Control of voltage reversal in serially stacked microbial fuel cells through manipulating current: Significance of critical current density

Abstract Voltage reversal is a critical issue for serially stacking microbial fuel cells (MFCs). It occurs when current density in stacked MFCs increases over critical current density ( j critical ). In this study, we clearly show that no voltage reversal occurs in stacked MFCs if current density is maintained below j critical where the anode and the cathode potential in an inferior unit become identical, with an external resistance placed between individual MFCs. We define threshold resistance (R threshold ) that enables current density below j critical in stacked MFCs, and demonstrate the validity of R threshold theoretically and experimentally. Voltage reversal is controlled in the stacked MFC equipped with R threshold by which the current density in the stacked MFC is kept below j critical . In comparison, a stacked MFC without R threshold faces voltage reversal over j critical . Energy loss in R threshold is comparable to energy loss with other voltage control methods, such as passive or active methods. However, the R threshold approach is a simple, inexpensive way of controlling voltage reversal, especially for small MFCs (