Conjugated molecular wires of rhenium bipyridine complexes were grown on flexible, lightweight, carbon-cloth electrodes through reductive diazonium electropolymerization. CO2 electrolysis studies ...reveal rapid (k cat ∼ 40 s–1) and selective (Faradaic efficiency >99%) conversion to CO with turnover numbers (TON) per rhenium site reaching ∼290 000 and catalytic currents (i cat) > 10 mA/cm2. This represents over an 80-fold increase in activity relative to our prior graphite systems and an ∼25-fold increase relative to the highest-performing immobilized rhenium bipyridine catalyst to date under analogous electrolysis conditions while maintaining prolonged activity. The high activity of these electrodes is explained by a mechanism initiated via electrochemical charging of the π-conjugated backbone followed by anion dissociation, CO2 coordination, and protonation. As numerous metal-bipyridine complexes are known for a broad scope of electrocatalytic transformations, these integrated carbon-cloth devices are anticipated to serve as a platform for future studies.
A cobalt complex supported by the 2-(diisopropylphosphaneyl)benzenethiol ligand was synthesized and its electronic structure and reactivity were explored. X-ray diffraction studies indicate a square ...planar geometry around the cobalt center with a trans arrangement of the phosphine ligands. Density functional theory calculations and electronic spectroscopy measurements suggest a mixed metal-ligand orbital character, in analogy to previously studied dithiolene and diselenolene systems. Electrochemical studies in the presence of 1 atm of CO
2
and Brønsted acid additives indicate that the cobalt complex generates syngas, a mixture of H
2
and CO, with faradaic efficiencies up to >99%. The ratios of H
2
: CO generated vary based on the additive. A H
2
: CO ratio of ∼3 : 1 is generated when H
2
O is used as the Brønsted acid additive. Chemical reduction of the complex indicates a distortion towards a tetrahedral geometry, which is rationalized with DFT predictions as attributable to the populations of orbitals with σ*(Co-S) character. A mechanistic scheme is proposed whereby competitive binding between a proton and CO
2
dictates selectivity. This study provides insight into the development of a catalytic system incorporating non-innocent ligands with pendant base moieties for electrochemical syngas production.
A cobalt complex supported by the 2-(diisopropylphosphaneyl)benzenethiol ligand was synthesized and its electronic structure and reactivity were explored.
Co(bds)
nBu
N (where bds = 1,2-benzenediselenolate) was identified as an electrocatalyst for the hydrogen evolution reaction. Mechanistic studies indicated that a black precipitate, which formed upon ...treating Co(bds)
with acid, as well as the one-electron reduced species, Co(bds)
, were viable catalytic intermediates. We propose two kinetically-competent pathways for H
evolution: EC and CE (E = electrochemical, C = chemical step).
Co(bds)2nBu4N (where bds = 1,2-benzenediselenolate) was identified as an electrocatalyst for the hydrogen evolution reaction. Mechanistic studies indicated that a black precipitate, which formed upon ...treating Co(bds)2- with acid, as well as the one-electron reduced species, Co(bds)22-, were viable catalytic intermediates. We propose two kinetically-competent pathways for H2 evolution: EC and CE (E = electrochemical, C = chemical step).
The solar-driven conversion of CO2 to value-added products provides a promising route for solar energy storage and atmospheric CO2 remediation. In this report, a variety of supporting electrode ...materials were successfully modified with a 2,2′-bipyridine-5,5′-bis(diazonium) rhenium complex through a surface-localized electropolymerization method. Physical characterization of the resulting multilayer films confirms that the coordination environments of the rhenium bipyridine tricarbonyl sites are preserved upon immobilization and that the polymerized catalyst moieties exhibit long-range structural order with uniform film growth. UV–vis studies reveal additional absorption bands in the visible region for the polymeric films that are not present in the analogous rhenium bipyridine complexes. Electrochemical studies with modified graphite rod electrodes show that the electrocatalytic activity of these films increases with catalyst loading up to an optimal value, beyond which electron and mass transport through the material become rate-limiting. Electrocatalytic studies performed at −2.25 V vs Fc/Fc+ for 2 h reveal CO production with faradaic efficiencies and turnover numbers up to 99% and 3606, respectively. Photocatalytic studies of the modified TiO2 devices demonstrate enhanced activity at low catalyst loadings, with turnover numbers up to 70 during 5 h of irradiation.
