Copper Sulfide Derived Nanoparticles Supported on Carbon for the Electrochemical Reduction of Carbon Dioxide

Marisol Tapia Rosales,Mahnaz Ghiasi Kabiri,Celso De Mello Donegá,Kristiaan H Helfferich,Peter Ngene,Petra E De Jongh,Christina H.M Van Oversteeg

doi:10.1149/ma2020-02633198mtgabs

Marisol Tapia Rosales, Mahnaz Ghiasi Kabiri + Show 5 more

Open Access

https://doi.org/10.1149/ma2020-02633198mtgabs

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Abstract

The electrocatalytic reduction of CO2 (CO2RR) and H+ (or H2O) into chemicals and fuels is attracting attention as a way to address current energy and environmental issues. One of the main focus in this field is the development and understanding of electrocatalysts that can promote the electrochemical CO2 reduction efficiently, and with high selectivity for the desired product. Copper electrodes are extensively studied and stand out because of their unique ability to produce a range of different products including hydrocarbons and oxygenates, which is ascribed to their intermediate binding strength for the CO intermediate. The use of oxide-derived Cu electrodes has arisen, because it promotes CO and COOH formation at low overpotentials, even though the electrodes are operating at potentials where the CuO should be reduced to metallic copper. Inspired by this, some recent studies have also shown that the use of sulfur-containing Cu or sulfide-derived Cu increases the selectivity towards formates, ethanol, propanol, or ethylene at intermediate overpotentials. The origin of these effects is still under debate, but it is often attributed to a change in the binding energy of the intermediates such as *OCHO, *COOH, and CO due to the formation of specific Cu surface structures or the presence of sub-surface sulfur or oxygen in the Cu or mixed phases.In this work, we investigated the phase stability and catalytic performance of carbon-supported sulfide (CuS and Cu2S) derived Cu nanoparticles in the electrochemical reduction of CO2 in aqueous media. The CuS@C and Cu2S@C nanoparticles were prepared via a novel, liquid phase sulfidation method, in which carbon-supported CuO (CuO@C) nanoparticles were converted to either CuS@C (25±13 nm) or Cu2S@C (17±1 nm) as shown in Figure 1a. The stability of the supported nanoparticles was investigated using cyclic voltammetry, where reduction peaks were observed in the first cathodic scans of both CuS@C and Cu2S@C (figure 1c). The reduction was monitored operando under CO2 reduction conditions using in-situ X-ray absorption spectroscopy (XAS). The in-situ XAS spectra showed that at a potential of -0.9V vs. the reversible hydrogen electrode (RHE), both CuS@C and Cu2S@C are reduced to metallic Cu@C. Finally, the products formed by the CuS@C and Cu2S@C-derived catalysts were compared to those of CuO@C-derived catalyst. At current densities of -1.5mA/cm2, the CuS@C- and Cu2S@C-derived catalysts show increased production of formate (figure 1d), while CO production is suppressed, in comparison to the CuO@C catalyst. Cu-sulfide derived catalyst showed differences in formate production, indicating the initial Cu-sulfide phase influences the product selectivity. Figure 1

Highlights

Several experimental and theoretical studies have demonstrated that the addition of sulfur modifies the performance of Cu catalysts. [14,15,16,17,18,19] Even though copper sulfide is unstable under CO2 and H+ reduction conditions, most studies show that some sulfur remains on the catalyst after reaction. [14,15,17,18,20,21] Many of these studies observed an increased selectivity towards formate, that is often attrib uted to a change in the binding energy between the sulfur-containing catalyst and key intermediates in CO2 reduction, such as *OCHO, *COOH and CO
Supported CuS and Cu2S catalysts were prepared via a novel, twostep synthesis route, in which carbon supported CuO nanoparticles (CuO@C) were converted into carbon supported CuS (CuS@C) or Cu2S (Cu2S@C) nanoparticles
Carbon-supported, Cu2-xS derived nanoparticles were studied for electrochemical CO2 reduction in aqueous media

Summary

Introduction

The electrochemical reduction of carbon dioxide (CO2) provides a promising route to produce chemicals and fuels in a sustainable manner. [1,2] The field of so called “solar fuels” has triggered the interest of many researchers, focusing on the development and understanding of electrocatalysts that can promote the electrochemical CO2 reduction efficiently and with high selectivity to the targeted product.The majority of the electrocatalysts studied for the reduction of CO2 are based on transition metals. [3,4] As already described by Hori et al in 1985, the catalytic performance of a catalyst highly depends on the metal used. [5] Metals such as gold [6,7], silver [8,9] and zinc produce mainly CO, whereas metals such as platinum, nickel and iron reduce only small amounts of CO2, leading to H2 as the main product formed via the competing hydrogen evolution reaction. [1,5,10] Interestingly, Cu can lead to a range of different H+ and CO2 reduction products, and much work is done in the field to obtain a better understanding of the catalytic activity of Cu and the selectivity of Cu electrodes. The use of oxide-derived Cu electrodes pro motes the production of CO and COOH at low overpotentials, even though the electrodes are operating at potentials where all oxide should be reduced to metallic copper. Inspired by these studies, in this work we investigated the catalytic performance and stability of copper sulfide (Cu2-xS) derived nano particles supported on carbon for electrochemical CO2 reduction. Two Cu2-xS catalysts with different starting compositions were studied, namely covellite (CuS) and chal cocite (Cu2S)

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