Cu-based catalysts for electrochemical carbon dioxide reduction

Abstract

After the Industrial Revolution, we have achieved remarkable technological advances. Until just a few decades ago, we thought that damaging the environment was not a big problem for technological advancement. However, recently, too many adverse effects are plaguing us in all areas around us such as extreme weather, and etc. due to excessive environmental destruction. In order to solve these environmental problems, the development of innovative green energy technologies is essential. In particular, electrochemical carbon dioxide reduction is considered one of the most promising technologies for future energy because it can convert carbon dioxide in the atmosphere into fuels or chemicals including C1 (carbon monoxide, formic acid, and methanol) to C2 products (acetate acid, ethylene, ethanol, and n-propanol). Cu is a unique metal catalyst that can produce a variety of hydrocarbons and oxygenates with acceptable amount. However, it is necessary to improve the performance such as selectivity, current density, and stability for industrially relevant application. Especially, selectivity in Cu-based catalysts is highly affected by the complicated interactions of a lot of reaction intermediates derived from CO2 and protons. Accordingly, it is important for Cu-based catalysts to control the coverage and kinetics of intermediates for selective reaction pathways. In this dissertation, we aim to present the strategies for the efficient and selective CO2RR products formation in Cu-based catalysts. We controlled the coverage and kinetics of intermediates in Cu-based catalysts by changing local electrolysis environment inducing the selective activation of the specific reaction pathways through nano-structured Cu catalysts, supply of different CO2 concentration, and Cu-based alloys for intrinsic active sites. Chapter 1, we introduce general research background about why should we do electrochemical CO2 reduction for future energy technology? And, specifically, why should we study Cu-based catalysts for electrochemical CO2 reduction? it will give you strong motivation. Chatper2, we show the enhanced C2+ products (C2H4 and C2H5OH) in meso-porous Cu structures. Changed local electrolysis such as increased local pH due to mass transfer limitation of reactants and products leads control of intermediate coverage resulting in the activation of C2+ reaction pathways. Chapter 3, we present that CO2 partial pressure is one of the key parameters for selective C2+ products formation. Although it is believed high concentration of surface bound CO is required for C2H4 formation, we show excessive supply of CO2 interferes with CO dimerization which is a key step for C2+ products. We confirm that operating parameters, CO2 concentration, can control the coverage and/or kinetics of intermediates. Chapter 4, we fabricated the CuNi alloy catalyst as a model system to investigate electronic structure-dependent CO2RR activity with minimized geometric effects. Strong CO adsorption by Ni in CuNi catalysts enhance CH4, HCOO-, and CH3COO- which are highly related to protonation in rate-determining step (RDS). This implies that strong intermediates adsorption can influence the controlled reaction pathways.