Enhanced C2 and C3 Product Selectivity in Electrochemical CO2 Reduction on Carbon-Doped Copper Oxide Catalysts Prepared by Deep Eutectic Solvent Calcination

Melanie Iwanow,Manuela Kaiser,Johannes Seidler,Michael Richter,Daniel Van Opdenbosch,Tobias Gärtner,Burkhard König,Volker Sieber,Cordt Zollfrank,Luciana Vieira

doi:10.3390/catal11050542

Abstract

Copper and its oxides are the main catalyst materials able to promote the formation of hydrocarbons from the electrocatalytic CO2 conversion. Herein, we describe a novel preparation method for carbon-doped copper oxide catalysts based on an oxidative thermal treatment of copper-containing deep eutectic solvents (DES). XRD and EDX analysis of the samples show that thermal treatment at 500 °C in air for a prolonged time (60 min) provides exclusively carbon-doped copper(II) oxide catalysts, whereas shorter calcination time leads to a mixture of less oxidized forms of copper (Cu2O and Cu0), CuO, and a higher carbon content from the DES. Chronoamperometry of the electrode containing the prepared materials in 0.5 M KHCO3 electrolyte show the reduction of CuO to less oxidized copper species. The materials prepared by the use of different DES, copper precursors and calcination times were used as electrocatalysts for the electrochemical CO2 reduction. Chemical analysis of the products reveals an enhanced selectivity toward C2 and C3 products for the catalyst prepared from the DES galactose-urea with copper nanoparticles and calcination for 60 min in air. The electrocatalytic activity of the prepared materials were compared to commercial CuO and showed a higher product concentration at −1.7 V vs. Ag/AgCl, with formation rates of 7.4, 6.0, and 10.4 µmol h−1 cm−2 for ethanol, n-propanol, and ethylene, respectively.

Highlights

The rising concentration of global atmospheric carbon dioxide since the beginning of industrialization (280 parts per million by volume to 365 ppmv) [1] requires a reduction of carbon dioxide release and solutions for its capture and utilization [2,3,4].Several technologies have been developed for CO2 capture involving point sources or direct air capture [5]
Carbon-doped copper oxide materials were produced by systematically varying the preparation parameters such as type of deep eutectic solvents (DES), copper precursor, pre-treatment atmosphere, calcination time, and temperature
The reported protocol demonstrates a promising, novel, and facile preparation method for carbon-containing copper oxide electrocatalysts based on deep eutectic solvent calcination, which show a remarkable performance for C2 and C3 products from electrochemical

Summary

Introduction

The rising concentration of global atmospheric carbon dioxide since the beginning of industrialization (280 parts per million by volume (ppmv) to 365 ppmv) [1] requires a reduction of carbon dioxide release and solutions for its capture and utilization [2,3,4].Several technologies have been developed for CO2 capture involving point sources or direct air capture [5]. As for the CO2 utilization, using CO2 for chemical synthesis of industrial relevant chemicals would be a sustainable solution for the utilization and for the replacement of fossil-based chemicals by CO2 -neutral alternatives. In this way, the electrochemical reduction of CO2 using directly renewable electricity is a promising conversion method toward carbon-neutral economy. The electrochemical carbon dioxide reduction (CO2 R) process can use CO2 as a building block for the synthesis of several value-added products. CO2 R offers a possibility for storing intermittent renewable energy, such as wind and solar, since it would be in principle relatively simple to ramp up and down according to the energy availability [6,7,8]

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Results

Conclusion