Covalently Grafting Cobalt Porphyrin onto Carbon Nanotubes for Efficient CO2 Electroreduction

Constructing Co4(SO4)4 Clusters within Metal-Organic Frameworks for Efficient Oxygen Electrocatalysis

Multinuclear metal clusters are ideal candidates to catalyze small molecule activation reactions involving the transfer of multiple electrons. However, synthesizing active metal clusters is a big challenge. Herein, on constructing an unparalleled Co4(SO4)4 cluster within porphyrin-based metal-organic frameworks (MOFs) and the electrocatalytic features of such Co4(SO4)4 clusters for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is reported. The reaction of CoII sulfate and metal complexes of tetrakis(4-pyridyl)porphyrin under solvothermal conditions afforded Co4-M-MOFs (M═Co, Cu, and Zn). Crystallographic studies revealed that these Co4-M-MOFs have the same framework structure, having the Co4(SO4)4 clusters connected by metalloporphyrin units through Co─Npyridyl bonds. In the Co4(SO4)4 cluster, the four CoII ions are chemically and symmetrically equivalent and are each coordinated with four sulfate O atoms to give a distorted cube-like structure. Electrocatalytic studies showed that these Co4-M-MOFs are all active for electrocatalytic OER and ORR. Importantly, by regulating the activity of the metalloporphyrin units, it is confirmed that the Co4(SO4)4 cluster is active for oxygen electrocatalysis. With the use of Co porphyrins as connecting units, Co4-Co-MOF displays the highest electrocatalytic activity in this series of MOFs by showing a 10 mA cm-2 OER current density at 357 mV overpotential and an ORR half-wave potential at 0.83 V versus reversible hydrogen electrode (RHE). Theoretical studies revealed the synergistic effect of two proximal Co atoms in the Co4(SO4)4 cluster in OER by facilitating the formation of O─O bonds. This work is of fundamental significance to present the construction of Co4(SO4)4 clusters in framework structures for oxygen electrocatalysis and to demonstrate the cooperation between two proximal Co atoms in such clusters during the O─O bond formation process.

Nonidealities in CO2 Electroreduction Mechanisms Revealed by Automation-Assisted Kinetic Analysis

In electrocatalysis, mechanistic analysis of reaction rate data often relies on the linearization of relatively simple rate equations; this is the basis for typical Tafel and reactant order dependence analyses. However, for more complex reaction phenomena, such as surface coverage effects or mixed control, these common linearization strategies will yield incomplete or uninterpretable results. Cohesive kinetic analysis, which is often used in thermocatalysis and involves quantitative model fitting for data collected over a wide range of reaction conditions, requires more data but also provides a more robust strategy for interrogating reaction mechanisms. In this work, we report a robotic system that improves the experimental workflow for collecting electrochemical rate data by automating sequential testing of up to 10 electrochemical cells, where each cell can have a different electrode, electrolyte, gas-phase reactant composition, and applied voltage. We used this system to investigate the mechanism of carbon dioxide electroreduction to carbon monoxide at several immobilized metal tetrapyrroles. Specifically, at cobalt phthalocyanine (CoPc), cobalt tetraphenylporphyrin (CoTPP), and iron phthalocyanine (FePc), we see signatures of complex reaction mechanisms, where observed bicarbonate and CO2 order dependences change with applied potential. We illustrate how phenomena such as electrolyte poisoning and potential-dependent degrees of rate control can explain the observed kinetic behaviors. Our mechanistic analysis suggests that CoPc and CoTPP share a similar reaction mechanism, akin to one previously proposed, whereas the mechanism for FePc likely involves a species later in the catalytic cycle as the most abundant reactive intermediate. Our study illustrates that complex reaction mechanisms that are not amenable to common Tafel and order dependence analyses may be quite prevalent across this class of immobilized metal tetrapyrrole electrocatalysts.

Experimentally validating sabatier plot by molecular level microenvironment customization for oxygen electroreduction

Microenvironmental modifications on metal sites are crucial to tune oxygen reduction catalytic behavior and decrypt intrinsic mechanism, whereas the stochastic properties of traditional pyrolyzed single-atom catalysts induce vague recognition on structure-reactivity relations. Herein, we report a theoretical descriptor relying on binding energies of oxygen adsorbates and directly associating the derived Sabatier volcano plot with calculated overpotential to forecast catalytic efficiency of cobalt porphyrin. This Sabatier volcano plot instructs that electron-withdrawing substituents mitigate the over-strong *OH intermediate adsorption by virtue of the decreased proportion of electrons in bonding orbital. To experimentally validate this speculation, we implement a secondary sphere microenvironment customization strategy on cobalt porphyrin-based polymer nanocomposite analogs. Systematic X-ray spectroscopic and in situ electrochemical characterizations capture the pronounced accessible active site density and the fast interfacial/outward charge migration kinetics contributions for the optimal carboxyl group-substituted catalyst. This work offers ample strategies for designing single-atom catalysts with well-managed microenvironment under the guidance of Sabatier volcano map.

Mitigating Cobalt Phthalocyanine Aggregation in Electrocatalyst Films through Codeposition with an Axially Coordinating Polymer

Cobalt phthalocyanine (CoPc) is a promising molecular catalyst for aqueous electroreduction of CO2, but its catalytic activity is limited by aggregation at high loadings. Codeposition of CoPc onto electrode surfaces with the coordinating polymer poly(4-vinylpyridine) (P4VP) mitigates aggregation in addition to providing other catalytic enhancements. Transmission and diffuse reflectance UV-vis measurements demonstrate that a combination of axial coordination and π-stacking effects from pyridyl moieties in P4VP serve to disperse cobalt phthalocyanine in deposition solutions and help prevent reaggregation in deposited films. Polymers lacking axial coordination, such as Nafion, are significantly less effective at cobalt phthalocyanine dispersion in both the deposition solution and in the deposited films. SEM images corroborate these findings through particle counts and morphological analysis. Electrochemical measurements show that CoPc codeposited with P4VPonto carbon electrode surfaces reduces CO2 with higher activity and selectivity compared to the catalyst codeposited with Nafion.

