A team of researchers has developed heat-resilient silver circuitry for devices such as next-generation fuel cells, high-temperature semiconductors, and solid oxide electrolysis cells for the automobile, energy, and aerospace industries.
For example, NASA developed a solid oxide electrolysis cell that enabled the Mars 2020 Perseverance rover to make oxygen from gas in the Martian atmosphere. To help such prototypes become commercial products, though, they’ll need to maintain their performance at high temperatures over long periods of time.
Solid oxide fuel cells work like solid oxide electrolysis cells in reverse. Rather than using energy to create gases or fuel, they create energy from those chemicals. The researchers are able to electrochemically react those gases to get electricity out and the process is more efficient than exploding fuel like an internal combustion engine.
Even without explosions, the fuel cell needs to withstand intense working conditions. The devices commonly operate at about 700 to 800 °C for 40,000 hours over their lifetime. That’s approximately 1,300 to 1,400 °F or about double the temperature of a commercial pizza oven. Over that lifetime, they are thermally cycling — cooling down and heating back up — during which circuit leads could pop off.
Thus, one of the hurdles facing this advanced technology is rather rudimentary: The conductive circuitry, often made from silver, needs to stick better to the underlying ceramic components. The secret to improving the adhesion was to add an intermediate layer of porous nickel between the silver and the ceramic.
By performing experiments and computer simulations of how the materials interact, the team optimized how it deposited the nickel on the ceramic. And to create the thin, porous nickel layers on the ceramic in a pattern or design of their choosing, the researchers turned to screen printing of the electronics.
Once the nickel is in place, the team puts it in contact with silver that’s melted at a temperature of about 1,000 °C. The nickel not only withstands that heat — its melting point is 1,455 °C — but it also distributes the liquified silver uniformly over its fine features using what’s called capillary action.
When the silver cools and solidifies, the nickel keeps it locked onto the ceramic, even in the 700 to 800 °C heat it would face inside a solid oxide fuel cell or a solid oxide electrolysis cell. This approach also has the potential to help other technologies where electronics can run hot.