Thin layer sonoelectrochemistry

Abstract

This research exploits mild sonication in a thin layer electrochemical cell to enhance rates of reaction in systems under voltammetric perturbation. Sound waves propagate through a thin layer of condensed ‡uid to provide energy to the electrode solution interface in the form of pressure and temperature. The sonic energy provided in three dimensions can be exploited to enhance rates of heterogeneous electron transfer as the energy is harnessed at the two dimensional electrode interface. Enhanced rates of heterogeneous electron transfer are of interest both for fundamental reasons and for exploitation in electrochemical energy systems.The initial pilot studies were directed at demonstrating the impact of acoustic energy on heterogenous electron transfer. Redox couples with di¤erent electron transfer rates were evaluated. Whereas compounds with reversible electron transfer kinetics demonstrated little improvement, redox couples such as ferric ion (Fe 3+ ) with slow electron transfer kinetics exhibited an increase in the standard heterogeneous electron transfer rate constant, k 0 with an increase in acoustic energy.The reduction of oxygen is a complex four proton, four electron process that is of technological importance. Slow kinetics of the oxygen reduction is a primary loss of e¢ ciency in electrochemical power sources. Much like the ferric ion, oxygen kinetic rats improve. Preliminary studies in the oxidation of methanol demonstrated a sonocatalyic e¤ect in methanol electrolysis that is of particular interest for the development of liquid based fuel cells.Sonication can both clean and destroy surface materials. The cleaning power inherent in sonication improves electrocatalysis and removes deposits and oxides 2 from the electrode surface. Abstract Approved:Thesis Supervisor

Why Sonochemistry in a Thin Layer? Constructive Interference

“…The waste heat in a TLS is negligible as cell temperature changes ≤1 °C over extended time of sonication. 26,27 No cavitation is observed.…”

“…In real systems, these conditions are not sufficient to establish cavitation or identify constructive interference as a major component of amplification in thin layers with cavitation. However, amplification is clearly demonstrated in experiments and models for thin layer systems with 30 and without 26,27 ] characterizes both summations. If time-independent β n does not approach zero, then exp[−kt/2] will tend to damp u(x, t) as t increases.…”

“…This is observed experimentally. 26 The rate pressure is delivered to the interface (x = 0) is power. For resonance at ω n , energy is delivered with each oscillation.…”

“…The model is consistent with TLS experiments demonstrated with an electrode as the reflective interface. 26,27 Figure 1. Sequential compression-rarefaction cycles are induced by irradiating bulk fluid with ultrasonic sound pressure oscillations.…”

“…24 Despite the limitations of the model assumptions, the outcomes of the model in underdamped conditions are consistent with the experimental results for sonoelectrochemistry undertaken in a thin layer configuration absent cavitation. 26,27 Solution. The problem is re-expressed as…”