Constructing Ionic Interfaces for Stable Electrochemical CO2 Reduction

The electrochemical CO2 reduction reaction (CO2RR) has emerged as a promising approach for sustainable carbon cycling and valuable chemical production. Various methods and strategies have been explored to boost CO2RR performance. One of the most promising strategies includes the construction of stable ionic interfaces on metallic or molecular catalysts using organic or inorganic cations, which has demonstrated a significant improvement in catalytic performance. The stable ionic interface is instrumental in adjusting adsorption behavior, influencing reactive intermediates, facilitating mass transportation, and suppressing the hydrogen evolution reaction, particularly under acidic conditions. In this Perspective, we provide an overview of the recent advancements in building ionic interfaces in the electrocatalytic process and discuss the application of this strategy to improve the CO2RR performance of metallic and molecular catalysts. We aim to convey the future trends and opportunities in creating ionic interfaces to further enhance carbon utilization efficiency and the productivity of CO2RR products. The emphasis of this Perspective lies in the pivotal role of ionic interfaces in catalysis, providing a valuable reference for future research in this critical field.

Bridging molecular photosensitizer and catalyst on carbon nanotubes toward enhanced selectivity and durability for CO2 photoreduction

Homogenous molecular photocatalysts for CO2 reduction, especially metal complex-based photosensitizer‒catalyst assemblages, have been attracting extensive research interests due to their efficiency and customizability. However, their low durability and recyclability limit practical applications. In this work, we immobilized the catalysts of metal terpyridyl complexes and the photosensitizer of [Ru(bpy)3]Cl2 onto the surface of carbon nanotubes through covalent bonds and electrostatic interactions, respectively, transforming the homogeneous system into a heterogeneous one. Our characterizations prove that these metal complexes are well dispersed on CNTs with a high loading (ca. 12 wt.%). Photocatalytic measurements reveal that catalytic activity is remarkably enhanced when the molecular catalysts are anchored, which is three times higher than that of homogeneous molecular catalysts. Moreover, when the photosensitizer of [Ru(bpy)3]Cl2 is immobilized, the side reaction of hydrogen evolution is completely suppressed and the selectivity for CO production reaches 100%, with its durability also significantly improved. This work provides an effective pathway for constructing heterogeneous photocatalysts based on rational assembly of efficient molecular photosensitizers and catalysts.

Novel metalloporphyrin covalently functionalized polyphosphazene nanotubes for boosting the hydrogen evolution reaction

Herein, we demonstrate the first example of a novel electrocatalytic hybrid system (CoTPP-PZSNT) with a push-pull motif to boost hydrogen evolution reaction (HER) activity. CoTPP-PZSNT exhibits an efficient HER activity, with overpotentials of 157 and 109 mV at 10 mA cm-2 in 1.0 M KOH and 0.5 M H2SO4 solutions, respectively. The HER performance of CoTPP-PZSNT outperforms many previously reported HER catalysts, due to efficient charge transfer between each component.

Surface modified copper foam with cobalt phthalocyanine carbon nanotube hybrids for tuning CO2 reduction reaction products

The CO2 reduction reaction (CO2RR) is a feasible way to convert this greenhouse gas into molecules of industrial interest. Herein we present the modification of the Cu foam cathode using molecular catalyst hybrid from cobalt phthalocyanine (CoPc) to increase selectivity and stability towards CO2RR products in a flow cell setup.

Porous Fe-Porphyrin as an Efficient Adsorbent for the Removal of Ciprofloxacin from Water

Antibiotics are widely used in medicine, but they are not fully metabolized in the body and can end up in wastewater. Conventional wastewater treatment methods fail to completely remove antibiotic residues, which can then enter rivers and streams. Adsorption is a promising technique for removing antibiotics from wastewater, even at low concentrations. The successful one-pot synthesis of an adsorbent, iron-containing porphyrin-based porous organic polymer (Fe-POP), was achieved through the reaction of pyrrole groups and terephthalaldehyde in the presence of FeCl3. Characterized by a substantial BET surface area of 597 m2 g-1, Fe-POP was systematically investigated for its adsorption potential in the removal of the antibiotic Ciprofloxacin (CIP) from aqueous solutions. By systematic variation of key parameters, including pH, adsorbent loading, and CIP concentration, the adsorption conditions were optimized. Under the optimal conditions at pH = 3, CIP concentration of 5 ppm, and 25 mg of Fe-POP, the maximum adsorption capacity reached an impressive 263 mg g-1. The robust adsorption behavior was elucidated through the fitting of experimental data to the Langmuir adsorption isotherm (R2 = 0.962) and the pseudo-second-order kinetic model (R2 = 0.999) with lower error values. These models suggested that the adsorption process predominantly involved chemical interactions between CIP molecules and the Fe-POP surface. Fe-POP exhibited a robust structure with a high adsorption capacity, showcasing its efficacy in removing CIP contaminants from water. Therefore, Fe-POP can be considered a valuable adsorbent for water treatment applications, specifically for antibiotic removal.

