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Low temperature solid oxide fuel cells (SOFCs) are a promising solution to revolutionize stationary, transportation, and personal power energy conversion efficiency. Through investigation of fundamental conduction mechanisms, we have developed the highest conductivity solid electrolyte, stabilized bismuth oxide (Dy0.08W0.04Bi0.88O0.36). To overcome its inherent thermodynamic instability in the anode environment, we invented a functionally graded bismuth oxide/ceria bilayered electrolyte. For compatibility with this bilayared electrolyte, we developed high performance bismuth ruthenate–bismuth oxide composite cathodes. Finally, these components were integrated into an anode-supported cell with an anode functional layer, resulting in an exceptionally high power density of ;2 W/cm2 at moderate temperatures (650 °C) and sufficient power down to 300–400 °C for most applications. Moreover, because SOFCs can operate on conventional fuels, these low temperature SOFCs provide one of the most efficient energy conversion technologies available without relying on a hydrogen infrastructure. I. INTRODUCTION

Transforming automotive power sources into higher efficiency technologies is vital to the stability of our environment, energy supply, and economy. The urgency of this transformation resulted in a major focus on plug-in hybrid electric vehicles (PHEVs). However, if the PHEVs are charged by conventional coal power plants at night and conventional internal combustion (IC) engines while in transit, the “well to wheels” reduction in CO2 is limited to the increase in efficiency gains afforded by the electric drive hybrid technology, rather than an increase in the actual hydrocarbon to electricity energy conversion process. Moreover, the range and cost of PHEVs are limited by the energy density of the batteries; and no current battery can compare on a kWh/kg or kWh/L basis with a liquid-fueled energy conversion (hydrocarbon to electricity) process. Unfortunately, IC engines are limited by Carnot efficiency, are far from pollution free, and convert chemical energy to mechanical energy rather than electric power needed by an electric drive vehicle thus requiring an additional mechanical to electrical energy conversion step. In contrast, the use of fuel cells (FCs) rather than an IC engine in a PHEV would result in a dramatic improvement in efficiency, reduction in emissions, and is directly amenable to an electric drive system. For high efficiency energy conversion, there has been a tremendous effort to develop solid oxide fuel cells (SOFC) operating at temperatures below 900 °C for cost and reliability considerations. Simultaneously, there has been a)

Address all correspondence to this author. e-mail: [email protected] This paper has been selected as an Invited Feature Paper. DOI: 10.1557/jmr.2012.194 J. Mater. Res., Vol. 27, No. 16, Aug 28, 2012

an even larger effort to increase the operating temperature of proton exchange membrane fuel cells (PEMFC) above 100 °C for performance and fuel poisoning considerations. Somewhere in between is the