title: Investigation and development of power-generating building material systems based on air-cathode microbial fuel cell using Geobacter sulfurreducens
Creators: name: Zhang, Shifan
Publisher: name: UNSPECIFIED
Year: 2023

description: The increasing environmental pollution, carbon emissions, and limited fossil fuel reserves necessitate the gradual replacement of fossil fuels with sustainable and renewable green energy sources. However, current green energy sources have specific requirements for their application, such as solar energy requiring sufficient sunlight and wind energy requiring sufficient wind without negative impacts on the environment. Hydrogen fuel cells are also gradually being utilized as a clean energy source. As a means of power generation, the key factor in fuel cells is the catalytic effect on the reaction. In nature, there exists a group of electrochemically active microorganisms that are widely distributed in soil and wastewater. They act as natural catalysts in fuel cells. Although these microbial fuel cells have seen significant improvements in power generation in recent years, their application has not been widely promoted due to cost. Concrete is the most widely used building material in the world. Its low raw material cost, high compressive strength, and simple production process make it an attractive and easily applicable material in the field of construction and building. If mineral materials can be used to make fuel cells, the manufacturing cost would be greatly reduced, which would greatly benefit the development of fuel cells. In order to use mineral materials as electrodes for fuel cells, they must have a low enough electrical resistance. This PhD research is based on the theory of percolation and studies two types of building materials, Portland cement and geopolymer, from a microstructural perspective. By comparing their differences in microstructure and the changes in electrical conductivity of their mixes in dry and wet conditions, it is found that when the volume fraction of conductive fillers exceeds its percolation threshold, the overall electrical conductivity of the composite is no longer related to its water content. In other words, the conductive mechanism in the mix is mainly in the form of electronic conduction, and the ionic conduction in the solution has little impact on the electrical conductivity of the mix. The geopolymer, due to their excellent microstructure, make it possible for direct electronic transitions of conductive fillers. Therefore, graphite-geopolymer composite have better electronic conductivity than graphite-portland cement composite at the same graphite content. To study the conductive mechanism of geopolymer and graphite mixture more in-depth, a Monte Carlo method was employed to simulate the percolation threshold of the mixture. The model, based on the HYMOSTRUC3D framework, is a three-dimensional model that considers the particle size distribution, and it can accurately describe the spatial distribution and interactions of different particles. By introducing the concept of effective volume fraction, the influence of pores on the mixture was eliminated. The effective medium model simulated the relationship between the overall electrical conductivity and graphite effective volume fraction, which was consistent with experimental data. The microstructural properties of geopolymers make it possible to create high-performance electrical conductive materials using low-cost graphite particles. The porous structure of this mixture also provides necessary growth space for microorganisms, leading to the formation of more biofilm. In order to verify the feasibility of this mineral-based electrode as a microbial fuel cell, a single-strain Geobacter sulfurreducens culture was used to cultivate a dual-chamber microbial fuel cell. During the one-week testing period, the microbial fuel cell with the graphite geopolymer anode had a peak operating current density of 155.9 A·s/cm² even higher than the operating current density of 144.5 A·s/cm² with graphite as the electrode. This research also explored the feasibility of large-scale application of microbial fuel cells using the mineral-based electrode. The study found that the mineral-based electrode can be used to power a green LED light, and by connecting 224 soil-based microbial fuel cells in series and parallel, and creating a control board for energy collection, it was possible to power a lighting system in a bike shed. The Ph.D. thesis demonstrates the feasibility of using mineral-based materials as electrodes in microbial fuel cells and explains the conductive mechanism in the composite. Due to its superior electrical conductivity, the mineral-based material can also be used in other types of fuel cells and even rechargeable batteries.