One of the most important parameters for the design of redox flow batteries is a uniform distribution of the electrolyte solution over the complete electrode area. The performance of redox flow batteries is usually investigated by general measurements of the cell in systematic experimental studies such as galvanostatic charge-discharge cycling. Local inhomogeneity within the electrode cannot be locally-resolved. In this study a printed circuit board (PCB) with a segmented current collector was integrated into a 40 cm2 all-vanadium redox flow battery to analyze the locally-resolved current density distribution of the graphite felt electrode. Current density distribution during charging and discharging of the redox flow battery indicated different limiting influences. The local current density in redox flow batteries mainly depends on the transport of the electrolyte solution. Due to this correlation, the electrolyte flow in the porous electrode can be visualized. A PCB electrode can easily be integrated into the flow battery and can be scaled to nearly any size of the electrode area. The carbon coating of the PCB enables direct contact to the corrosive electrolyte, whereby the sensitivity of the measurement method is increased compared to state-of-the-art methods
