Modulation Strategies of Cu-based electrocatalysts for Enhancing Electrocatalytic CO2 Conversion

Abstract

Electrocatalytic CO2 reduction (ECR) into value-added chemicals and fuels using renewable energy contributes to global decarbonization, offering an elegant solution for achieving carbon neutrality and fostering sustainable development of human society. However, this strategy highly relies on the rational design of catalysts to enhance product selectivity and activity. To advance CO2 conversion technology, systematic and comprehensive studies on ECR are urgently needed to demonstrate the origins of catalytic activity, elucidate the relationship between structural defects of catalysts and catalytic activity, and reveal the dynamic evolution of active sites under ECR reaction conditions. In this thesis, mechanistic studies and functional catalyst design are extended from lab scale to large scale. The regulation of grain boundaries structures and local microenvironments is employed to stabilize oxidized copper species, thereby enhancing the selective production of desired products. Firstly, at the lab scale, we introduce oxidation and alloying strategies into grain boundaries systems. Low-loading Ag and water oxidation induce oxygen enrichment at the grain boundaries, leading to a grain boundary oxidation effect. In situ characterizations indicate that the grain boundaries and grain boundary oxidation effects contribute to strengthening resistance of the oxidative Cuδ+ species to the electrochemical reduction. Experimental and theoretical results demonstrate that in intricate grain boundaries assemblies, the oxidation state of copper plays a crucial role in the C2+ product pathway, while the nanoalloy effect tends to the formation of CH4 product. Secondly, to achieve the industrial-scale ECR to multi-carbon products with high selectivity using membrane electrode assembly (MEA) electrolyzers, we introduce activated carbon black with different functional groups to modulate the interfacial microenvironment of Cu nanoparticles, enhancing CO coverage to suppress hydrogen evolution reaction (HER). In situ multimodal characterizations consistently reveal that in situ generated strongly oxidative hydroxyl radicals can create a locally oxidative microenvironment on the catalyst surface, stabilizing the Cuδ+ species and leading to an irreversible and asynchronous change in morphology and valence, yielding high-curvature nanowhiskers. The well-stabilized Cuδ+-OH species serve as active sites during MEA testing. By comprehending this mechanism, we achieve selective ethylene production with a Faradaic efficiency (FE) of 55.6% for C2H4 at a current density of 316 mA cm-2. The insight of these reaction mechanisms bridges the gap between lab-scale studies and industrial-scale implementation, contributing to the development of sustainable and carbon-neutral industries.