No abstract

A spectroelectrochemical cell is described that enables confocal Raman microscopy studies of electrode-supported films. The confocal probe volume (∼1 μm3) was treated as a fixed-volume reservoir for the observation of potential-induced changes in chemical composition at microscopic locations within an ∼20 μm thickness layer of a redox polymer cast onto a 3 mm diameter carbon disk electrode. Using a Raman system with high collection efficiency and wavelength reproducibility, spectral subtraction achieved excellent rejection of background interferences, opening opportunities for measuring within micrometer-scale thickness redox films on widely available, low-cost, and conventional carbon disk electrodes. The cell performance and spectral difference technique are demonstrated in experiments that detect transformations of redox-active molecules exchanged into electrode-supported ionomer membranes. The in situ measurements were sensitive to changes in the film oxidation state and swelling/deswelling of the polymer framework in response to the uptake and discharge of charge-compensating electrolyte ions. The studies lay a foundation for confocal Raman microscopy as a quantitative in situ probe of processes within electrode-immobilized redox polymers under development for a range of applications, including electrosynthesis, energy conversion, and chemical sensing.

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.