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A significant number of molecular catalysts have been developed for electrochemical CO 2 reduction with high efficiency and selectivity; however, testing of these electrocatalysts in an application-ready system is lacking. Here, we present an example of a nonaqueous flow cell electrolyzer with [Ni(cyclam)] 2+ as the homogeneous electrocatalyst for CO 2 reduction. Using ferrocene as a sacrificial electron donor and ammonium salts as both electrolyte and proton donor, efficient catalytic CO 2 reduction is achieved. The nonaqueous design shows high selectivity for the reduction of CO 2 to CO (>80%) and achieves high current densities with a graphite felt working electrode (up to 50 mA·cm -2 with 0.5 M proton donor in MeCN solution), producing >40 mL·h -1 of CO. The choice of a molecular electrocatalyst, solvent, and proton donor are the key factors for achieving high activity with an efficient flow electrolyzer and the eventual development of a viable continuous process.

The interligand charge dynamics of the lowest singlet metal-to-ligand charge-transfer states ( 1 MLCT S 1 states) of a series of quadruply bonded trans-Mo 2 (NN) 2 (O 2 C-X) 2 paddlewheel compounds are investigated, where NN is a π-accepting phenylpropiolamidinate ligand and O 2 C-X (X = Me, t Bu, T i PB, or CF 3 ) is an auxiliary carboxylate ligand. The compounds show strong light absorption in the visible region due to MLCT transitions from the Mo 2 center to the NN ligands. The transferred electron density was followed by femtosecond time-resolved infrared (fs-TRIR) spectroscopy with vibrational reporters such as the ethynyl groups on the NN ligands. The observed fs-TRIR spectra show that these compounds have asymmetric 1 MLCT S 1 excited states where the transferred electron mainly resides on a single NN ligand. The presence of interligand electron transfer (ILET) is suggested to explain the shape of the ν(C≡C) bands and the influence of auxiliary ligands and solvents on the interligand electronic coupling. The ILET in the 1 MLCT S 1 state is shown to be sensitive to the functional groups on the auxiliary ligands while being less responsive to changes in solvents.

Four photophysically interesting dimolybdenum paddlewheel compounds are synthesized and characterized: I and II contain amide ligand (N,3-diphenyl-2-propynamide), and III and IV contain thioamide ligand (N,3-diphenyl-2-propynethioamide). I and III are trans-Mo 2 L 2 (O 2 C-T i PB) 2 -type compounds, and II and IV are Mo 2 L 4 -type compounds, where O 2 C-T i PB is 2,4,6-triisopropylbenzoate. I-IV display strong light absorption due to metal to ligand charge transfer (MLCT) transitions from molybdenum to the amide/thioamide ligands. Charge transfer dynamics in the MLCT excited states of I-IV have been examined using femtosecond transient absorption (fs-TA) spectroscopy and femtosecond time-resolved infrared (fs-TRIR) spectroscopy. The asymmetric amide/thioamide ligands show two forms of regioarrangements in the paddlewheel compounds. Analyses of the ν(C≡C) bands in the fs-TRIR spectra of I and II show similar electron density distribution over ligands in their 1 MLCT S 1 states where only two amide ligands are involved and the transferred electron is mainly localized on one of them. The fs-TRIR spectra of III and IV, however, show different charge distribution patterns where the transferred electron is fully delocalized over two thioamide ligands in III and partially delocalized in IV. Fast interligand electron transfer (ILET) was recognized as the explanation for the various charge distribution patterns, and ILET was shown to be influenced by both the ligands and the ligand arrangements.

Two dimolybdenum compounds featuring amidinate ligands with a C≡C bond, Mo2(NN)4 (I), where NN = N,N'-diphenylphenylpropiolamidinate, and trans-Mo2(NN)2(T(i)PB)2 (II), where T(i)PB = 2,4,6-triisopropylbenzoate, have been prepared and structurally characterized by single-crystal X-ray crystallography. Together with Mo2(DAniF)4 (III), where DAniF = N,N'-bis(p-anisyl)formamidinate, all three compounds have been studied with steady-state UV-vis, IR, and time-resolved spectroscopy methods. I and II display intense metal to ligand charge transfer (MLCT). Singlet state (S1) lifetimes of I-III are determined to be 0.7, 19.1, and 2.0 ps, respectively. All three compounds have long-lived triplet state (T1) lifetimes around 100 μs. In femtosecond time-resolved infrared (fs-TRIR) experiments, one ν(C≡C) band is observed at the S1 state for I but two for II, which indicate different patterns of charge distribution. The electron would have to be localized on one NN ligand in I and partially delocalized over two NN ligands in II to account for the observations. The result is a standard showcase of excited-state mixed valence in coordination compounds.

Large-scale assembly of graphenes in a well-controlled macroscopic fashion is important for practical applications. We have developed a facile and straightforward approach for continuous fabrication of neat, morphology-defined, graphene-based hollow fibers (HFs) via a coaxial two-capillary spinning strategy. With a high throughput, HFs and necklace-like HFs of graphene oxide have been well-controlled produced with the ease of functionalization and conversion to graphene HFs via simply thermal or chemical reduction. This work paves the way toward the mass production of graphene-based HFs with desirable functionalities and morphologies for many of important applications in fluidics, catalysis, purification, separation, and sensing.

Manipulating graphene through engineering for macroscopic assemblies of practical importance is a big challenge. We develop a dually geometric confinement approach for the scalable preparation of meter-long graphene microtubings (μGTs) with a tunable diameter. They have strength comparable to graphene fiber and can be shaped to hierarchical multichannel μGT systems in a straightforward way. Of particular importance, μGTs can be selectively functionalized in a site-specific outer-wall, inner-wall, outer/inner-wall, and within-wall fashion, which endows the μGTs with unique properties for desirable applications. Apart from the magnetically and photoelectronically responsive μGTs developed here, a self-powered micromotor made of Pt inner-wall modified μGT showing agile motion in aqueous medium has been also achieved. Beyond the applications demonstrated in this study, the well-defined μGT systems can also play essential role in other important fields such as fluidics, catalysis, purification, separation, and sensing.