The RT-SOFC is a room temperature fuel cell in which nano-structured oxides such as YSZ (yttria stabilized zirconia) or SDC (samaria doped ceria) are used as electrolytes. Due to the configuration as concentration cell only water is used and produced during operation of the fuel cell.
Conventional solid oxide fuel cells (SOFCs) need operation temperatures above 800 °C. In contrast, the RT-SOFC works at room temperature. This low operation temperature and
the relatively simple and low cost production of the RT-SOFC enable economic production of electric energy.
• Proton conducting fuel cell
• Operation at room temperature
• Low cost production
• Economic operation
• Clean production of electric energy
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The conversion of chemical energy to electrical energy through the use of fuel cells is an important step in the transition to a hydrogen-based economy. Of the many types of fuel cells, solid oxide fuel cells (SOFCs), employing either oxygen ions or protons as charge carriers, provide an efficient, environmentally benign, and fuel-flexible power generation system that can be adapted for small power units (including mobile applications) and for large scale power plants. However, SOFCs require high temperatures (800–1000 °C), a condition that presents material degradation problems, as well as other technological complications and economic obstacles. Numerous attempts have been made to find alteranative systems that can be operated at lower temperatures.
We report here unprecedented observations of power generation at temperatures as low as room temperature using dense bulk nanostructured yttria-stabilized zirconia (YSZ) and samaria- doped ceria (SDC) as electrolytes. This behavior is observed only when the material is nanostruc-tured (grain size ? 15 nm). Open circuit electromotive force (emf) (up to 180 mV for YSZ and 400 mV for SDC) and closed circuit currents (? 6 nA for YSZ and 30 nA for SDC) were measured from water concentration cells, indicating proton conduction within the nanostructured oxides. These results show that with optimization, viable power generation using water concentration cells at room temperature is a possible goal.
Low-temperature protonic conduction has been reported before for polymeric electrolytes and for structurally hydrated (i.e., hydrous) oxides. However, these materials have limitations that have largely restricted their further considerations for practical utilization. Polymeric electrolytes (e.g., Nafion) have limitations with respect to thermal stability, so that they are mostly limited to temperatures below 100 °C. In addition, polymeric systems require a catalyst whose optimal operation temperature is inconsistent with the thermal stability of the polymer. Another factor for these systems is the cost.
We were successful in making dense, bulk nanostructured YSZ (8 mol % yttria) and SDC (20 mol % samaria) with a grain size of ?15 nm through the use of field-activated sintering of nanopowders.We found ionic conductivity at low temperatures in structurally unhydrated YSZ only when the grain size of the material is in the nanoscale.In the present work, we use these materials as electrolytes and demonstrate electrical power generation at room temperature using water concentration cells.