One of our research concerns is to determine the rate-determining step (RDS) for the overall lithium and hydrogen insertion into and desertion from lithium/hydrogen insertion compounds. The “slowest” reaction step among the series of reaction steps of the overall reaction is often referred to as the RDS, which is the most strongly disturbed (hindered) from the equilibrium for the RDS. In the same sense, other reaction steps are called relatively “fast” reactions for which the equilibria are practically undisturbed. Therefore, the RDS is quantitatively evaluated in terms of the overpotential, (overvoltage) η, which is defined as the difference in potential between the instantaneous actual and equilibrium values and/or “relaxation (time)” delineated by the time lag between the electrical voltage (potential) and current. The overpotential and relaxation time are also measured relative to the electrochemical equilibrium values of a “linear system,” which is effective for the constraint of electrical energy |zFE| ≪ thermal energy RT. Here, z means the oxidation number, F the Faradaic constant (96,485°C mol−1), E the electrode potential, R the gas constant, and T the absolute temperature.
KeywordsPotential Step Exchange Current Density Complex Impedance Plane Ladder Network Electrical Field Force
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