Electronic Structure Design of Transition Metal-Based Catalysts for Electrochemical Carbon Dioxide Reduction

With the increasingly serious greenhouse effect, the electrochemical carbon dioxide reduction reaction (CO2RR) has garnered widespread attention as it is capable of leveraging renewable energy to convert CO2 into value-added chemicals and fuels. However, the performance of CO2RR can hardly meet expectations because of the diverse intermediates and complicated reaction processes, necessitating the exploitation of highly efficient catalysts. In recent years, with advanced characterization technologies and theoretical simulations, the exploration of catalytic mechanisms has gradually deepened into the electronic structure of catalysts and their interactions with intermediates, which serve as a bridge to facilitate the deeper comprehension of structure-performance relationships. Transition metal-based catalysts (TMCs), extensively applied in electrochemical CO2RR, demonstrate substantial potential for further electronic structure modulation, given their abundance of d electrons. Herein, we discuss the representative feasible strategies to modulate the electronic structure of catalysts, including doping, vacancy, alloying, heterostructure, strain, and phase engineering. These approaches profoundly alter the inherent properties of TMCs and their interaction with intermediates, thereby greatly affecting the reaction rate and pathway of CO2RR. It is believed that the rational electronic structure design and modulation can fundamentally provide viable directions and strategies for the development of advanced catalysts toward efficient electrochemical conversion of CO2 and many other small molecules.

Backbone Engineering of Polymeric Catalysts for High-Performance CO2 Reduction in Bipolar Membrane Zero-Gap Electrolyzer

Bipolar membranes (BPMs) have emerged as a promising solution for mitigating CO2 losses, salt precipitation and high maintenance costs associated with the commonly used anion-exchange membrane electrode assembly for CO2 reduction reaction (CO2RR). However, the industrial implementation of BPM-based zero-gap electrolyzer is hampered by the poor CO2RR performance, largely attributed to the local acidic environment. Here, we report a backbone engineering strategy to improve the CO2RR performance of molecular catalysts in BPM-based zero-gap electrolyzers by covalently grafting cobalt tetraaminophthalocyanine onto a positively charged polyfluorene backbone (PF-CoTAPc). PF-CoTAPc shows a high acid tolerance in BPM electrode assembly (BPMEA), achieving a high FE of 82.6 % for CO at 100 mA/cm2 and a high CO2 utilization efficiency of 87.8 %. Notably, the CO2RR selectivity, carbon utilization efficiency and long-term stability of PF-CoTAPc in BPMEA outperform reported BPM systems. We attribute the enhancement to the stable cationic shield in the double layer and suppression of proton migration, ultimately inhibiting the undesired hydrogen evolution and improving the CO2RR selectivity. Techno-economic analysis shows the least energy consumption (957 kJ/mol) for the PF-CoTAPc catalyst in BPMEA. Our findings provide a viable strategy for designing efficient CO2RR catalysts in acidic environments.

Uncoordinated amino groups of MIL-101 anchoring cobalt porphyrins for highly selective CO2 electroreduction

Electrocatalytic carbon dioxide reduction reaction (CO2RR) presents a sustainable route to address energy crisis and environmental issues, where the rational design of catalysts remains crucial. Metal-organic frameworks (MOFs) with high CO2 capture capacities have immense potential as CO2RR electrocatalysts but suffer from poor activity. Herein we report a redox-active cobalt protoporphyrin grafted MIL-101(Cr)-NH2 for CO2 electroreduction. Material characterizations reveal that porphyrin molecules are covalently attached to uncoordinated amino groups of the parent MOF without compromising its well-defined porous structure. Furthermore, in situ spectroscopic techniques suggest inherited CO2 concentrate ability and more abundant adsorbed carbonate species on the modified MOF. As a result, a maximum CO Faradaic efficiency (FECO) up to 97.1% and a turnover frequency of 0.63 s-1 are achieved, together with FECO above 90% within a wide potential window of 300 mV. This work sheds new light on the coupling of MOFs with molecular catalysts to enhance catalytic performances.

A replacement strategy for regulating local environment of single-atom Co-SxN4-x catalysts to facilitate CO2 electroreduction

The performances of single-atom catalysts are governed by their local coordination environments. Here, a thermal replacement strategy is developed for the synthesis of single-atom catalysts with precisely controlled and adjustable local coordination environments. A series of Co-SxN4-x (x = 0, 1, 2, 3) single-atom catalysts are successfully synthesized by thermally replacing coordinated N with S at elevated temperature, and a volcano relationship between coordinations and catalytic performances toward electrochemical CO2 reduction is observed. The Co-S1N3 catalyst has the balanced COOH*and CO* bindings, and thus locates at the apex of the volcano with the highest performance toward electrochemical CO2 reduction to CO, with the maximum CO Faradaic efficiency of 98 ± 1.8% and high turnover frequency of 4564 h-1 at an overpotential of 410 mV tested in H-cell with CO2-saturated 0.5 M KHCO3, surpassing most of the reported single-atom catalysts. This work provides a rational approach to control the local coordination environment of the single-atom catalysts, which is important for further fine-tuning the catalytic performance.

Multiscale CO2 Electrocatalysis to C2+ Products: Reaction Mechanisms, Catalyst Design, and Device Fabrication

Electrosynthesis of value-added chemicals, directly from CO2, could foster achievement of carbon neutral through an alternative electrical approach to the energy-intensive thermochemical industry for carbon utilization. Progress in this area, based on electrogeneration of multicarbon products through CO2 electroreduction, however, lags far behind that for C1 products. Reaction routes are complicated and kinetics are slow with scale up to the high levels required for commercialization, posing significant problems. In this review, we identify and summarize state-of-art progress in multicarbon synthesis with a multiscale perspective and discuss current hurdles to be resolved for multicarbon generation from CO2 reduction including atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes, and macroscale electrolyzers with guidelines for future research. The review ends with a cross-scale perspective that links discrepancies between different approaches with extensions to performance and stability issues that arise from extensions to an industrial environment.

