Microfluidics‐Assisted Synthesis of Hierarchical Cu₂O Nanocrystal as C₂‐Selective CO₂ Reduction Electrocatalyst

Abstract

Copper‐based catalysts have attracted enormous attention due to their high selectivity for C2+ products during the electrochemical reduction of CO2 (CO2RR). In particular, grain boundaries on the catalysts contribute to the generation of various Cu coordination environments, which have been found essential for C—C coupling. However, smooth‐surfaced Cu2O nanocrystals generally lack the ability for the surface reorganization to form multiple grain boundaries and desired Cu undercoordination sites. Flow chemistry armed with the unparalleled ability to mix reaction mixture can achieve a very high concentration of unstable reaction intermediates, which in turn are used up rapidly to lead to kinetics‐driven nanocrystal growth. Herein, the synthesis of a unique hierarchical structure of Cu2O with numerous steps (h‐Cu2O ONS) via flow chemistry‐assisted modulation of nanocrystal growth kinetics is reported. The surface of h‐Cu2O ONS underwent rapid surface reconstruction under CO2RR conditions to exhibit multiple heterointerfaces between Cu2O and Cu phases, setting the preferable condition to facilitate C—C bond formation. Notably, the h‐Cu2O ONS obtained the increased C2H4 Faradaic efficiency from 31.9% to 43.5% during electrocatalysis concurrent with the morphological reorganization, showing the role of the stepped surface. Also, the h‐Cu2O ONS demonstrated a 3.8‐fold higher ethylene production rate as compared to the Cu2O nanocube.

Increasing CO Binding Energy and Defects by Preserving Cu Oxidation State via O2-Plasma-Assisted N Doping on CuO Enables High C2+ Selectivity and Long-Term Stability in Electrochemical CO2 Reduction

“…Tailoring the electronic structure of Cu can promote C–C coupling by optimizing the binding energy between Cu and the CO intermediate, leading to enhanced selectivity for C 2+ products. Also, the electronic structure of Cu can be regulated by creating Cu δ+ sites on the Cu surface via the oxide-derived Cu (OD-Cu), promoting the electroreduction of carbon dioxide. ,− Moreover, the increased grain boundaries and undercoordinated Cu sites also play an important role in facilitating C–C coupling. ,, To obtain high C 2+ selectivity in a Cu-based catalyst for the CO 2 RR, we chose a strategy of changing the bonding environment and the density of the catalytic active site simultaneously. First, to convert CO 2 to C 2+ hydrocarbon products, such as ethylene, the existence of CO as an intermediate product at a high concentration on the catalytic surface is important.…”

Polymer-Covered Copper Catalysts Alter the Reaction Pathway of the Electrochemical CO2 Reduction Reaction

“… 5 Notably, Cu is the only metal that can form various C 1 and C 2 products by optimizing the binding energies of intermediates via surface structure modification. In particular, two main design concepts have emerged to enhance the product selectivity of Cu-based catalysts: (1) utilizing the Cu surface structural features (i.e., grain boundary and vacancy) or doping other metals 6 , 7 and (2) changing the catalytic interface where the reaction takes place by using organic ligands or forming the triple-phase boundary. 8 , 9 …”

Benchmarking of commercial Cu catalysts in CO2electro-reduction using a gas-diffusion type microfluidic flow electrolyzer

“…5,15–17 CO 2 RR performance with over 60% faradaic efficiency of C 2+ products at current densities >100 mA cm −2 has been achieved in numerous recent reports. 18–23 Owing to the structural complexity of the gas-diffusion electrode (GDE) and varied configurations of flow electrolyzers employed in the literature, it is unclear whether the reported CO 2 RR performance reflects the intrinsic activity of the catalysts, as it is commonly assumed, or features of flow reactors. 5,15,24,25…”

“…1 M KOH was chosen as the electrolyte because primary CO 2 RR studies that utilize gas-diffusion type microfluidic flow electrolyzers are typically conducted in alkaline conditions. 3,21,33 The FEs of the three Cu catalysts at constant current densities from 50 to 400 mA cm −2 are shown in Fig. 2.…”