Sturcture Analysis Based On Carbon Foam And Stainless Steel Felt And The Effect On Electricity Generation Performance Of Electrochemically Active Biofilm

In this paper, the electrochemically active biofilms(EAB) on reticulated vitreous carbon(RVC) and stainless steel felt(SSF) electrodes in the three-electrode system were studied including the analysis of porous structures of RVC and SSF, the relations between porous structures and electrocatalytic performance of EAB, and the structure optimizations of the macro-porous materials.(1) The porous structures of RVC and SSF were analyzed. By establishing structural units of RVC was proved to have the fairly similar structure with the natural bubble which was regarded as periodic partitions of a certain unit(truncated octahedra with slightly curved faces or a combination of dodecahedrons and tetrakaidecahedrons). The struts in RVC foam were solidified from Plateau borders which were considered as channels for fluid passing freely within original natural bubbles. As a result, these struts were naturally, and efficiently interconnected, resulting in a platform of 3-D network with much higher surface area for biofilm attaching and better permeability for mass transfer. In comparison, SSF showed relatively irregular pore structures which can be considered as triangular units trough connecting stainless steel layers. Thus, the SSF showed wide range of sizes and relatively rough surfaces.(2) The experimental results of bioreactor in three-electrode system suggested that electrocatalytic ability of EAB on RVC and SSF can be significantly improved than non-porous materials. EAB on 100 PPI(Pores per inch) RVC(33.63 A m-2) and BZ100D(19.79 A m-2) as electrodes had the highest current densities, which was 6.60 and 3.71 times higher than that of PG(5.11 A m-2), respectively.(3) Relations between diverse parameters of RVC materials and current production ability were found from analyzing foam structure and kinetics of electrode reaction. Specific surface area and permeability, as determined by porosity and pore size, were proved to be two dominant factors to affect current production of EAB on macro-porous materials. Macro-pore size in the range of 124.8 μm(100 PPI-compressed RVC) to 600.9 μm(80 PPI RVC) were speculated to be suitable for increasing EAB catalytic performance. In addition, different stirring speeds showed different influences for the catalytic performance of EAB on various RVC materials. Stirring speed and permeability determined effective biofilm attaching surface area and stirring speed from 1000 rpm to 1400 rpm was found to be suitable for 100 PPI RVC. From our results, the foam structure was proved to be more suitable for for enhancing EAB electricity generation capability than SSF felt structure.(4) The relation between porosity or pore size and specific surface area or permability of macro-porous materials were studies through MATLAB simulation, and the results showed that it is contradictory to have the optimal structure possessing both possible largest specific surface area(75%, small pore diameter) and highest permeability(high porosity and small pore diameter). Thus it is the key factor to choose the suitable porosity as well as pore size for macro-porous materials structure optimization. In this study, 100 PPI RVC and BZ100 D SSF were proved to have better structures characteristics due to large specific surface area as well as high permeability is suitable for enhancing electricity generation capability of EAB.