Microfluidic Platforms And Fundamental Electrocatalysis Studies For Fuel Cell Applications

A clear need exists for novel approaches to producing and utilizing energy in more efficient ways, in light of society0́9s ever increasing demand as well as growing concerns with respect to climate change related to CO2 emissions. The development of low temperature fuel cell technologies will continue to play an important role in many alternative energy conversion strategies, especially for portable electronics and automotive applications. However, widespread commercialization of fuel cell technologies has yet to be achieved due to a combination of high costs, poor durability and, system performance limitations (Chapter 1). Developing a better understanding of the complex interplay of electrochemical, transport, and degradation processes that govern the performance and durability of novel fuel cell components, particularly catalysts and electrodes, within operating fuel cells is critical to designing robust, inexpensive configurations that are required for commercial introduction. Such detailed in-situ investigations of individual electrode processes are complicated by other factors such as water management, uneven performance across electrodes, and temperature gradients. Indeed, too many processes are interdependent on the same few variable parameters, necessitating the development of novel analytical platforms with more degrees of freedom. Previously, membraneless microfluidic fuel cells have been developed to address some of the aforementioned fuel cell challenges (Chapter 2). At the microscale, the laminar nature of fluid flow eliminates the need for a physical barrier, such as a stationary membrane, while still allowing ionic transport between electrodes. This enables the development of many unique and innovative fuel cell designs. In addition to addressing water management and fuel crossover issues, these laminar flow-based systems allow for the independent specification of individual stream compositions (e.g., pH). Furthermore, the use of a liquid electrolyte enables the simple in-situ analysis of individual electrode performance using an off-the-shelf reference electrode. These advantages can be leveraged to develop microfluidic fuel cells as versatile electro-analytical platforms for the characterization and optimization of catalysts and electrodes for both membrane- and membraneless fuel cells applications. To this end, a microfluidic hydrogen-oxygen (H2/O2) fuel cell has been developed which utilizes a flowing liquid electrolyte instead of a stationary polymeric membrane. For analytical investigations, the flowing stream (i) enables autonomous control over electrolyte parameters (i.e., pH, composition) and consequently the local electrode environments, as well as (ii) allows for the independent in-situ analyses of catalyst and/or electrode performance and degradation characteristics via an external reference electrode (e.g., Ag/AgCl). Thus, this microfluidic analytical platform enables a high number of experimental degrees of freedom, previously limited to a three-electrode electrochemical cell, to be employed in the construct of working fuel cell. Using this microfluidic H2/O2 fuel cell as a versatile analytical platform, the focus of this work is to provide critical insight into the following research areas: 0́Ø Identify the key processes that govern the electrode performance and durability in alkaline fuel cells as a function of preparation methods and operating parameters (Chapter 3). 0́Ø Determine the suitability of a novel Pt-free oxygen reduction reaction catalyst embedded in gas diffusion electrodes for acidic and alkaline fuel cell applications (Chapter 4). 0́Ø Establish electrode structure-activity relationships by aligning in-situ electrochemical analyses with ex-situ microtomographic (MicroCT) structural analyses (Chapter 5). 0́Ø Investigate the feasibility and utility of a microfluidic-based vapor feed direct methanol fuel cell (VF-DMFC) configuration as a power source for portable applications (Chapter 6). In all these areas, the information garnered from these in-situ analytical platforms will advance the development of more robust and cost-effective electrode configurations and thus more durable and commercially-viable fuel cell systems (both membrane-based and membraneless).

This first book to focus on a comprehensive description on DMFC electrocatalysis draws a clear picture of the current status of DMFC technology, especially the advances, challenges and perspectives in the field. Leading researchers from universities, government laboratories and fuel cell industries in North America, Europe and Asia share their knowledge and information on recent advances in the fundamental theories, experimental methodologies and research achievements. In order to help readers better understand the science and technology of the subject, some important and representative figures, tables, photos, and comprehensive lists of reference papers are also included, such that all the information needed on this topic may be easily located. An indispensable source for physical, catalytic, electro- and solid state chemists, as well as materials scientists and chemists in industry.

