MOF-Templated Sulfurization of Atomically Dispersed Manganese Catalysts Facilitating Electroreduction of CO₂ to CO

Abstract

To reach a carbon-neutral future, electrochemical CO2 reduction reaction (eCO2RR) has proven to be a strong candidate for the next-generation energy system. Among potential materials, single-atom catalysts (SACs) serve as a model to study the mechanism behind the reduction of CO2 to CO, given their well-defined active metal centers and structural simplicity. Moreover, using metal–organic frameworks (MOFs) as supports to anchor and stabilize central metal atoms, the common concern, metal aggregation, for SACs can be addressed well. Furthermore, with their turnability and designability, MOF-derived SACs can also extend the scope of research on SACs for the eCO2RR. Herein, we synthesize sulfurized MOF-derived Mn SACs to study effects of the S dopant on the eCO2RR. Using complementary characterization techniques, the metal moiety of the sulfurized MOF-derived Mn SACs (MnSA/SNC) is identified as MnN3S1. Compared with its non-sulfur-modified counterpart (MnSA/NC), the MnSA/SNC provides uniformly superior activity to produce CO. Specifically, a nearly 30% enhancement of Faradaic efficiency (F.E.) in CO production is observed, and the highest F.E. of approximately 70% is identified at −0.45 V. Through operando spectroscopic characterization, the probing results reveal that the overall enhancement of CO production on the MnSA/SNC is possibly caused by the S atom in the local MnN3S1 moiety, as the sulfur atom may induce the formation of S–O bonding to stabilize the critical intermediate, *COOH, for CO2-to-CO. Our results provide novel design insights into the field of SACs for the eCO2RR.

Synthetic strategies for MOF-based single-atom catalysts for photo- and electro-catalytic CO2 reduction

“…Tan and collaborators adopt mixed metal node stabilization strategy mentioned above to synthesize Mn-SACs (Tan et al, 2021). The MOFs with Mn and Zn nodes were prepared by adding the organic ligand methylimidazole into the mixed solution of Mn and Zn salts.…”

Heteroatom‐Doped Asymmetric Metal‐Nx‐C Single Atom Catalysts for Electrochemical CO2 Reduction Reaction

“…The spin symmetry of the regulated Co center makes it easier to adsorb the spin-symmetric intermediate *OCHO, [55] while the high spin state of the regulated Ni center provides more 3d electrons and promotes the formation of the intermediate COOH. [56] (3) Distortion of the local coordination structure, likewise caused by doping of Cl, F, S, leads to the electron enrichment of the metal center (Ni, Mn, Zn, Sn), [29,[60][61]63,70] which affects the adsorption strength of the intermediate species as mentioned in (1), thus have a huge effect on the ECR reaction rate and selectivity for the prepared catalysts.…”

“…When a S atom replaces a N atom around Mn, the formed MnN 3 S 1 site can stabilize the *COOH intermediate. Due to the difference in electronegativity and their dimensions between S and N atoms, the normal coplanar metallic part of the SAC (MnN 4 ) is distorted to a non‐coplanar metallic part for MnN 3 S 1 .As a result, the O atom at the OH end of *COOH may move closer to the S atom and subsequently form a S−O bond to delocalize the electron density and stabilize the *COOH intermediate (Figure 7(a)) [60] . The MnN 4 structure with an axial Cl atom coordination undergoes the same structural distortion during ECR, similar to MnSA/SNC [61] .…”

“…From the perspective of reaction process, (1) the modulation of the electronic structure of the central metal has a huge effect on the adsorption and desorption behaviors of the intermediates generated in the ECR process. Such as the adsorption intensity of *COOH, [25,[32][33]38,[48][49]54,56,[60][61]69,71] *OCHO [55,59] and *COH, [58] thus influence the selectivity for various products formed in ECR process; (2) the doping of heteroatom like S in Fe-N-C, modified electronic structure of the metal center can hasten the dissociation of H 2 O into *H, [39,51,63] accelerating the first step of the electron-proton coupling process in the ECR for the production of CO, thus increase the selectivity of the prepared M-SACs for CO generation.…”

In situ probing the dynamic reconstruction of copper–zinc electrocatalysts for CO2 reduction

“…1 Attention to energy-and environment-related issues has driven significant efforts in CO 2 conversion technologies. [2][3][4] The electrochemical CO 2 reduction reaction (CO 2 RR) is emerging as a viable method to consume excess carbon dioxide in the atmosphere and store chemical energy in value-added chemicals. [5][6][7] Therefore, efforts have been devoted to exploring efficient electrocatalysts with high selectivity for the CO 2 RR because CO 2 can be converted into formate, methanol (CH 3 OH), methane (CH 4 ), ethylene (C 2 H 4 ) ethanol (C 2 H 5 OH), etc.…”