Physicochemical constraints on the in-situ deposited phenoxazine mediated electron shuttling process

Abstract

Resazurin (RZ), a typical phenoxazine mediator, can be deposited in situ onto an electrode in the form of resorufin (RR) during extracellular electron transfer (EET) process, which could result in a sustainable current generation. However, the physicochemical constraints on the in-situ deposition mechanism remain unclear. In this study, the critical parameters of the in-situ deposition of electron-shuttling phenoxazine were explored. The concentration of RZ and the applied potential were found to be two key factors that influence deposition. The critical concentration and critical external potential for deposition were also revealed. Deposition was found to increase with increasing initial RZ concentration and external potential. With −3 mV being the critical potential, deposition was found to vary most at potentials around −3 mV, whereas deposition was stable when the external potential exceeded +241 mV. A concentration of 20 μM was found to be critical, as it is the minimum concentration of RZ required for depositing RR at all potentials. According to the theoretical analysis, the in-situ deposition was determined by the equilibrium status of dissolution-precipitation and reduction-oxidation in the system. This study would be beneficial for understanding the natural electron shuttling processes and high-efficient electrode modification.