Abstract
The research on electrochemical carbon molecule oxidation started in the past years as new electrochemistries were researched for new fuel cells systems and batteries that may line up as backup energy supply and storage systems in off-grid and on-grid microgrids, as modeled by our group at the University of Twente [1-3]. By lining up these two disciplines we hope to support the bridge between new electrochemical systems on one side, (pilot) production with partner companies, prediction, and validation of systems upon implementation in microgrids by our group. The electrochemical oxidation of glycerol in alkaline aqueous solution has been studied on gold and gold coated metals (Zn-Au and Cu-Au) by voltammetry and EIS (Electrochemical impedance spectroscopy) for possible use in a new fuel cell as an outlet for the excess glycerol that is produced in the biodiesel industry. The observations show that the gold surface may change upon cycling by cyclic voltammetry. Besides, the current density shows non-linear behavior with the square root of the scan rate, implying that the reaction is not totally controlled by diffusion. EIS analysis using the EQUIVCRT software revealed that one out of twenty tested equivalent circuits fitted the data well at potentials of -0.05 V,- 0.15 V and -0.25 V vs. Ag/AgCl, identifying resistors and a Warburg element in parallel with the double layer capacitance, the elements are possibly related to the presence of double layers associated with hydroxypyrovate and oxalate ions. The results are consistent with the low-frequency error fitting analysis (10-4), AC Simulink-Matlab fitting responds and the Kronig-Kramers transform test. The tested Zn-Au and Cu-Au electrodes show similar voltammetry behavior as the gold electrode, as witnessed by the results of cycle analysis and the scan rate analysis. The discharge chronoamperometry test further shows that the Zn-Au electrode and Cu-Au have higher current densities than the gold electrode at a potential of -0.25 V vs. Ag/AgCl (5 mA cm-2, 4.5 mA cm-2, and 3 mA cm-2 respectively).
Highlights
The growing amount of biodiesel produced worldwide leads to more than two million tons of glycerol entering the market yearly [4]
This research aims to yield to an approach for a possible development of a glycerol fuel cell by observing the glycerol oxidation mechanism and kinetics using a gold electrode in alkaline media
Silver and a glassy carbon have less catalytic effect for glycerol oxidation which is in-line with research performed by Song [31]
Summary
The growing amount of biodiesel produced worldwide leads to more than two million tons of glycerol entering the market yearly [4]. The countries with high production of biodiesel (e.g. USA, Germany and Colombia) are facing serious challenges with the glycerol overproduction changing the value of glycerol dramatically [5]. This specific situation has led to consistently generated low glycerol prices, making glycerol a bio-waste product in the need for new market alternatives. One alternative to valorise glycerol might come from electrochemical oxidation which may give way to oxygenated materials with higher market value (tartronic acid, dihydroxyacetone, and glycolic acid, among others) [6]. The electrochemical oxidation of glycerol may be performed using a fuel cell. To store hydrogen is still a challenge due to its high volatility and safety concerns [8], one alternative to the problem is to use a fuel that
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