In situ Electropolymerized 3D Microporous Cobalt-Porphyrin Nanofilm for Highly Effective Molecular Electrocatalytic Reduction of Carbon Dioxide

Electrocatalytic CO2 reduction reaction (CO2 RR) based on molecular catalysts, for example, cobalt porphyrin, is promising to enhance the carbon cycle and mitigate current climate crisis. However, the electrocatalytic performance and accurate evaluations remain problems because of either the low loading amount or the low utilization rate of the electroactive CoN4 sites. Herein a monomer is synthesized, cobalt(II)-5,10,15,20-tetrakis(3,5-di(thiophen-2-yl)phenyl)porphyrin (CoP), electropolymerized onto carbon nanotubes (CNTs) networks, affording a molecular electrocatalyst of 3D microporous nanofilm (EP-CoP, 2-3 nm thickness) with highly dispersed CoN4 sites. The new electrocatalyst shortens the electron transfer pathway, accelerates the redox kinetics of CoN4 sites, and improves the durability of the electrocatalytic CO2 RR. From the intrinsic redox behavior of CoN4 sites, the effective utilization rate is obtained as 13.1%, much higher than that of the monomer assembled electrode (5.8%), and the durability is also promoted dramatically (>40 h) in H-type cells. In commercial flow cells, EP-CoP can achieve a faradic efficiency for CO (FECO ) over 92% at an overpotential of 160 mV. At a higher overpotential of 620 mV, the working current density can reach 310 mA cm-2 with a high FECO of 98.6%, representing the best performance for electrodeposited molecular porphyrin electrocatalysts.

Promoting CO2 Dynamic Activation via Micro-Engineering Technology for Enhancing Electrochemical CO2 Reduction

Optimizing the coordination structure and microscopic reaction environment of isolated metal sites is promising for boosting catalytic activity for electrocatalytic CO₂ reduction reaction (CO₂ RR) but is still challenging to achieve. Herein, a newly electrostatic induced self-assembly strategy for encapsulating isolated Ni-C₃ N₁ moiety into hollow nano-reactor as I-Ni SA/NHCRs is developed, which achieves FE_CO  of 94.91% at -0.80 V, the CO partial current density of ≈-15.35 mA cm^-2 , superior to that with outer Ni-C₂ N₂ moiety (94.47%, ≈-12.06 mA cm^-2 ), or without hollow structure (92.30%, ≈-5.39 mA cm^-2 ), and high FE_CO of ≈98.41% at 100 mA cm^-2 in flow cell. COMSOL multiphysics finite-element method and density functional theory (DFT) calculation illustrate that the excellent activity for I-Ni SA/NHCRs should be attributed to the structure-enhanced kinetics process caused by its hollow nano-reactor structure and unique Ni-C₃ N₁ moiety, which can enrich electron on Ni sites and positively shift d-band center to the Fermi level to accelerate the adsorption and activation of CO₂ molecule and *COOH formation. Meanwhile, this strategy also successfully steers the design of encapsulating isolated iron and cobalt sites into nano-reactor, while I-Ni SA/NHCRs-based zinc-CO₂ battery assembled with a peak power density of 2.54 mW cm-^-2 is achieved.

Electroreduction of Carbon Dioxide to Acetate using Heterogenized Hydrophilic Manganese Porphyrins

The electrochemical reduction of carbon dioxide (CO₂ ) to value-added chemicals is a promising strategy to mitigate climate change. Metalloporphyrins have been used as a promising class of stable and tunable catalysts for the electrochemical reduction reaction of CO₂ (CO₂ RR) but have been primarily restricted to single-carbon reduction products. Here, we utilize functionalized earth-abundant manganese tetraphenylporphyrin-based (Mn-TPP) molecular electrocatalysts that have been immobilized via electrografting onto a glassy carbon electrode (GCE) to convert CO₂ with overall 94 % Faradaic efficiencies, with 62 % being converted to acetate. Tuning of Mn-TPP with electron-withdrawing sulfonate groups (Mn-TPPS) introduced mechanistic changes arising from the electrostatic interaction between the sulfonate groups and water molecules, resulting in better surface coverage, which facilitated higher conversion rates than the non-functionalized Mn-TPP. For Mn-TPP only carbon monoxide and formate were detected as CO₂ reduction products. Density-functional theory (DFT) calculations confirm that the additional sulfonate groups could alter the C-C coupling pathway from *CO→*COH→*COH-CO to *CO→*CO-CO→*COH-CO, reducing the free energy barrier of C-C coupling in the case of Mn-TPPS. This opens a new approach to designing metalloporphyrin catalysts for two carbon products in CO₂ RR.

Emerging materials for electrochemical CO2 reduction: progress and optimization strategies of carbon-based single-atom catalysts

The electrochemical CO₂ reduction reaction can effectively convert CO₂ into promising fuels and chemicals, which is helpful in establishing a low-carbon emission economy. Compared with other types of electrocatalysts, single-atom catalysts (SACs) immobilized on carbon substrates are considered to be promising candidate catalysts. Atomically dispersed SACs exhibit excellent catalytic performance in CO₂RR due to their maximum atomic utilization, unique electronic structure, and coordination environment. In this paper, we first briefly introduce the synthetic strategies and characterization techniques of SACs. Then, we focus on the optimization strategies of the atomic structure of carbon-based SACs, including adjusting the coordination atoms and coordination numbers, constructing the axial chemical environment, and regulating the carbon substrate, focusing on exploring the structure-performance relationship of SACs in the CO₂RR process. In addition, this paper also briefly introduces the diatomic catalysts (DACs) as an extension of SACs. At the end of the paper, we summarize the article with an exciting outlook discussing the current challenges and prospects for research on the application of SACs in CO₂RR.