The reduction of CO2 into higher energy products such as carbon-based fuels and feedstocks is an attractive strategy for mitigating the continuous rise in CO2 emissions associated with the growing ...global energy demand. Rhenium tricarbonyl complexes bearing 2,2'-bipyridine (2,2'-bpy) ligands are well-established molecular electrocatalysts for the selective reduction of CO2 to CO. Construction of efficient devices for this electrochemical process requires the immobilization of electrocatalysts to electrode surfaces. To integrate Re(2,2'-bpy)(CO)3 fragments into a covalent organic framework (COF), Re(5,5'-diamine-2,2'-bpy)(CO)3Cl (1) was synthesized and electrochemically investigated. Complex 1 is an active and selective electrocatalyst for the reduction of CO2 to CO with excellent faradaic efficiency (99%). The presence of the amine substituents leads to a destabilization of the π* orbital of the 5,5'-diamine-2,2'-bpy ligand with respect to the metal center. Therefore, 1 requires more negative potentials (-2.47 V vs. Fc+/0) to reach the doubly reduced catalytically active species. DFT studies were conducted to understand the electronic structure of 1, and support the destabilizing effect of the amine substituents. The Re-2,2'-bpy fragments were successfully integrated into a COF containing 2,2'-bpy moieties (COF-2,2'-bpy) via a post-metallation synthetic route to generate COF-2,2'-bpy-Re. A composite of COF-2,2'-bpy-Re, carbon black, and polyvinylidene fluoride (PVDF) was readily immobilized onto glassy carbon electrodes and electrocatalytic CO2 reduction to CO was observed at -2.8 V vs. Fc0/+, with a faradaic efficiency of 81% for CO production.
A search for mixing between active neutrinos and light sterile neutrinos has been performed by looking for muon neutrino disappearance in two detectors at baselines of 1.04 and 735 km, using a ...combined MINOS and MINOS+ exposure of 16.36×10^{20} protons on target. A simultaneous fit to the charged-current muon neutrino and neutral-current neutrino energy spectra in the two detectors yields no evidence for sterile neutrino mixing using a 3+1 model. The most stringent limit to date is set on the mixing parameter sin^{2}θ_{24} for most values of the sterile neutrino mass splitting Δm_{41}^{2}>10^{-4} eV^{2}.
We report on a new analysis of neutrino oscillations in MINOS using the complete set of accelerator and atmospheric data. The analysis combines the ν(μ) disappearance and ν(e) appearance data using ...the three-flavor formalism. We measure |Δm(32)(2)| = 2.28-2.46 × 10(-3) eV(2) (68% C.L.) and sin(2)θ(23) = 0.35-0.65 (90% C.L.) in the normal hierarchy, and |Δm(32)(2)| = 2.32-2.53 × 10(-3) eV(2) (68% C.L.) and sin(2)θ(23) = 0.34-0.67 (90% C.L.) in the inverted hierarchy. The data also constrain δ(CP), the θ(23} octant degeneracy and the mass hierarchy; we disfavor 36% (11%) of this three-parameter space at 68% (90%) C.L.
We report measurements of oscillation parameters from ν(μ) and ν(μ) disappearance using beam and atmospheric data from MINOS. The data comprise exposures of 10.71×10(20) protons on target in the ...ν(μ)-dominated beam, 3.36×10(20) protons on target in the ν(μ)-enhanced beam, and 37.88 kton yr of atmospheric neutrinos. Assuming identical ν and ν oscillation parameters, we measure |Δm2| = (2.41(-0.10)(+0.09))×10(-3) eV2 and sin2(2θ) = 0.950(-0.036)(+0.035). Allowing independent ν and ν oscillations, we measure antineutrino parameters of |Δm2| = (2.50(-0.25)(+0.23))×10(-3) eV2 and sin2(2θ) = 0.97(-0.08)(+0.03), with minimal change to the neutrino parameters.
We report results of a search for oscillations involving a light sterile neutrino over distances of 1.04 and 735 km in a ν_{μ}-dominated beam with a peak energy of 3 GeV. The data, from an exposure ...of 10.56×10^{20} protons on target, are analyzed using a phenomenological model with one sterile neutrino. We constrain the mixing parameters θ_{24} and Δm_{41}^{2} and set limits on parameters of the four-dimensional Pontecorvo-Maki-Nakagawa-Sakata matrix, |U_{μ4}|^{2} and |U_{τ4}|^{2}, under the assumption that mixing between ν_{e} and ν_{s} is negligible (|U_{e4}|^{2}=0). No evidence for ν_{μ}→ν_{s} transitions is found and we set a world-leading limit on θ_{24} for values of Δm_{41}^{2}≲1 eV^{2}.
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