Tokyo Institute of Technology: New Ba7Nb4MoO20-Based Materials with High Oxygen-Ion Conductivity Could Open Sustainable Future

Scientists at Tokyo Institute of Technology (Tokyo Tech), Imperial and High Energy Accelerator Research Organization (KEK) Institute of Materials Structure Science, discover new Ba7Nb4MoO20-based materials with high oxygen-ion (oxide-ion O2-) conductivities—”the hexagonal perovskite-related oxides”—and shed light on the underlying mechanisms responsible for their conductivity. Their findings lead the way to uncovering other similar materials, furthering research on developing low-cost and scalable renewable energy technologies.

Over the past few years, fuel cells have become a focal point of research in eco-friendly technology because of their superior abilities to store and produce renewable energy and clean fuel. A typical type of fuel cell gaining ground is the oxide-ion-conducting fuel cell, which is primarily made of materials through which oxide ions (oxygen ions: O2-), can easily move. New materials with higher conductivity at low and intermediate temperatures, provide a number of advantages over commonly used fuel cells based on yttria-stabilized zirconia (YSZ) electrolytes, such as higher power generation efficiency, longer lifetimes, and lower costs.

However, only a limited number of such materials are known and their application to developing fuel cells has largely remained at the laboratory scale. To truly achieve a sustainable energy economy, new oxide-ion conductors with high conductivity need to be discovered that can allow low-cost and efficient scaling up of these technologies.

Scientists from Tokyo Tech, Imperial and KEK set out to address this need, and in a recent study, identified a new oxide-ion-conducting material that may be a representative of an entire family of oxide-ion conductors.

The material in question has the chemical formula Ba7Nb3.9Mo1.1O20.05 and is classified as a “hexagonal perovskite-related oxide.” Prof Masatomo Yashima, who led the study, explains: “Ba7Nb3.9Mo1.1O20.05 shows a wide stability range and predominantly oxide-ion conduction in the oxygen partial pressure range from 2 × 10-26 to 1 atm. Surprisingly, bulk conductivity of Ba7Nb3.9Mo1.1O20.05, 5.8 × 10-4 S/cm, is remarkably high at 310 oC, and higher than bismuth oxide- and zirconia-based materials (Fig. 1).”* Prof Stephen Skinner comments that the fast oxide ion transport was unambiguously confirmed using the 18O tracer diffusion technique at Imperial.

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