Electro-Synthesis of Organic Compounds with Heterogeneous Catalysis

Electro-organic synthesis has attracted a lot of attention in pharmaceutical science, medicinal chemistry, and future industrial applications in energy storage and conversion. To date, there has not been a detailed review on electro-organic synthesis with the strategy of heterogeneous catalysis. In this review, the most recent advances in synthesizing value-added chemicals by heterogeneous catalysis are summarized. An overview of electrocatalytic oxidation and reduction processes as well as paired electrocatalysis is provided, and the anodic oxidation of alcohols (monohydric and polyhydric), aldehydes, and amines are discussed. This review also provides in-depth insight into the cathodic reduction of carboxylates, carbon dioxide, CC, C≡C, and reductive coupling reactions. Moreover, the electrocatalytic paired electro-synthesis methods, including parallel paired, sequential divergent paired, and convergent paired electrolysis, are summarized. Additionally, the strategies developed to achieve high electrosynthesis efficiency and the associated challenges are also addressed. It is believed that electro-organic synthesis is a promising direction of organic electrochemistry, offering numerous opportunities to develop new organic reaction methods.

CO2 Electroreduction on Carbon-Based Electrodes Functionalized with Molecular Organometallic Complexes—A Mini Review

Heterogeneous electrochemical CO2 reduction has potential advantages with respect to the homogeneous counterpart due to the easier recovery of products and catalysts, the relatively small amounts of catalyst necessary for efficient electrolysis, the longer lifetime of the catalysts, and the elimination of solubility problems. Unfortunately, several disadvantages are also present, including the difficulty of designing the optimized and best-performing catalysts by the appropriate choice of the ligands as well as a larger heterogeneity in the nature of the catalytic site that introduces differences in the mechanistic pathway and in electrogenerated products. The advantages of homogeneous and heterogeneous systems can be preserved by anchoring intact organometallic molecules on the electrode surface with the aim of increasing the dispersion of active components at a molecular level and facilitating the electron transfer to the electrocatalyst. Electrode functionalization can be obtained by non-covalent or covalent interactions and by direct electropolymerization on the electrode surface. A critical overview covering the very recent literature on CO2 electroreduction by intact organometallic complexes attached to the electrode is summarized herein, and particular attention is given to their catalytic performances. We hope this mini review can provide new insights into the development of more efficient CO2 electrocatalysts for real-life applications.

Recent Advances in the Use of CoPc-MWCNTs Nanocomposites as Electrochemical Sensing Materials

Cobalt phthalocyanine multiwalled carbon nanotubes (CoPc-MWCNTs), a nanocomposite, are extraordinary electrochemical sensing materials. This material has attracted growing interest owing to its unique physicochemical properties. Notably, the metal at the center of the metal phthalocyanine structure offers an enhanced redox-active behavior used to design solid electrodes for determining varieties of analytes. This review extensively discusses current developments in CoPc-MWCNTs nanocomposites as potential materials for electrochemical sensors, along with their different fabrication methods, modifying electrodes, and the detected analytes. The advantages of CoPc-MWCNTs nanocomposite as sensing material and its future perspectives are carefully reviewed and discussed.

Atomically Thin, Ionic-Covalent Organic Nanosheets for Stable, High-Performance Carbon Dioxide Electroreduction

The incorporation of charged functional groups is effective to modulate the activity of molecular complexes for the CO₂ reduction reaction (CO₂ RR), yet long-term heterogeneous electrolysis is often hampered by catalyst leaching. Herein, an electrocatalyst of atomically thin, cobalt-porphyrin-based, ionic-covalent organic nanosheets (CoTAP-iCONs) is synthesized via a post-synthetic modification strategy for high-performance CO₂ -to-CO conversion. The cationic quaternary ammonium groups not only enable the formation of monolayer nanosheets due to steric hindrance and electrostatic repulsion, but also facilitate the formation of a *COOH intermediate, as suggested by theoretical calculations. Consequently, CoTAP-iCONs exhibit higher CO₂ RR activity than other cobalt-porphyrin-based structures: an 870% and 480% improvement of CO current densities compared to the monomer and neutral nanosheets, respectively. Additionally, the iCONs structure can accommodate the cationic moieties. In a flow cell, CoTAP-iCONs attain a very small onset overpotential of 40 mV and a stable total current density of 212 mA cm^-2 with CO Faradaic efficiency of >95% at -0.6 V for 11 h. Further coupling the flow electrolyzer with commercial solar cells yields a solar-to-CO conversion efficiency of 13.89%. This work indicates that atom-thin, ionic nanosheets represent a promising structure for achieving both tailored activity and high stability.

Heterogenised Molecular Catalysts for Sustainable Electrochemical CO2 Reduction

There has been a rapid rise in interest regarding the advantages of support materials to protect and immobilise molecular catalysts for the carbon dioxide reduction reaction (CO₂ RR) in order to overcome the weaknesses of many well-known catalysts in terms of their stability and selectivity. In this Review, the state of the art of different catalyst-support systems for the CO₂ RR is discussed with the intention of leading towards standard benchmarking for comparison of such systems across the most relevant supports and immobilisation strategies, taking into account these multiple pertinent metrics, and also enabling clearer consideration of the necessary steps for further progress. The most promising support systems are described, along with a final note on the need for developing more advanced experimental and computational techniques to aid the rational design principles that are prerequisite to prospective industrial upscaling.

Bottom-Up Interfacial Design of Covalent Organic Frameworks for Highly Efficient and Selective Electrocatalysis of CO2

Assembling molecular catalytic centers into crosslinked networks is widely used to fabricate heterogeneous catalysts but they often suffer loss in activity and selectivity accompanied by unclear causes. Here, a strategy for the construction of heterogeneous catalysts to induce activity and selectivity by bottom-up introduction of segregated electron-conduction and mass-transport interfaces into the catalytic materials is reported. The catalytic skeletons are designed to possess different π orderings for electron motion and the open channels are tailored to install finely engineered walls for mass transport, so that origins of activity and selectivity are correlated. The resultant covalent organic framework catalysts with ordered π skeletons and solvophobic pores increase activity by two orders of magnitude, enhance selectivity and energy efficiency by 70-fold, and broaden the voltage range, to promote CO₂ transformation under ambient conditions. The results open a way to precise interfacial design of actionable heterogeneous catalysts for producing feedstocks from CO₂ .

