Deforming lanthanum trihydride for superionic conduction.

With strong reducibility and high redox potential, the hydride ion (H - ) is a reactive hydrogen species and an energy carrier. Materials that conduct pure H - at ambient conditions will be enablers of advanced clean energy storage and electrochemical conversion technologies 1,2 . However, rare earth trihydrides, known for fast H migration, also exhibit detrimental electronic conductivity 3-5 . Here we show that by creating nanosized grains and defects in the lattice, the electronic conductivity of LaH x can be suppressed by more than five orders of magnitude. This transforms LaH x to a superionic conductor at -40 °C with a record high H - conductivity of 1.0 × 10 -2  S cm -1 and a low diffusion barrier of 0.12 eV. A room-temperature all-solid-state hydride cell is demonstrated.