Improving CO2 electroconversion by customizing the hydroxyl microenvironment around a semi-open Co-N2O2 configuration.

Constructing local microenvironments is one of the important strategies to improve the electrocatalytic performances, such as in electrochemical CO2 reduction (ECR). However, effectively customizing these microenvironments remains a significant challenge. Herein, utilizing carbon nanotube (CNT) heterostructured semi-open Co-N2O2 catalytic configurations (Co-salophen), we have demonstrated the role of the local microenvironment on promoting ECR through regulating the location of hydroxyl groups. Concretely, compared with the maximum Faradaic efficiency (FE) of 62% for carbon monoxide (CO) presented by Co-salophen/CNT without a hydroxyl microenvironment, the designed Co-salophen-OH3/CNT, featuring hydroxyl groups at the Co-N2O2 structural opening, shows remarkable CO2-to-CO electroreduction activity across a wide potential window, with the FE of CO up to 95%. In particular, through the deuterium kinetic isotope experiments and theoretical calculations, we decoded that the hydroxyl groups act as a proton relay station, promoting the efficient transfer of protons to the Co-N2O2 active sites. The finding demonstrates a promising molecular design strategy for enhancing electrocatalysis.

Enzyme-Inspired Microenvironment Engineering of a Single-Molecular Heterojunction for Promoting Concerted Electrochemical CO2 Reduction.

Challenges remain in the development of novel multifunctional electrocatalysts and their industrial operation on low-electricity pair-electrocatalysis platforms for the carbon cycle. Herein, an enzyme-inspired single-molecular heterojunction electrocatalyst ((NHx )16 -NiPc/CNTs) with specific atomic nickel centers and amino-rich local microenvironments for industrial-level electrochemical CO2 reduction reaction (eCO2 RR) and further energy-saving integrated CO2 electrolysis is designed and developed. (NHx )16 -NiPc/CNTs exhibit unprecedented catalytic performance with industry-compatible current densities, ≈100% Faradaic efficiency and remarkable stability for CO2 -to-CO conversion, outperforming most reported catalysts. In addition to the enhanced CO2 capture by chemisorption, the sturdy deuterium kinetic isotope effect and proton inventory studies sufficiently reveal that such distinctive local microenvironments provide an effective proton ferry effect for improving local alkalinity and proton transfer and creating local interactions to stabilize the intermediate, ultimately enabling the high-efficiency operation of eCO2 RR. Further, by using (NHx )16 -NiPc/CNTs as a bifunctional electrocatalyst in a flow cell, a low-electricity overall CO2 electrolysis system coupling cathodic eCO2 RR with anodic oxidation reaction is developed to achieve concurrent feed gas production and sulfur recovery, simultaneously decreasing the energy input. This work paves the new way in exploring molecular electrocatalysts and electrolysis systems with techno-economic feasibility.

Atomically Structural Regulations of Carbon-Based Single-Atom Catalysts for Electrochemical CO2 Reduction.

The electrochemical carbon dioxide reduction reaction (CO2 RR) converting CO2 into value-added chemicals and fuels to realize carbon recycling is a solution to the problem of renewable energy shortage and environmental pollution. Among all the catalysts, the carbon-based single-atom catalysts (SACs) with isolated metal atoms immobilized on conductive carbon substrates have shown significant potential toward CO2 RR, which intrigues researchers to explore high-performance SACs for fuel and chemical production by CO2 RR. Especially, regulating the coordination structures of the metal centers and the microenvironments of the substrates in carbon-based SACs has emerged as an effective strategy for the tailoring of their CO2 RR catalytic performance. In this review, the current in situ/operando study techniques and the fundamental parameters for CO2 RR performance are first briefly presented. Furthermore, the recent advances in synthetic strategies which regulate the atomic structures of the carbon-based SACs, including heteroatom coordination, coordination numbers, diatomic metal centers, and the microenvironments of substrates are summarized. In particular, the structure-performance relationship of the SACs toward CO2 RR is highlighted. Finally, the inevitable challenges for SACs are outlined and further research directions toward CO2 RR are presented from the perspectives.

Metal-Organic Layers Leading to Atomically Thin Bismuthene for Efficient Carbon Dioxide Electroreduction to Liquid Fuel.

Electrochemical reduction of CO2 to valuable fuels is appealing for CO2 fixation and energy storage. However, the development of electrocatalysts with high activity and selectivity in a wide potential window is challenging. Herein, atomically thin bismuthene (Bi-ene) is pioneeringly obtained by an in situ electrochemical transformation from ultrathin bismuth-based metal-organic layers. The few-layer Bi-ene, which possesses a great mass of exposed active sites with high intrinsic activity, has a high selectivity (ca. 100 %), large partial current density, and quite good stability in a potential window exceeding 0.35 V toward formate production. It even deliver current densities that exceed 300.0 mA cm-2 without compromising selectivity in a flow-cell reactor. Using in situ ATR-IR spectra and DFT analysis, a reaction mechanism involving HCO3 - for formate generation was unveiled, which brings new fundamental understanding of CO2 reduction.

Triazine-Cored Lanthanide-Based Metal-Organic Frameworks Featuring Unique Water Chains and Strong Characteristic Emissions.

A new triazine-cored tricarboxylic acid, N,N',N"-1,3,5-triazine-2,4,6-triyltris(cis-4-aminocyclohexane-carboxylic acid) (H3 L), has been prepared by replacing the chlorine atoms of cyanuric chloride with cis-4-aminocyclohexane-carboxylic acid, which has been used for the construction of a series of triazine-cored lanthanide-based metal-organic frameworks (MOFs). All these MOFs were structurally authenticated, revealing that they are isostructural and exist as two-dimensional (2D) coordination networks with the general formula [Ln(L)(H2 O)2 ]⋅5.5 H2 O (Ln=1⋅Gd, 2⋅Tb, 3⋅Eu). A unique one-dimensional water chain, composed of primary tetrameric cyclic rings and dodecameric cyclic rings, has been found entrapped in the lattice. Moreover, all these compounds display bright characteristic photoluminescence. Particularly, for 1, apart from the strong blue emission peak (Φf =20.6 %) corresponding to the intraligand transition under near-UV excitation, the characteristic emissions of Gd3+ cation (Φf =5.0 %) were unexpectedly observed upon excitation at 273 nm.