(587d) Catalytic Combustion for Direct Thermal-to-Electrical Energy Conversion

The demand for portable electronic devices is increasing, as is their power requirement. At the same time, the focus has been on making these portable devices smaller and lighter. Battery technology is becoming less attractive as an option to meet the power requirements of today's portable devices, primarily due to energy density limitations. The relatively high energy densities of hydrocarbons render them an attractive option for portable power generation. The combustion of hydrocarbon fuels is a common process for releasing stored energy, either for direct thermal-to-electrical energy conversion in thermophotovoltaic or thermoelectric schemes or to drive the production of a more usable energy vector such as hydrogen. Direct thermal-to-electrical energy conversion allows for power generation with few moving parts and minimal systems integration. To date, significant progress has been made in understanding portable power generation systems. However, the development of a robust, cost-effective device generating usable power that approaches the energy density of a liquid fuel remains an open challenge.

The development of portable combustion-based devices with high energy-conversion efficiency requires a fundamental understanding of several areas related to high temperature operation. Thermal management issues such as heat loss pathways and minimization of thermal gradients within the reactor play an important role in the feasibility of a combustion-based device. Material integration is also a significant challenge for high-temperature operation, as differences in thermal expansion lead to thermal stresses. Additionally, mechanically robust packaging techniques that allow for necessary thermal isolation must be developed for high temperature reactors.

A catalytic combustion-based device intended for direct thermal-to-electrical energy conversion through thermoelectrics has been investigated. A silicon reactor has been designed with a parallel channel structure similar to that of a monolith. The system has been fabricated using standard silicon microprocessing techniques. Computational fluid dynamics techniques have been used to investigate the temperature and concentration profiles in the reactor. The combustor has been designed to achieve high thermal conversion efficiency while addressing system challenges such as mechanically robust fluidic connections and minimal parasitic power losses for pressurization of air. The combustor was designed to release approximately 350 watts of thermal energy with an operating temperature below 500ºC. The system has been used to study the catalytic combustion of butane in air over an alumina-supported platinum wash coat. This work provides a platform for further development of portable power generation devices with attractive energy and power densities.