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 ((NH_x )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. (NH_x )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 (NH_x )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.

Structural Regulation of Coupled Phthalocyanine-Porphyrin Covalent Organic Frameworks to Highly Active and Selective Electrocatalytic CO2 Reduction

Covalent organic frameworks (COFs) have been applied as potential electrocatalysts for CO₂ reduction reaction (CO₂ RR) due to their adjustable architecture and porous feature. Herein, tetraanhydrides of 2,3,9,10,16,17,23,24-octacarboxyphthalocyanine cobalt(II) (CoTAPc) are used as nodes to couple with 5,15-di(4-aminophenyl)-10,20-diphenylporphyrin (DAPor) or 5,15,10,20-tetrayl(4-aminophenyl)porphyrin (TAPor) via imidization reaction to fabricate novel coupled phthalocyanine-porphyrin Type 1:2 (CoPc-2H₂ Por) or Type 1:1 (CoPc-H₂ Por) COFs. Electrocatalytic CO₂ RR experiments show that both Type 1:2 and Type 1:1 COFs exhibit the maximum Faraday efficiency over 90% with high stability, while the Type 1:2 COF (CoPc-2H₂ Por) delivers lower overpotential, higher current density, and CO selectivity than Type 1:1 COF (CoPc-H₂ Por) and CoPc monomer. Theoretical and experimental results reveal that the better CO₂ RR activity of CoPc-2H₂ Por than CoPc-H₂ Por can be attributed to its larger pore size and conjugate structure, which then cause more efficient electron transfer, adsorption/activation of CO₂ , faster mass transfer, and reaction kinetics. This work provides a new idea in the structural design of COF-based electrocatalyst for efficient CO₂ RR.

Transient Solid-State Laser Activation of Indium for High-Performance Reduction of CO2 to Formate

Deficiencies in understanding the local environment of active sites and limited synthetic skills challenge the delivery of industrially-relevant current densities with low overpotentials and high selectivity for CO₂ reduction. Here, a transient laser induction of metal salts can stimulate extreme conditions and rapid kinetics to produce defect-rich indium nanoparticles (L-In) is reported. Atomic-resolution microscopy and X-ray absorption disclose the highly defective and undercoordinated local environment in L-In. In a flow cell, L-In shows a very small onset overpotential of ≈92 mV and delivers a current density of ≈360 mA cm^-2 with a formate Faradaic efficiency of 98% at a low potential of -0.62 V versus RHE. The formation rate of formate reaches up to 6364.4 µmol h^-1mgIn-1$mg_{{\rm{In}}}^{--1}$ , which is nearly 39 folds higher than that of commercial In (160.7 µmol h^-1mgIn-1$mg_{{\rm{In}}}^{--1}$ ), outperforming most of the previous results that have been reported under KHCO₃ environments. Density function theory calculations suggest that the defects facilitate the formation of *OCHO intermediate and stabilize the *HCOOH while inhibiting hydrogen adsorption. This study suggests that transient solid-state laser induction provides a facile and cost-effective approach to form ligand-free and defect-rich materials with tailored activities.

The integration of bio-catalysis and electrocatalysis to produce fuels and chemicals from carbon dioxide

The dependence on fossil fuels has caused excessive emissions of greenhouse gases (GHGs), leading to climate changes and global warming. Even though the expansion of electricity generation will enable a wider use of electric vehicles, biotechnology represents an attractive route for producing high-density liquid transportation fuels that can reduce GHG emissions from jets, long-haul trucks and ships. Furthermore, to achieve immediate alleviation of the current environmental situation, besides reducing carbon footprint it is urgent to develop technologies that transform atmospheric CO₂ into fossil fuel replacements. The integration of bio-catalysis and electrocatalysis (bio-electrocatalysis) provides such a promising avenue to convert CO₂ into fuels and chemicals with high-chain lengths. Following an overview of different mechanisms that can be used for CO₂ fixation, we will discuss crucial factors for electrocatalysis with a special highlight on the improvement of electron-transfer kinetics, multi-dimensional electrocatalysts and their hybrids, electrolyser configurations, and the integration of electrocatalysis and bio-catalysis. Finally, we prospect key advantages and challenges of bio-electrocatalysis, and end with a discussion of future research directions.

Single-Atom Metal Anchored Zr6-Cluster-Porphyrin Framework Hollow Nanocapsules with Ultrahigh Active-Center Density for Electrocatalytic CO2 Reduction

Designing earth-abundant electrocatalysts toward highly efficient CO₂ reduction has significant importance to decrease the global emission of greenhouse gas. Herein, we propose an efficient strategy to anchor non-noble metal single atoms on Zr₆-cluster-porphyrin framework hollow nanocapsules with well-defined and abundant metal-N₄ porphyrin sites for efficient electrochemical CO₂ reduction. Among different transition metal single atoms (Mn, Fe, Co, Ni, and Cu), Co single-atom anchored Zr₆-cluster-porphyrin framework hollow nanocapsules demonstrated the highest activity and selectivity for CO production. The rich Co-N₄ active centers and hierarchical porous structure contribute to enhanced CO₂ adsorption capability and moderate binding strength of reaction intermediates, thus facilitating *CO desorption and CO₂-to-CO conversion. The Co-anchored nanocapsules maintain high efficiency and well-preserved stability during long-term electrocatalysis tests. Moreover, the Co-anchored nanocapsules exhibit a remarkable solar-to-CO energy conversion efficiency of 12.5% in an integrated solar-driven CO₂ reduction/O₂ evolution electrolysis system when powered by a custom large-area [Cs_0.05(FA_0.85MA_0.15)_0.95]Pb_0.9(I_0.85Br_0.15)₃-based perovskite solar cell.

