Cu Vacancy Induced Product Switching from Formate to CO for CO₂ Reduction on Copper Sulfide

Abstract

Cu is commonly modified with sulfur to obtain high selectivity for formate since S can promote the formation of the key *OCHO intermediate along the formate pathway. In the present work, we demonstrate that Cu-vacancies on copper sulfide can surprisingly switch the formate pathway to the CO pathway, and the concentration of Cu vacancies can deterministically regulate the CO faradaic efficiency and partial current density. The J CO of SNC@Cu1.96S (Cu1.96S coated sulfur, nitrogen-co-doped carbon) can reach 37.2 mA cm–2 in an H cell, which is the highest among the Cu-based catalysts and comparable to other top CO production catalysts. According to DFT calculations, the Cu vacancies formed in copper sulfide change the electronic structures of the S sites in such a way that the H* takes a large Gibbs free energy, which in turn suppresses the formation of formate. However, the resulting fewer surface Cu cations and more surface S anions weakens the adsorbate–metal interaction, synergizing the adsorption structural transition of the surface intermediates from *OCHO (two O–Cu bonds) to *COOH (one C–Cu bond) in favor of CO production.

Hydrothermal Synthesis of CuS Catalysts for Electrochemical CO2 Reduction: Unraveling the Effect of the Sulfur Precursor

“…Another idea suggests that the Cu vacancy in CuS catalyst plays an important role in CO 2 RR. , Cu vacancy would alter the electronic structures of the S sites in CuS catalyst and thus impeding the HCOOH generation pathway by increasing the free energy for *H formation. In addition, the reduced ratio of the Cu cations to surface S anions had weakened the adsorbate-metal interaction, which was favorable for CO generation via promoting the *COOH pathway . In this work, we conclude that the presence of V s in the CuS catalyst promotes CO production in CO 2 RR by lowering the energy barrier of the *COOH intermediates.…”

“…For instance, in the work by Zhao et al, CuS nanosheets grown on nickel foam (NF) were fabricated, and the nanosheet morphology had facilitated *CO protonation, which had enabled highly selective CO 2 RR to CH 4 over the CuS@NF catalyst . Li et al reported that Cu-vacancies formed in CuS catalysts altered the electronic structures of the S sites, increased the energy barrier of H* formation, and favored the formation of the *COOH intermediate, thus switching the formate pathway to the CO pathway …”

“…Li et al reported that Cu-vacancies formed in CuS catalysts altered the electronic structures of the S sites, increased the energy barrier of H* formation, and favored the formation of the *COOH intermediate, thus switching the formate pathway to the CO pathway. The desired SNC@Cu 1.96 S and SNC@Cu x S catalysts exhibited high CO selectivity of 85.2% and 51.6% @ −0.84 V vs RHE . Shao et al correlated the ECR performance of CuS catalysts with their crystalline structure, morphology, and particle size, and the h-CuS MCs catalyst showed a moderate CO selectivity of 32.7% @ −0.16 V vs RHE .…”

MOF-Transformed In2O3-x@C Nanocorn Electrocatalyst for Efficient CO2 Reduction to HCOOH

“…Oxygen vacancy in catalysts has shown beneficial roles in promoting the activation of CO 2 for one thing and in accelerating electron transfer for another. However, how to maximize the advantages of vacancies still requires more delicate material designs [15,[25][26][27][28][29]. Due to the good conductivity, carbon paper and carbon cloth are commonly used to support powder electrocatalysts.…”

CeOx Promoted Electrocatalytic CO2 Reduction to Formate by Assisting in the Critical Hydrogenation Step

“…First, CO 2 is a thermodynamically stable and chemically inert molecule ( ), , meaning that we have to consume a substantial amount of energy for driving CO 2 RR at a practicable rate. Second, since there are many kinds of CO 2 reduction products and the equilibrium potentials of these electrochemical reactions are very close, it is difficult to obtain a single product. − Finally, the competing hydrogen evolution reaction (HER) has a strong impact on the faradaic efficiency of CO 2 RR in aqueous solution. , To improve the activity and selectivity of CO 2 RR, researchers have introduced many useful strategies on catalyst design such as nanostructures, , crystal facets control, and defect engineering …”