Photochemical Reduction Of CO2 Research Articles

Selective CO2 Photoconversion on Low-Coordinate TiO2

The selective conversion of CO2 into desired hydrocarbon products remains a challenge in photocatalysis. In this issue of Chem, Feng and colleagues report a strong-magnetic-field-assisted strategy for forming active low-coordinate (100) facets on TiO2 nanotubes, enabling selective photoconversion of CO2 into the C2 product C2H5OH under visible light.

Selective photocatalytic reduction of CO2 to CO mediated by a [FeFe]-hydrogenase model with a 1,2-phenylene S-to-S bridge

Photocatalytic reduction of CO2 to CO is a promising approach for storing solar energy in chemicals and mitigating the greenhouse effect of CO2. Our recent studies revealed that [(μ-bdt)Fe2(CO)6] (1, bdt = benzene-1,2-dithiolato), a [FeFe]-hydrogenase model with a rigid and conjugate S-to-S bridge, was catalytically active for the selective photochemical reduction of CO2 to CO, while its analogous complex [(μ-edt)Fe2(CO)6] (2, edt = ethane-1,2-dithiolato) was inactive. In this study, it was found that the turnover number of 1 for CO evolution reached 710 for the 1/[Ru(bpy)3]2+/BIH (BIH = 1,3-dimethyl-2-phenyl-2,3-dihydro-1<I>H</I>-benzo[d]-imidazole) system under optimal conditions over 4.5 h of visible-light irradiation, with a turnover frequency of 7.12 min−1 in the first hour, a high selectivity of 97% for CO, and an internal quantum yield of 2.8%. Interestingly, the catalytic selectivity of 1 can be adjusted and even completely switched in a facile manner between the photochemical reductions of CO2 to CO and of protons to H2 simply by adding different amounts of triethanolamine to the catalytic system. The electron transfer in the photocatalytic system was studied by steady-state fluorescence and transient absorption spectroscopy, and a plausible mechanism for the photocatalytic reaction was proposed.

(Invited) New Directions to Development of Photocatalytic CO2 Reduction

The artificial systems which can convert CO2 to useful and energy-rich compounds by using renewable energy especially solar energy should be developed because the human beings have produced a huge amount of CO2 mainly from fossil resources for making energy. We have been tackling this target by using transition-metal complexes as main players. In this presentation, I mainly talk about three projects, i.e., (1) highly efficient supramolecular photocatalysts with both functions as photosensitizer and catalysts, (2) reduction of low concentration of CO2 using metal-complex catalysts, and (3) photocatalytic CO2 coupled to water oxidation.1. Highly efficient supramolecular photocatalysts for CO2 reduction1 Since CO2 is the most oxidized state of carbon, one-electron reduction of CO2 is an extraordinarily high endergonic reaction. From the viewpoints of low-energy light application, the multi-electron reduction of CO2 via chemical reactions promises to be a more valuable process. This is a main reason why both a photosensitizer and a catalyst are required to promote efficient photocatalytic CO2 reduction.We have developed so-called supramolecular photocatalyts where the photosensitizer and the catalyst are combined to each other with a bridging ligand. This bonding in the supramolecular photocatalysts can accelerate electron transfer between the two components, which improves the performance of the photocatalytic system. In particular, this advantage should be heightened on the surface of photofunctional solid materials as described below.2. Reduction of low concentration of CO2 using metal-complex photocatalysts2 Exhaust gases from such as thermal power plants and iron manufactures contained several % - 20% of CO2. Although several methods such as adsorption and desorption methods using amines and membrane filtration have been already developed for enrichment of CO2, these procedures require high energy consumption. If low concentration of CO2 can be directly reduced by artificial methods, it should give a new direction of researches for artificial photosynthesis.In this presentation, I report such systems using CO2-capturing properties of metal complexes. It has been reported that fac-[ReI(diimine)(CO)3X]n+ can work as both photocatalyst and electrocatalysts for CO2 reduction. We found that the Re complexes also have CO2-capturing properties with the assistance of triethanolamine (TEOA) as shown in the eq.1. Although this reaction is in equilibrium, the equilibrium constant is very large (K = 1.7 x 103 M-1). This means that the Re complex can efficiently capture CO2 from gases containing low concentration of CO2 such as 1% CO2. This type of CO2adducts work as a catalyst for photochemical reduction of CO2. A Ru(II)-Re(I) supramolecular photocatalyst consisting of a [Ru(diimine)3]+ type photosensitizer unit and the Re complex as a catalyst unit efficiently photocatalyzed reduction of low concentration of CO2 (even 1% CO2).3. Photocatalytic CO2 coupled to water oxidation3 The molecular photocatalytic systems have another weakness, i.e., weak oxidation power in the excited state. For practical application, water should be used as an electron donor. For overcoming this problem, we have developed a hybrid system consisting of the supramolecular photocatalyst and semiconductor electrodes. The hybrid photoelectrochemical cell consisting of a NiO-RuRe hybrid photocathode and a CoOx/TaON photoanode showed the activity for visible-light-driven CO2 reduction with water as a reductant to generate CO and O2 (Figure).

