Polymer-derived SiOC Ceramics as New Electrode Materials for Microbial Fuel Cell Applications

The increased demand for energy sources and solutions for global warming have required great efforts regarding the development and optimization of renewable energy devices. Among the available technologies, microbial fuel cells (MFCs) arise as a single system, wherein electricity is produced from the biomass using bacteria as biocatalyst, while the wastewater is treated. Traditional MFCs are composed of an anode chamber, where an electroactive biofilm is developed, and a cathode chamber, separated by an ion conducting membrane. The main reactions occur during the interaction of bacteria and electrode surfaces, therefore the anode has been considered as a fundamental component in an MFC. Furthermore, the oxygen reduction reaction (ORR), which takes place at the cathode is often limiting the performance as a result of its slow reaction kinetics. An ideal MFC anode material should enable the electron transfer with simultaneous microbial attachment, while cathode materials should have a high reduction potential. Thus far, mainly carbon-based electrode materials are applied in MFC. However, their electrochemical oxidative degradation and limited active reaction sites for microbial adhesion still restrict their use. In this work, silicon oxycarbide (SiOC)-based electrodes are synthesized targeting the development of cost-effective electrode materials to improve electrochemical performance in MFCs. The materials were prepared by the polymer-derived ceramics (PDCs) route, using poly(methyl silsesquioxane) and poly(methyl phenyl silsesquioxane) as precursors tailoring the properties by varying pyrolysis temperatures and incorporating conductive phases and further fillers. The influence of pyrolysis temperature and incorporation of conductive materials on functional properties and electrical conductivity was investigated and discussed along with first investigation of biofilm development on SiOC-based ceramic surfaces. Their applicability in MFC was investigated throughout several types of bioelectrochemical setups and compared with commercially available carbon materials. Maximum power density values varying from 30 to 211 mW m-2 were obtained, which showed a two to three-fold increase when compared to carbon felt, attributed to its porous structures and surfaces properties. In terms of wastewater treatment, chemical oxygen demand (COD) removal efficiency of about 85% was demonstrated. Additional studies revealed the correlation of performance with surface properties emphasizing hydrophilicity as major aspect followed by specific surface area. In addition, cobalt/nickel-containing SiOC-based nitrogen(N)-doped ceramic electrocatalysts were produced as a new class for the ORR and studied under acidic, neutral and alkaline conditions. The N-doped (Co)SiOC catalyst exhibited significantly higher ORR activity suggesting its promising applicability. Based on the properties and results obtained, the proposed and investigated new class of SiOC-based porous materials have a high potential to be considered in MFC technology.