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1. Active Sites of Cobalt Phthalocyanine in Electrocatalytic CO ₂ Reduction to Methanol

   https://doi.org/10.1002/anie.202310623  

   Rooney, Conor L.; Lyons, Mason; Wu, Yueshen; Hu, Gongfang; Wang, Maoyu; Choi, Chungseok; Gao, Yuanzuo; Chang, Chun‐Wai; Brudvig, Gary W.; Feng, Zhenxing; et al (January 2024, Angewandte Chemie International Edition)

   Abstract Many metal coordination compounds catalyze CO₂electroreduction to CO, but cobalt phthalocyanine hybridized with conductive carbon such as carbon nanotubes is currently the only one that can generate methanol. The underlying structure–reactivity correlation and reaction mechanism desperately demand elucidation. Here we report the first in situ X‐ray absorption spectroscopy characterization, combined with ex situ spectroscopic and electrocatalytic measurements, to study CoPc‐catalyzed CO₂reduction to methanol. Molecular dispersion of CoPc on CNT surfaces, as evidenced by the observed electronic interaction between the two, is crucial to fast electron transfer to the active sites and multi‐electron CO₂reduction. CO, the key intermediate in the CO₂‐to‐methanol pathway, is found to be labile on the active site, which necessitates a high local concentration in the microenvironment to compete with CO₂for active sites and promote methanol production. A comparison of the electrocatalytic performance of structurally related porphyrins indicates that the bridging aza‐N atoms of the Pc macrocycle are critical components of the CoPc active site that produces methanol. In situ X‐ray absorption spectroscopy identifies the active site as Co(I) and supports an increasingly non‐centrosymmetric Co coordination environment at negative applied potential, likely due to the formation of a Co−CO adduct during the catalysis. 

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2. An active, stable cubic molybdenum carbide catalyst for the high-temperature reverse water-gas shift reaction

   https://doi.org/10.1126/science.adl1260  

   Ahmadi_Khoshooei, Milad; Wang, Xijun; Vitale, Gerardo; Formalik, Filip; Kirlikovali, Kent O; Snurr, Randall Q; Pereira-Almao, Pedro; Farha, Omar K (May 2024, Science)

   Although technologically promising, the reduction of carbon dioxide (CO₂) to produce carbon monoxide (CO) remains economically challenging owing to the lack of an inexpensive, active, highly selective, and stable catalyst. We show that nanocrystalline cubic molybdenum carbide (α-Mo₂C), prepared through a facile and scalable route, offers 100% selectivity for CO₂reduction to CO while maintaining its initial equilibrium conversion at high space velocity after more than 500 hours of exposure to harsh reaction conditions at 600°C. The combination of operando and postreaction characterization of the catalyst revealed that its high activity, selectivity, and stability are attributable to crystallographic phase purity, weak CO-Mo₂C interactions, and interstitial oxygen atoms, respectively. Mechanistic studies and density functional theory (DFT) calculations provided evidence that the reaction proceeds through an H₂-aided redox mechanism. 

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3. Recent progress in electrochemical reduction of carbon dioxide on metal single‐atom catalysts

   https://doi.org/10.1002/ese3.1036  

   Huo, Siming; Lu, Jessie; Wang, Xianqin (December 2021, Energy Science & Engineering)

   Abstract Electrochemical reduction reaction of CO₂(CO₂RR) is a promising technology for alleviating the global warming caused by the emission of CO₂. This technology, however, is still in the stage of finding efficient catalysts. The catalysts must be able to convert CO₂to other carbon‐based products with high activity and selectivity to valuable chemicals. In this review, previous development of heteroatom‐doped metal‐free carbon materials (H‐CMs) is briefly summarized. Recent progress of CO₂RR promoted by metal single‐atom catalysts (M‐SACs) is then discussed with emphasis on the synthesis of M‐SACs, the catalytic performance, and reaction mechanisms. The high temperature pyrolysis method and electrodeposition are attracting attentions recently to prepare M‐SACs with high metal loading on N‐doped carbon materials, a very active M‐SACs system for the CO₂RR. Theoretical calculations of free energy change on active sites, the Operando X‐ray absorption near edge structure (XANES), and Bader charge analysis reveal a significant role of metal oxidation state and charge transfer between metal atoms and absorbed CO. The challenges and perspectives for the extensive applications of M‐SACs in CO₂RR are also discussed in this review. 