Influence of oxygen vacancies on the performance of ZnO nanoparticles towards CO2 photoreduction in different aqueous solutions

CO2 photoreduction is a promising technique for fuel production using semiconductors as photocatalysts. However, introducing defects on the crystal structure of the photocatalysts affects greatly on its photocatalytic activity. In this regard, defected ZnO nanoparticles were synthesized at 300, 350, and 400 °C by thermal decomposition method. XPS data revealed the presence of oxygen vacancies for ZnO samples. These results were furtherly confirmed by Raman, FTIR, and SEM analysis. It was pointed out that Methanol was the major attainable product through the photochemical reduction of CO2 under UV-light. Importantly, the created oxygen vacancies have played a dynamic role in facilitating the charge transfer rather than recombination sites, hence improving the catalytic activity. The highest efficiency was detected over ZnO sample prepared at 350 °C using HCO3− anion in aqueous solution with about 113 umol/g maximum yield of methanol. Different scenarios were discussed implying the synergic effect of anion type and oxygen vacancies. A hypothesis investigation of the reaction mechanism of CO2 photoreduction over ZnO was proposed.

An Electrochemical and Spectroscopic Study on Re(CO)3(L)Cl in Dimethylformamide (L = 2,2'‐Bipyridine)

Herein, we present an in‐depth study of the redox chemistry of Re(CO)3(L)Cl (1) in dimethylformamide (dmf). Previous reports on 1 focused on acetonitrile (MeCN) and tetrahydrofuran (thf) as solvent, although the complex exhibits also a good activity in dmf in the electrochemical and photochemical CO2 reduction reaction. The combination of scan rate dependent CV data and IR spectroelectrochemical (IR‐SEC) experiments allows to derive a mechanistic scenario for the coupled electrochemical and chemical steps after reduction of the title compound. The relative reaction rates of competing pathways are distinctly different with regard to MeCN. The dimer [Re(CO)3(L)]2, which is the main species after initial reduction of 1 in MeCN, is barely formed in dmf and [Re(CO)3(L)Cl]– is stable. IR‐SEC data allowed to identify crucial intermediates alongside the reduction pathway of 1, and digital simulation of the CV data allowed to derive rate constants for the individual reaction steps.

Visible‐Light Photochemical Reduction of CO2 to CO Coupled to Hydrocarbon Dehydrogenation

AbstractResearch on the photochemical reduction of CO2, initiated already 40 years ago, has with few exceptions been performed by using amines as sacrificial reductants. Hydrocarbons are high‐volume chemicals whose dehydrogenation is of interest, so the coupling of a CO2 photoreduction to a hydrocarbon‐photodehydrogenation reaction seems a worthwhile concept to explore. A three‐component construct was prepared including graphitic carbon nitride (g‐CN) as a visible‐light photoactive semiconductor, a polyoxometalate (POM) that functions as an electron acceptor to improve hole–electron charge separation, and an electron donor to a rhenium‐based CO2 reduction catalyst. Upon photoactivation of g‐CN, a cascade is initiated by dehydrogenation of hydrocarbons coupled to the reduction of the polyoxometalate. Visible‐light photoexcitation of the reduced polyoxometalate enables electron transfer to the rhenium‐based catalyst active for the selective reduction of CO2 to CO. The construct was characterized by zeta potential, IR spectroscopy, thermogravimetry, scanning electron microscopy (SEM) and energy dispersive X‐ray spectroscopy (EDS). An experimental Z‐scheme diagram is presented based on electrochemical measurements and UV/Vis spectroscopy. The conceptual advance should promote study into more active systems.

