[EN] Redox-polymer nanoparticles are a promising solution to avoid the detrimental dissolution of organic electrode materials while showing discrete redox processes. In this work, catechol-based redox-active polymer nanoparticles (cRPNs) were synthesized through one-step emulsion polymerization with a tunable size from 25 to 150 nm. The fresh cRPNs were characterized and showed a reversible redox process centered at 0.50 V (vs. Ag/AgCl) in 1 M H2SO4. Unexpectedly, the cRPN latex aged after days passing from white to pink. This aging resulted in a shift of its redox potential toward higher values, which could be associated to autoxidation of the catechol groups and subsequent crosslinking of NPs due to catechol dimer formation. Finally, we compared the performance of fresh and aged cRPNs in a hybrid supercapacitor device, proving how the aging effect had some benefits such as an increase in the voltage output, specific capacitance, cyclability and Coulombic efficiencies of the device.