Mechanistic insights into CO conversion to CO using cyano manganese complexes.

Without the use of a photosensitizer, [Mn(bpy)(CO)(CN)] (MnCN) can photochemically form [Mn(bpy)(CO)], the active species for CO reduction. While cases of the axial X-ligand dissociating upon irradiation of -[M(N-N)(CO)X] complexes (M = Mn or Re; N-N = bipyridine (bpy) ligand; X = halogen or pseudohalogen) are well documented, the axial cyanide ligand is retained when either [Mn(bpy)(CO)(CN)] or [Mn(mesbpy)(CO)(CN)], MnCN(mesbpy), are irradiated anaerobically. Infrared and UV-vis spectroscopies indicate the formation of [Mn(bpy)(CO)(MeCN)(CN)] (s-MnCN) as the primary product during the irradiation of MnCN.

Direct Synthesis of 1-Butanol with High Faradaic Efficiency from CO Utilizing Cascade Catalysis at a Ni-Enhanced (CrO)GaO Electrocatalyst.

Electrochemical transformation of CO into energy-dense liquid fuels provides a viable solution to challenges regarding climate change and nonrenewable resource dependence. Here, we report on the modification of a Cr-Ga oxide electrocatalyst through the introduction of nickel to generate a catalyst that generates 1-butanol at unprecedented faradaic efficiencies (ξ = 42%). This faradaic efficiency occurs at -1.

Elucidating the mechanism of photochemical CO reduction to CO using a cyanide-bridged di-manganese complex.

The complex, [{[Mn(bpy)(CO)]}(μ-CN)] (Mn2CN+), has previously been shown to photochemically reduce CO to CO. The detailed mechanism behind its reactivity was not elucidated. Herein, the photoevolution of this reaction is studied in acetonitrile (MeCN) using IR and UV-vis spectroscopy.

Using Light and Electrons to Bend Carbon Dioxide: Developing and Understanding Catalysts for CO Conversion to Fuels and Feedstocks.

Our global society generates an unwieldy amount of CO per unit time. Therefore, the capture of this greenhouse gas must involve a diverse set of strategies. One solution to this problem is the conversion of CO into a more useful chemical species.

Reduction-induced CO dissociation by a [Mn(bpy)(CO)][SbF] complex and its relevance in electrocatalytic CO reduction.

[Mn(bpy)(CO)3Br] is recognized as a benchmark electrocatalyst for CO2 reduction to CO, with the doubly reduced [Mn(bpy)(CO)3]- proposed to be the active species in the catalytic mechanism. The reaction of this intermediate with CO2 and two protons is expected to produce the tetracarbonyl cation, [Mn(bpy)(CO)4]+, thereby closing the catalytic cycle. However, this species has not been experimentally observed.

Elucidating the origins of enhanced CO reduction in manganese electrocatalysts bearing pendant hydrogen-bond donors.

Complexes of the general form [Mn(X)(CO)bpy] (X = a variety of monodentate ligands, bpy = 2,2'-bipyridine) have been reported to act as electrocatalysts for the reduction of CO to CO. In this work, a series of phenol and anisole substituted bipyridine ligands were synthesized and ligated to a manganese metal center in order to probe for an intramolecular hydrogen-bonding interaction in the transition state of CO reduction. Ligands without the ability to intramolecularly hydrogen bond displayed decreased catalytic current density compared to those with the ability to hydrogen bond with CO.

Mechanistic insights into C2 and C3 product generation using NiAl and NiGa electrocatalysts for CO reduction.

Thin films of Ni3Al and Ni3Ga on carbon solid supports have been shown to generate multi-carbon products in electrochemical CO2 reduction, an activity profile that, until recently, was ascribed exclusively to Cu-based catalysts. This catalytic behavior has introduced questions regarding the role of each metal, as well as other system components, during CO2 reduction. Here, the significance of electrode structure and solid support choice in determining higher- versus lower-order reduction products is explored, and the commonly invoked Fischer-Tropsch-type mechanism of CO2 reduction to multi-carbon products is indirectly probed.

Single-Crystal Growth and Characterization of the Chalcopyrite Semiconductor CuInTe for Photoelectrochemical Solar Fuel Production.

Transition-metal chalcogenides are a promising family of materials for applications as photocathodes in photoelectrochemical (PEC) H generation. A long-standing challenge for chalcopyrite semiconductors is characterizing their electronic structure, both experimentally and theoretically, because of their relatively high-energy band gaps and spin-orbit coupling (SOC), respectively. In this work, we present single crystals of CuInTe, whose relatively small optically measured band gap of 0.

A cyanide-bridged di-manganese carbonyl complex that photochemically reduces CO to CO.

Manganese(i) tricarbonyl complexes such as [Mn(bpy)(CO)3L] (L = Br, or CN) are known to be electrocatalysts for CO2 reduction to CO. However, due to their rapid photodegradation under UV and visible light, these monomeric manganese complexes have not been considered as photocatalysts for CO2 reduction without the use of a photosensitizer. In this paper, we report a cyanide-bridged di-manganese complex, {[Mn(bpy)(CO)3]2(μ-CN)}ClO4, which is both electrocatalytic and photochemically active for CO2 reduction to CO.

Design of a Catalytic Active Site for Electrochemical CO2 Reduction with Mn(I)-Tricarbonyl Species.

The design, synthesis, and assessment of a new manganese-centered catalyst for the electrochemical reduction of CO2 is described. The reported species, MnBr(6-(2-hydroxyphenol)-2,2'-bipyridine)(CO)3, includes a ligand framework with a phenolic proton in close proximity to the CO2 binding site, which allows for facile proton-assisted C-O bond cleavage. As a result of this modification, seven times the electrocatalytic current enhancement is observed compared to MnBr(2,2'-bipyridine)(CO)3.

