Surface and electrochemical studies of a carbon dioxide probe based on conducting polypyrrole

Abstract

This paper reports on the development of a Severinghaus carbon dioxide probe using polypyrrole (PPy) as the pH-indicator electrode. The electrochemically synthesized bicarbonate-doped PPy gave satisfactory potentiometric properties as pH-indicator electrode: sub-Nernstian response with a slope, m, of −39.06 mV pH −1 at buffer solutions of pH 3–10, excellent linearity, r, of −0.999, and relatively fast response time, average t r=3.6 min for three replicates ( n=3). For the CO 2 probe design, the PPy/HCO 3 −-coated Pt electrode was coupled with a miniaturized Ag/AgCl reference electrode. A thin layer (∼0.5 mm) of 300 μl of 0.001 M NaHCO 3 internal electrolyte is sandwiched between the two electrodes and the Teflon gas permeable membrane. The optimized CO 2 probe exhibited good potentiometric properties ( linearity=8.78×10 −5 to 2.70×10 −3 M CO 2 with r=−0.993; m=−47.42 mV/decade [CO 2] with RSD=17.04% at n=3; LOD=3.93×10 −5 M CO 2 and t r=4.71 min) when used only in one calibration measurement. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques were used to study the surfaces of the CO 2 probe components: PPy/HCO 3 − film and Teflon gas permeable membrane. This study highlights the use of these surface-sensitive techniques to understand the electrochemical behavior of the fabricated CO 2 probe. A correlation was made between the surface characteristics of the sensor components with the low reproducibility and repeatability of the sensor responses.