Supercapacitive MnO2/PEDOT: PSS Modified 3D-Printed Polymeric Micro-Pillar Electrode for Extraction of Photosynthetic Electrons

Abstract

Photosynthetic bio-electrochemical cells (PBECs) have been reported as having promising potential for the renewable energy field. When photosynthesis occurs, photosynthetic electrons (PEs) were generated and excited in photosystem II by sunlight. These PEs were transferred via photosynthetic apparatuses in thylakoid membranes (TMs) and finally consumed to reduce NADP. So far, several attempts have been made to maximize the extraction of PEs from the TMs. Firstly, a micro-pillar electrode was demonstrated to enhance PEs extraction by maximizing the contact area with TMs [1]. As another study, for effective electrical connections with TMs, carbon nanotubes (CNTs) [2], or graphene oxide (GO) [3] were utilized to enhance PEs harvesting. Furthermore, supercapative materials were exploited to improve the performance of TM-based PBECs. For instance, PEs harvesting was enhanced in Au electrode modified with ruthenium dioxide (RuO2) nanosheets compared to a pristine Au electrode [4]. In another study, a dual-feature electrode of Au and PEDOT was introduced to collect and store PEs [5]. Although there were various attempts to harvest PEs effectively, their electrodes were still limited to the two-dimension. Thus, it is required that a three-dimensional electrode with supercapacitance to achieve more efficient PEs harvesting for practical application.In this work, we propose a supercapacitive MnO2/PEDOT:PSS-modified 3D-printed polymeric micro-pillar electrode to efficiently collect and spontaneously store the PEs. For the maximization of PE harvesting, diameter, pitches (center to center), and aspect ratio (A/R) of the micro-pillars were controlled. To fabricate the current collection layer, Au was sputtered on the 4-aminothiophenol coated stereolithographically (SLA) printed micro-pillar substrate. PEDOT:PSS was electrodeposited as secondary current collect and adhesion layer between Au and MnO2. Then, MnO2 was electrochemically deposited on PEDOT:PSS layer for efficient attachment with TMs and storage of PEs. Finally, TMs were carefully dip-coated on MnO2/PEDOT:PSS micro-pillar electrode. The morphology of each step in the electrode fabrication was analyzed by optical microscopy and scanning electron microscopy (SEM). The enhanced electrochemical surface area (ECSA) of 3D-printed MnO2/PEDOT:PSS micro-pillar electrode was compared to flat electrode using cyclic voltammetry (CV). The capacitive performance of 3D-printed TM/MnO2/PEDOT:PSS micro-pillar electrode was carefully analyzed using CV and Galvano charge-discharge measurements. Measured ECSA of MnO2/PEDOT:PSS micro-pillar electrode was 5 folds increase than that of flat electrode. MnO2/PEDOT:PSS micro-pillar electrode was achieved 4 folds and 180 folds larger than PEDOT:PSS and Au micro-pillar electrode, respectively. 212 F/g of gravimetric and 257 mF/cm2 of areal capacitance were measured in 3D-printed MnO2/PEDOT:PSS micro-pillar electrode. It was confirmed that PEs can be electrochemically extracted from TM deposited 3D-printed MnO2/PEDOT:PSS micro-pillar electrode using CV. To measure a light-triggered PE current, a standard three electrode system was configured with a 3D-printed TM/MnO2/PEDOT:PSS micro-pillar electrode. The light-driven PE current of 27 μA/cm2 was measured in a 3D-printed MnO2/PEDOT:PSS micro-pillar electrode under 100 mW/cm2 of illumination with a bias potential of 0.5 V versus Ag/AgCl.