Pulsed Electrolysis Promotes CO2 Reduction to Ethanol on Heterostructured Cu2O/Ag Catalysts.

The electrochemical conversion of carbon dioxide (CO2) into ethanol with high added value has attracted increasing attention. Here, an efficient catalyst with abundant Cu2O/Ag interfaces for ethanol production under pulsed CO2 electrolysis is reported, which is composed of Cu2O hollow nanospheres loaded with Ag nanoparticles (named as se-Cu2O/Ag). The CO2-to-ethanol Faradaic efficiency is prominently improved to 46.3% at a partial current density up to 417 mA cm-2 under pulsed electrolysis conditions in a neutral flow cell, notably outperforming conventional Cu catalysts during static electrolysis. In situ spectroscopy reveals the stabilized Cu+ species of se-Cu2O/Ag during pulsed electrolysis and the enhanced adsorbed CO intermediate (*CO)coverage on the heterostructured catalyst. Density functional theory (DFT) calculations further confirm that the Cu2O/Ag heterostructure stabilizes the *CO intermediate and promotes the coupling of *CO and adsorbed CH intermediate (*CH). Meanwhile, the stable Cu+ species under pulsed electrolysis favor the hydrogenation of adsorbed HCCOH intermediate (*HCCOH) to adsorbed HCCHOH intermediate (*HCCHOH) on the pathway to ethanol. The synergistic effect between the enhanced generation of *CO on Cu2O/Ag and regenerated Cu+ species under pulsed electrolysis steers the reaction pathway toward ethanol. This work provides some insights into selective ethanol production from CO2 electroreduction via combined catalyst design and non-steady state electrolysis.

Customizing CO2 Electroreduction by Pulse-Induced Anion Enrichment.

Electrochemically converting CO2 into specified high-value products is critical for carbon neutral economics. However, governing the product distribution of the CO2 electroreduction on Cu-based catalysts remains challenging. Herein, we put forward an anion enrichment strategy to efficiently dictate the route of *CO reduction by a pulsed electrolysis strategy. Upon periodically applying a positive potential on the cathode, the anion concentration in the vicinity of the electrode increases apparently. By adopting KF, KCl, and KHCO3 as electrolytes, the dominant CO2 electroreduction product on commercial Cu foil can be tuned into CO (53% ± 2.5), C2+ (76.6 ± 2.1%), and CH4 (42.6 ± 2.1%) under pulsed electrolysis. Notably, one can delicately tailor the ratios of CO/CH4, CH4/C2+, and C2+/CO by simply changing the composition of the electrolyte. Density functional theory calculations demonstrate that locally enriched anions can affect the key CO2RR intermediates in different ways owing to their specific electronegativity and volume, which leads to the distinct selectivity. The present study highlights the importance of tuning ionic species at the electrode-electrolyte interface for customizing the CO2 electroreduction products.

Modulating Electron Density of Ni-N-C Sites by N-doped Ni for Industrial-level CO2 Electroreduction in Acidic Media.

Electro-chemically reducing CO2 in a highly acidic medium is promising for addressing the issue of carbonate accumulation. However, the hydrogen evolution reaction (HER) typically dominates the acidic CO2 reduction. Herein, we construct an efficient electro-catalyst for CO formation based on a core-shell structure, where nitrogen-doped Ni nanoparticles coexist with nitrogen-coordinated Ni single atoms. The optimal catalyst demonstrates a significantly improved CO faradaic efficiency (FE) of 96.7 % in the acidic electrolyte (pH=1) at an industrial-scale current density of 500 mA cm-2 . Notably, the optimal catalyst maintains a high FE of CO exceeding 90 % (current density=500 mA cm-2 ) in the electrolyte with a wide pH range from 0.67 to 14. In-situ spectroscopic characterization and density functional theory calculations show that the local electron density of Ni-N-C sites is enhanced by N-doped Ni particles, which facilitates the formation of *COOH intermediate and the adsorption of *CO. This study demonstrates the potential of a hybrid metal/Ni-N-C interface in boosting acidic CO2 electro-reduction.

Enhanced CO Affinity on Cu Facilitates CO2 Electroreduction toward Multi-Carbon Products.

Electrochemical CO2 reduction reaction (CO2 RR) is a promising strategy for waste CO2 utilization and intermittent electricity storage. Herein, it is reported that bimetallic Cu/Pd catalysts with enhanced *CO affinity show a promoted CO2 RR performance for multi-carbon (C2+) production under industry-relevant high current density. Especially, bimetallic Cu/Pd-1% catalyst shows an outstanding CO2 -to-C2+ conversion with 66.2% in Faradaic efficiency (FE) and 463.2 mA cm-2 in partial current density. An increment in the FE ratios of C2+ products to CO  for Cu/Pd-1% catalyst further illuminates a preferable C2+ production. In situ Raman spectra reveal that the atop-bounded CO is dominated by low-frequency band CO on Cu/Pd-1% that leads to C2+ products on bimetallic catalysts, in contrast to the majority of high-frequency band CO on Cu that favors the formation of CO. Density function theory calculation confirms that bimetallic Cu/Pd catalyst enhances the *CO adsorption and reduces the Gibbs free energy of the CC coupling process, thereby favoring the formation of C2+ products.

Hetero-Interfaces on Cu Electrode for Enhanced Electrochemical Conversion of CO2 to Multi-Carbon Products.

Electrochemical CO2 reduction reaction (CO2RR) to multi-carbon products would simultaneously reduce CO2 emission and produce high-value chemicals. Herein, we report Cu electrodes modified by metal-organic framework (MOF) exhibiting enhanced electrocatalytic performance to convert CO2 into ethylene and ethanol. The Zr-based MOF, UiO-66 would in situ transform into amorphous ZrOx nanoparticles (a-ZrOx), constructing a-ZrOx/Cu hetero-interface as a dual-site catalyst. The Faradaic efficiency of multi-carbon (C2+) products for optimal UiO-66-coated Cu (0.5-UiO/Cu) electrode reaches a high value of 74% at - 1.05 V versus RHE. The intrinsic activity for C2+ products on 0.5-UiO/Cu electrode is about two times higher than that of Cu foil. In situ surface-enhanced Raman spectra demonstrate that UiO-66-derived a-ZrOx coating can promote the stabilization of atop-bound CO* intermediates on Cu surface during CO2 electrolysis, leading to increased CO* coverage and facilitating the C-C coupling process. The present study gives new insights into tailoring the adsorption configurations of CO2RR intermediate by designing dual-site electrocatalysts with hetero-interfaces.