Abstract
Microbial Fuel Cells (MFCs) are biological fuel cells based on the oxidation of fuels by electrogenic bacteria to generate an electric current in electrochemical cells. There are several methods that can be employed to improve their performance. In this study, the effects of gold surface modification with different thiol molecules were investigated for their implementation as anode electrodes in micro-scale MFCs (µMFCs). Several double-chamber µMFCs with 10.4 µL anode and cathode chambers were fabricated using silicon-microelectromechanical systems (MEMS) fabrication technology. µMFC systems assembled with modified gold anodes were operated under anaerobic conditions with the continuous feeding of anolyte and catholyte to compare the effect of different thiol molecules on the biofilm formation of Shewanella oneidensis MR-1. Performances were evaluated using polarization curves, Electrochemical Impedance Spectroscopy (EIS), and Scanning Electron Microcopy (SEM). The results showed that µMFCs modified with thiol self-assembled monolayers (SAMs) (cysteamine and 11-MUA) resulted in more than a 50% reduction in start-up times due to better bacterial attachment on the anode surface. Both 11-MUA and cysteamine modifications resulted in dense biofilms, as observed in SEM images. The power output was found to be similar in cysteamine-modified and bare gold µMFCs. The power and current densities obtained in this study were comparable to those reported in similar studies in the literature.
Highlights
Microbial Fuel Cells (MFCs) are bioreactors converting the energy stored in chemical bonds of organic compounds into electrical energy via the catalytic activity of electrogenic bacteria under anaerobic conditions [1,2,3]
The cost of gold electrodes constricts their employment in large systems, they are widely used for Micromachines 2020, 11, 703 the cost of gold electrodes constricts their employment in large systems, they are widely used for fundamental research in miniaturized micro-scale MFC systems [20]
Since the introduction of carboxylic acid on the surface led to an increase in the hydrophilicity, the water contact angle decreased approximately 11 degrees, which is in good agreement with the literature [34,35]
Summary
Microbial Fuel Cells (MFCs) are bioreactors converting the energy stored in chemical bonds of organic compounds (e.g., glucose, lactate, etc.) into electrical energy via the catalytic activity of electrogenic bacteria under anaerobic conditions [1,2,3]. Since thiols with carboxyl or amine functional groups can bind to proteins on the bacterial membrane, the functionalization of gold surfaces with such groups will favor bacterial attachment [22,23] and this may, in turn, accelerate biofilm formation These self-assembled monolayers may increase the electron transfer resistance, depending on the length of the carbon chain of the molecule to be used [24]. Some studies have shown that more current was generated by creating an SAM of carboxyl terminated alkanethiols compared to non-functionalized gold electrodes [22,26] This was explained by the phenomenon in which carboxylic acid could accommodate cytochromes on the electrode surface through very strong hydrogen bonding with the peptide bonds in the protein backbone
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