Architectures for individual and stacked micro single chamber solid oxide fuel cells

Abstract

Solid oxide fuel cells (SOFCs) are electrochemical conversion devices that convert various fuel sources directly into electrical energy at temperatures ranging from 600°C to 1000°C. These high temperatures could potentially allow the direct use of various hydrocarbon fuel sources and hydrogen, without the need for expensive noble metal catalysis. Conventional SOFCs are designed in a two-chamber system, separating the fuel and oxidant flow to the anode and cathode, respectively. However, fuel cell manufacturing cost and robustness have proven to be the main challenges to rapid commercialization. A promising alternate method to achieve these requirements and to open up new architecture designs for the SOFC is the development of single-chamber solid oxide fuel cells (SC-SOFCs). SC-SOFCs avoid many of the manufacturing challenges associated with conventional SOFCs, and have shown optimal performance between 500°C and 800°C. This reduces the need for high temperature sealing and a complicated manifold structure; however it also reduces the partial pressure of the gases at the electrodes, which reduces the theoretical obtainable voltage.

(cont.) Microfabrication techniques such as photolithography, sputtering, and photo-resist liftoff were used to create various micro SC-SOFC that are 25-400microns long and 15-40microns wide, utilizing platinum and gold for the electrodes and YSZ as the electrolyte. After successfully fabricating these micro SC-SOFCs, the fuel cells were tested in a microprobestation with a custom gas chamber enclosure, which was exposed to CH4:02:N2 at 20:20:100 ccm or 40:20:100 ccm. A switch in the OCV from a negative voltage to a positive voltage was observed around 600°C, possible indicating change in electrochemical reactions with temperature. An OCV of [approx.] 0.4V and peak power density of 27[mu]W/cm2 at 900°C in a 1:1 methane:oxygen ratio was achieved. A stack of 10 micro SC-SOFCs as fabricated showing a cumulative OCV of 3.3 V, of an average 0.33 V per cell at 600°C in a 2:1 methane:oxygen ratio. Ongoing research will involve characterizing micro SC-SOFCs to understand the fundamental reaction mechanisms, electrode materials, and architectures to obtain dense, high performing stacks of micro SC-SOFCs.