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Environmental chemistry 2020 -A Practical Approach in Glycerol Oxidation for the Development of A Glycerol Fuel Cell- D.F. Quintero Pulido- University of Twente

D F Quintero Pulido

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 will  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 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 also 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).

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Glycerol Gold Fuel cells Oxidation Electrodes Voltammetry Electrochemical impedance spectroscopy Current density Chronoamperometry Oxalates Biofuels Electrochemical oxidation Electrochemistry Biodiesel Linings Equivalent circuits Resistors Cyclic voltammetry Industry Capacitance

Keywords:

Microgrids; Voltammetry; Oxidation; Gold; Glycerol; Impedance

Introduction:

The growing amount of biodiesel produced worldwide leads to more than two million tons of glycerol entering the market yearly . Glycerol is used in the pharmaceuticals, cosmetics and food industries. However, the current production rate already surpasses the capacities needed by these industries. The countries with high production of biodiesel (e.g. USA, Germany and Colombia) are facing serious challenges with the glycerol overproduction changing the worth of glycerol dramatically . This specific situation has led to consistently generated low glycerol prices, making glycerol a bio-waste product in the need for brand  new market alternatives. One alternative to valorise glycerol might come from electrochemical oxidation which may drop  oxygenated materials with higher value (tartronic acid, dihydroxyacetone, and glycolic acid, among others) . The electrochemical oxidation of glycerol is also be  performed using a electric  cell. Fuel cells can convert directly a fuel into electricity . One common fuel use in fuel cells is H2 and its production is accepted  in chemical production plants. However, to store hydrogen is still a challenge due to its high volatility and safety concerns , one alternative to the problem is to use a fuel that is liquid under ambient conditions. There are different types of fuels that were tested in the past as possible alternative fuels such as, hydrazine, organic compounds, and formic acid . Nevertheless, there are technical and commercial necessities that a fuel must comply in order to be used in a fuel cell e.g. availability, transport, safety, and cost. Taking this into account, the quantity of possible fuels is reduced to a few types.

Experimental Methods:

Electrochemical coating: Glassy carbon, Zn, and Cu (area 0.072 cm2) were immersed first in a solution of 1 M H2SO4 for a few seconds to remove impurities, then rinsed with demi-water and dried for an hour. Each of the electrodes was immersed separately in an electrochemical cell with 0.01 M AuBr2 as the electrolyte. AuBr2 was selected for electroplating as the subproducts of the electrodeposition are more environmentally friendly than common gold cyanate electrodeposition . The cathode material used was carbon graphite and no reference electrode was used. Then, a potential of two Volts  was fixed in the cell for 30 s so as  to develop a layer of gold as witnessed by a change in color on the electrode. During the experiment, any smell of bromine was not detected. After the electrode plating method, the electrodes were rinsed with demi-water and dried during the night

Results and Discussion

Analysis of catalyst for glycerol oxidation

In order to gain insight into the glycerol oxidation, cyclic voltammetry is used on the different catalyst as shown in Figure 2. The goal was to get a fast comparison of the electrochemistry of various  catalyst in the same electrolyte. The measurements were done at 100 mV/s in 1 M glycerol in 1 M NaOH.