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

6 Bipolar Electrochemistry for Synthesis

Bipolar electrochemistry has gained remarkable interest in recent years, especially in the fields of materials science and organic electrosynthesis. This is due to the interesting features of this particular electrochemical technology, such as the contactless nature of the electrochemical reactions, the use of low concentrations of supporting electrolytes, and the synergetic action of electrophoresis and electrolysis. In this chapter, the most important contributions regarding bipolar electrochemistry for the electrosynthesis of novel functional materials are reviewed. These contributions include the most traditional industrial applications and bipolar reactors for electroorganic synthesis, as well as innovative approaches for the fabrication of anisotropic materials and gradient surfaces. The peculiar characteristics of bipolar electrochemistry in these fields are emphasized.

Blatter Radicals as Bipolar Materials for Symmetric Redox-Flow Batteries

Redox-active organic molecules are promising charge-storage materials for redox-flow batteries (RFBs), but material crossover between posolyte/negolyte and chemical degradation are limiting factors in the performance of all-organic RFBs. We demonstrate that the bipolar electrochemistry of 1,2,4-benzotriazin-4-yl (Blatter) radicals allows construction of batteries with symmetric electrolyte composition. Cyclic voltammetry shows that these radicals retain reversible bipolar electrochemistry also in the presence of water. The redox potentials of derivatives with a C(3)-CF3 substituent are least affected by water and, moreover, these compounds show >90% capacity retention after charge/discharge cycling in a static H-cell for seven days (ca. 100 cycles). Testing these materials in a flow regime at 0.1 M concentration of active material confirmed the high cycling stability under conditions relevant for RFB operation, and demonstrated that polarity inversion in a symmetric flow battery may be used to rebalance the cell. Chemical synthesis provides insight in the nature of the charged species by spectroscopy and (for the oxidized state) X-ray crystallography. The stability of these compounds in all three states of charge highlights the potential for application in symmetric organic redox-flow batteries.

Biofabrication of controllable alginate hydrogel cell scaffolds based on bipolar electrochemistry

Bipolar electrochemistry successfully realized the electrodeposition of calcium alginate hydrogels in specific target areas in tissue engineering. However, the shape and quantity of three-dimensional cannot be accurately controlled. We presented a novel growth model for fabricating hydrogels based on bipolar electrochemical by patterned bipolar electrodes using photolithography. This work highlights pattern customization and quantitative control of hydrogels in cell culture platforms. Furthermore, alginate hydrogels with different heights can be controlled by adjusting the key parameters of the growth model. This strategy exhibits promising potential for cell-oriented scaffolds in tissue engineering.