Microfluidic platforms for the investigation of fuel cell catalysts and electrodes

摘要

A clear need exists for novel approaches to producing and utilizing energy in more efficient ways, in light of society’s 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:•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).•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).•Establish electrode structure-activity relationships by aligning in-situ electrochemical analyses with ex-situ microtomographic (MicroCT) structural analyses (Chapter 5).•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).