Urea-Based Multipoint Hydrogen-Bond Donor Additive Promotes Electrochemical CO₂ Reduction Catalyzed by Nickel Cyclam

We report that a urea-based multipoint hydrogen-bond donor additive leads to an enhancement in activity for electrochemical CO₂ reduction to CO catalyzed by Ni cyclam without altering this catalyst’s high selectivity for CO₂ versus proton reduction. Comparison of peak catalytic currents in the presence of a bis­(aryl)­urea additive versus an isostructural amide as a one-point hydrogen-bond counterpart, as well as other weakly coordinating acids with comparable p<i>K</i>_a values, reveals that the urea preferentially augments CO₂ electrocatalysis. This observation suggests that the ability of the urea to form cooperative hydrogen-bond interactions is critical for the observed increases in activity rather than its acidity alone. Indeed, the boost in catalytic activity is observed in acetonitrile electrolyte containing up to 1 M water, indicating the organourea’s role as a cocatalyst rather than a stoichiometric additive. This work establishes a starting point for applying principles of organocatalysis to electrocatalysis, where rational design and implementation of organic additives to electrocatalytic platforms can be a promising avenue to enhance activity and/or control product selectivity without requiring elaborate ligand synthesis

Nanowire–Bacteria Hybrids for Unassisted Solar Carbon Dioxide Fixation to Value-Added Chemicals

Direct solar-powered production of value-added chemicals from CO₂ and H₂O, a process that mimics natural photosynthesis, is of fundamental and practical interest. In natural photosynthesis, CO₂ is first reduced to common biochemical building blocks using solar energy, which are subsequently used for the synthesis of the complex mixture of molecular products that form biomass. Here we report an artificial photosynthetic scheme that functions via a similar two-step process by developing a biocompatible light-capturing nanowire array that enables a direct interface with microbial systems. As a proof of principle, we demonstrate that a hybrid semiconductor nanowire–bacteria system can reduce CO₂ at neutral pH to a wide array of chemical targets, such as fuels, polymers, and complex pharmaceutical precursors, using only solar energy input. The high-surface-area silicon nanowire array harvests light energy to provide reducing equivalents to the anaerobic bacterium, <i>Sporomusa ovata</i>, for the photoelectrochemical production of acetic acid under aerobic conditions (21% O₂) with low overpotential (η < 200 mV), high Faradaic efficiency (up to 90%), and long-term stability (up to 200 h). The resulting acetate (∼6 g/L) can be activated to acetyl coenzyme A (acetyl-CoA) by genetically engineered <i>Escherichia coli</i> and used as a building block for a variety of value-added chemicals, such as <i>n</i>-butanol, polyhydroxybutyrate (PHB) polymer, and three different isoprenoid natural products. As such, interfacing biocompatible solid-state nanodevices with living systems provides a starting point for developing a programmable system of chemical synthesis entirely powered by sunlight

Supramolecular Ga₄L₆^12– Cage Photosensitizes 1,3-Rearrangement of Encapsulated Guest via Photoinduced Electron Transfer

The K₁₂Ga₄L₆ supramolecular cage is photoactive and enables an unprecedented photoreaction not observed in bulk solution. Ga₄L₆^12– cages photosensitize the 1,3-rearrangement of encapsulated cinnamyl­ammonium cation guests from the linear isomer to the higher energy branched isomer when irradiated with UVA light. The rearrangement requires light and guest encapsulation to occur. The Ga₄L₆^12– cage-mediated reaction mechanism was investigated by UV/vis absorption, fluorescence, ultrafast transient absorption, and electrochemical experiments. The results support a photoinduced electron transfer mechanism for the 1,3-rearrangement, in which the Ga₄L₆^12– cage absorbs photons and transfers an electron to the encapsulated cinnamyl­ammonium ion, which undergoes C–N bond cleavage, followed by back electron transfer to the cage and recombination of the guest fragments to form the higher energy isomer

Supramolecular Porphyrin Cages Assembled at Molecular–Materials Interfaces for Electrocatalytic CO Reduction

Conversion of carbon monoxide (CO), a major one-carbon product of carbon dioxide (CO₂) reduction, into value-added multicarbon species is a challenge to addressing global energy demands and climate change. Here we report a modular synthetic approach for aqueous electrochemical CO reduction to carbon–carbon coupled products via self-assembly of supramolecular cages at molecular–materials interfaces. Heterobimetallic cavities formed by face-to-face coordination of thiol-terminated metalloporphyrins to copper electrodes through varying organic struts convert CO to C2 products with high faradaic efficiency (FE = 83% total with 57% to ethanol) and current density (1.34 mA/cm²) at a potential of −0.40 V vs RHE. The cage-functionalized electrodes offer an order of magnitude improvement in both selectivity and activity for electrocatalytic carbon fixation compared to parent copper surfaces or copper functionalized with porphyrins in an edge-on orientation

A Molecular Surface Functionalization Approach to Tuning Nanoparticle Electrocatalysts for Carbon Dioxide Reduction

Conversion of the greenhouse gas carbon dioxide (CO₂) to value-added products is an important challenge for sustainable energy research, and nanomaterials offer a broad class of heterogeneous catalysts for such transformations. Here we report a molecular surface functionalization approach to tuning gold nanoparticle (Au NP) electrocatalysts for reduction of CO₂ to CO. The <i>N</i>-heterocyclic (NHC) carbene-functionalized Au NP catalyst exhibits improved faradaic efficiency (FE = 83%) for reduction of CO₂ to CO in water at neutral pH at an overpotential of 0.46 V with a 7.6-fold increase in current density compared to that of the parent Au NP (FE = 53%). Tafel plots of the NHC carbene-functionalized Au NP (72 mV/decade) vs parent Au NP (138 mV/decade) systems further show that the molecular ligand influences mechanistic pathways for CO₂ reduction. The results establish molecular surface functionalization as a complementary approach to size, shape, composition, and defect control for nanoparticle catalyst design