Radio frequency response as a non-destructive readout associated with tensile-strength degradation in nanoporous carbon electrodes

This study investigates radio frequency (RF) transmission as a non-destructive electrical readout associated with tensile-strength degradation in nanoporous carbon electrodes subjected to repeated freeze–thaw (F–T) cycling under water immersion. After 60 cycles, tensile strength decreased by 31%, whereas the mean Young’s modulus showed no clear monotonic change over the investigated cycle range. Structural analyses indicated surface roughening and changes in nanoscale pore metrics, while macropore-scale structural changes were not discernible across the investigated exposure states. DC resistance, sheet resistance, and RF S-parameter responses were then compared with the group-mean tensile-strength changes across the F–T exposure states to evaluate their relative responsiveness to tensile-strength degradation. Among the evaluated electrical metrics, the S₂₁-derived RF response at 0.84 GHz exhibited the largest baseline-referenced relative change and the highest response-to-strength-loss ratio at each degraded exposure state (0.664–1.488 MPa⁻¹), compared with sheet resistance (0.153–0.582 MPa⁻¹) and DC resistance (0.0504–0.491 MPa⁻¹). Together, these findings support RF S₂₁ as a damage-sensitive electrical readout associated with the mechanical degradation state of nanoporous carbon electrodes.