Temperature Pulse Driven Sulfurization and Desulfurization of CuO for Enhanced H₂S Quantification

In this study, we report a power-efficient and highly selective H2S gas sensing platform based on a pulse-modulated sensor of nanostone-structured CuO thin films. Nanostone morphology chemiresistive sensors exposed to H2S at moderate temperatures (∼150 °C) undergo irreversible surface transformations, converting the active CuO phase into highly conductive CuS or Cu2S, which results in unstable current output and loss of sensing capability. To address this, we introduce a dynamic pulse modulation technique that cyclically toggles the sensing temperature ON and OFF at 200 °C, enabling in situ regeneration of CuO from CuS without external thermal treatment. This effect is attributed to enhanced sulfur desorption kinetics and reactivation of surface oxygen during cooling cycles, which collectively disrupt the thermodynamic equilibrium that stabilizes Cu-S bonds under continuous heating. Morphological features, such as a nanostone-like surface texture and vertically aligned columnar grain architecture, further contribute to rapid gas diffusion, increased surface reactivity, and improved charge transport pathways. Experiments reveal that pulse modulation decrease reaction and recovery time, increase long-term stability, and material reversibility, even at higher H2S concentrations where irreversible behavior is typically observed.