Promoting CO2 Electroreduction to Multi-Carbon Products by Hydrophobicity-Induced Electro-Kinetic Retardation.

Advancing the performance of the Cu-catalyzed electrochemical CO2 reduction reaction (CO2 RR) is crucial for its practical applications. Still, the wettable pristine Cu surface often suffers from low exposure to CO2 , reducing the Faradaic efficiencies (FEs) and current densities for multi-carbon (C2+ ) products. Recent studies have proposed that increasing surface availability for CO2 by cation-exchange ionomers can enhance the C2+ product formation rates. However, due to the rapid formation and consumption of *CO, such promotion in reaction kinetics can shorten the residence of *CO whose adsorption determines C2+ selectivity, and thus the resulting C2+ FEs remain low. Herein, we discover that the electro-kinetic retardation caused by the strong hydrophobicity of quaternary ammonium group-functionalized polynorbornene ionomers can greatly prolong the *CO residence on Cu. This unconventional electro-kinetic effect is demonstrated by the increased Tafel slopes and the decreased sensitivity of *CO coverage change to potentials. As a result, the strongly hydrophobic Cu electrodes exhibit C2+ Faradaic efficiencies of ≈90 % at a partial current density of 223 mA cm-2 , more than twice of bare or hydrophilic Cu surfaces.

Boosting CO2 Electroreduction to C2H4 via Unconventional Hybridization: High-Order Ce4+ 4f and O 2p Interaction in Ce-Cu2O for Stabilizing Cu.

Efficient conversion of carbon dioxide (CO2) into value-added materials and feedstocks, powered by renewable electricity, presents a promising strategy to reduce greenhouse gas emissions and close the anthropogenic carbon loop. Recently, there has been intense interest in Cu2O-based catalysts for the CO2 reduction reaction (CO2RR), owing to their capabilities in enhancing C-C coupling. However, the electrochemical instability of Cu+ in Cu2O leads to its inevitable reduction to Cu0, resulting in poor selectivity for C2+ products. Herein, we propose an unconventional and feasible strategy for stabilizing Cu+ through the construction of a Ce4+ 4f-O 2p-Cu+ 3d network structure in Ce-Cu2O. Experimental results and theoretical calculations confirm that the unconventional orbital hybridization near Ef based on the high-order Ce4+ 4f and 2p can more effectively inhibit the leaching of lattice oxygen, thereby stabilizing Cu+ in Ce-Cu2O, compared with traditional d-p hybridization. Compared to pure Cu2O, the Ce-Cu2O catalyst increased the ratio of C2H4/CO by 1.69-fold during the CO2RR at -1.3 V. Furthermore, in situ and ex situ spectroscopic techniques were utilized to track the oxidation valency of copper under CO2RR conditions with time resolution, identifying the well-maintained Cu+ species in the Ce-Cu2O catalyst. This work not only presents an avenue to CO2RR catalyst design involving the high-order 4f and 2p orbital hybridization but also provides deep insights into the metal-oxidation-state-dependent selectivity of catalysts.