Metal-Coordinated Phthalocyanines as Platform Molecules for Understanding Isolated Metal Sites in the Electrochemical Reduction of CO2

Prediction of C2N-Supported Double-Atom Catalysts with Individual/Integrated Descriptors for Electrochemical and Thermochemical CO2 Reduction

Electrochemical/thermochemical CO2 reduction reactions (CO2RR) on double-atom catalysts (DACs) have emerged as a novel frontier in energy and environmental catalysis. However, the lack of investigation of the underlying structure-property relationship greatly limits the rational design and practical application of related catalysts. Herein, we carried out a comprehensive theoretical study on CO2RR catalyzed by a series of C2N-supported transition metals to shed light on this issue. We demonstrate that the activity of DAC can be obviously improved by judicious manipulation of metal type, and CoNi with the highest reactivity and excellent selectivity is identified as the most promising candidate for both electroreduction and thermoreduction processes. Then, based on systemically electronic and structural analysis, various quantitative structure-property relationships are established. The results reveal that key interaction and reaction properties of elementary steps can be quantitatively determined directly from individual descriptors, including key species, charge transfer, d-orbital center, bond length, spectroscopic signals, etc, while for total reaction, the integrated descriptors designed by a novel and effective three-step strategy have much better performance. The proposed ability of quantitative prediction of the catalytic property utilizing physically interpretable parameters can significantly broaden the applicability of catalytic descriptors for materials design, thus leading to indispensable guidelines for related DACs.

Structural Reconstruction of Copper-Based Catalysts in CO2 Electroreduction Reaction: A Comprehensive Review

The escalating concerns over climate change and environmental pollution have intensified the pursuit for sustainable solutions to mitigate CO2 emissions, with the electrochemical CO2 reduction reaction (CO2RR) emerging as a promising strategy to convert CO2 into valuable chemicals and fuels. Central to this process is the development of efficient electrocatalysts, where Cu-based catalysts have garnered significant attention due to their high activity towards multi-carbon products. However, understanding of structural reconstruction of Cu-based catalysts under operational conditions presents a substantial challenge, complicating the identification of real active sites and the elucidation of structure-performance relationships. Herein, we first highlight the fundamental principles governing the structural reconstruction in CO2RR, encompassing both thermodynamic and kinetic perspectives. We then introduce advanced Operando techniques employed to monitor the structural changes of catalysts. The review further delves into the dynamic evolution behaviors of Cu-based catalysts, including atomic rearrangement and morphology evolution, with a focus on correlating these behaviors with catalytic properties such as activity, selectivity, and stability. Finally, we discuss cases of emerging strategies, such as heteroatom doping and electrolyte engineering, that hold promise for manipulating the structural reconstruction of Cu-based catalysts, and we explore future opportunities in this rapidly evolving field.

Shielding CO2-Philic Sites in Trimmed Covalent Organic Framework Pores by Atomic Layer Deposition

Strong adsorptive sites toward unwanted gas molecules in porous framework materials often lead to reversed sorption selectivity, creating tremendous challenges for enhancing the diffusion-driven membrane separations targeted at the weakly adsorbed species in the gas pair. While post-synthetic modification methods have been reported to downsize the pores in covalent organic frameworks (COFs), effective approaches to shield the highly adsorptive sites within the pores are rarely explored. Here, a solvent-less pore modification strategy is developed using atomic layer deposition (ALD). it is shown that controlled amounts of ZnO can be uniformly deposited into the COF pores, offering the ability to fine-tune the pore dimensions. Moreover, the Zn─O moieties grown into the COF pore are found to interact with the CO2-philic ketoenamine groups, and substantially reduce the CO2 solubility by 72.4% in the COF membrane. Accordingly, the simultaneously increased diffusion selectivity and sorption selectivity for H2/CO2 lead to a 330% improvement of the permselectivity in membrane separation, demonstrating the efficacy of the strategy for pore engineering in COFs.

