Herein, an effective tandem catalysis strategy is developed to improve the selectivity of the CO2 RR towards C2 H4 by multiple distinct catalytic sites in local vicinity. An earth-abundant elements-based tandem electrocatalyst PTF(Ni)/Cu is constructed by uniformly dispersing Cu nanoparticles (NPs) on the porphyrinic triazine framework anchored with atomically isolated nickel-nitrogen sites (PTF(Ni)) for the enhanced CO2 RR to produce C2 H4 . The Faradaic efficiency of C2 H4 reaches 57.3 % at -1.1 V versus the reversible hydrogen electrode (RHE), which is about 6 times higher than the non-tandem catalyst PTF/Cu, which produces CH4 as the major carbon product. The operando infrared spectroscopy and theoretic density functional theory (DFT) calculations reveal that the local high concentration of CO generated by PTF(Ni) sites can facilitate the C-C coupling to form C2 H4 on the nearby Cu NP sites. The work offers an effective avenue to design electrocatalysts for the highly selective CO2 RR to produce multicarbon products via a tandem route.

Highly Selective Tandem Electroreduction of CO2 to Ethylene over Atomically Isolated Nickel–Nitrogen Site/Copper Nanoparticle Catalysts

With the disruptive carbon cycle being blamed for global warming, the plausible electrocatalytic CO2 reduction reaction (CO2RR) to form valuable C2+ hydrocarbons and feedstock is becoming a hot topic. Cu-based electrocatalysts have been proven to be excellent CO2RR alternatives for high energy value-added products in this regard. However, the selectivity of CO2RR to form C2+ products via Cu-based catalysts suffers from a high overpotential, slow reaction kinetics, and low selectivity. This review attempts to discuss various cutting-edge strategies for understanding catalytic design such as Cu-based catalyst surface engineering, tuning Cu bandgap via alloying, nanocatalysis, and the effect of the electrolyte and pH on catalyst morphology. The most recent advances in in situ spectroscopy and computational techniques are summarized to fully comprehend reaction mechanisms, structural transformation/degradation mechanisms, and crystal facet loss with subsequent effects on catalyst activity. Furthermore, approaches for tuning Cu interactions are discussed from four key perspectives: single-atom catalysts, interfacial engineering, metal-organic frameworks, and polymer-incorporated materials, which provide new insights into the selectivity of C2+ products. Finally, major challenges are outlined, and potential prospects for the rational design of catalysts for robust CO2RR are proposed. The integration of catalytic design with mechanistic understanding is a step forward in the promising advancement of CO2RR technology for industrial applications.

Electrochemical CO
 2 Reduction to C
 2+ Products Using Cu-Based Electrocatalysts: A Review

Metal-organic frameworks (MOFs) are a new class of porous crystalline materials constructed from organic ligands and metal ions/clusters. Owing to their unique advantages, they have attracted more and more attention in recent years and numerous studies have revealed their great potential in various applications. Many important applications of MOFs inevitably involve harsh alkaline operational environments. To achieve high performance and long cycling life in these applications, high stability of MOFs against bases is necessary. Therefore, the construction of base-stable MOFs has become a critical research direction in the MOF field. This review gives a historic summary of the development of base-stable MOFs in the last few years. The key factors that can determine the robustness of MOFs under basic conditions are analyzed. We also demonstrate the exciting achievements that have been made by utilizing base-stable MOFs in different applications. In the end, we discuss major challenges for the further development of base-stable MOFs. Some possible methods to address these problems are presented.

Construction and application of base-stable MOFs: a critical review.

Major issues in photocatalysis include improving charge carrier separation efficiency at the interface of semiconductor photocatalysts and rationally developing efficient hierarchical heterostructures. Surface continuous growth deposition is used to make hollow Cu2-x S nanoboxes, and then simple hydrothermal reaction is used to make core-shell Cu2-x S@ZnIn2 S4 S-scheme heterojunctions. The photothermal and photocatalytic performance of Cu2-x S@ZnIn2 S4 is improved. In an experimental hydrogen production test, the Cu2-x S@ZnIn2 S4 photocatalyst produces 4653.43 µmol h-1 g-1 of hydrogen, which is 137.6 and 13.8 times higher than pure Cu2-x S and ZnIn2 S4 , respectively. Furthermore, the photocatalyst exhibits a high tetracycline degradation efficiency in the water of up to 98.8%. For photocatalytic reactions, the hollow core-shell configuration gives a large specific surface area and more reactive sites. The photocatalytic response range is broadened, infrared light absorption enhanced, the photothermal effect is outstanding, and the photocatalytic process is promoted. Meanwhile, characterizations, degradation studies, active species trapping investigations, energy band structure analysis, and theoretical calculations all reveal that the S-scheme heterojunction can efficiently increase photogenerated carrier separation. This research opens up new possibilities for future S-scheme heterojunction catalyst design and development.

Hollow Nanoboxes Cu2-x S@ZnIn2 S4 Core-Shell S-Scheme Heterojunction with Broad-Spectrum Response and Enhanced Photothermal-Photocatalytic Performance.

The exploration of novel systems for the electrochemical CO2 reduction reaction (CO2 RR) for the production of hydrocarbons like CH4 remains a giant challenge. Well-designed electrocatalysts with advantages like proton generation/transferring and intermediate-fixating for efficient CO2 RR are much preferred yet largely unexplored. In this work, a kind of Cu-porphyrin-based large-scale (≈1.5 μm) and ultrathin nanosheet (≈5 nm) has been successfully applied in electrochemical CO2 RR. It exhibits a superior FE CH 4 of 70 % with a high current density (-183.0 mA cm-2 ) at -1.6 V under rarely reported neutral conditions and maintains FE CH 4 >51 % over a wide potential range (-1.5 to -1.7 V) in a flow cell. The high performance can be attributed to the construction of numerous hydrogen-bonding networks through the integration of diaminotriazine with Cu-porphyrin, which is beneficial for proton migration and intermediate stabilization, as supported by DFT calculations. This work paves a new way in exploring hydrogen-bonding-based materials as efficient CO2 RR catalysts.

