Dramatic Drop in Cell Resistance through Induced Dipoles and Bipolar Electrochemistry

The use of slurries of conducting particles has been considered a way to extend the electrode area in some energy storage electrochemical cells. When suspensions of conducting particles are used in electrolytes a decreased impedance is observed, even for concentrations much lower than the theoretical percolation limits. Indeed, it is known that polarization occurs when a conducting material is immersed in an electrolyte in presence of electric fields, and bipolar electrochemistry processes may occur. This work demonstrates the dramatic drop in resistance for electrochemical cells with just a few macroscopic conducting pieces immersed in the electrolyte, in the absence of any electrical contact, through bipolar induction. Furthermore, mediation of soluble redox species between adjacent induced poles of opposite charge results in an additional mechanism for charge transfer, contributing further to the decrease in impedance. Relevant parameters like size, geometry, and spatial occupation of inducible pieces within the electric field, are relevant. Remarkably, the effects observed can explain some empirical observations previously reported for carbon suspensions and slurries. Thus, no electronic percolation requiring particle contact, nor ordering, are needed to explain the good performance associated to lowered impedance These results suggest new engineering designs for electrochemical cells with enhanced currents.The authors thank financing from the Ministry of Science of Spain (MAT2015-65192-R, and RTI2018-097753-B-I00, RTI2018-099826-B-I00, MAT2017-91404-EXP), and Severo Ochoa Program (SEV-2015-0496 and CEX2019-000917-S). LLA thanks the Ramon y Cajal Program contract (RYC-2013-12640).With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).Peer reviewe