Unprecedented room-temperature electrical power generation using nanoscale fluorite-structured oxide electrolytes

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.([1,2]) 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.([3,4]) However, SOFCs require high temperatures (800-1000 degrees C), a condition that presents material degradation problems,([5,6]) as well as other technological complications and economic obstacles.([7]) Numerous attempts have been made to find alternative systems that can be operated at lower temperatures.([8,9]) 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 nanostructured (grain size similar to 15 nm). Open circuit electromotive force (emf) (up to 180 mV for YSZ and 400 mV for SDC) and closed circuit currents (similar to 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.