How temperature increase drives energy loss in fuel cells

By splitting water molecules, fuel cells can turn electricity into hydrogen fuel. Running in the opposite direction, they consume hydrogen fuel to cleanly power multiple sectors. Typically, heat is a key ingredient for achieving high energy conversion efficiencies that can beat out combustion-based engines.

But like a dripping pipe, fuel cells can leak efficiency. In a study published in PRX Energy, scientists from the Lawrence Livermore National Laboratory (LLNL) Quantum Simulation Group revealed how high operating temperatures could increase electrical leakage in a widely studied fuel cell material.

“Traditionally, models don’t fully account for temperature-induced vibrations,” said Shenli Zhang, LLNL physicist and first author of the study. “But our calculations show that this effect is far from negligible—especially for operation temperatures above 600 Kelvin that are typical for these cells.”

The paper dives deep into the microscopic world of barium zirconate, a common solid-oxide electrolyte, using state-of-the-art quantum mechanics simulations. Inside this electrolyte, the team searched for electrons and the holes they leave behind after they escape from an atom.

“We don’t want the transport electrons or holes inside the cell because this consumes the input energy but doesn’t contribute to the energy conversion process,” said Zhang. “This process decreases the energy conversion efficiency of the cell, so we want to avoid it.”

With their simulations, the team examined the lattice vibrations in the atomic structure of the electrolyte material. High temperature vibrations pushed the valence band of electrons upward, essentially bringing the negatively charged particles closer to escape. The researchers observed four times more positively charged holes in the system when accounting for higher temperatures—meaning that four times as many unhelpful electrons escaped.

By tweaking model parameters, the group developed a simulation protocol to estimate the number of electrons and holes as a function of temperature.

“These insights help us quantify just how much electrical leakage is tied to temperature, and they give us a better handle on designing materials or operating conditions to minimize those losses,” said co-author Joel Varley, LLNL scientist and project lead.

Looking ahead, the scientists aim to extend the work to other solid-oxide electrolyte materials and accelerate the process with machine learning potentials.