Catalysts for improved selectivity and performance in ethanol electrolysis cells

Alqdeimat, Diala Akram (2022) Catalysts for improved selectivity and performance in ethanol electrolysis cells. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (5MB)

Abstract

The importance of direct ethanol fuel cell (DEFC) technology for a sustainable energy future has resulted in comprehensive studies of the electrochemical oxidation of ethanol. Ethanol is oxidized completely to produce CO₂ during the ethanol oxidation reaction (EOR). However, many studies found that ethanol is oxidized to produce acetic acid, acetaldehyde, and CO₂. As a result, the efficiency of the DEFC is decreased. Furthermore, many issues have hampered DEFC adoption, including low current densities, low faradic efficiencies. To overcome these problems, anode catalysts (binary and ternary) have been developed to increase the efficiency of DEFCs. Our research focused on the development of catalysts that have high activity for the EOR and selectivity for breaking the C-C bond to form CO₂. Moreover, a secondary objective is the evaluation of catalysts to investigate the performance and selectivity of an electrolysis cell. To avoid any chemical reaction between ethanol and oxygen, an electrolysis cell was employed instead of a fuel cell (an ethanol electrolysis cell is similar to an ethanol fuel cell, but oxygen gas is replaced by nitrogen gas at the cathode and the cell reaction is driven by an applied potential). As a result, accurate results are possible. PtNiₓ/C catalysts (x is the Ni:Pt atomic ratio) were synthesized in various solvents (propylene glycol (PG) and ethylene glycol (EG)) by using a polyol method. Then, they were treated with acetic acid to increase the coverage of Pt at the surface. Electrochemical analysis was carried out by cyclic voltammetry in 0.100 M ethanol and 1 M H₂SO₄ (aq) (at ambient temperature) to study the activity of these catalysts toward the oxidation of ethanol. A catalyst prepared in propylene glycol was more active toward the oxidation of ethanol than a catalyst prepared in the same way in ethylene glycol, exhibiting less poisoning at the PtNi/C(PG) catalyst by adsorbed CO. Treatment of the PtNi/C(PG) catalyst with acetic acid to remove surface Ni further enhanced the activity toward ethanol oxidation, while it did not affect the activity of PtNi/C(EG). The performance and selectivity toward the EOR were investigated for PtNiₓ/C catalysts in a nine-anode PEM electrolysis cell. It was found that acid treatment of PtNi/C(PG) and PtNi/C(EG) increased the production of CO2. However, it did not enhance the performance of catalyst. Also, there was no improvement in the performance for PtNiₓ/C catalysts relative to Pt, indicating that the incorporation of Ni with Pt does not improve the slow kinetics at low potentials. Furthermore, the nine-anode PEM electrolysis cell was used to evaluate the performance and selectivity of commercial catalysts (PtNi/C, PtCu/C, and PtFe/C) for the EOR. The goal of this research was to figure out how each metal (Ni, Cu, and Fe) impacts the activity of Pt on the EOR. Results showed that Cu as a secondary metal has more ability to produce CO₂ than Fe and Ni. However, none of these metals increase the performance at low potentials relative to Pt. Finally, PtRu/C and PtRuCu/C catalysts were synthesized. The effect of Cu with Pt and Ru on the EOR and CO₂ yield was explored. It was found that Cu with Pt and Ru increases the production of CO₂ relative to PtRu. Also, the performance at low potentials was higher for PtRuCu/C and PtRu/C relative to Pt. Based on our results, preparing catalyst with Cu would increase the faradaic efficiency of a DEFC and decrease the production of acetic acid.

Actions (login required)

View Item