Fig. 2: Characteristics of O–H stretch vibration and proton conduction with and without MIR irradiation.

a Schematics of the electrical conductivity measurement setup. The MIR radiation covers the wavelength range of O–H stretch vibration. b Vibrational profile of O–H stretch vibration band (ν_O–H) characterized by DRIFTS (red). The orange shadow shows the typical emission spectrum of the CW MIR light. c Typical EIS spectra at 160 °C in wet N₂ with (red) and without (blue) MIR i0rradiation at an effective MIR power density (p) of 195.2 mW cm⁻². The insets illustrate the magnification of bulk features near 150 kHz, and the equivalent circuit used for fitting. The reversibility of proton conductivity enhancement is represented by single-frequency Z’ at (d) 150 kHz for bulk (brown) and (e) 1 kHz for GB (turquoise). The yellow shadows highlight the time intervals for MIR irradiation. The dashed red and grey lines show steady-state Z’ averages with and without irradiation respectively; error bands indicate the corresponding standard deviations. f Comparison of bulk and GB proton conductivities deconvoluted from c and corresponding enhancement ratio of conductivity (Δσ/σ). The error bars in (f) incorporate standard deviations from three parallel measurements and fitting errors per sample across three samples prepared using the same method. Source data are provided in the Source Data file.