Implanting Numerous Hydrogen-Bonding Networks in a Cu-Porphyrin-Based Nanosheet to Boost CH4 Selectivity in Neutral-Media CO2 Electroreduction.

Conversion from CO2 to C2H4 is important for the development of energy and the environment, but the high energy barrier of hydrogenation of the *CO intermediate and C-C coupling step tend to result in C1 compounds as the main product and thus restrict the generation of C2H4. Here, we report a metal-organic framework (denoted as PcCu-Cu-O), composed of 2,3,9,10,16,17,23,24-octahydroxyphthalo-cyaninato)copper(II) (PcCu-(OH)8) ligands and the square-planar CuO4 nodes, as the electrocatalyst for CO2 to C2H4. Compared with the discrete molecular copper-phthalocyanine (Faradaic efficiency (FE) of C2H4 = 25%), PcCu-Cu-O exhibits much higher performance for electrocatalytic reduction of CO2 to C2H4 with a FE of 50(1)% and a current density of 7.3 mA cm-2 at the potential of -1.2 V vs RHE in 0.1 M KHCO3 solution, representing the best performance reported to date. In-situ infrared spectroscopy and control experiments suggested that the enhanced electrochemical performance may be ascribed to the synergistic effect between the CuPc unit and the CuO4 unit, namely the CO on the CO-producing site (CuO4 site) can efficiently migrate and dimerize with the *CO intermediate adsorbed on the C2H4-producing site (CuPc), giving a lower C-C dimerization energy barrier.

Highly Selective CO2 Electroreduction to C2H4 Using a Metal-Organic Framework with Dual Active Sites.

Reducing CO2 into fuels via photochemical reactions relies on highly efficient photocatalytic systems. Herein, we report a new and efficient photocatalytic system for CO2 reduction. Driven by electrostatic attraction, an anionic metal-organic framework Cu-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) as host and a cationic photosensitizer [Ru(phen)3]2+ (phen = 1,10-phenanthroline) as guest were self-assembled into a photocatalytic system Ru@Cu-HHTP, which showed high activity for photocatalytic CO2 reduction under laboratory light source (CO production rate of 130(5) mmol g-1 h-1, selectivity of 92.9%) or natural sunlight (CO production rate of 69.5 mmol g-1 h-1, selectivity of 91.3%), representing the remarkable photocatalytic CO2 reduction performance. More importantly, the photosensitizer [Ru(phen)3]2+ in Ru@Cu-HHTP is only about 1/500 in quantity reported in the literature. Theoretical calculations and control experiments suggested that the assembly of the catalysts and photosensitizers via electrostatic attraction interactions can provide a better charge transfer efficiency, resulting in high performance for photocatalytic CO2 reduction.

Electrostatic Attraction-Driven Assembly of a Metal-Organic Framework with a Photosensitizer Boosts Photocatalytic CO2 Reduction to CO.

Highly Efficient Electroconversion of CO2 into CH4 by a Metal–Organic Framework with Trigonal Pyramidal Cu(I)N3 Active Sites

A Cu(111)@metal-organic framework as a tandem catalyst for highly selective CO2 electroreduction to C2H4.


 Here, we report a Cu-based metal-organic framework (Cu-DBC), constructed by the large π-conjugated ligand dibenzo-[g,p]chrysene-2,3,6,7,10,11,14,15-octaol and the square-pyramidal CuO5 nodes, as the photo-coupled electrocatalysts for CO2 reduction to CH4. Under visible light, it exhibits high performance for photocatalytic reduction of CO2 to CH4 with selectivity of 100% and rate of 1.04 μmol g-1 h-1, without additional photosensitizer. Importantly, at -1.4 V vs. RHE, it exhibits high performance for photo-coupled electroreduction of CO2 to CH4 with a Faradaic efficiency (CH4) of 93% and current density of 10.4 A g-1. Theoretical calculations, in-situ infrared spectroscopy investigation and Mott–Schottky measurements showed that the large conjugated ligand in Cu-DBC has the suitable lowest unoccupied molecular orbital (LUMO) to match well with the reduction potential of CO2/CH4 and serves as a photoswitch to regulate electron transfer pathway to the metal center, resulting highly selective photocatalytic reduction or photo-coupled electroreduction of CO2 to CH4.

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A large π-conjugated ligand in metal-organic framework as opticalswitch to regulate the electron transfer pathway for highly selective reduction of CO2 to CH4

Hao-Lin Zhu

Papers

Highly Selective CO2 Electroreduction to C2H4 Using a Metal-Organic Framework with Dual Active Sites.

Electrostatic Attraction-Driven Assembly of a Metal-Organic Framework with a Photosensitizer Boosts Photocatalytic CO2 Reduction to CO.

Highly Efficient Electroconversion of CO2 into CH4 by a Metal–Organic Framework with Trigonal Pyramidal Cu(I)N3 Active Sites

A Cu(111)@metal-organic framework as a tandem catalyst for highly selective CO2 electroreduction to C2H4.

A large π-conjugated ligand in metal-organic framework as opticalswitch to regulate the electron transfer pathway for highly selective reduction of CO2 to CH4