Electronic tuning of defect-rich ultrathin nitrogen-doped porous carbon nanosheets supported metal phthalocyanine catalysts for CO2 electroreduction

Electrocatalytic CO2 reduction (CO2RR) driven by renewable energy represents a promising technology toward carbon neutrality. Metal phthalocyanines (MPcs) exhibit promise as molecular catalysts for CO2RR, however, their practical application is hindered by intrinsic limitations: poor electrical conductivity, easy aggregation, and inadequate active sites accessibility. Herein, we report defect-rich ultrathin N-doped porous carbon nanosheets (UNPCS) synthesized via molten salt-assisted pyrolysis of two-dimensional ZIF-L, serving as an advanced substrate to immobilize molecularly dispersed MPcs. The UNPCS substrate synergistically combines carbon defects and N-dopants to tune the electronic structure of metals, while its hierarchical porosity and high specific surface area (1529.7 m2 g-1) facilitate mass transport and expose abundant active sites. The optimized CoPc@UNPCS achieves a current density of -24.7 mA cm-2 at -1.0 V vs. RHE, which is 15.3 times higher than that of pristine CoPc. The incorporation of Co/Fe diatomic sites in CoFePc@UNPCS further enhances performance, achieving a peak FECO of 95.9 % and sustaining FECO > 90 % over a broader potential range in an H-cell. Notably, an industrial-relevant current density of -222.3 mA cm-2 at -1.0 V vs. RHE over CoFePc@UNPCS was obtained in a flow cell. Density functional theory (DFT) calculations reveal that MPc@UNPCS (M = Co, Fe) lowers the energy barrier for *COOH formation while maintaining a low *CO desorption energy, thereby optimizing reaction kinetics. This work establishes a scalable synthesis strategy for diatomic site catalysts and elucidates the critical interplay between substrate engineering and electronic tuning in advancing CO2RR technologies.

Engineered Spatial Confinement of Cu Single-Atoms with Diagonal N─Cu─N Motifs for High-Rate CO2 Methanation

The renewable-electricity-powered carbon dioxide reduction (eCO2R) to value-added fuels and feedstocks like methane (CH4) holds the sustainable and economically viable carbon cycle at meaningful scales. However, this kinetically challenging eight-electron multistep deep-reduction encounters insufficient catalyst design principles to steer complex CO2 reduction pathways. Utilizing atomic copper (Cu) structures with unitary active sites can boost eCO2R-to-CH4 selectivity due to the efficient suppression of unwanted C─C coupling. Herein, we report a sequential ion exchange strategy to fabricate periodic Cu single-atom catalysts within a polymeric carbon nitride (PCN) matrix, where the uniformly dispersed, diagonally coordinated N─Cu─N configuration hosts low-valent Cuδ+ centers. Leveraging the periodic N-anchoring sites with delocalized π-electron conjugation in the PCN matrix, the isolated Cu sites are obtained with an interatomic distance of ∼4.2 Å under high metal-loading conditions. This engineered spatial configuration effectively inhibits C─C coupling to avoid subsequent multicarbon product formation. The optimized Cu1/PCN demonstrates exceptional eCO2R-to-CH4 performance, achieving 71.1% CH4 Faradaic efficiency with a high partial current density of 426.6 mA cm-2 at -1.50 V versus reversible hydrogen electrode, outpacing the state-of-the-art catalysts. This work delves into effective concepts for steering desirable reaction pathways via precisely modulating active site structures at the atomic level to create favorable microenvironments.

Activity-Selectivity Trends in Electrochemical Urea Synthesis: Co-Reduction of CO2 and Nitrates Over Single-Site Catalysts

Electrochemical co-reduction of carbon dioxide and nitrates (CO2NO3RR) holds promise for sustainable urea production. However, the sluggish kinetics of the sixteen-electron transfer and unclear mechanistic understanding strongly impede its development. Here, combined experimental and computational approaches are employed to screen a series of metal phthalocyanine as model catalysts (MPcs, M = Zn, Co, Ni, Cu, and Fe) to uncover the activity-selectivity trends in electrochemical CO2NO3RR. The theoretical simulations reveal that the thermodynamics of urea synthesis is significantly influenced by key intermediates, where the enhanced adsorption of *HOOCNO, coupled with reduced adsorptions of *N and *COOH, and moderate adsorption of *H2O, can significantly promote the urea production. ΔG*HOOCNO-ΔG*N-ΔG*COOH+ΔG*H2O as a potential descriptor is proposed for predicting the efficiency of CO2NO3RR toward urea formation. The findings provide systematic guidance for the future design of high-efficiency catalysts for urea electrosynthesis, addressing a crucial need for sustainable nitrogen fixation.

