Chelating N‐Heterocyclic Carbene Ligands Enable Tuning of Electrocatalytic CO2 Reduction to Formate and Carbon Monoxide: Surface Organometallic Chemistry

Reported here is the chelate effect as a design principle for tuning heterogeneous catalysts for electrochemical CO₂ reduction. Palladium functionalized with a chelating tris‐N‐heterocyclic carbene (NHC) ligand (Pd‐timtmb^Me) exhibits a 32‐fold increase in activity for electrochemical reduction of CO₂ to C1 products with high Faradaic efficiency (FE_C1=86 %) compared to the parent unfunctionalized Pd foil (FE=23 %), and with sustained activity relative to a monodentate NHC‐ligated Pd electrode (Pd‐mimtmb^Me). The results highlight the contributions of the chelate effect for tailoring and maintaining reactivity at molecular‐materials interfaces enabled by surface organometallic chemistry.     

Unlocking the Electrocatalytic Activity of Antimony for CO2 Reduction by Two‐Dimensional Engineering of the Bulk Material

Two‐dimensional (2D) materials are known to be useful in catalysis. Engineering 3D bulk materials into the 2D form can enhance the exposure of the active edge sites, which are believed to be the origin of the high catalytic activity. Reported herein is the production of 2D “few‐layer” antimony (Sb) nanosheets by cathodic exfoliation. Application of this 2D engineering method turns Sb, an inactive material for CO₂ reduction in its bulk form, into an active 2D electrocatalyst for reduction of CO₂ to formate with high efficiency. The high activity is attributed to the exposure of a large number of catalytically active edge sites. Moreover, this cathodic exfoliation process can be coupled with the anodic exfoliation of graphite in a single‐compartment cell for in situ production of a few‐layer Sb nanosheets and graphene composite. The observed increased activity of this composite is attributed to the strong electronic interaction between graphene and Sb.     

In‐Situ Nanostructuring and Stabilization of Polycrystalline Copper by an Organic Salt Additive Promotes Electrocatalytic CO2 Reduction to Ethylene

Bridging homogeneous molecular systems with heterogeneous catalysts is a promising approach for the development of new electrodes, combining the advantages of both approaches. In the context of CO₂ electroreduction, molecular enhancement of planar copper electrodes has enabled promising advancement towards high Faradaic efficiencies for multicarbon products. Besides, nanostructured copper electrodes have also demonstrated enhanced performance at comparatively low overpotentials. Herein, we report a novel and convenient method for nanostructuring copper electrodes using N,N′‐ethylene‐phenanthrolinium dibromide as molecular additive. Selectivities up to 70 % for C_≥2 products are observed for more than 40 h without significant change in the surface morphology. Mechanistic studies reveal several roles for the organic additive, including: the formation of cube‐like nanostructures by corrosion of the copper surface, the stabilization of these nanostructures during electrocatalysis by formation of a protective organic layer, and the promotion of C_≥2 products.     

Selective Reduction of CO2 to a Formate Equivalent with Heterobimetallic Gold‐ ‐ ‐Copper Hydride Complexes

A series of heterobimetallic complexes containing three‐center, two‐electron Au−H−Cu bonds have been prepared from addition of a parent gold hydride to a bent d¹⁰ copper(I) fragment. These highly unusual heterobimetallic complexes represent a missing link in the widely investigated series of neutral and cationic coinage metal hydride complexes containing Cu−H−Cu and M−H−M⁺ moieties (M=Cu, Ag). The well‐defined heterobimetallic hydride complexes act as precatalysts for the conversion of CO₂ into HCO₂Bpin with HBpin as the reductant. The selectivity of the heterobimetallic complexes for the catalytic production of a formate equivalent surpasses that of the parent monomeric Group 11 complexes.     

Isolated Square‐Planar Copper Center in Boron Imidazolate Nanocages for Photocatalytic Reduction of CO2 to CO

Photocatalytic reduction of CO₂ to value‐added fuel has been considered to be a promising strategy to reduce global warming and shortage of energy. Rational design and synthesis of catalysts to maximumly expose the active sites is the key to activate CO₂ molecules and determine the reaction selectivity. Herein, we synthesize a well‐defined copper‐based boron imidazolate cage (BIF‐29) with six exposed mononuclear copper centers for the photocatalytic reduction of CO₂. Theoretical calculations show a single Cu site including weak coordinated water delivers a new state in the conduction band near the Fermi level and stabilizes the *COOH intermediate. Steady‐state and time‐resolved fluorescence spectra show these Cu sites promote the separation of electron–hole pairs and electron transfer. As a result, the cage achieves solar‐driven reduction of CO₂ to CO with an evolution rate of 3334 μmol g^?1 h^?1 and a high selectivity of 82.6 %.     

From Supramolecular Species to Self‐Templated Porous Carbon and Metal‐Doped Carbon for Oxygen Reduction Reaction Catalysts

The preparation of carbon materials usually involves the decomposition of precursors and the reorganization of the as‐generated fragments. However, the cleavage of bonds and the simultaneous formation of new bonds at nearly the same positions prevents effective yet precise fabrication. Herein, a supramolecular precursor, cucurbit[6]uril, that contains multiple bonds with distinct bond strengths is proposed to decouple the twin problem of simultaneous bond cleavage and formation, allowing multistage transformations to hierarchical porous carbon and metal‐doped carbon in a single yet effective pyrolysis step without the need of a template or additional purification. As a proof‐of‐concept, the Fe‐doped carbon electrocatalysts realized a Pt/C‐like half‐wave potential of 0.869 V vs. RHE and small Tafel slope of 51.3 mV dec^?1 in oxygen reduction reaction.     

