Firefighters are exposed to complex smoke containing volatile, semivolatile, aromatic, and particulate-associated organic contaminants that accumulate on skin, clothing, and protective equipment. Conventional gas sensors monitor only selected airborne species, while passive samplers require laboratory analysis and cannot provide continuous exposure assessment. To address this limitation, we developed a proof-of-concept mass-capacitor that integrates contaminant absorption and electrical sensing within a single polydimethylsiloxane/functionalized carbon nanotube (PDMS/f-CNT) composite coated on interdigitated electrodes (IDEs). Unlike conventional sensors that report the instantaneous concentration of selected compounds, the proposed platform functions as both a sorptive collector and an electrical transducer. It continuously converts contaminant uptake, retention, and release into a time-resolved electrical response. For firefighter applications, this mass-capacitor bridges the gap between passive sorptive samplers and conventional real-time gas sensors. It enables continuous tracking of the cumulative sorbed contamination burden without requiring offline laboratory analysis or restricting the measurement to selected airborne species. A custom potentiostat applied staircase cyclic excitation, while Fast Fourier Transform (FFT)-assisted processing enabled extraction of the differential charge, $\mathsf{\Delta }Q$ as an indicator of contaminant loading. The sensor was evaluated using smoke generated from cotton, paper, wood, and synthetic fibers. Compared with PDMS alone, the PDMS/f-CNT composite produced an approximately 24-fold higher response with minimal humidity interference (≈80% RH). Limits of detection ranged from 0.08 to 0.26 ppm, while repeated smoke exposures produced stepwise increases in ΔQ, demonstrating continuous tracking of cumulative contaminant loading. These results establish the feasibility of the mass-capacitor concept and introduce a new approach for real-time monitoring of the accumulated organic contamination burden rather than the instantaneous concentration of individual airborne compounds.

This work provides the first demonstration of FFTCCV as a dual-purpose method, serving both as a real-time diagnostic tool and as a phase- and morphology-engineering strategy. By adjusting the scan rate, FFTCCV directs the crystallographic evolution of Ni (OH)₂ on Ni foam—stabilizing α-nanoflakes at 0.7 V·s⁻¹ and β-platelets at 0.007 V·s⁻¹—while simultaneously enabling electrode-resolved ΔQ tracking and predictive state-of-health (SoH) monitoring. This approach enabled the precise regulation of electrode morphology and phase composition, yielding high areal capacitance (546.5 mF·cm⁻² at 5 mA·cm⁻²) with ~75% retention after 3000 cycles. These improvements advance the development of high-performance micro-supercapacitors, facilitating their integration into wearable and miniaturized devices where compact and durable energy storage is required. Beyond performance enhancement, FFTCCV also enabled continuous monitoring of capacitance during extended operation (up to 40,000 s). By recording both anodic and cathodic responses, the method provided time-resolved insights into device stability and revealed characteristic signatures of electrode degradation, phase transitions, and morphological changes. Such detection allows recognition of early failure pathways that are not accessible through conventional testing. This monitoring capability functions as an embedded health sensor, offering a pathway for predictive diagnosis of supercapacitor failure. Such functionality is particularly important for energy-driven actuators and smart materials, where uninterrupted operation and preventive maintenance are critical. FFTCCV therefore provides a scalable strategy for developing energy-autonomous microsystems with improved performance and real-time state-of-health monitoring.