Potassium-selective solid contact electrodes with poly(amidoacid) Cu(I) complex, electron-ion exchanging resin and different sorts of carbon black in the transducer layer

Potassium-selective solid-contact electrodes (ISEs) with various transducer layers are studied by means of the zero-current potentiometry, electrochemical impedance spectroscopy, chronopotentiometry, and SEM. The study is focused on the stability of the ISE potentials over time. A relatively good stability is shown by ISEs with (i) C60 and C70 fullerene-enriched carbon black (SD = 5.7 mV over 80 days) and with (ii) the combination of ordinary carbon black, poly(amidoacid) Cu(I) complex, and electron-ion exchanging resin in the transducer layer (SD = 3.3 mV over 80 days). Passing a current through the ISEs results in polarization which can be decomposed into a decaying exponent (slow redox reaction) and a diffusional polarization at the interface between the membrane and the transducer layer. There is no correlation between the exponential component of the polarization and the long-term stability of the ISE potentials, whereas the latter correlates with the diffusional part of the polarization. In turn, the diffusional polarization is low when the transducer layer contains the primary ion (K+), and/or the electronic conductor in the transducer layer has a higher specific surface area and/or smaller pores.