Electrochemical Sensors with Carbon-Based Thick-Film Working Electrodes: Correlating Structure with Electrochemical...

Integrated electrochemical sensors (IESs) offer rapid and efficient detection of environmental pollutants, but their broader practical implementation requires overcoming common challenges associated with reproducible fabrication and long-term stability. In this work, these challenges were addressed using a thick-film approach to fabricate IESs with graphite-glass, glassy carbon, and carbon black working electrodes (WEs) by screen printing followed by firing at 850 °C. The relationship between the structure of the carbon-based WEs and the electrochemical performance of the IESs was systematically investigated using cyclic voltammetry (CV) in combination with X-ray powder diffraction, transmission electron microscopy (TEM), and scanning TEM. The analyses revealed distinct morphologies and structural ordering of the carbon WEs, which directly affect their electron-transfer kinetics, adsorption behaviour, capacitive response, and electrochemically active surface area. The ordered structure of the graphite-glass WE was associated with lower capacitance and faster electron-transfer kinetics, as determined from the CV response of the IES. In contrast, the disordered structure of the carbon black WE was associated with higher capacitance and slower kinetics of the IES. The glassy carbon-based IES exhibited kinetics similar to those of the carbon black-based IES, but with the lowest capacitance, resulting in the greatest signal definition. Consequently, although all IESs exhibited wide operating potential windows (-1.6 V to +1.0 V vs Ag/AgCl) and fast heterogeneous electron-transfer kinetics towards the [Fe(CN)₆]^3-/4- redox probe (7.6 × 10^-3-15.5 × 10^-3 cm s^-1), the carbon materials differed in their electrochemical response and signal definition. Importantly, all IESs demonstrated excellent reproducibility (relative standard deviation < 2.4%), operational stability with less than 5% signal loss after 1000 CV cycles, and shelf-life stability exceeding 30 days. These findings demonstrate that tailoring the carbon structure of the screen-printed thick-film WEs enables reproducible fabrication of stable and reliable IESs while providing a versatile strategy for tuning their electrochemical performance towards application-specific requirements.