Retaining the specific capacitance under electrochemical stress: A pH-induced self-protection mechanism for manganese dioxide pseudocapacitive electrodes

In this study, we report the enhanced electrochemical performance of a MnO2 electrode modified with a pH-sensitive co-polymer, activated at acidic pH, and designed to counteract MnO2 degradation in aqueous aqueous pseudocapacitors. The conformation of this polymer is controlled by the local pH changes that occur at the electrode/electrolyte interface during electrochemical stress associated to oxygen evolution.As a proof of concept, we demonstrate that the addition of the pH-sensitive polymer contributes to improved electrode integrity and lifetime under over-polarization with oxygen evolution. After undergoing 10 cycles of electrochemical stress, the MnO2/pH-sensitive polymer composite retains ∼ 70 % of its capacitance. This remarkable result stands in stark contrast with the pristine MnO2 electrode which fails catastrophically under the same stress conditions. We believe that this pH-induced self-protection mechanism represents a significant advancement in the development of novel smarter self-healing electroactive materials for the next generation of energy storage devices.