as an anode because of its high current density and excellent poisoning tolerance.

Technical-economic cost modeling as a technology management tool: A case study of membranes for PEM fuel cells

Purpose – The purpose of this paper is to show how technical-economical cost modeling can help in steering research and development to target key production cost elements of new products based on emerging technologies.Design/methodology/approach – The authors demonstrate the development and use of a technical-economic cost model (TCM) of the proton exchange membrane (PEM) in fuel cells to steer research to produce more economical and reliable products. A TCM is developed to depict how the production cost per unit varies depending on the different fabrication methods, production rate limitations, material selection, labor distribution, energy consumption, financial parameters and the target production volume. By using such an approach in the design, research time and resources can be saved by prioritizing R&D and production scale-up options at an early stage.Findings – The results of this study show the importance of applying technical-economic cost model (TCM) techniques on early stage research projects to steer the development for resolving key problematic figures. As a case study, a cost analysis platform has been established to apply this technique by analyzing different manufacturing and R&D options for producing durable PEM fuel cells. The projected manufacturing cost of the PEM is found to be lower than previously estimated and the enhanced durability does not significantly impact this production cost.Originality/value – Production is an important factor in informing NPD targets and R&D direction. And yet it is difficult to estimate scaled up production cost for prototype products and components in the R&D lab. Technical-economic cost models (TCM) are a tool to assist decision-making in technology portfolio management and NPD.

Advances in Microfluidic Fuel Cells

Publisher Summary This chapter provides background and reviews recent advances in microfluidic fuel cells. In microfluidic fuel cells, all components and functions including fluid delivery, reaction sites, and electrodes are confined to a microfluidic channel. Microfluidic fuel cells typically operate in a co-laminar flow configuration without a physical barrier, such as a membrane, to separate the anode and the cathode. The chapter covers the theory, fabrication, unit cell development, performance achievements, design considerations, and scale-up options of microfluidic fuel cells, and examines the advances in these areas with particular emphasis on microfluidic fuel cell architectures. Furthermore, relevant microfluidic biofuel cell developments are described, particularly as they present opportunities for future work in this multidisciplinary field. Looking ahead, the main opportunities and challenges associated with the technology are described along with suggested directions for further research and development.