Using the Surface Features of Plant Matter to Create All-Polymer Pseudocapacitors with High Areal Capacitance

Controlling mesoscale organization in thick films of electroactive polymers is crucial for studying and optimizing charge and ion transport in these disordered materials. Conventional approaches focus on directing long-range polymer aggregation and/or crystallization during film formation by using interfaces, flow and/or shear forces. Here, we describe an alternative method that takes advantage of naturally textured biological substrates and vapor-coating to structure thick-conjugated polymer films. Reactive vapor-coating is a technique that enables in situ synthesis of doped conjugated polymers inside a reduced-pressure reactor. Reactive vapor deposition conformally coats the surface of plant matter, such as leaves and flower petals, with conducting polymer films while leaving these living substrates undamaged. Importantly, the intricate surface features of plant matter are faultlessly reproduced in the coating, effectively creating thick, high-surface-area, electrochemically active conducting polymer electrodes on plant matter. A microstructured, 10 μm thick film of p-doped poly(3,4-ethylenedioxythiophene) on a pilea involucrata leaf acts as an all-polymer pseudocapacitor with a higher areal capacitance (142 mF/cm²) than an analogous film on a planar plastic substrate lacking microstructure (50 mF/cm²). Taken together, reactive vapor deposition and microstructured plant matter present a unique combination of processing technique and substrate than can yield a diverse library of controllably microstructured electronic polymer films.