Low-cost flexible laminated graphene paper solid-contact ion-selective electrodes

We report here the fabrication of laminated graphene paper solid-contact ion-selective electrodes (SCISE) with performance characteristics equal to the state of the art SCISEs. Several identical and flexible graphene paper electrodes were first prepared from commercially available graphene paper with a standard pouch laminator in a single lamination step to a price of less than $1 per electrode. After that the solid contact consisting of polyaniline (PANI) doped with dinonylnaphthalene sulfonic acid and the K+-selective plasticized poly(vinyl chloride) membrane were deposited in two steps by drop casting on the surface of the graphene paper. The lamination of 10–15 identical graphene paper electrodes takes only one minute and we obtained fully functional graphene paper electrodes in ca. 40 min, including all manual pre-fabrication steps and 10 min of argon plasma cleaning to remove organic contaminants from the graphene surface. We found that plasma cleaning was necessary to improve the reversibility of the electron transfer of the Fe(CN)63−/4− redox couple. The laminated graphene paper K-SCISEs had a Nernstian slope of 56.9 ± 0.1 mV pK-1, a high E° reproducibility of ±4.4 mV (n = 6) still after more than 24 h, high selectivity against Na+, Li+, H+, Mg2+ and Ca2+, and they showed no water layer formation, light and oxygen gas sensitivity.· However, we observed a minor response to carbon dioxide (pH) because of the pH response of PANI. In this work, we show that laminated graphene paper electrodes are a cost-effective alternative for example to commercially available glassy carbon and platinum rod electrodes.