A Simple Nanocellulose Coating for Self‐Cleaning upon Water Action: Molecular Design of Stable Surface Hydrophilicity

Coating solid surfaces with cellulose nanofibril (CNF) monolayers via physical deposition was found to keep the surfaces free of a variety of oils, ranging from viscous engine oil to polar n ‐butanol, upon water action. The self‐cleaning function was well correlated with the unique molecular structure of the CNF, in which abundant surface carboxyl and hydroxy groups are uniformly, densely, and symmetrically arranged to form a polar corona on a crystalline nanocellulose strand. This isotropic core–corona configuration offers new and easily adoptable guidance to design self‐cleaning surfaces at the molecular level. Thanks to its excellent self‐cleaning behavior, the CNF coating converted conventional meshes into highly effective membranes for oil–water separation with no prior surface treatment required.     

Aqueous CO2 Reduction with High Efficiency Using α‐Co(OH)2‐Supported Atomic Ir Electrocatalysts

Electrochemical reduction of CO₂ into energy‐dense chemical feedstock and fuels provides an attractive pathway to sustainable energy storage and artificial carbon cycle. Herein, we report the first work to use atomic Ir electrocatalyst for CO₂ reduction. By using α‐Co(OH)₂ as the support, the faradaic efficiency of CO could reach 97.6 % with a turnover frequency (TOF) of 38290 h^?1 in aqueous electrolyte, which is the highest TOF up to date. The electrochemical active area is 23.4‐times higher than Ir nanoparticles (2 nm), which is highly conductive and favors electron transfer from CO₂ to its radical anion (CO₂^.?). Moreover, the more efficient stabilization of CO₂^.? intermediate and easy charge transfer makes the atomic Ir electrocatalyst facilitate CO production. Hence, α‐Co(OH)₂‐supported atomic Ir electrocatalysts show enhanced CO₂ activity and stability.     

Orientation of an Amphiphilic Copolymer to a Lamellar Structure on a Hydrophobic Surface and Implications for CO2 Capture Membranes

The structural orientation of an amphiphilic crystalline polymer to a highly ordered microphase‐separated lamellar structure on a hydrophobic surface is presented. It is formed by the surface graft polymerization of poly(ethylene glycol)behenyl ether methacrylate onto poly(trimethylsilyl) propyne in the presence of allylamine. In particular, allylamine plays a pivotal role in controlling the crystalline phase, configuration, and permeation properties. The resulting materials are effectively used to improve the CO₂ capture property of membranes. Upon the optimization of the reaction conditions, a high CO₂ permeability of 501 Barrer and a CO₂/N₂ ideal selectivity of 77.2 are obtained, which exceed the Robeson upper bound limit. It is inspiring to surpass the upper bound limit via a simple surface modification method.     

Highly Efficient,Selective, and Stable CO2 Electroreduction on a Hexagonal Zn Catalyst

Electrocatalytic CO₂ conversion into fuel is a prospective strategy for the sustainable energy production. However, still many parts of the catalyst such as low catalytic activity, selectivity, and stability are challenging. Herein, a hierarchical hexagonal Zn catalyst showed highly efficient and, more importantly, stable performance as an electrocatalyst for selectively producing CO. Moreover, we found that its high selectivity for CO is attributed to morphology. In electrochemical analysis, Zn (101) facet is favorable to CO formation whereas Zn (002) facet favors the H₂ evolution during CO₂ electrolysis. Indeed, DFT calculations showed that (101) facet lowers a reduction potential for CO₂ to CO by more effectively stabilizing a ^.COOH intermediate than (002) facet. This further suggests that tuning the crystal structure to control (101)/(002) facet ratio of Zn can be considered as a key design principle to achieve a desirable product from Zn catalyst.     

Role of the Adsorbed Oxygen Species in the Selective Electrochemical Reduction of CO2 to Alcohols and Carbonyls on Copper Electrodes

The electrochemical reduction of CO₂ into fuels has gained significant attention recently as source of renewable carbon‐based fuels. The unique high selectivity of copper in the electrochemical reduction of CO₂ to hydrocarbons has called much interest in discovering its mechanism. In order to provide significant information about the role of oxygen in the electrochemical reduction of CO₂ on Cu electrodes, the conditions of the surface structure and the composition of the Cu single crystal electrodes were controlled over time. This was achieved using pulsed voltammetry, since the pulse sequence can be programmed to guarantee reproducible initial conditions for the reaction at every fraction of time and at a given frequency. In contrast to the selectivity of CO₂ reduction using cyclic voltammetry and chronoamperometric methods, a large selection of oxygenated hydrocarbons was found under alternating voltage conditions. Product selectivity towards the formation of oxygenated hydrocarbon was associated to the coverage of oxygen species, which is surface‐structure‐ and potential‐dependent.     

CO2‐Assisted Fabrication of Two‐Dimensional Amorphous Molybdenum Oxide Nanosheets for Enhanced Plasmon Resonances

As a remarkable class of plasmonic materials, two dimensional (2D) semiconductor compounds have attracted attention owing to their controlled manipulation of plasmon resonances in the visible light spectrum, which outperforms conventional noble metals. However, tuning of plasmonic resonances for 2D semiconductors remains challenging. Herein, we design a novel method to obtain amorphous molybdenum oxide (MoO₃) nanosheets, in which it combines the oxidation of MoS₂ and subsequent supercritical CO₂‐treatment, which is a crucial step for the achievement of amorphous structure of MoO₃. Upon illumination, hydrogen‐doped MoO₃ exhibits tuned surface plasmon resonances in the visible and near‐IR regions. Moreover, a unique behavior of the amorphous MoO₃ nanosheets has been found in an optical biosensing system; there is an optimum plasmon resonance after incubation with different BSA concentrations, suggesting a tunable plasmonic device in the near future.