Molecular Engineering of CoII Porphyrins with Asymmetric Architecture for Improved Electrochemical CO2 Reduction

The electrochemical reduction of carbon dioxide (CO₂ ) based on molecular catalysts has attracted more attention, owing to their well-defined active sites and rational structural design. Metal porphyrins (PorMs) have the extended π-conjugated backbone with different transition metals, endowing them with unique CO₂ reduction properties. However, few works focus on the investigation of symmetric architecture of PorMs as well as their aggregation behavior to CO₂ reduction. In this work, a series of Co^II porphyrins (PorCos) with symmetric and asymmetric substituents were used as model of molecular catalysts for CO₂ reduction. Owing to the electron donating effect of 2,6-dimethylbenzene (DMB), bandgaps of the complexes became narrower with the increasing number of DMB. As electrocatalysts, all PorCos exhibited promising electrocatalytic CO₂ reduction performance. Among the three molecules, asymmetric Co^II porphyrin (as-PorCo) showed the lowest onset potential of -288 mV and faradaic efficiencies exceeding 93 % at -0.6 V vs. reversible hydrogen electrode, which is highly competitive among the reported state-of-art porphyrin-based electrocatalysts. The CO₂ reduction performance depended on π-π stacking between PorCo with carbon nanotubes (CNTs) and adjacent PorCos, which could be readily controlled by atomically positioned DMB in PorCo. Density functional theory calculations also suggested that the charge density between PorCo and CNT was highest due to the weak steric hindrance in as-PorCo, providing the new insight into molecular design of catalysts for efficient electrochemical CO₂ reduction.

Atomic- and Molecular-Level Modulation of Dispersed Active Sites for Electrocatalytic CO2 Reduction

Global climate changes have been impacted by the excessive CO 2 emission, which exacerbates the environmental problems. Electrochemical CO 2 reduction (CO 2 RR) offers the solution for utilizing CO 2 as feedstocks for value-added products while potentially mitigating the negative effects. Owing to the extreme stability of CO 2 , selectivity and efficiency are crucial factors in the development of CO 2 RR electrocatalysts. Recently, single-atom catalysts have emerged as potential electrocatalysts for CO 2 reduction. They generally comprise of atomically- and molecularly dispersed active sites over conductive supports, which enable atomic-level and molecular-level modulations. In this minireview, catalyst preparations, principle of modulations, and reaction mechanisms are summarised together with related recent advances. The atomic-level modulations are first discussed, followed by the molecular-level modulations. Finally, the current challenges and future opportunities are provided as guidance for further developments regarding the discussed topics.

Immobilization strategies for porphyrin-based molecular catalysts for the electroreduction of CO2

The ever-growing level of carbon dioxide (CO2) in our atmosphere, is at once a threat and an opportunity. The development of sustainable and cost-effective pathways to convert CO2 to value-added chemicals is central to reducing its atmospheric presence. Electrochemical CO2 reduction reactions (CO2RRs) driven by renewable electricity are among the most promising techniques to utilize this abundant resource; however, in order to reach a system viable for industrial implementation, continued improvements to the design of electrocatalysts is essential to improve the economic prospects of the technology. This review summarizes recent developments in heterogeneous porphyrin-based electrocatalysts for CO2 capture and conversion. We specifically discuss the various chemical modifications necessary for different immobilization strategies, and how these choices influence catalytic properties. Although a variety of molecular catalysts have been proposed for CO2RRs, the stability and tunability of porphyrin-based catalysts make their use particularly promising in this field. We discuss the current challenges facing CO2RRs using these catalysts and our own solutions that have been pursued to address these hurdles.

Rational-Designed Principles for Electrochemical and Photoelectrochemical Upgrading of CO2 to Value-Added Chemicals

The chemical transformation of carbon dioxide (CO₂ ) has been considered as a promising strategy to utilize and further upgrade it to value-added chemicals, aiming at alleviating global warming. In this regard, sustainable driving forces (i.e., electricity and sunlight) have been introduced to convert CO₂ into various chemical feedstocks. Electrocatalytic CO₂ reduction reaction (CO₂ RR) can generate carbonaceous molecules (e.g., formate, CO, hydrocarbons, and alcohols) via multiple-electron transfer. With the assistance of extra light energy, photoelectrocatalysis effectively improve the kinetics of CO₂ conversion, which not only decreases the overpotentials for CO₂ RR but also enhances the lifespan of photo-induced carriers for the consecutive catalytic process. Recently, rational-designed catalysts and advanced characterization techniques have emerged in these fields, which make CO₂ -to-chemicals conversion in a clean and highly-efficient manner. Herein, this review timely and thoroughly discusses the recent advancements in the practical conversion of CO₂ through electro- and photoelectrocatalytic technologies in the past 5 years. Furthermore, the recent studies of operando analysis and theoretical calculations are highlighted to gain systematic insights into CO₂ RR. Finally, the challenges and perspectives in the fields of CO₂ (photo)electrocatalysis are outlined for their further development.

