Dye and Redox Shuttle Interactions to Promote Fast Electron Transfer in Dye-Sensitized Solar Cells

Harnessing the sun\u27s power using dye-sensitized solar cells (DSCs) is a possible answer to address the energy challenge. Increasing the performance of DSC devices by increasing the rate of productive electron transfers is critically essential. In this regard, to increase the rate of electron transfers from the redox shuttle to the dye, a strategy of coordinating the redox shuttle through non-covalent interactions such as Lewis acid-Lewis base interactions, π-stacking interactions, and halogen bonding interactions to the dye are considered. DSC devices were fabricated using newly synthesized dyes and redox shuttle pairs to study each strategy. The performance of the devices was evaluated using current-voltage measurements, incident photon-to-current conversion efficiency (IPCE), and small modulate photovoltage transient (SMPVT) measurements. Electron transfer kinetics were evaluated using transient absorption spectroscopy (TAS). Results show that dye binding to the redox shuttle via Lewis acid-Lewis base interactions and π-stacking interactions increases dye regeneration rate and dramatically higher DSC device performances are obtained under fluorescent lighting (13.0% PCE with Lewis acid-Lewis base interactions 22.8% with π-stacking interactions). Furthermore, the study of halogen bonding interactions between the dye and redox shuttle shows that stronger halogen bonding interactions lead to less recombination loss and improved open-circuit voltage (VOC) and short-circuit current density (JSC) in DSC

N-heterocyclic carbene gold complexes in a photocatalytic CO2 reduction reaction

Molecular catalysts that are durable and highly selective in the photocatalytic CO2 reduction reaction (PCO2RR) are in high demand. Molecular gold complexes are underexplored in the CO2RR manifold despite heterogeneous gold- CO2 reduction catalyst counterparts being frequently studied. In this report, a series of N-heterocyclic carbene (NHC)-ligated Au complexes are evaluated in the PCO2RR with an added photosensitizer (tris(2-phenylpyridine)iridium, Ir(ppy)3). The complexes were each studied with and without an added activator used to open a coordination site on the Au complexes. Results show an example of an exceptionally durable PCO2RR catalyst lasting >100 h with high product selectivity for CO. Heterogeneity tests reveal no evidence of a nonhomogeneous active catalyst, and structure-activity relationships of the molecular complexes are discussed

Molecular Au(I) Complexes In the Photosensitized Photocatalytic CO\u3csub\u3e2\u3c/sub\u3e Reduction Reaction

Five Au complexes are evaluated for the reduction reaction of CO2 via cyclic voltammetry and in a photocatalytic system. Electrochemically, the complexes were all evaluated for pre-association with CO2 prior to electrochemical reduction and for thermodynamic favorability for CO2 reduction in photocatalytic systems. The complexes were evaluated in photocatalytic reactions using an Ir-based photosensitizer and a sacrificial electron donor for the conversion of CO2 to CO. Au-complex counterion effects on the photocatalytic reaction were analyzed by varying weakly coordinating counterions with significant performance changes noted. At low Au-complex concentrations, a high TON value of 700 was observed

Ruthenium (II) Complexes of CNC Pincers and Bipyridine in the Photocatalytic CO₂ Reduction Reaction to CO Using Visible Light: Catalysis, Kinetics, and Computational Insights

A series of five ruthenium (II) complexes containing a tridentate CNC pincer ligand, a bidentate 2,2′-bipyridine (bpy) ligand, and a monodentate ligand (chloride, bromide, or acetonitrile) were synthesized. The CNC pincer ligands used imidazole or benzimidazole-derived N-heterocyclic carbenes (NHCs) as the C donors and a 4-methoxy-substituted central pyridyl ring as the N donor. All of the complexes were characterized by analytical, spectroscopic, and single-crystal X-ray diffraction methods. These complexes were used as catalysts for visible-light-driven CO2 reduction in the presence and absence of an external photosensitizer (PS). Notably, complex 4C with a benzimidazole-derived CNC pincer ligand and bromide as the monodentate ligand was the most active catalyst tested for both sensitized and self-sensitized CO2 reduction. Thus, this catalyst was the subject of further mechanistic studies using transient absorption spectroscopy (TAS), absorption spectroelectrochemistry (SEC), and computational studies. A mechanism has been proposed for self-sensitized CO2 reduction involving (1) light excitation of the catalyst, (2) reduction by sacrificial donors, (3) halide loss, and (4) CO2 binding to form [RuCO2]+ as the catalyst resting state. The timeline for these steps and the structures of key intermediates are all supported by experimental observations (including TAS and SEC) and supporting computational studies. Subsequent steps in the cycle past [RuCO2]+ were not experimentally observable, but they are supported by computations. Experiments were also used to explain the differences observed for sensitized catalysis. Catalyst 4C is an unusually active catalyst for both sensitized and self-sensitized CO2 reduction, and thus being able to understand how it functions and which steps are turnover-limiting is an important development facilitating the design of commercially viable catalysts for solar fuel formation

