ELECTRODE/ELECTROLYTE INTERFACES: STRUCTURE AND KINETICS OF CHARGE TRANSFER
When a metal is partly immersed in an electrolyte, a potential is set up across the two phases, i.e., at the electrode/electrolyte interface. The phases may be solids (metals or alloys, semiconductors, insulators), liquids (ionic liquids, molten salts, neutral solutions), or gases (polar or non polar). The more common terminology in electrochemistry is that a double layer is set up at the interface. There are several reasons for a potential difference being set up across the interface of two phases, the most common one being the charge transfer occurring across the interface. During this process, a charge separation will occur because of electron transfer across the interface. Other reasons for the occurrence of potential differences are due to surface-active groups in the ionizable media (liquid, solid, or gas) and orientation of permanent or induced dipoles. The double layer at the interface between two phases has electrical, compositional, and structural characteristics. The electrical and compositional characteristics deal with the excess charge densities on each phase and the structural one with the distribution of the constituents (ions, electrons, dipoles, and neutral molecules) in the two phases, including the interfacial region. For the purposes of understanding and analyzing the electrical, compositional, and structural aspects relevant to the electrochemical reactions that occur in fuel cells, a brief description of the evolution of the theoretical aspects of the structure of the double layer, as applied to electrode/electrolyte interfaces, across which chargetransfer reactions occur, is presented in this section.
KeywordsFuel Cell Double Layer Electrochemical Reaction Charge Transfer Resistance Exchange Current Density
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