Language：English   Publisher：Advanced Science  

Metal complexes with flexible redox and coordination properties possibly act as ingenious electrocatalysts to activate stable molecules such as CO<inf>2</inf>. To date, most studies have focused on mononuclear complexes in electrochemical CO<inf>2</inf> reduction (eCO<inf>2</inf>R). However, the development of electrocatalysts that operate at low overpotentials while maintaining high selectivity remains a critical challenge. Herein, it is demonstrated that the use of a dinuclear metal complex exhibiting cooperation of two metal centers can be an effective strategy for addressing this issue. The focused catalyst is a Co^II dinuclear complex (2) bearing two Co^II ions in close proximity, whose coordination environment is similar to that of a typical mononuclear complex, Co^II tetraphenylporphyrin (1). Based on experimental and computational studies, it is clarified that 2 exhibits simultaneous two-electron reduction prior to CO<inf>2</inf> activation, which allows bypassing the reaction step that hinders the catalytic cycle on 1. Furthermore, metal-to-metal electron transfer and a CO<inf>2</inf>-derived intermediate bridging over two metal centers are found in the catalytic cycle of 2, which would contribute to low activation barrier. It is then concluded that the cooperative functions of the two metal centers are the key to the efficient eCO<inf>2</inf>R performance.

DOI： 10.1002/advs.202508361

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PubMed

Language：English   Publisher：Angewandte Chemie International Edition  

Electrocatalytic carbon dioxide (CO<inf>2</inf>) reduction reaction (CO<inf>2</inf>RR) has emerged as a promising strategy for sustainable energy conversion and carbon utilization. Despite intensive research efforts, the understanding of intermediates and pathways leading from CO<inf>2</inf>RR to multicarbon (C<inf>2+</inf>) chemicals remains incomplete. The challenge is to gain insight into the activation of adsorbed CO and the subsequent pathways. Here, we design a specially tailored Cu nanowire array facing a hydrophobic interface as an electrode to highly enhance Raman signals in the in situ environment, allowing sensitive observation of the sequential change of various elusive intermediates during CO<inf>2</inf>RR, such as CO, CH<inf>2</inf>, CO coexisting with CH<inf>2</inf>, CH<inf>2</inf>CO, and CH<inf>3</inf>. Density functional theory calculations reveal that the C─C coupling during CO<inf>2</inf>RR originates from an asymmetric coupling between CH<inf>2</inf> and CO to form CH<inf>2</inf>CO, identified as the rate-determining step in the formation of C<inf>2+</inf> products. These findings deepen the understanding of the C─C coupling processes, which are crucial for advancing catalyst development in electrochemical CO<inf>2</inf> upgrading.

DOI： 10.1002/anie.202502740

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Language：English   Publisher：ACS Applied Materials and Interfaces  

CO2 electroreduction (eCO2R) holds promise as an environmentally friendly approach to reducing greenhouse gas emissions. Cu is a representative catalyst with high eCO2R activity. However, its selectivity for CH4 synthesis is still insufficient due to the slow eight-electron transfer to a single carbon, the predominance of C-C coupling reactions toward C2+ products on Cu, as well as occurrence of the hydrogen evolution reaction. Here, for high CH4 selectivity, we demonstrate a genuine hydrogen supply to atomically dispersed Cu sites (AD-Cu) via the cooperative function of oxygen vacancy (VO) formed on defective black anatase TiO2 (Cu-TiO2-H2), that is prepared by exposing Cu-doped TiO2 (Cu-TiO2) to hydrogen gas. Cu-TiO2-H2 exhibited a remarkable Faradaic efficiency for CH4 production of 63% and a partial current density of −120 mA cm-2. The catalytic mechanism for the high CH4 selectivity was elucidated using a variety of spectroscopies, such as electron spin resonance, reversed double-beam photoacoustic spectroscopy (RDB-PAS) and in situ Raman measurements, with the support of quantum chemical calculations. In situ Raman measurements revealed that Cu-TiO2-H2 greatly accelerates proton consumption for the hydrogenation of *CO intermediates and that the surface pH on Cu-TiO2-H2 is sufficiently high to stabilize *CHO intermediates, key species for CH4 formation. DFT calculations support the stability of the intermediates during the process of forming *CHO. All our results suggest that VO contiguous to AD-Cu on Cu-TiO2-H2 promotes water dissociation and smoothly supplies hydrogen to AD-Cu on Cu-TiO2-H2, thus facilitating CH4 formation in eCO2R.

DOI： 10.1021/acsami.5c00484

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of the American Chemical Society  

Metal-organic framework (MOF) glasses have emerged as a new class of organic-inorganic hybrid glass materials. Considerable efforts have been devoted to unraveling the macroscopic dynamics of MOF glasses by studying their rheological behavior; however, their microscopic dynamics remain unclear. In this work, we studied the effect of vitrification on linker dynamics in ZIF-62 by solid-state 2H nuclear magnetic resonance (NMR) spectroscopy. 2H NMR relaxation analysis provided a detailed picture of the mobility of the ZIF-62 linkers, including local restricted librations and a large-amplitude twist; these details were verified by molecular dynamics. A comparison of ZIF-62 crystals and glasses revealed that vitrification does not drastically affect the fast individual flipping motions with large-amplitude twists, whereas it facilitates slow cooperative large-amplitude twist motions with a decrease in the activation barrier. These observations support the findings of previous studies, indicating that glassy ZIF-62 retains permanent porosity and that short-range disorder exists in the alignment of ligands because of distortion of the coordination angle.

DOI： 10.1021/jacs.3c13156

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Publisher：Angewandte Chemie International Edition  

Ionic conduction in highly designable and porous metal–organic frameworks has been explored through the introduction of various ionic species (H⁺, OH⁻, Li⁺, etc.) using post-synthetic modification such as acid, salt, or ionic liquid incorporation. Here, we report on high ionic conductivity (σ>10⁻² S cm⁻¹) in a two-dimensionally (2D)-layered Ti-dobdc (Ti<inf>2</inf>(Hdobdc)<inf>2</inf>(H<inf>2</inf>dobdc), H<inf>4</inf>dobdc: 2,5-dihydroxyterephthalic acid) via LiX (X=Cl, Br, I) intercalation using mechanical mixing. The anionic species in lithium halide strongly affect the ionic conductivity and durability of conductivity. Solid-state pulsed-field gradient nuclear magnetic resonance (PFG NMR) verified the high mobility of H⁺ and Li⁺ ions in the temperature range of 300–400 K. In particular, the insertion of Li salts improved the H⁺ mobility above 373 K owing to strong binding with H<inf>2</inf>O. Furthermore, the continuous increase in Li⁺ mobility with temperature contributed to the retention of the overall high ionic conductivity at high temperatures.

DOI： 10.1002/anie.202301284

Scopus

Language：English   Book type：Scholarly book

DOI： 10.1007/978-981-99-7062-9