Descriptor for electro-oxidation of glycerol with high-efficiency bifunctional Cu-Nx single atom catalyst and coupled with hydrogen evolution/carbon dioxide reduction

Electrochemical glycerol oxidation reaction (GOR) presents a promising approach for converting excess glycerol (GLY) into high-value-added products. However, the complex mechanism and the challenge of achieving selectivity for diverse products make GOR difficult to address in both experimental and theoretical studies. In this work, three nitrogen-doped graphene-supported copper single-atom catalysts (CuNx@Gra SACs, x = 2-4) were selected as the model system due to their simple structure, excellent conductivity and high structural stability. Density functional theory (DFT) calculations were employed to gain deeper insight into the catalytic mechanism. The DFT results revealed that both CuN2@Gra and CuN3@Gra follow the same optimal pathway, leading to the formation of formic acid as a key product. The GOR activity and selectivity of CuNx@Gra catalysts follow the trend CuN3@Gra > CuN2@Gra > CuN4@Gra. Subsequent microkinetic analysis, based co on the DFT-derived energetics, confirmed this predicted activity sequence. The GOR activity determined by the limiting potential (UL) is correlate well with changes in the adsorption free energy (ΔGGLY*), the d-band centers of axial dz2 orbitals (εdz2) and integrated crystal orbital Hamilton population (ICOHP). Notably, the simple descriptor ΔGGLY* exhibits a good linear correlation with the free energies of other adsorbates, clarifying the conversion relationships between reaction intermediates and simplifying the understanding of reaction complexity. Moreover, computational results indicate that CuN2@Gra and CuN3@Gra systems can serve as both anode catalysts (for GOR) and cathode catalysts (CO2 reduction for CuN2@Gra and H2 evolution for CuN3@Gra). This study offers insights for designing efficient electrocatalysts, enhancing GLY utilization.

Ligand Engineering of Co-N4 Single-Atom Catalysts for Highly-Active and Stable Acidic Oxygen Evolution

The development of stable and efficient single-atom catalysts (SACs) for the oxygen evolution reaction (OER) in acidic media remains challenging. This work reports a novel NH3-assisted pyrolysis strategy to synthesize Co-N4 SACs with controlled nitrogen coordination environments on crumpled graphene supports. The pyrrolic N4-coordinated Co sites demonstrate superior OER activity compared to their pyridinic counterparts, achieving an overpotential of 351 mV at 10 mA cm-2 in 0.5 m H2SO4. Combined density functional theory calculations and operando X-ray absorption spectroscopy reveal that the pyrrolic coordination environment facilitates enhanced OH- adsorption and subsequent OER kinetics due to its unique electronic structure and geometric flexibility. A multi-layered protective mechanism in the pyrrolic system enables exceptional stability during long-term acidic OER operation, stemming from higher defect formation energy of Co sites and strategic distribution of sacrificial nitrogen species in the graphene network. These findings provide fundamental insights into designing stable single-atom catalysts for challenging electrochemical applications.

