Sulfite-Assisted Acetate Conversion from CO Electroreduction

The efficient acetate conversion from CO electroreduction is challenging due to the poor selectivity at high reaction rate, which requires the competition with H2 and other C2+ (i.e., ethylene, ethanol, n-propanol) reduction products. Electrolyte engineering is one of the efficient strategies to regulate the reaction microenvironment. In this work, the adding of sulfite (SO32-) with high nucleophilicity in KOH electrolytes was demonstrated to enable improving the CO-to-acetate conversion via generating a S-O chemical bond between SO32- and oxygenated *C2 intermediates (i.e., *CO-CO, *CO-COH) compared with that in pure KOH system on both synthesized Cu(200)- and normal commercial Cu(111)-facets-exposed metallic Cu catalysts. As a result, the prepared Cu(200)-facets-exposed metallic Cu catalyst with surface ions modification showed an superior Faradaic efficiency of 63.6% at -0.6 A·cm-2, and extraordinary absolute value of peak partial current density as high as 1.52 A·cm-2 with adding SO32- in KOH electrolytes, compared to the best reported values in both CO and CO2 electroreduction. Our work suggests an attractive strategy to introduce the oxyanion with high nucleophilicity in electrolytes to regulate the microenvironment for industrial-current-density electrosynthesis of acetate from CO electroreduction.

Metal-Organic Framework Derived Cu-Ag Interface for Selective Carbon Monoxide Electroreduction to Acetate

Electrochemical carbon monoxide reduction reaction (CORR) is a potential way to obtain high-value multi-carbon (C2+ ) products. However, achieving high selectivity to acetate is still a challenge. Herein, we develop a two-dimensional Ag-modified Cu metal-organic framework (Ag0.10 @CuMOF-74) that demonstrates Faradaic efficiency (FE) for C2+ products up to 90.4 % at 200 mA cm-2 and an acetate FE of 61.1 % with a partial current density of 122.2 mA cm-2 . Detailed investigations show that the introduction of Ag on CuMOF-74 favors the generation of abundant Cu-Ag interface sites. In situ attenuated total reflection surface enhanced infrared absorption spectroscopy confirms that these Cu-Ag interface sites improve the coverage of *CO and *CHO and the coupling between each other and stabilize key intermediates *OCCHO and *OCCH2 , thus significantly promoting to the acetate selectivity on Ag0.10 @CuMOF-74. This work provides a high-efficiency pathway for CORR to C2+ products.

Enriching Reaction Intermediates in Multishell Structured Copper Catalysts for Boosted Propanol Electrosynthesis from Carbon Monoxide

Fine-tuned catalysts that alter the diffusion kinetics of reaction intermediates is of great importance for achieving high-performance multicarbon (C₂₊) product generation in carbon monoxide (CO) reduction. Herein, we conduct a structural design based on Cu₂O nanoparticles and present an effective strategy for enhancing propanol electrosynthesis from CO. The electrochemical characterization, operando Raman monitoring, and finite-element method simulations reveal that the multishell structured catalyst can realize the enrichment of C₁ and C₂ intermediates by nanoconfinement space, leading to the possibility of further coupling. Consequently, the multishell copper catalyst realizes a high Faraday efficiency of 22.22 ± 0.38% toward propanol at the current density of 50 mA cm^-2.

Computational Design of a Two-Dimensional Copper Carbide Monolayer as a Highly Efficient Catalyst for Carbon Monoxide Electroreduction to Ethanol

Rationally designing stable and low-cost electrocatalysts with high efficiency is of great significance for the large-scale electrochemical reduction of carbon monoxide (eCOR) to high-value-added multicarbon products. Inspired by the tunable atomic structures, abundant active sites, and excellent properties of two-dimensional (2D) materials, in this work, we designed several novel 2D C-rich copper carbide materials as eCOR electrocatalysts by performing an extensive structural search and comprehensive first-principles computations. According to the computed phonon spectra, formation energies, and ab initio molecular dynamics simulations, we screened out two highly stable candidates, i.e., CuC₂ and CuC₅ monolayers with metallic features. Interestingly, the predicted 2D CuC₅ monolayer exhibits superior eCOR performance for C₂H₅OH synthesis with high catalytic activity (low limiting potential of -0.29 V and small activation energy for C-C coupling of 0.35 eV) and high selectivity (significant suppressing effect on the side reactions). Thus, we predicted that the CuC₅ monolayer holds great potential as an eligible electrocatalyst for CO conversion to multicarbon products, which could motivate more study to develop highly efficient electrocatalysts in similar binary noble-metal compounds.

