Compressible sponge electrodes by oxidative molecular layer deposition (oMLD) of polyethylenedioxythiophene (PEDOT) onto open-cell polyurethane sponges

Abstract

The formation of compressible porous sponge electrodes is appealing to overcome diffusion limitations in porous electrodes for applications including electrochemical energy storage, electrochemical water desalination, and electrocatalysis. Previous work has employed wet chemical synthesis to deliver conductive materials into porous polymer sponge supports, but these approaches struggle to produce functional electrodes due to (1) poor electrical connectivity of the conductive network and (2) mechanical rigidity of the foam after coating. In this work we employ oxidative molecular layer deposition (oMLD) via sequential gas-phase exposures of 3,4 ethylenedioxythiophene (EDOT) and molybdenum pentachloride (MoCl₅) oxidant to imbibe polyurethane (PU) sponges with electrically-conductive and redox-active poly(3,4 ethylenedioxythiophene) (PEDOT) coatings. We analyze the oMLD deposition on compressive PU sponges and modify the reaction conditions to obtain mechanically compressible and electrically conductive sponge electrodes. We specifically identify the importance MoCl₅dose time to enhance the conductivity of the sponges and the importance of EDOT purge time to preserve the mechanical properties of the sponges. Controlling these variables produces an electrically conductive PEDOT network within the sponge support with reduced impact on the sponge's mechanical properties, offering advantages over wet-chemical synthesis approaches. The compressible, conductive sponges we generate have the potential to be used as compressible electrodes for water desalination, energy storage, and electrocatalysis.

Keywords: compressible; electrodes; oxidative molecular layer deposition; polyethylenedioxythiophene; sponge.