Development of an Electrochemical Micro Flow Reactor EMFR

Development of an Electrochemical Micro Flow Reactor (EMFR) for electrocatalytic studies of methanol oxidation and fuel cell applications. Nallakkan Arvindan*, Eric Stuve* and Karl Böhringer** * Department of Chemical Engineering, **Department of Electrical Engineering, University of Washington, Seattle, WA-98195. 1. Abstract 3. Electrochemical Micro-Flow Reactors (EMFR) The ongoing work has used advances in MEMS fluidic technology commonly used in the area of biological and chemical analysis, to develop novel experimental techniques for conventional surface science research on single crystal surfaces to study chemical reactions at the atomic scale. We have developed the technology to fabricate microreactor chips from silicon and glass wafers. The fabricated micro reactor chips which are presently under testing and optimization will be used to study methanol electrocatalysis at high temperatures on single crystal platinum and modified platinum surfaces. This will enable us to understand the reaction mechanisms and can pave the way to design and optimize catalyst nanoparticles that will enhance direct methanol fuel cell (DMFC) performance. Concurrently we are also developing a set up to interface the micro reactor chips with an ultra high vacuum system to perform Differential Electrochemical Mass Spectrometry (DEMS). The reactor on chip (ROC) technology that we have developed will be further extended, to fabricate micro fuel cells based on methanol to serve as catalyst testing stations to study new catalyst nanoparticles under fuel cell conditions. 2. Introduction A DMFC produces electricity by direct conversion of methanol to carbon dioxide and protons at the anode. Nanoparticles of Platinum and Platinum based alloys are used as electrocatalysts to facilitate the reactions. However, the current performance of the DMFC is far from that required for successful commercialization. The main problem lies in poor catalysts giving rise to slower oxidation kinetics as a result of intermediates formed during methanol oxidation at the anode that poisons the electrocatalyst. Understanding the mechanism of the methanol oxidation reaction is critical to the design, development and optimization of novel catalyst nanoparticles that can enhance DMFC performance. Microreactors provide the tools needed to perform high temperature experiments involving multiple electrolyte systems, providing for high degree of control over the reaction environment and safe handling of hazardous materials at high temperatures. 5. Reactor on Chip features: Easy to fabricate, control, maintain and replace when necessary. Microfabrication / reaction Technology Multiple electrolyte handling capability with automated fluidic delivery system. Reactor on Chip On-Chip Palladium/Hydrogen thin film reference electrode On-Chip Platinum thin film counter and auxiliary electrodes. Reaction Mechanisms Integrated heaters and temperature sensors on chip provide rapid heating and effective temperature control. Can be modified and used with other experimental protocols like DEMS (Differential Electrochemical Mass Spectroscopy) and Ultra High Vacuum Studies. Catalyst Design Safe to handle highly corrosive and dangerous acids like Perchloric acid and Sulfuric acid at high temperatures. Figure 2. EMFR made from Silicon Catalyst Testing Completely automated control system developed using Lab. View for reactor operation and data acquisition. and Glass Miniaturized Test Stations (Fuel cells) 4. Microfabrication Figure 3. Glass wafers: Lithography Metal deposition Metal Lift off Figure 6. CV obtained from the EMFR 6. Conclusion (a) Mask (b) Finished glass chip Figure 4. EMFR Layout Silicon Pt RTD’s Given the enormous advantages that microreactors can provide over existing methods of experimentation, we have developed procedures for the fabrication of an electrochemical micro flow reactor to perform high temperature electrocatalytic studies involving multiple electrolytes. This technology can be further extended to fabricate miniaturized catalyst testing stations and fuel cells. Pt Heaters Fluidic Channels 7. Acknowledgements Pd Reference electrode Pt Counter Electrode Figure 1. DMFC Electrocatalysis Overview • Washington Technology Center(WTC) microfabrication facility. • Financial Support • National Science Foundation • Center for Nanotechnology, University of Washington