Operando Mössbauer Spectroscopic Tracking the Metastable State of Atomically Dispersed Tin in Copper Oxide for Selective CO₂ Electroreduction

Abstract

Metastable state is the most active catalyst state that dictates the overall catalytic performance and rules of catalytic behaviors; however, identification and stabilization of the metastable state of catalyst are still highly challenging due to the continuous evolution of catalytic sites during the reaction process. In this work, operando 119Sn Mössbauer measurements and theoretical simulations were performed to track and identify the metastable state of single-atom Sn in copper oxide (Sn1–CuO) for highly selective CO2 electroreduction to CO. A maximum CO Faradaic efficiency of around 98% at −0.8 V (vs. RHE) over Sn1–CuO was achieved at an optimized Sn loading of 5.25 wt. %. Operando Mössbauer spectroscopy clearly identified the dynamic evolution of atomically dispersed Sn4+ sites in the CuO matrix that enabled the in situ transformation of Sn4+–O4–Cu2+ to a metastable state Sn4+–O3–Cu+ under CO2RR conditions. In combination with quasi in situ X-ray photoelectron spectroscopy, operando Raman and attenuated total reflectance surface enhanced infrared absorption spectroscopies, the promoted desorption of *CO over the Sn4+–O3 stabilized adjacent Cu+ site was evidenced. In addition, density functional theory calculations further verified that the in situ construction of Sn4+–O3–Cu+ as the true catalytic site altered the reaction path via modifying the adsorption configuration of the *COOH intermediate, which effectively reduced the reaction free energy required for the hydrogenation of CO2 and the desorption of the *CO, thereby greatly facilitating the CO2-to-CO conversion. This work provides a fundamental insight into the role of single Sn atoms on in situ tuning the electronic structure of Cu-based catalysts, which may pave the way for the development of efficient catalysts for high-selectivity CO2 electroreduction.

Deciphering Structure‐Activity Relationship Towards CO2 Electroreduction over SnO2 by A Standard Research Paradigm

“…In electrolysis, complicated factors, including the electrolyte and pH, determine the surface states of electrocatalysts, where various reactions occur for targeted products [2a,9c] . However, the simple catalyst model in most cases leads to the intrinsic defect of deviating from the realistic reaction surface, particularly in varied solution environments.…”

Multiple Tuning of the Local Environment Enables Selective CO2 Electroreduction to Ethylene in Neutral Electrolytes

“…As shown in Figure S9 (Supporting Information), after the electrochemical reduction at −0.6 versus RHE for 10 mins, Raman peaks at 286.7 and 465.3 cm −1 for CuO and Cu 2 O disappear, indicating that the CuO NWs has been completely reduced to metallic Cu. [12,37] Therefore, the electrochemical reduction at −0.6 versus RHE for 1 h is enough to completely reduce CuO to Cu NWs. Furthermore, we performed quasi in situ XPS according to literatures.…”

Harnessing single-atom catalysts for CO2electroreduction: a review of recent advances

“…129 (g) 119 Sn Mo ¨ssbauer spectroscopy as a probe technique to track the catalyst's metastable species. 130 environment of the single atomic sites. By fitting the results from EXAFS, important parameters such as bond length and coordination numbers can be inferred.…”

“…Chen et al reported a copper oxide-supported atomically dispersed Sn catalyst for the CO 2 RR. 130 In their study, they employed 119 Sn Mo ¨ssbauer spectroscopy as a probe technique to track the catalyst's metastable species. The Mo ¨ssbauer spectroscopy results revealed that the atomically dispersed Sn 4+ sites on the CuO substrate underwent a transformation from Sn 4+ -O 4 -Cu 2+ to a metastable state of Sn 4+ -O 3 -Cu + during the CO2RR (Fig.…”