Planar, low-cost, flexible, and fully laminated graphene paper pseudo-reference and potassium-selective electrodes

We report for the first time a one-step fabrication by lamination of inexpensive graphene paper (GP) based Ag/AgCl pseudo-reference (RE) and K⁺-selective coated-film electrodes forming the novelty of this work. Contrary to our previous work about laminated GP solid-contact electrodes, the electrode fabrication in this work does not require manual drop casting steps after the lamination, simplifying the fabrication and making it suitable for mass production. We also eliminated the need of the solid contact and simplified the electrode construction by placing the plasticized potassium-selective PVC membrane (ISM) directly on the GP functioning as combined electrode substrate and ion-to-electron transducer. Both Ag/AgCl and the ISMs were pre-deposited on rectangular GP sheets (10 ×100 mm²) before placing them inside laminating pouches and feeding them through an office laminator after which the electrodes were ready for use. Five batches of 32 pseudo-REs had a very good E⁰ reproducibility of ± 2.8 mV. The K⁺-electrodes had a slope and detection limit of 57.4 ± 0.3 mV/pK (n = 4) and 6 × 10^-7 M, and the E⁰ reproducibility was in the best case only ± 1.2 mV matching the performance of nonlaminated K⁺-electrodes. This work demonstrates that the ISMs are compatible with the lamination where the temperature can momentarily rise to ca. 130 ºC.