Ruthenium (II) Complexes of CNC Pincers and Bipyridine in the Photocatalytic CO₂ Reduction Reaction to CO Using Visible Light: Catalysis, Kinetics, and Computational Insights

A series of five ruthenium (II) complexes containing a tridentate CNC pincer ligand, a bidentate 2,2′-bipyridine (bpy) ligand, and a monodentate ligand (chloride, bromide, or acetonitrile) were synthesized. The CNC pincer ligands used imidazole or benzimidazole-derived N-heterocyclic carbenes (NHCs) as the C donors and a 4-methoxy-substituted central pyridyl ring as the N donor. All of the complexes were characterized by analytical, spectroscopic, and single-crystal X-ray diffraction methods. These complexes were used as catalysts for visible-light-driven CO2 reduction in the presence and absence of an external photosensitizer (PS). Notably, complex 4C with a benzimidazole-derived CNC pincer ligand and bromide as the monodentate ligand was the most active catalyst tested for both sensitized and self-sensitized CO2 reduction. Thus, this catalyst was the subject of further mechanistic studies using transient absorption spectroscopy (TAS), absorption spectroelectrochemistry (SEC), and computational studies. A mechanism has been proposed for self-sensitized CO2 reduction involving (1) light excitation of the catalyst, (2) reduction by sacrificial donors, (3) halide loss, and (4) CO2 binding to form [RuCO2]+ as the catalyst resting state. The timeline for these steps and the structures of key intermediates are all supported by experimental observations (including TAS and SEC) and supporting computational studies. Subsequent steps in the cycle past [RuCO2]+ were not experimentally observable, but they are supported by computations. Experiments were also used to explain the differences observed for sensitized catalysis. Catalyst 4C is an unusually active catalyst for both sensitized and self-sensitized CO2 reduction, and thus being able to understand how it functions and which steps are turnover-limiting is an important development facilitating the design of commercially viable catalysts for solar fuel formation

Ruthenium (II) Complexes of CNC Pincers and Bipyridine in the Photocatalytic CO₂ Reduction Reaction to CO Using Visible Light: Catalysis, Kinetics, and Computational Insights

A series of five ruthenium (II) complexes containing a tridentate CNC pincer ligand, a bidentate 2,2′-bipyridine (bpy) ligand, and a monodentate ligand (chloride, bromide, or acetonitrile) were synthesized. The CNC pincer ligands used imidazole or benzimidazole-derived N-heterocyclic carbenes (NHCs) as the C donors and a 4-methoxy-substituted central pyridyl ring as the N donor. All of the complexes were characterized by analytical, spectroscopic, and single-crystal X-ray diffraction methods. These complexes were used as catalysts for visible-light-driven CO2 reduction in the presence and absence of an external photosensitizer (PS). Notably, complex 4C with a benzimidazole-derived CNC pincer ligand and bromide as the monodentate ligand was the most active catalyst tested for both sensitized and self-sensitized CO2 reduction. Thus, this catalyst was the subject of further mechanistic studies using transient absorption spectroscopy (TAS), absorption spectroelectrochemistry (SEC), and computational studies. A mechanism has been proposed for self-sensitized CO2 reduction involving (1) light excitation of the catalyst, (2) reduction by sacrificial donors, (3) halide loss, and (4) CO2 binding to form [RuCO2]+ as the catalyst resting state. The timeline for these steps and the structures of key intermediates are all supported by experimental observations (including TAS and SEC) and supporting computational studies. Subsequent steps in the cycle past [RuCO2]+ were not experimentally observable, but they are supported by computations. Experiments were also used to explain the differences observed for sensitized catalysis. Catalyst 4C is an unusually active catalyst for both sensitized and self-sensitized CO2 reduction, and thus being able to understand how it functions and which steps are turnover-limiting is an important development facilitating the design of commercially viable catalysts for solar fuel formation