Efficient Humidity Sensing and Stable Moisture Energy Generation with Polyaniline Emeraldine Base – Poly(sodium 4‑styrenesulfonate) Thin Film

The sensitive response of conjugated polymers to humidity has been exploited in a wide range of applications. The emeraldine salt (ES) form of polyaniline is one of the most popular systems explored owing to its high and tunable electrical conductivity. We show that the emeraldine base (EB) thin film fabricated via a polyelectrolyte (poly­(sodium 4-styrenesulfonate), NaPSS) templated solution synthesis is a significantly more efficient humidity sensor than the more protonated forms including the ES. The EB-NaPSS thin film exhibits a sensing responsivity of 93% in the RH% range 11–85, compared to 44% with the ES analogue; the sensing is quick and highly reversible. Unlike the ES, the EB-NaPSS thin film also exhibits a nonlinear I–V characteristic under high humidity conditions. It is shown to be an easily fabricated new entrant to the emerging family of moisture energy generation systems. A simple device structure with an imposed RH% gradient and series connection of five units allowed a stable open-circuit voltage (V OC) of ∼1 V to be extracted for over 36 h. Impedance spectroscopy provides insight into the mechanistic aspects that lead to the humidity-related responses of the thin films. The scalability of these simple devices promises potential applications.