Experimental and numerical study of performance heterogeneities in a vanadium redox flow battery

An experimental investigation of global and local polarization curves and impedance spectra of a 25 cm2 segmented vanadium redox flow battery is carried out, in order to have an insight on electrode-distributor interplay and on operation heterogeneity and the causes thereof. From the analysis of local polarization curves and impedance spectra of the positive electrode, it is found that the serpentine suffers of mass transport issues in the area near the outlet, while the interdigitated shows those issues in the central area of the electrode. Instead, the negative electrode shows a higher homogeneity of operation, since it is characterized by a kinetic dominated regime and poorly influenced by mass transport. The experimental campaign is supported by a 3D numerical model that couples fluid dynamics and electrochemistry, fitted on experimental data and then validated extensively, also locally, in different operative conditions, with different flow fields and different electrolytes configurations.