A comprehensive survey of theoretical andexperimental concepts in fuel cell chemistry Fuel cell science is undergoing significant development, thanks, in part, to a spectacular evolution of the electrocatalysis concepts, and both new theoretical and experimental methods. Responding to the need for a definitive guide to the field, Fuel Cell Science provides an up-to-date, comprehensive compendium of both theoretical and experimental aspects of the field. Designed to inspire scientists to think about the future of fuel cell technology, Fuel Cell Science addresses the emerging field of bio-electrocatalysis and the theory of heterogeneous reactions in fuel cell science and proposes potential applications for electrochemical energy production. The book is thorough in its coverage of the electron transfer process and structure of the electric double layer, as well as the development of operando measurements. Among other subjects, chapters describe: Recently developed strategies for the design, preparation, and characterization of catalytic materials for fuel cell electrodes, especially for new fuel cell cathodes A wide spectrum of theoretical and computational methods, with?the aim of?developing?new fuel cell catalysis concepts and improving existing designs to increase their performance.? Edited by two leading faculty, the book: Addresses the emerging fields of bio-electrocatalysis for fuel cells and theory of heterogeneous reactions for use in fuel cell catalysis Provides a survey of experimental and theoretical concepts in these new fields Shows the evolution of electrocatalysis concepts Describes the chemical physics of fuel cell reactions Forecasts future developments in electrochemical energy production and conversion Written for electrochemists and electrochemistry graduate students, electrocatalysis researchers, surface and physical chemists, chemical engineers, automotive engineers, and fuel cell and energy-related researchers, this modern compendium can help today's best minds meet the challenges in fuel science technology.

Increasing innovations and applications make microfluidics a versatile choice for researchers in many disciplines. This book consists of multiple review chapters that aim to cover recent advances and new applications of microfluidics in biology, electronics, energy, and materials sciences. It provides comprehensive views of various aspects of microfluidics ranging from fundamentals of fabrication, flow control, and droplet manipulation to the most recent exploration in emerging areas such as material synthesis, imaging and novel spectroscopy, and marriage with electronics. The chapters have many illustrations showcasing exciting results. This book should be useful for those who are eager to learn more about microfluidics as well as researchers who want to pick up new concepts and developments in this fast-growing field.

Microfluidic fuel cells and batteries represent a special type of electrochemical power generators that can be miniaturized and integrated in a microfluidic chip. Summarizing the initial ten years of research and development in this emerging field, this SpringerBrief is the first book dedicated to microfluidic fuel cell and battery technology for electrochemical energy conversion and storage. Written at a critical juncture, where strategically applied research is urgently required to seize impending technology opportunities for commercial, analytical, and educational utility, the intention is for this book to be a ‘one-stop shop’ for current and prospective researchers in the general area of membraneless, microfluidic electrochemical energy conversion. As the overall goal of the book is to provide a comprehensive resource for both research and technology development, it features extensive descriptions of the underlying fundamental theory, fabrication methods, and cell design principles, as well as a thorough review of previous contributions in this field and a future outlook with recommendations for further work. It is hoped that the content will entice and enable new research groups and engineers to rapidly gain traction in their own laboratories towards the development of next generation microfluidic electrochemical cells.

The breakdown of organic substances to retrieve energy is a naturally occurring process in nature. Catabolic microorganisms contain enzymes capable of accelerating the disintegration of simple sugars and alcohols to produce separated charge in the form of electrons and protons as byproducts that can be harvested extracellularly through an electrochemical cell to produce electrical energy directly. Bioelectrochemical energy is then an appealing green alternative to other power sources. However, a number of fundamental questions must be addressed if the technology is to become economically feasible. Power densities are low, hence the electron flow through the system: bacteria-electrode connectivity, the volumetric limit of catalyst loading, and the rate-limiting step in the system must be understood and optimized. This project investigated the miniaturization of microbial fuel cells to explore the scaling of the biocatalysis and generate a platform to study fundamental microstructure effects. Ultra-micro-electrodes for single cell studies were developed within a microfluidic configuration to quantify these issues and provide insight on the output capacity of microbial fuel cells as well as commercial feasibility as power sources for electronic devices. Several devices were investigated in this work. The first prototype consisted of a gold array anode on a silicon dioxide passivation layer that intended to imitate yet simplify the complexity of a 3D carbon structure on a 2D plane. Using Geobacter sulfurreducens, an organism believed to utilize direct electron transfer to electrodes, the 1 mm2 electrode demonstrated a maximum current density of 1.4 [mu]A and 120 nW of power after 10 days. In addition, the transient current-voltage responses were analyzed over the bacterial colonization period. The results indicated that over a 6-day period, the bacteria increased the capacitance of the cell 5-orders-of-magnitude and decreased the resistance by 3X over the bare electrode. Furthermore, over short experimental scales (hours), the RC constant was maintained but capacitance and resistance were inversely related. As the capacitance result coincides with expected biomass increase over the incubation period, it may be possible for an electrical spectroscopy (impedance) non-invasive technique to be developed to estimate biomass on the electrode. Similarly, the R and C relationship over short experimental scales could be explored further to provide insight on biolm morphology. Lastly, fluorescence and SEM microscopy were used to observe the biofilm development and demonstrated that, rather than growing at even density, the bacteria nucleated at points on the electrode, and dendritically divided, until joining to form the "dense" biofilm. In addition, viable microorganisms undergoing cell division were found dozens of microns from electrode surfaces without visible pili connections. To investigate single-cell catalysis or microstructure effects, a sub-micro-liter microfluidic single-channel MFC with an embedded reference electrode and solid-state nal electron acceptor was developed. The system allowed for parallel (16) working ultra-micro-electrodes and was microscopy compatible. With Geobacter sulfurreducens, the semiconducting ITO electrodes demonstrated forward bias behavior and suitability for anodic characterization. The first prototype demonstrated, with 179 cells on the electrode, a per cell contribution of 223 fA at +400 mV (vs. SHE). The second prototype with a 7 [mu]m diameter electrode produced a current density of 3.9 pA/[mu]m2 (3.9 A/m2) at +200 mV (vs. SHE) and a signal-to-noise ratio (SNR) of 4.9 when inoculated at a seeding density of 109 cells/mL. However, diluting the sample by 10x produced an SNR of 0.5, suggesting that obtaining single cell electron transfer rates to an electrode over short experimental time scales may not be possible with the system as tested. Nevertheless, the platform allows microstructure characterization and multiplexing within a single microfluidic chamber.

