Electrochemical Oxidation of Organic Fuels at Rotating and Flow through Electrodes

Abstract

Oxidation of small organic molecules (SOM) has been one of the most active targets of investigation in electrochemistry for several decades. One of the main reasons is that SOM such as formic acid, methanol, and ethanol, can be used to produce electrical power through their oxidation in fuel cells [1]. These devices have the potential to produce close to 100% energy efficiency in theory. However, practically this level of efficiency has not been achieved for SOM so far due to deficiencies such as slow and incomplete oxidation of the fuel. For enhancement of the energy efficiency, a comprehensive study of the electrocatalytic oxidation mechanisms and average number of exchanged electrons of SOM as fuels are fundamental. One of the widespread approaches for these studies is applying hydrodynamic methods due to their ability to emulate the hydrodynamic conditions of a fuel cell anode.We have applied rotating disc voltammetry (RDV) and flow cells to study the electrocatalytic oxidation of ethanol, methanol and formic acid. Using RDV the measured current can be separated into its kinetic and mass transport components and this provides reproducible and controllable conditions for kinetic and mechanistic studies [2]. The number of electrons transferred for ethanol oxidation at room temperature was found to be ca. 3.5 [3], which agrees with literature reports of product distributions. Also, we showed that accurate kinetic currents could be obtained for formic acid oxidation using RDV [4]. One hundred percent faradaic efficiency and a diffusion coefficient in good agreement with literature values were obtained for methanol oxidation at a PtRu black catalyst using RDV [5]. Our next approach was to design a flow-through electrolysis cell in order to evaluate the reliability of findings from RDV by product analysis. The organic fuel solution passes through the working and counter electrodes in line, and the cell exhaust is collected for spectroscopic analysis by H-NMR. Also, a CO2 detector was used for real-time measurements. Despite its simple design, this flow cell can provide valuable information regarding the kinetics and stoichiometry of catalytic electrooxidation of organic fuels.[1] G. L. Soloveichik, Beilstein, J. Nanotechnol, 5, 1399–1418 (2014).[2] A.J. Bard, L.R. Faulkner, Electrochemical methods. Fundamentals and applications, 2nd ed. 2001, Weily, New York, (2001).[3] A. Sayadi and P. G. Pickup, Electrochimica Acta, 215, 84-92 (2016).[4] A. Sayadi and P. G. Pickup, Electrochimica Acta, 199, 12-17 (2016).[5] A. Sayadi, and P. G. Pickup, Special V. G. Levich Issue of Russ. J. Electrochemistry, 53, 1183–1192 (2017).