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4. 2D Copper Tetrahydroxyquinone Conductive Metal–Organic Framework for Selective CO ₂ Electrocatalysis at Low Overpotentials

   https://doi.org/10.1002/adma.202004393  

   Majidi, Leily; Ahmadiparidari, Alireza; Shan, Nannan; Misal, Saurabh N.; Kumar, Khagesh; Huang, Zhehao; Rastegar, Sina; Hemmat, Zahra; Zou, Xiaodong; Zapol, Peter; et al (February 2021, Advanced Materials)

   Abstract Metal–organic frameworks (MOFs) are promising materials for electrocatalysis; however, lack of electrical conductivity in the majority of existing MOFs limits their effective utilization in the field. Herein, an excellent catalytic activity of a 2D copper (Cu)‐based conductive MOF, copper tetrahydroxyquinone (CuTHQ), is reported for aqueous CO₂reduction reaction (CO₂RR) at low overpotentials. It is revealed that CuTHQ nanoflakes (NFs) with an average lateral size of 140 nm exhibit a negligible overpotential of 16 mV for the activation of this reaction, a high current density of ≈173 mA cm⁻²at −0.45 V versus RHE, an average Faradaic efficiency (F.E.) of ≈91% toward CO production, and a remarkable turnover frequency as high as ≈20.82 s⁻¹. In the low overpotential range, the obtained CO formation current density is more than 35 and 25 times higher compared to state‐of‐the‐art MOF and MOF‐derived catalysts, respectively. The operando Cu K‐edge X‐ray absorption near edge spectroscopy and density functional theory calculations reveal the existence of reduced Cu (Cu⁺) during CO₂RR which reversibly returns to Cu²⁺after the reaction. The outstanding CO₂catalytic functionality of conductive MOFs (c‐MOFs) can open a way toward high‐energy‐density electrochemical systems. 

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5. Insights into Heterogeneous Catalysts under Reaction Conditions by In Situ/Operando Electron Microscopy

   https://doi.org/10.1002/aenm.202202097  

   Cheng, Han‐Wen; Wang, Shan; Chen, Guanyu; Liu, Zhengwang; Caracciolo, Dominic; Madiou, Merry; Shan, Shiyao; Zhang, Jincang; He, Heyong; Che, Renchao; et al (August 2022, Advanced Energy Materials)

   Abstract The advancement of clean energy and environment depends strongly on the development of efficient catalysts in a wide range of heterogeneous catalytic reactions, which has benefited from transmission electron microscopic techniques in determining the atomic‐scale morphologies and structures. However, it is the morphology and structure under the catalytic reaction conditions that determine the performance of the catalyst, which has captured a surge of interest in developing and applying in situ/operando transmission electron microscopic techniques in heterogeneous catalysis. The major theme of this review is to highlight some of the most recent insights into heterogeneous catalysts under the relevant reaction conditions using in situ/operando transmission electron microscopic techniques. Rather than a comprehensive overview of the basic principles of in situ/operando techniques, this review focuses on the insights into the atomic‐scale/nanoscale details of various catalysts ranging from single‐component to multicomponent catalysts under heterogeneous catalytic, electrocatalytic, and photocatalytic reaction conditions involving both gas–solid and liquid–solid interfaces. This focus is coupled with discussions of the correlation of the atomic, molecular, and nanoscale morphology, composition, and structure with the catalytic properties under the reaction conditions, shining light on the challenges and opportunities in design of nanostructured catalysts for clean and sustainable energy applications. 

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