Visible-Light Photochemical Reduction of CO2 to CO Coupled to Hydrocarbon Dehydrogenation.

Research on the photochemical reduction of CO2 , initiated already 40 years ago, has with few exceptions been performed by using amines as sacrificial reductants. Hydrocarbons are high-volume chemicals whose dehydrogenation is of interest, so the coupling of a CO2 photoreduction to a hydrocarbon-photodehydrogenation reaction seems a worthwhile concept to explore. A three-component construct was prepared including graphitic carbon nitride (g-CN) as a visible-light photoactive semiconductor, a polyoxometalate (POM) that functions as an electron acceptor to improve hole-electron charge separation, and an electron donor to a rhenium-based CO2 reduction catalyst. Upon photoactivation of g-CN, a cascade is initiated by dehydrogenation of hydrocarbons coupled to the reduction of the polyoxometalate. Visible-light photoexcitation of the reduced polyoxometalate enables electron transfer to the rhenium-based catalyst active for the selective reduction of CO2 to CO. The construct was characterized by zeta potential, IR spectroscopy, thermogravimetry, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). An experimental Z-scheme diagram is presented based on electrochemical measurements and UV/Vis spectroscopy. The conceptual advance should promote study into more active systems.

Sterically hindered Re- and Mn-CO2 reduction catalysts for solar energy conversion.

Novel molecular Re and Mn tricarbonyl complexes bearing a bipyridyl ligand functionalised with sterically hindering substituents in the 6,6'-position, [M(HPEAB)(CO)3(X)] (M/X = Re/Cl, Mn/Br; HPEAB = 6,6'-{N-(4-hexylphenyl)-N(ethyl)-amido}-2,2'-bipyridine) have been synthesised, fully characterised including by single crystal X-ray crystallography, and their propensity to act as catalysts for the electrochemical and photochemical reduction of CO2 has been established. Controlled potential electrolysis showed that the catalysts are effective for electrochemical CO2-reduction, yielding CO as the product (in MeCN for the Re-complex, in 95 : 5 (v/v) MeCN : H2O mixture for the Mn-complex). The recyclability of the catalysts was demonstrated through replenishment of CO2 within solution. The novel catalysts had similar reduction potentials to previously reported complexes of similar structure, and results of the foot-of-the-wave analysis showed comparable maximum turnover rates, too. The tentative mechanisms for activation of the pre-catalysts were proposed on the basis of IR-spectroelectrochemical data aided by DFT calculations. It is shown that the typical dimerisation of the Mn-catalyst was prevented by incorporation of sterically hindering groups, whilst the Re-catalyst undergoes the usual mechanism following chloride ion loss. No photochemical CO2 reduction was observed for the rhenium complex in the presence of a sacrificial donor (triethylamine), which was attributed to the short triplet excited state lifetime (3.6 ns), insufficient for diffusion-controlled electron transfer. Importantly, [Mn(HPEAB)(CO)3Br] can act as a CO2 reduction catalyst when photosensitised by a zinc porphyrin under red light irradiation (λ > 600 nm) in MeCN : H2O (95 : 5); there has been only one reported example of photoactivating Mn-catalysts with porphyrins in this manner. Thus, this work demonstrates the wide utility of sterically protected Re- and Mn-diimine carbonyl catalysts, where the rate and yield of CO-production can be adjusted based on the metal centre and catalytic conditions, with the advantage of suppressing unwanted side-reactions through steric protection of the vacant coordination site.

Self-assembled CoTiO3 nanorods with controllable oxygen vacancies for the efficient photochemical reduction of CO2 to CO

CoTiO3 with oxygen vacancies was used as a cocatalyst for the photochemical reduction of CO2 to CO. The bond length of the double bond between C and O in CO2 increases from 1.17 Å to 1.25 Å in the activation step.

Integrated nano-architectured photocatalysts for photochemical CO2 reduction.

Recent advances in nanotechnology, especially the development of integrated nanostructured materials, have offered unprecedented opportunities for photocatalytic CO2 reduction. Compared to bulk semiconductor photocatalysts, most of these nanostructured photocatalysts offer at least one advantage in areas such as photogenerated carrier kinetics, light absorption, and active surface area, supporting improved photochemical reaction efficiencies. In this review, we briefly cover the cutting-edge research activities in the area of integrated nanostructured catalysts for photochemical CO2 reduction, including aqueous and gas-phase reactions. Primarily explored are the basic principles of tailor-made nanostructured composite photocatalysts and how nanostructuring influences photochemical performance. Specifically, we summarize the recent developments related to integrated nanostructured materials for photocatalytic CO2 reduction, mainly in the following five categories: carbon-based nano-architectures, metal-organic frameworks, covalent-organic frameworks, conjugated porous polymers, and layered double hydroxide-based inorganic hybrids. Besides the technical aspects of nanostructure-enhanced catalytic performance in photochemical CO2 reduction, some future research trends and promising strategies are addressed.

