Deconvoluting Charge Transfer Mechanisms in Conducting Redox Polymer-Based Photobioelectrocatalytic Systems

Abstract

Poor electrochemical communication between biocatalysts and electrodes is a limitation to bioelectrocatalysis efficiency. An extensive library of polymers has been developed to alleviate this limitation. Conducting-redox polymers(CRPs) are a versatile tool with high structural/functional tunability. While charge transport in CRPs is well characterized, the understanding of charge transport mechanisms facilitated by CRPs within photobioelectrocatalytic systems remains limited. This study is a comprehensive analysis dissecting the complex kinetics of photobioelectrodes to provide a mechanistic overview of charge transfer during photobioelectrocatalysis. We quantitatively compare two biohybrids of metal-free CRP(polydihydroxyaniline) and photobiocatalyst(chloroplasts), formed utilizing two deposition strategies (‘mixed’ and ‘layered’). The superior photobioelectrocatalytic performance of the ‘layered’ biohybrid compared to the ‘mixed’ is justified in terms of rate(Dapp), thermodynamic and kinetic barriers (H,Ea), frequency of molecular collisions(D0) during electron transport, and rate/resistance to heterogeneous electron transfer(k0,RCT). Our results indicate that the primary electron transfer mechanism across the biohybrids, constituting the CRP, is thermally activated intra- and inter-molecular electron hopping, as opposed to a polaron transfer model typical for branched CRP- or conducting polymer(CP)-containing biohybrids in literature. This work underscores the significance of subtle interplay between CRP structure and deposition strategy in tuning the interface, and the structural classification of CRPs in bioelectrocatalysis.