C-C Coupling Is Unlikely to Be the Rate-Determining Step in the Formation of C2+ Products in the Copper-Catalyzed Electrochemical Reduction of CO

The identity of the rate-determining step (RDS) in the electrochemical CO reduction reaction (CORR) on Cu catalysts remains unresolved because: 1) the presence of mass transport limitation of CO; and 2) the absence of quantitative correlation between CO partial pressure (p_CO ) and surface CO coverage. In this work, we determined CO adsorption isotherms on Cu in a broad pH range of 7.2-12.9. Together with electrokinetic data, we demonstrate that the reaction orders of adsorbed CO at p_CO <0.4 and >0.6 atm are 1^st and 0^th , respectively, for multi-carbon (C₂₊ ) products on three Cu catalysts. These results indicate that the C-C coupling is unlikely to be the RDS in the formation of C₂₊ products in the CORR. We propose that the hydrogenation of CO with adsorbed water is the RDS, and the site competition between CO and water leads to the observed transition of the CO reaction order.

In Situ Topotactic Transformation of an Interstitial Alloy for CO Electroreduction

Electrochemical reduction of CO to value-added products holds promise for storage of energy from renewable sources. Copper can convert CO into multi-carbon (C₂₊ ) products during CO electroreduction. However, developing a Cu electrocatalyst with a high selectivity for CO reduction and desirable production rates for C₂₊ products remains challenging. Herein, highly lattice-disordered Cu₃ N with abundant twin structures as a precursor electrocatalyst is examined for CO reduction. Through in situ activation during the CO reduction reaction (CORR) and concomitant release of nitrogen, the obtained metallic Cu° catalyst particles inherit the lattice dislocations present in the parent Cu₃ N lattice. The de-nitrified catalyst delivers an unprecedented C₂₊ Faradaic efficiency of over 90% at a current density of 727 mA cm^-2 in a flow cell system. Using a membrane electrode assembly (MEA) electrolyzer with a solid-state electrolyte (SSE), a 17.4 vol% ethylene stream and liquid streams with concentration of 1.45 m and 230 × 10^-3 m C₂₊ products at the outlet of the cathode and SSE-containment layer are obtained.

Harmonizing the Electronic Structures of the Adsorbate and Catalysts for Efficient CO2 Reduction

In CO₂ electroreduction, the critical bottleneck lies in the CO₂ activation which requires high overpotentials. CO₂ activation is related to both the electronic structures of catalysts and those of adsorbates, thus an ideal catalyst should match its electronic structures with those of the adsorbate. Here, we harmonized the electronic structures of the adsorbate and Mn-doped In₂S₃ nanosheets for efficient CO₂ reduction. The introduction of Mn dopants into In₂S₃ nanosheets enhanced both the Faradaic efficiency (FE) for carbonaceous products and current density (j). At -0.9 V vs RHE, Mn-doped In₂S₃ nanosheets exhibited a remarkable FE of 92% for carbonaceous product at a high j of 20.1 mA cm^-2. Mechanistic studies revealed that Mn doping enabled the harmonic overlaps between the p orbitals of O atoms and d orbitals of Mn atoms near the conduction band edge of Mn-doped In₂S₃ nanosheets during the activation of CO₂. Due to the unique electronic structures of the coadsorbed configurations, Mn-doped In₂S₃ nanosheets exhibited an energy barrier for CO₂ activation into HCOO* lower than that over pristine In₂S₃ nanosheets.

Enhanced Electrocatalytic Reduction of CO2 via Chemical Coupling between Indium Oxide and Reduced Graphene Oxide

The chemical coupling interaction has been explored extensively to boost heterogeneous catalysis, but the insight into how chemical coupling interaction works on CO₂ electroreduction remains unclear. Herein we demonstrate how the chemical coupling interaction between porous In₂O₃ nanobelts and reduced graphene oxide (rGO) could substantially improve the electrocatalytic activity toward CO₂ electroreduction. Such an In₂O₃-rGO hybrid catalyst showed 1.4-fold and 3.6-fold enhancements in Faradaic efficiency and specific current density for the formation of formate at -1.2 V versus reversible hydrogen electrode relative to the catalyst prepared by physically loading of In₂O₃ nanobelts onto rGO, respectively. The density functional theory calculations and electrochemical analysis together revealed that the chemical coupling interaction boosted CO₂ electroreduction activity by improving electrical conductivity and stabilizing key intermediate HCOO^-*. The present work not only deepens an understanding of chemical coupling effect but also provides an effective lever to optimize the catalytic performance toward CO₂ electroreduction.