Potassium alleviating power overshoot and promoting carbon capture of bufferless algae microbial fuel cells

Abstract

Power overshoot makes microbial fuel cell (MFC) unable to work normally under high current densities, limiting its application in carbon capture. Herein, effects of cations in medium on overshoot are compared using bufferless MFCs filled by saline or algae suspension containing Na+ or K+. Furthermore, the relationship between cation type and CO2 sequestration abilities of algae MFCs are analyzed under continuous flow mode. As a result, K+ helps to inhibit oxygen leakage while promote proton transport through Nafion separator. Transmembrane diffusion coefficient of oxygen in Na+ saline medium is 1.41 × 10−4 cm·s−1, which decreases to 0.91 × 10−4 cm·s−1 in K+ group. K+ as well as cathodic biofilms or algae cells attribute to overshoot alleviation. No matter saline or algal medium, MFCs containing K+ exhibit better electrochemical properties and achieve more than 40% and 20% increases in maximum power and current densities. Carbon capture capacities of algae MFCs are promoted over 40% in the presence of K+. Under the inlet CO2 concentration of 1% v/v, 5% v/v and 10% v/v, CO2 removal efficiencies of single-chamber algae MFCs containing K+ are 27.46 ± 1.07%, 35.51 ± 1.24% and 39.15 ± 1.35%. This work provides a new strategy for the optimization of MFC power generation and carbon capture by simply adjusting the cations in the solution matrix.