Effects of Membrane Cation Transport on pH and Microbial Fuel Cell Performance

TLDR

Nafion membranes, prized for proton conductivity in PEMFCs, are also used in MFCs but suffer operational issues because they transport abundant non‑proton cations (Na⁺, K⁺, NH₄⁺, Ca²⁺, Mg²⁺) that are present at much higher concentrations than protons. The study aimed to quantify membrane cation transport in an operating MFC and assess its impact on MFC performance in wastewater treatment. The authors measured cation transport in a running MFC and evaluated its effects on charge balance, cathode conductivity, pH, and overall performance. They found that non‑proton cations dominate charge transport, raising cathode conductivity and pH while reducing MFC performance, underscoring the need to account for cation transport in future MFC designs.

Abstract

Due to the excellent proton conductivity of Nafion membranes in polymer electrolyte membrane fuel cells (PEMFCs), Nafion has been applied also in microbial fuel cells (MFCs). In literature, however, application of Nafion in MFCs has been associated with operational problems. Nafion transports cation species other than protons as well, and in MFCs concentrations of other cation species (Na+, K+, NH4+, Ca2+, and Mg2+) are typically 105 times higher than the proton concentration. The objective of this study, therefore, was to quantify membrane cation transport in an operating MFC and to evaluate the consequences of this transport for MFC application on wastewaters. We observed that during operation of an MFC mainly cation species other than protons were responsible for the transport of positive charge through the membrane, which resulted in accumulation of these cations and in increased conductivity in the cathode chamber. Furthermore, protons are consumed in the cathode reaction and, consequently, transport of cation species other than protons resulted in an increased pH in the cathode chamber and a decreased MFC performance. Membrane cation transport, therefore, needs to be considered in the development of future MFC systems.