Bifunctional polypyrrole-based conductive paper towards simultaneous efficient solar-driven water evaporation and electrochemical energy storage

The thriving solar-driven water evaporation (SDWE) technology is considered the ideal candidate for next-generation water treatment because of its high efficiency, environment-friendliness, and low cost. The irresistible trend of diversified energy demand presents multi-functional requirements for a successful SWDE. However, the current SDWE technology rarely breaks through this technical dilemma. Here, we have designed a bifunctional polypyrrole-based capacitor to achieve water purification and energy storage. The hydrophilicity of the filter paper and the high light absorptance of polypyrrole (96.18%) promote the generation of solar steam. The evaporation rate of the PPy-200 (Polypyrrole-200) filter paper reached 1.54 kg m⁻² h⁻¹ under 1 kW m⁻². Interestingly, the symmetric supercapacitor assembled with PPy-based filter paper electrodes could simultaneously realize efficient evaporation (1.94 kg m⁻² h⁻¹) and electrochemical energy storage. As a single electrode, the PPy-200 filter paper exhibited ultra-high specific capacitance (4129.50 mF cm⁻²) and favorable cycling stability (71.16% after 4000 cycles). More importantly, the capacitance of PP-PPy-200 (Polyvinyl alcohol/Polyethylene glycol-Polypyrrole-200) increased to 2.55 times under one sun illumination. This work not only points out a direction for solar thermal utilization, but also provides new design inspiration for high-efficiency flexible electrochemical energy storage devices.