Surface morphology and surface energy of anode materials influence power outputs in a multi-channel mediatorless bio-photovoltaic (BPV) system

Abstract

Bio-photovoltaic cells (BPVs) are a new photo-bio-electrochemical technology for harnessing solar energy using the photosynthetic activity of autotrophic organisms. Currently power outputs from BPVs are generally low and suffer from low efficiencies. However, a better understanding of the electrochemical interactions between the microbes and conductive materials will be likely to lead to increased power yields. In the current study, the fresh-water, filamentous cyanobacterium Pseudanabaena limnetica (also known as Oscillatoria limnetica) was investigated for exoelectrogenic activity. Biofilms of P. limnetica showed a significant photo response during light-dark cycling in BPVs under mediatorless conditions. A multi-channel BPV device was developed to compare quantitatively the performance of photosynthetic biofilms of this species using a variety of different anodic conductive materials: indium tin oxide-coated polyethylene terephthalate (ITO), stainless steel (SS), glass coated with a conductive polymer (PANI), and carbon paper (CP). Although biofilm growth rates were generally comparable on all materials tested, the amplitude of the photo response and achievable maximum power outputs were significantly different. ITO and SS demonstrated the largest photo responses, whereas CP showed the lowest power outputs under both light and dark conditions. Furthermore, differences in the ratios of light : dark power outputs indicated that the electrochemical interactions between photosynthetic microbes and the anode may differ under light and dark conditions depending on the anodic material used. Comparisons between BPV performances and material characteristics revealed that surface roughness and surface energy, particularly the ratio of non-polar to polar interactions (the CQ ratio), may be more important than available surface area in determining biocompatibility and maximum power outputs in microbial electrochemical systems. Notably, CP was readily outperformed by all other conductive materials tested, indicating that carbon may not be an optimal substrate for microbial fuel cell operation.

A Bioelectrochemical Approach to Characterize Extracellular Electron Transfer by Synechocystis sp. PCC6803

“…In a simple variation on this idea, electrons provided by the anode can be used by microorganisms to produce desired chemicals in the reductive reactions at the cathode, a process referred to as microbial electrosynthesis [5], [6], [7]. By utilizing photosynthetic organisms in the anode, water can be used as the electron source in a device that is referred to as a bio-photovoltaic cell (BPV) [8], [9], [10], [11], [12], [13], [14], [15]. In principle, a BPV can be used for solar-powered, CO 2 -neutral production of chemicals or electricity.…”

A synthetic biology approach to engineering living photovoltaics

“…For electrodes that do not directly permeate the insulating cell membrane, the electrical and surface characteristics of the anode plays a critical role in extracellular electron transfer 26 . Anodes modified with a flexible redox polymer 27 , porous ceramic materials 28 , indium tin oxide-coated materials 29 , and nanomaterials 30 were shown to enhance electron transfer compared to conventional carbon-based anodes.…”

“…This limitation has been identified from multiple, experimental studies which, when taken together, identify membrane transport as the rate-limiting step: (1) rapid, increased photocurrent from isolated photosynthetic membrane fractions containing fewer photosynthetic complexes compared to whole-cell measurements 22 , (2) high currents obtained by inserting a nanoelectrode into the photosynthetic membranes of a chloroplast 67 , (3) improved electron transfer by engineering the electrode surfaces for improved interaction with the cell membrane 18,29,68 , (4) enhanced photocurrent extraction in the presence of membrane-permeable mediators 16,20,69 , and (5) comparative analysis calculating a lower charge extraction rate than predicted from oxygen evolution rates 70 .…”

Iron reduction by the cyanobacterium Synechocystis sp. PCC 6803

“…Understanding the rate of iron reduction is important not only for fundamental understanding at the cellular level, but also for applications that make use of this reductive capacity of whole cells [21,22]. In a bio-electrochemical cell, electrons harvested from cells by redox mediators such as potassium ferricyanide, K 3 [Fe(CN) 6 ], can be used as a fuel source at an anode for electricity production, or used at a cathode to produce secondary products.…”