Considering the Influence of Polymer-Catalyst Interactions on the Chemical Microenvironment of Electrocatalysts for the CO2 Reduction Reaction

The electrochemical CO₂ reduction reaction (CO₂RR) is an attractive method for capturing intermittent renewable energy sources in chemical bonds, and converting waste CO₂ into value-added products with a goal of carbon neutrality. Our group has focused on developing polymer-encapsulated molecular catalysts, specifically cobalt phthalocyanine (CoPc), as active and selective electrocatalysts for the CO₂RR. When CoPc is adsorbed onto a carbon electrode and encapsulated in poly(4-vinylpyridine) (P4VP), its activity and reaction selectivity over the competitive hydrogen evolution reaction (HER) are enhanced by three synergistic effects: a primary axial coordination effect, a secondary reaction intermediate stabilization effect, and an outer-coordination proton transport effect. We have studied multiple aspects of this system using electrochemical, spectroscopic, and computational tools. Specifically, we have used X-ray absorption spectroscopy measurements to confirm that the pyridyl residues from the polymer are axially coordinated to the CoPc metal center, and we have shown that increasing the σ-donor ability of nitrogen-containing axial ligands results in increased activity for the CO₂RR. Using proton inventory studies, we showed that proton delivery in the CoPc-P4VP system is controlled via a proton relay through the polymer matrix. Additionally, we studied the effect of catalyst, polymer, and graphite powder loading on CO₂RR activity and determined best practices for incorporating carbon supports into catalyst-polymer composite films.In this Account, we describe these studies in detail, organizing our discussion by three types of microenvironmental interactions that affect the catalyst performance: ligand effects of the primary and secondary sphere, substrate transport of protons and CO₂, and charge transport from the electrode surface to the catalyst sites. Our work demonstrates that careful electroanalytical study and interpretation can be valuable in developing a robust and comprehensive understanding of catalyst performance. In addition to our work with polymer encapsulated CoPc, we provide examples of similar surface-adsorbed molecular and solid-state systems that benefit from interactions between active catalytic sites and a polymer system. We also compare the activity results from our systems to other results in the CoPc literature, and other examples of molecular CO₂RR catalysts on modified electrode surfaces. Finally, we speculate how the insights gained from studying CoPc could guide the field in designing other polymer-electrocatalyst systems. As CO₂RR technologies become commercially viable and expand into the space of flow cells and gas-diffusion electrodes, we propose that overall device efficiency may benefit from understanding and promoting synergistic polymer-encapsulation effects in the microenvironment of these catalyst systems.

Application of Porous Materials for CO2 Reutilization: A Review

CO2 reutilization processes contribute to the mitigation of CO2 as a potent greenhouse gas (GHG) through reusing and converting it into economically valuable chemical products including methanol, dimethyl ether, and methane. Solar thermochemical conversion and photochemical and electrochemical CO2 reduction processes are emerging technologies in which solar energy is utilized to provide the energy required for the endothermic dissociation of CO2. Owing to the surface-dependent nature of these technologies, their performance is significantly reliant on the solid reactant/catalyst accessible surface area. Solid porous structures either entirely made from the catalyst or used as a support for coating the catalyst/solid reactants can increase the number of active reaction sites and, thus, the kinetics of CO2 reutilization reactions. This paper reviews the principles and application of porous materials for CO2 reutilization pathways in solar thermochemical, photochemical, and electrochemical reduction technologies. Then, the state of the development of each technology is critically reviewed and evaluated with the focus on the use of porous materials. Finally, the research needs and challenges are presented to further advance the implementation of porous materials in the CO2 reutilization processes and the commercialization of the aforementioned technologies.

Promoting CO2 Electroreduction Kinetics on Atomically Dispersed Monovalent Zn(I) Sites by Rationally Engineering Proton-feeding Centers

Electrocatalytic reduction of CO2 (CO2RR) to value-added chemicals is of great significance for CO2 utilization. Due to the slow proton-feeding rates from sluggish water dissociation kinetics, however, the CO2RR process involving multi-electron and proton transfer is greatly limited by poor selectivity and low yield. Herein, we develop an atomically dispersed monovalent zinc anchored on nitrogenated carbon nanosheets (Zn/NC NSs) as an efficient catalyst for CO2RR. Benefiting from the unique coordination environment and atomic dispersion, the optimized Zn/NC NSs exhibits a superior CO2RR performance, featured by a high current density up to 50 mA cm-2 with an outstanding CO Faradaic efficiency of ～95%. The center Zn(I) atom coordinated with three N atoms and one N atom that bridge over two adjacent graphitic edge (Zn-N3+1) is identified as the catalytically active site by thorough structural characterizations. In-situ attenuated total reflectance infrared absorption spectroscopy results reveal that the twisted Zn-N3+1 structure accelerates the CO2 activation and protonation in the rate-determining step of *CO2 to *COOH on the rationally engineered proton-feeding centers, while theoretical calculations elucidate that atomically dispersed Zn-N3+1 moieties decrease the potential barriers for the intermediate COOH* formation, promoting the proton-coupled CO2RR kinetics and boosting the overall catalytic performance. A rechargeable Zn-CO2 battery based on the Zn/NC NS cathode delivers a maximal power density of 1.8 mW cm-2.

Advances and Challenges for the Electrochemical Reduction of CO2 to CO: From Fundamentals to Industrialization

The electrochemical carbon dioxide reduction reaction (CO₂ RR) provides an attractive approach to convert renewable electricity into fuels and feedstocks in the form of chemical bonds. Among the different CO₂ RR pathways, the conversion of CO₂ into CO is considered one of the most promising candidate reactions because of its high technological and economic feasibility. Integrating catalyst and electrolyte design with an understanding of the catalytic mechanism will yield scientific insights and promote this technology towards industrial implementation. Herein, we give an overview of recent advances and challenges for the selective conversion of CO₂ into CO. Multidimensional catalyst and electrolyte engineering for the CO₂ RR are also summarized. Furthermore, recent studies on the large-scale production of CO are highlighted to facilitate industrialization of the electrochemical reduction of CO₂ . To conclude, the remaining technological challenges and future directions for the industrial application of the CO₂ RR to generate CO are highlighted.