An artificial photosynthesis system comprising a covalent triazine framework as an electron relay facilitator for photochemical carbon dioxide reduction

A ternary electron transfer relay photocatalytic system for CO2 reduction was fabricated by decorating a porphyrin-based covalent triazine framework with α-Fe2O3 nanoparticles, and then further coupled with a Ru complex photosensitizer.

Unexpected Roles of Triethanolamine in the Photochemical Reduction of CO2 to Formate by Ruthenium Complexes.

A series of 4,4'-dimethyl-2,2'-bipyridyl ruthenium complexes with carbonyl ligands were prepared and studied using a combination of electrochemical and spectroscopic methods with infrared detection to provide structural information on reaction intermediates in the photochemical reduction of CO2 to formate in acetonitrile (CH3CN). An unsaturated 5-coordinate intermediate was characterized, and the hydride-transfer step to CO2 from a singly reduced metal-hydride complex was observed with kinetic resolution. While triethanolamine (TEOA) was expected to act as a proton acceptor to ensure the sacrificial behavior of 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole as an electron donor, time-resolved infrared measurements revealed that about 90% of the photogenerated one-electron reduced complexes undergo unproductive back electron transfer. Furthermore, TEOA showed the ability to capture CO2 from CH3CN solutions to form a zwitterionic alkylcarbonate adduct and was actively engaged in key catalytic steps such as metal-hydride formation, hydride transfer to CO2 to form the bound formate intermediate, and dissociation of formate ion product. Collectively, the data provide an overview of the transient intermediates of Ru(II) carbonyl complexes and emphasize the importance of considering the participation of TEOA when investigating and proposing catalytic pathways.

Photo‐Assisted Electrocatalytic Reduction of CO2: A New Strategy for Reducing Catalytic Overpotentials

AbstractElectrochemical and photochemical reduction of CO2 are both well‐established, independent catalytic routes toward producing added‐value chemicals. The potential for any cross‐reactivity has, however, hardly been explored so far. In this report, we assess a system primarily using spectroelectrochemical monitoring, where photochemistry assists the cathodic activation of precursor complexes fac‐[Mn(CO)3(2,2′‐bipyridine)Br] and [Mo(CO)4(6,6′‐dimethyl‐2,2′‐bipyridine)] to lower the catalytic overpotential needed to trigger the electrocatalytic reduction of CO2 to CO. Following the complete initial 1e− reduction of the parent complexes, the key photochemical cleavage of the Mn−Mn and Mo−CO bonds in the reduction products, [Mn(CO)3(2,2′‐bipyridine)]2 and [Mo(CO)4(6,6′‐dimethyl‐2,2′‐bipyridine)].−, respectively, generates the 2e−‐reduced, 5‐coordinate catalysts, [Mn(CO)3(2,2′‐bipyridine)]− and [Mo(CO)3(6,6′‐dimethyl‐2,2′‐bipyridine)]2− appreciably closer to the initial cathodic wave R1. Experiments under CO2 confirm the activity of both electrocatalysts under the photoirradiation with 405 nm and 365 nm light, respectively. This remarkable achievement corresponds to a ca. 500 mV positive shift of the catalytic onset compared to the exclusive standard electrocatalytic activation.

Magnetic Hollow Spheres Assembled from Graphene-Encapsulated Nickel Nanoparticles for Efficient Photocatalytic CO2 Reduction

The exploitation of efficient, robust, and easily recyclable catalysts is highly desirable for photochemical CO2 reduction to produce fuels and chemicals. Herein, we demonstrate the preparation of Ni@GC magnetic hollow spheres composed of metallic Ni nanoparticles surrounded by few-layered graphitic carbon (GC) for photocatalytic CO2 reduction with high efficiency. The Ni@GC hollow spheres were prepared by thermal annealing a Ni-containing metal–organic framework (Ni-MOF) under N2 atmosphere. A series of physiochemical characterizations reveal that the Ni@GC hollow spheres are successfully synthesized with large surface area and highly porous structure. In the presence of Ni–C bonding, the porous Ni@GC material can efficiently accelerate the separation and transportation of photoexcited charges, as well as improve CO2 adsorption. With the cooperation of a ruthenium photosensitizer under visible light irradiation, the Ni@GC catalyst exhibits a high CO2-to-CO conversion activity, giving a superior CO-produc...