Exploring the effect of axial ligand substitution (X = Br, NCS, CN) on the photodecomposition and electrochemical activity of [MnX(N-C)(CO)3] complexes.

The synthesis, electrochemical activity, and relative photodecomposition rate is reported for four new Mn(i) N-heterocyclic carbene complexes: [MnX(N-ethyl-N'-2-pyridylimidazol-2-ylidine)(CO)3] (X = Br, NCS, CN) and [MnCN(N-ethyl-N'-2-pyridylbenzimidazol-2-ylidine)(CO)3]. All compounds display an electrocatalytic current enhancement under CO2 at the potential of the first reduction, which ranges from -1.53 V to -1.

Anodized indium metal electrodes for enhanced carbon dioxide reduction in aqueous electrolyte.

The interactions of CO2 with indium metal electrodes have been characterized for electrochemical formate production. The electrode oxidation state, morphology, and voltammetric behaviors were systematically probed. It was found that an anodized indium electrode stabilized formate production over time compared to etched indium electrodes and indium electrodes bearing a native oxide in applied potential range of -1.

NHC-containing manganese(I) electrocatalysts for the two-electron reduction of CO2.

The synthesis and characterization of the first catalytic manganese N-heterocyclic carbene complexes are reported: MnBr(N-methyl-N'-2-pyridylbenzimidazol-2-ylidine)(CO)3 and MnBr(N-methyl-N'-2-pyridylimidazol-2-ylidine)(CO)3. Both new species mediate the reduction of CO2 to CO following two-electron reduction of the Mn(I) center, as observed with preparative scale electrolysis and verified with (13)CO2. The two-electron reduction of these species occurs at a single potential, rather than in two sequential steps separated by hundreds of millivolts, as is the case for previously reported MnBr(2,2'-bipyridine)(CO)3.

p-type CuRhO2 as a self-healing photoelectrode for water reduction under visible light.

Polycrystalline CuRhO2 is investigated as a photocathode for the splitting of water under visible irradiation. The band edge positions of this material straddle the water oxidation and reduction redox potentials. Thus, photogenerated conduction band electrons are sufficiently energetic to reduce water, while the associated valence band holes are energetically able to oxidize water to O2.

Direct reduction of carbon dioxide to formate in high-gas-capacity ionic liquids at post-transition-metal electrodes.

As an approach to combat the increasing emissions of carbon dioxide in the last 50 years, the sequestration of carbon dioxide gas in ionic liquids has become an attractive research area. Ionic liquids can be made that possess incredibly high molar absorption and specificity characteristics for carbon dioxide. Their high carbon dioxide solubility and specificity combined with their high inherent electrical conductivity also creates an ideal medium for the electrochemical reduction of carbon dioxide.

Electrochemistry of aqueous pyridinium: exploration of a key aspect of electrocatalytic reduction of CO2 to methanol.

The mechanism by which pyridinium (pyrH(+)) is reduced at a Pt electrode is a matter of recent controversy. The quasireversible cyclic voltammetric wave observed at -0.58 V vs SCE at a Pt electrode was originally proposed to correspond to reduction of pyrH(+) to pyridinyl radical (pyrH(•)).

Electrocatalytic carbon dioxide activation: the rate-determining step of pyridinium-catalyzed CO2 reduction.

The reactivity of reduced pyridinium with CO(2) was investigated as a function of catalyst concentration, temperature, and pressure at platinum electrodes. Concentration experiments show that the catalytic current measured by cyclic voltammetry increases linearly with pyridinium and CO(2) concentrations; this indicates that the rate-determining step is first order in both. The formation of a carbamate intermediate is supported by the data presented.

Using a one-electron shuttle for the multielectron reduction of CO2 to methanol: kinetic, mechanistic, and structural insights.

Pyridinium and its substituted derivatives are effective and stable homogeneous electrocatalysts for the aqueous multiple-electron, multiple-proton reduction of carbon dioxide to products such as formic acid, formaldehyde, and methanol. Importantly, high faradaic yields for methanol have been observed in both electrochemical and photoelectrochemical systems at low reaction overpotentials. Herein, we report the detailed mechanism of pyridinium-catalyzed CO(2) reduction to methanol.

Selective solar-driven reduction of CO2 to methanol using a catalyzed p-GaP based photoelectrochemical cell.

With rising atmospheric CO2 levels, there has been increasing interest in artificial photosynthetic schemes for converting this greenhouse gas into valuable fuels and small organics. Photoelectrochemical schemes for activating the inert CO2 molecule, however, operate at excessive overpotentials and thus do not convert actual light energy to chemical energy. Here we describe the selective conversion of CO2 to methanol at a p-GaP semiconductor electrode with a homogeneous pyridinium ion catalyst, driving the reaction with light energy to yield faradaic efficiencies near 100% at potentials well below the standard potential.

Autoreduction of Pd-Co and Pt-Co cyanogels: exploration of cyanometalate coordination chemistry at elevated temperatures.

Cyanogels are coordination polymers made from the reaction of a chlorometalate and a cyanometalate in aqueous solution, which undergo a sol-gel transition to form stable gels. At temperatures above 240 degrees C, the cyanide ligand acts as a reducing agent and reduces the metal centers to lower oxidation states. To understand the mechanism of the autoreduction, the thermal reduction of the Pd-Co cyanogel system formed by the reaction of PdCl4(2-) and Co(CN)6(3-) was studied in an inert atmosphere.