Mid-infrared light resonance-enhanced proton conductivity in ceramics.

Ionic transport in solids is a critical process for energy devices including batteries and fuel cells. To improve ionic transport, an emerging approach is the selective excitation of atomic vibrations related to the mobile ions. However, there is limited direct experimental evidence demonstrating enhanced macroscopic ionic conductivity through this approach. Here, we use a 140 mW continuous-wave mid-infrared (MIR) light to excite the O-H stretch vibration in proton-conducting yttrium-doped barium zirconate. We observe reversible enhancement of 36.8% in bulk, and 53.0% in grain boundary proton conductivities, controlled by MIR irradiation. Decreases in the activation energy and prefactor for bulk proton conduction suggest possible reduction in activation entropy and attempt frequency of proton hopping. We rationalize the enhancement as the excitation of O-H stretch vibrational states, followed by the relaxation into lattice vibration modes, modulating the potential energy surface of the proton. Our findings highlight MIR irradiation as a power-saving strategy to optimize the performance and operation cost of solid-state electrochemical devices by selective modulation of the vibrational properties.