Controlling Hydrogen Evolution during Photoreduction of CO2 to Formic Acid Using [Rh(R-bpy)(Cp*)Cl]+ Catalysts: A Structure-Activity Study.

The photochemical reduction of CO2 to formic acid catalyzed by a series of [Rh(4,4'-R-bpy)(Cp*)Cl]+ and [Rh(5,5'-COOH-bpy)(Cp*)Cl]+ complexes (Cp* = pentamethylcyclopentadienyl, bpy = 2,2'-bipyridine, and R = OCH3, CH3, H, COOC2H5, CF3, NH2, or COOH) was studied to assess how modifications in the electronic structure of the catalyst affect its selectivity, defined as the HCOOH:H2 product ratio. A direct molecular-level influence of the functional group on the initial reaction rate for CO2 versus proton reduction reactions was established. Density functional theory computations elucidated for the first time the respective role of the [RhH] and [Cp*H] tautomers, recognizing rhodium hydride as the key player for both reactions. In particular, our calculations explain the observed tendency of electron-donating substituents to favor CO2 reduction by means of decreasing the hydricity of the Rh-H bond, resulting in a lower hydride transfer barrier toward formic acid production as compared to substituents with an electron-withdrawing nature that favor more strongly the reduction of protons to hydrogen.

An Ir(III) Complex Photosensitizer With Strong Visible Light Absorption for Photocatalytic CO2 Reduction.

A cyclometalated iridium(III) complex having 2-(pyren-1-yl)-4-methylquinoline ligands [Ir(pyr)] has a strong absorption band in the visible region (ε444nm = 67,000 M−1 cm−1) but does not act as a photosensitizer for photochemical reduction reactions in the presence of triethylamine as an electron donor. Here, 1,3-dimethyl-2-(o-hydroxyphenyl)-2,3-dihydro-1H-benzo[d]imidazole (BI(OH)H) was used instead of the amine, demonstrating that BI(OH)H efficiently quenched the excited state of Ir(pyr) and can undergo the photochemical carbon dioxide (CO2) reduction catalyzed by trans(Cl)-Ru(dmb)(CO)2Cl2 (dmb = 4,4′-dimethyl-2,2′-bipyridine, Ru) to produce formate as the main product. We also synthesized a binuclear complex combining Ir(pyr) and Ru via an ethylene bridge and investigated its photochemical CO2 reduction activity in the presence of BI(OH)H.

Bifunctional metal–organic frameworks toward photocatalytic CO2 reduction by post-synthetic ligand exchange

Photocatalytic reduction of CO2 to useful fuel has been identified as a promising strategy to address the energy and environmental issues. Development of well-defined photocatalysts toward CO2 reduction has attracted increasing interest to gain insight into the reactive mechanism. Herein, by post-synthetic ligand exchange, a bifunctional Re-based metal–organic framework (MOF) was successfully prepared. It not only serves as a photosensitizer but also acts as a catalyst for photochemical reduction of CO2. Furthermore, it is found that a Re-based MOF containing 30% Re-based ligands displays improved activity compared to MOF with 100% Re-based ligands. This work provides clues to the design and synthesis of bifunctional MOFs toward photocatalytic CO2 reduction. A bifunctional UiO-67-Re was developed as a photocatalyst for CO2 reduction by post-synthetic ligand exchange strategy. Its synthesis and photocatalytic performance were investigated.