In the 1990s, the idea of developing miniaturized devices that integrate functions other than what normally are carried out at the laboratory level was conceived, and the so-called "lab-on-a-chip" (LOC) devices emerged as one of the most important research areas. LOC devices exhibit advantages related to the use of microfluidic channels such as small sample and reagent consumption, portability, low-power consumption, laminar flow, and higher surface area/volume ratio that enhances both thermal dissipation and electrochemical kinetics. Fuel cells are electrochemical devices that convert chemical energy to electrical energy. These are considered as one of the greener ways to generate electricity because typical fuel cells produce water and heat as the main reaction byproducts. The technical challenges to develop systems at the microscale and the advantages of microfluidics exhibited an important impact on fuel cells for several reasons, mainly related to avoid inherent problems of gaseous-based fuel cells. As a result, the birth of a new type of fuel cells as microfluidic fuel cells (MFCs) took place. The first microfluidic fuel cell was reported in 2002. This MFC was operated with liquid fuel/oxidant and had the advantage of the low laminar flow generated using a "Y" microfluidic channel to separate the anodic and cathodic streams, resulting in an energy conversion device that did not require a physical barrier to separate both streams. This electrochemical system originated a specific type of MFCs categorized as membraneless also called colaminar microfluidic fuel cells. Since that year, numerous works focused on the nature of fuels, oxidants and anodic/cathodic electrocatalysts, and cell designs have been reported. The limiting parameters of this kind of devices toward their use in portable applications are related to their low cell performances, small mass activity, and partial selectivity/durability of electrocatalysts. On the other hand, it has been observed that the cell design has a high effect on the cell performance due to internal cell resistances and the crossover effect. Furthermore, current technology is growing faster than last centuries and new microfabrication technologies are always emerging, allowing the development of smaller and more powerful microfluidic energy devices. In this chapter, the application of microfluidics in membraneless fuel cells is addressed in terms of evolution of cell designs of miniaturized microfluidic fuel cells as a result of new discoveries in microfabrication technology and the use of several fuels and electrocatalysts for specific and selective applications.

In this work, a microfluidics approach is applied to two fuel cell related projects; the study of deformation and contact angle hysteresis on water invasion in porous media and the introduction of bubble fuel cells. This work was carried out as collaboration between the microfluidics and CFCE groups in the Department of Mechanical Engineering at the University of Victoria. Understanding water transport in the porous media of Polymer Electrolyte Membrane fuel cells is crucial to improve performance. One popular technique for both numeric simulations and experimental micromodels is pore network modeling, which predicts flow behavior as a function of capillary number and relative viscosity. An open question is the validity of pore network modeling for the small highly non-wetting pores in fuel cell porous media. In particular, current pore network models do not account for deformable media or contact angle hysteresis. We developed and tested a deformable microfluidic network with an average hydraulic diameter of 5?m, the smallest sizes to date. At a capillary number and relative viscosity for which conventional theory would predict strong capillary fingering behavior, we report almost complete saturation. This work represents the first experimental pore network model to demonstrate the combined effects of material deformation and contact angle hysteresis. Microfluidic fuel cells are small scale energy conversion devices that take advantage of microscale transport phenomena to reduce size, complexity and cost. They are particularly attractive for portable electronic devices, due to their potentially high energy density. The current state of the art microfluidic fuel cell uses the laminar flow of liquid fuel and oxidant as a membrane. Their performance is plagued by a number of factors including mixing, concentration polarization, ohmic polarization and low fuel utilization. In this work, a new type of microfluidic fuel cell is conceptualized and developed that uses bubbles to transport fuel and oxidant within an electrolyte. Bubbles offer a phase boundary to prevent mixing, higher rates of diffusion, and independent electrolyte selection. One particular bubble fuel cell design produces alternating current. This work presents, to our knowledge, the first microfluidic chip to produce bubbles of alternating composition in a single channel, class of fuel cells that use bubbles to transport fuel and oxidant and fuel cell capable of generating alternating current.