Effects of substrate roughness on the fabrication and properties of Ag/AgCl pseudo-reference electrodes for solid-state electrochemical sensors.

Solid-state silver/silver chloride pseudo-reference electrodes (PREs) are critical for miniaturized, low-cost disposable electrochemical sensors. This work systematically explores the coupling effects of substrate roughness and NaClO chlorination parameters on AgCl film microstructure and electrode electrochemical performance. Magnetron sputtering was used to deposit Cr adhesive layer/Ag functional bilayer films on three substrates with graded surface roughness: baking paper, smooth glass, and mechanically roughened glass. The Ag layers were converted to AgCl via chemical chlorination using sodium hypochlorite solutions with two concentrations (0.5 wt% and 14 wt%). Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) were adopted to characterize AgCl nucleation, grain growth, densification, and delamination behaviors, whereas open-circuit potential (OCP) and cyclic voltammetry (CV) measurements quantified electrode potential drift, repeatability, and long-term stability. The results demonstrate that mild 0.5 wt% NaClO combined with optimized chlorination time yields compact, uniform and strongly adherent AgCl coatings on all substrates; the optimal durations are 240 s for baking paper, 210 s for roughened glass and 90 s for smooth glass. In contrast, 14 wt% high-concentration NaClO accelerates initial nucleation yet induces severe grain coarsening and structural defects. Surface roughening effectively enhances interfacial anchoring of AgCl layers and alleviates structural degradation under extended chlorination. This comparative study provides straightforward guidance for fabricating high-stability coating-free solid-state PREs.