Enhanced photocatalytic reduction of CO2 using CdS/Mn2O3 nanocomposite photocatalysts on porous anodic alumina support with solar concentrators

Photocatalytic reduction of CO2 has gained interest due to dual benefits of reduction of global warming and production of synthetic fuels. In this work, we report photochemical reduction of CO2 using CdS and CdS/Mn2O3 nanocomposites as photocatalyst supported on porous anodic alumnia (PAA) support. Incomplete anodization of an aluminum film substrate leaves a thin layer of aluminum in the middle that improves mechanical integrity and retain electrical conductivity of the support. The rod shaped crystals of CdS, grown on the support’s pore surface form a crumpled sheet like structure that helps in trapping of light energy incident on the catalyst surface. The photocatalytic reduction of CO2 was performed under the direct sunlight, using reflectors like flat mirrors, compound parabola, and concentrating Fresnel lens to direct solar radiation onto the catalytic surface. The combination of Fresnel lens as concentrator and CdS/Mn2O3 nanocomposite as the catalyst gave exceptional increase in the photocatalytic activity when compared with CdS alone, with a peak formation rate of 52.2 μmol/g.cat/hr of C2H5OH, 1392.3 μmol/g.cat/hr of HCOOH and H2 production at the rate of 2766 μmol/g.cat/hr.

Design and Construction of Functional Supramolecular Metalloprotein Assemblies.

Nature puts to use only a small fraction of metal ions in the periodic table. Yet, when incorporated into protein scaffolds, this limited set of metal ions carry out innumerable cellular functions and execute essential biochemical transformations such as photochemical H2O oxidation, O2 or CO2 reduction, and N2 fixation, highlighting the outsized importance of metalloproteins in biology. Not surprisingly, elucidating the intricate interplay between metal ions and protein structures has been the focus of extensive structural and mechanistic scrutiny over the last several decades. As a result of such top-down efforts, we have gained a reasonably detailed understanding of how metal ions shape protein structures and how protein structures in turn influence metal reactivity. It is fair to say that we now have some idea-and in some cases, a good idea-about how most known metalloproteins function and we possess enough insight to quickly assess the modus operandi of newly discovered ones. However, translating this knowledge into an ability to construct functional metalloproteins from scratch represents a challenge at a whole different level: it is one thing to know how an automobile works; it is another to build one. In our quest to build new metalloproteins, we have taken an original approach in which folded, monomeric proteins are used as ligands or synthons for building supramolecular complexes through metal-mediated self-assembly (MDPSA, Metal-Directed Protein Self-Assembly). The interfaces in the resulting protein superstructures are subsequently tailored with covalent, noncovalent, or additional metal-coordination interactions for stabilization and incorporation of new functionalities (MeTIR, Metal Templated Interface Redesign). In an earlier Account, we had described the proof-of-principle studies for MDPSA and MeTIR, using a four-helix bundle, heme protein cytochrome cb562 (cyt cb562), as a model building block. By the end of those studies, we were able to demonstrate that a tetrameric, Zn-directed cyt cb562 complex (Zn4:M14) could be stabilized through computationally prescribed noncovalent interactions inserted into the nascent protein-protein interfaces. In this Account, we first describe the rationale and motivation for our particular metalloprotein engineering strategy and a brief summary of our earlier work. We then describe the next steps in the "evolution" of bioinorganic complexity on the Zn4:M14 scaffold, namely, (a) the generation of a self-standing protein assembly that can stably and selectively bind metal ions, (b) the creation of reactive metal centers within the protein assembly, and (c) the coupling of metal coordination and reactivity to external stimuli through allosteric effects.

Electrochemical and Photochemical Reduction of CO2 Catalyzed by Re(I) Complexes Carrying Local Proton Sources

The novel rhenium complexes fac-Re(pdbpy)(CO)3Cl (pdbpy = 4-phenyl-6-(phenyl-2,6-diol)-2,2′-bipyridine), 1, and fac-Re(ptbpy)(CO)3Cl (ptbpy = 4-phenyl-6-(phenyl-3,4,5-triol)-2,2′-bipyridine), 2, have been synthesized, and the single crystal X-ray diffraction (SC-XRD) structure of 1 was solved. The electrochemical behaviors of the complexes in acetonitrile under Ar and their catalytic performances for CO2 reduction with added water and MeOH are discussed. A detailed IR spectroelectrochemical study under Ar and CO2 atmospheres coupled with DFT calculations allows the identification of reduced species and the interpretation of the reduction mechanisms. Comparison between the rhenium complexes and the corresponding Mn derivatives Mn(pdbpy)(CO)3Br, 3, and Mn(ptbpy)(CO)3Br, 4, has been also considered. Finally, photostimulated conversion of the CO2 was investigated with catalysts (1, 3, and 4) under visible light irradiation (λ > 420 nm) in acetonitrile as solvent. Remarkably, 1 and 3 catalysts were active towa...