Carbon Monoxide-Tolerant Palladium-Based Electrocatalyst for Carbon Dioxide Reduction

Abstract

The utilization of carbon dioxide (CO 2 ) for the production of fuels and valuable chemicals has gained increasing attention as a strategy for solving both global energy and environmental issues.[1] Among the various proposed methods, the electrochemical reduction of CO 2 using electricity powered by renewable resources is attractive, and numerous electrode materials capable of converting CO 2 to carbon monoxide (CO), formate, methanol, methane, and other hydrocarbons have been identified in the past few decades. However, there still remain several fundamental challenges in the electrocatalytic reduction of CO 2 , such as high overpotential and low Faradaic efficiency due to the competitive hydrogen evolution reaction. Recently, it was reported that a palladium (Pd) nanoparticle electrode can reduce CO 2 to formate with high energy efficiency (with low overpotential) [1]. However, the electrode was also reported to be deactivated by adsorption of CO which is produced as a byproduct. In this study, to suppress the deactivation by CO, we focused on a Pd nanoparticle electrode modified covered with copper (Cu) because the binding energy of CO on Cu was reported to be weaker than that on Pd [3]. In addition, it is known that Cu monolayer can be formed on Pd support by using underpotential deposition (UPD) [4]. Thus, we prepared a Pd nanoparticle electrode covered with Cu monolayer (Cu/Pd electrode) and examined its CO 2 reduction activity and tolerance to CO. A Pd nanoparticle electrode was prepared by loading homogeneous catalyst ink onto a fluorine-doped tin oxide (FTO) electrode. The ink was composed of a mixture of Pd-supporting carbon black powder, Nafion, and isopropanol. The Pd-supporting carbon black powder was purchased from Premetek. UPD of Cu was carried out by holding the electrode potential at 0.35 V vs. reversible hydrogen electrode (RHE) for 50 s in a mixed solution of 50 mM sulfuric acid (H 2 SO 4 ) and 50 mM copper sulfate (CuSO 4 ). Electrolyses were performed in a gas-tight two-compartment electrochemical cell with a piece of anion exchange membrane as the separator. An aqueous solution of 0.5 M sodium hydrogen carbonate (NaHCO 3 ) saturated with CO 2 was used as an electrolyte. Figure 1 shows chronoamperograms for CO 2 reduction of Pd and Cu/Pd electrodes measured at -0.15 V vs RHE. In the initial stage, the current density of a Cu/Pd electrode was smaller than that of a Pd electrode. This is plausible because the surface area of Pd exposed to the electrolyte decreased by deposition of Cu. However, the Cu/Pd electrode was active for CO 2 reduction even after deposition of Cu and production of formate was confirmed by analysis of the electrolyte using gas chromatograph (GC). Notably, the reduction current of the Cu/Pd electrode maintained more steadily than that of the Pd electrode during long-term electrolysis, suggesting that the electrodeposited Cu monolayer improved the tolerance to CO. To examine the effect of Cu layer on CO adsorption, CO 2 reduction activity in the presence of CO was also investigate. When CO was introduced into the electrolyte by bubbling, the current density of both Pd and Cu/Pd electrodes decreased, however the degree of deactivation of the Cu/Pd electrode was less than that of the Pd electrode. These results indicate that the covering of Pd nanoparticle with Cu monolayer improves its tolerance to CO without losing CO 2 reduction activity. References [1] M. Aresta, A. Dibenedetto, A. Angelini, Chem. Rev. , 2014 , 114 , 1709-1742. [2] X. Min and M. W. Kanan, J. Am. Chem. Soc. , 2015 , 137 , 4701-4708. [3] A. A. Peterson and J. K. Nørskov, J. Phys. Chem. Lett. , 2012 , 3 , 251-258. [4] T. Chierchie and C. Mayer, Electrochim. Acta , 1988 , 33 , 341-345. Figure 1

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Identifiers

DOI

10.1149/ma2016-02/40/3031

Journal

ECS Meeting Abstracts

Year

2016