New fuel cell design is safer to use and burns hydrocarbons directly

Carbonate-superstructured solid fuel cell

Four years ago, Hu and his team of researchers were looking to improve solid oxide fuel cells (SOFCs). The focus was on reducing the operating temperature of the SOFC, the researchers looked at superstructures materials to create an interface between the electrolyte and melted carbonate that could serve as an ultrafast channel for oxygen ion transfer.

Typically, SOFCs operate at temperatures above 1472 Fahrenheit (800 degrees Celsius) since solid electrolytes have low ion transfer rates at lower temperatures. Hu's research resulted in a carbonate-superstructure solid fuel cell (CSSFC) that delivered fast ion transfers at temperatures as low as 878 Fahrenheit (470 degrees Celsius).

Theoretically, lower operating temperatures offer high efficiency and lower fabrication costs. He is also confident that it will make them safer to operate when compared to other solid fuel cells.

With hydrocarbon fuels, though, lower operating temperatures are problematic since they slow down fuel oxidation and cause coking - accumulation of carbon deposits, further reducing fuel cell efficiency and performance.

To test their hypothesis, Hu's team fabricated a device prototype in the lab and put it through some tests. "In our experiments, the CSSFC exhibited ultrahigh oxygen ionic conductivity at 550 degrees Celsius, achieving rapid oxidation of hydrocarbon fuel. This led to an unprecedented high open-circuit voltage of 1.041 volts, a very high peak power density of 215 milliwatts per square centimeter, and excellent coking resistance using dry methane fuel," Hu said in a press release.

Hu also estimates that the CSSFC fuel efficiency could reach as much as 60 percent. In comparison, combustion engines being phased out today have energy efficiencies of not more than 35 percent. The CSSFC's higher efficiency could also mean lower emissions in vehicles and power plants.

The research findings were published in the Proceedings of the National Academy of Sciences.

Study abstract:

A basic requirement for solid oxide fuel cells (SOFCs) is the sintering of electrolyte into a dense impermeable membrane to prevent the mixing of fuel and oxygen for a sufficiently high open-circuit voltage (OCV). However, herein, we demonstrate a different type of fuel cell, a carbonate-superstructured solid fuel cell (CSSFC), in which in situ generation of superstructured carbonate in the porous samarium-doped ceria layer creates a unique electrolyte with ultrahigh ionic conductivity of 0.17 S⋅cm−1 at 550 °C. The CSSFC achieves unprecedented high OCVs (1.051 V at 500 °C and 1.041 V at 550 °C) with methane fuel. Furthermore, the CSSFC exhibits a high peak power density of 215 mW⋅cm−2 with dry methane fuel at 550 °C, which is higher than all reported values of electrolyte-supported SOFCs. This provides a different approach for the development of efficient solid fuel cells.