Real-time humidity-sensing properties of ionically conductive Ni(II)-based metallo-supramolecular polymers

Metallo-supramolecular polymers composed of Ni(II) ions and bis(2,9-dimethyl-1,10-phenanthroline) showed ionic conductivity, which enhanced by about four orders of magnitude with increasing relative humidity from 30 to 98% RH, in the film state. Four Ni(II)-based polymers with different counter anions were synthesized to investigate the ionic conduction mechanism. The highest ionic conductivity (5 x 10(-2) S cm(-1)) at 98% RH was observed in the polymer with chloride ions as the counter anion. The Grotthuss-type proton transfer mechanism was indicated by the low activation energy (0.21 eV) for the ionic conduction. The polymer film prepared on an interdigitated electrode showed dynamic humidity-sensing properties based on the quick and large current-response to humidity change.