Direct-ink writing of PDC-based SiOC anodes for microbial fuel cells

Abstract

Among many applications of porous polymer-derived ceramics (PDCs), when used in microbial fuel cells (MFCs) they can lead to appropriate performance due to the possibility of tailoring the surface properties of the material used as electrode. One of the limitations is the pore clogging during biofilm formation which can be solved by using direct-ink writing (DIW) processing instead of tape-casting. In this work a PDCbased SiOC ink composition used in previous work for tape-casting was adapted to DIW method. These 3D structures will be used later as MFCs anodes to avoid pore clogging and enhance current density. Additionally, the influence of azodicarbonamide on the formation of surface pores was studied. The inks were produced via DIW using 580 μm nozzle diameter or tape-casting, followed by drying at room temperature and pyrolysis at 1000°C for the ceramic conversion of the green bodies. To obtain the ideal viscosity to DIW and print structures that did not collapsed even after layer-by-layer addition, the solid loading of the ink was increased from 70 to 85 wt.% increasing the yield point from 25.87 ± 2.24 to 1141.33 ± 32.33 Pa. Results from scanning electron microscope, mercury intrusion porosimetry and nitrogen adsorption indicate a pore structure of the produced samples with an average pore window size ranging from 0.21 to 105 μm, being higher the lower the solid loading is, and a specific surface area from 21.95 to 82.51m²g−1 , being higher the lower the azodicarbonamide is and when using DIW method processing. These finding are a good indicative to the adequate biofilm formation during further MFC applications. The functional properties were assessed by vapor adsorption, electrochemical spectroscopy and chemical stability analysis. All samples showed a hydrophilic behavior and chemical stability independent of the method, solid loading or amount of azodicarbonamide used. The electrical conductivity ranged from 0.57 ± 0.01 to 1.89 ± 0.32 Sm−1 , being higher the lower the azodicarbonamide amount is. Lastly, even after increasing the azodicarbonamide from 17 to 29 wt.% in solid phase, the open porosity on the surface still remained mostly the same. Overall, the obtained PDC-based SiOC ink could be adapted to the DIW and proved to be promising to be applied as anodes for MFC in the future.