We report that a postsynthesis physical process (freeze–thaw cycles) can reform the microstructure of conductive polymer hydrogels from clustered nanoparticles to interconnected nanosheets, leading to enhanced mechanical and electrochemical properties. The polyaniline–poly(vinyl alcohol) hydrogel after five freeze–thaw cycles (PPH-5) showed remarkable tensile strength (16.3 MPa), large elongation at break (407%), and high electrochemical capacitance (1053 F·g–1). The flexible supercapacitor based on PPH-5 provided a large capacitance (420 mF·cm–2 and 210 F·g–1) and high energy density (18.7 W·h·kg–1), whose robustness was demonstrated by its 100% capacitance retention after 1000 galvanostatic charge–discharge cycles or after 1000 mechanical folding cycles. The outstanding performance enables PPH-5 based supercapacitor as a promising power device for flexible electronics, which also demonstrates the merit of freeze–thaw cycles for enhancing the performance of functional hydrogels.Keywords: conducting polymers hydrogels; flexible supercapacitors; freeze−thaw cycles; polyaniline; supramolecular self-assembly;

Herein we report a simple electrochemical approach to synthesize cobalt-based nanosheet arrays as efficient and robust electrocatalysts for overall water splitting in alkaline electrolytes. The Co nanosheet array and CoFeBO nanosheet array are electrochemically deposited on Ni foam electrodes, which are able to drive a large current density at low overpotentials, and offer stable operation under heavy-loading conditions over an extended period, exceeding the performance of Pt/C and IrO2. To the best of our knowledge, the CoFeBO NS‖Co NS couple is currently the most active and stable non-noble electrocatalyst pair for overall water splitting in alkaline electrolytes. In addition, the facile synthesis method is suitable for designing and screening highly active and stable electrocatalysts with micro- and nano-structures.