The Proximal Protonation Source in Cu-NHx-C Single Atom Catalysts Selectively Boosts CO2 to Methane Electroreduction

Regulating the coordination environment of active sites has proved powerful for tapping into their catalytic activity and selectivity in homogeneous catalysis, yet the heterogeneous nature of copper single-atom catalysts (SACs) makes it challenging. This work reports a bottom-up approach to construct a SAC (rGO@Cu-N(Hx)-C) by inlaying preformed amine coordinated Cu2+ units into reduced graphene oxide (rGO), permitting molecular level revelation on how the proximal N-site functional groups (N-H or N-CH3) impact on the carbon dioxide reduction reaction (CO2RR). It is demonstrated that the N-H moiety of rGO@Cu-NHx-C can serve as an in situ protonation agent to accelerate the CO2-to-methane reduction kinetics, delivering a methane current density (163 mA/cm2) 2.42-times that with the -CH3 substituted counterpart rGO@Cu-N-C. Operando spectroscopic studies and theoretical calculations elucidate that the high methane faradaic efficiency (77.1 %) achieved here is enabled by opening up the energetically favorable formyl pathway (*OCHO pathway) against the traditional *CO pathway that normally leads to various CO2RR products other than methane. Our strategy sets the stage to precisely modulate single-atom catalysts for efficient and selective electrochemical CO2 reduction.

Two-Dimensional Transition Metal Dichalcogenides (2D TMDs) Coupled With Zero-Dimensional Nanomaterials (0D NMs) for Advanced Photodetection

The integration of 2D transition metal dichalcogenides (TMDs) with other materials presents a promising approach to overcome inherent limitations and enable the development of novel functionalities. In particular, 0D nanomaterials (0D NMs) offer notable advantages for photodetection, including broadband light absorption, size-dependent optoelectronic properties, high quantum efficiency, and good compatibility. Herein, the integration of 0D NMs with 2D TMDs to develop high-performance photodetectors is reviewed. The review provides a comprehensive overview of different types of 0D NMs, including plasma nanoparticles (NPs), up-conversion NPs, quantum dots (QDs), nanocrystals (NCs), and small molecules. The discussion starts with an analysis of the mechanism of 0D NMs on 2D TMDs in photodetection, exploring various strategies for improving the performance of hybrid 2D TMDs/0D NMs. Recent advancements in photodetectors combining 2D TMDs with 0D NMs are investigated, particularly emphasizing critical factors such as photosensitivity, photogain, specific detectivity, and photoresponse speed. The review concludes with a summary of the current status, highlighting the existing challenges and prospective developments in the advancement of 0D NMs/2D TMDs-based photodetectors.

Phthalocyanine nickel enhanced composite solid-state electrolytes with homogenous and fast Li-ion conduction for high-voltage Li-metal batteries

Herein, a novel composite solid-state polymer electrolytes (CSEs) was regulated by introducing CoNi-MOF (Metal-organic framework) @NiPc (Nickel phthalocyanine) nanofiller (CMN) into PEO (polyethylene oxide) matrix. In this novel system, the NiPc uniformly wrapped around the surface of MOF through hydrogen bond bridging, avoiding the agglomeration of the MOF particles. The chemisorption between Ni2+ in NiPc and the O atoms in the bis(triffuoromethanesulfonyl)imide anion (TFSI-) restricted the mobility of the anions within the CSEs, which improved the release of Li+ ions from the NiPcLi. In addition, the π-π conjugated groups present in NiPc facilitated a spontaneous formation of additional lithium ion transport channels within the PEO (polyethylene oxide) matrix. The novel CSEs displayed a Li+ transference number of 0.79 and ionic conductivity (2.65 × 10-4 S cm-1). The nitro groups at the peripheral position of NiPc acted as intermediaries that firmly combined the PEO and MOF via the formation of mutual hydrogen bonds, avoiding the shedding of active materials from the base polymer and ensuring long-term stability. Moreover, the decrease in the HOMO (highest occupied molecular orbital) energy level of the obtained CSEs indicated an improvement in its ability to resist oxidation. Consequently, an Li//Li(Ni0.8Co0.1Mn0.1O2) (NCM811) high-voltage battery containing the obtained CSEs displayed good performance. The Li+ transport and enhanced electrochemical stability window of the MNPL were further revealed by theoretical calculations. Overall, these results demonstrated a new strategy for the design and preparation of high-performance CSEs through the introduction of multifunctional MPc (Metal phthalocyanine) for solid-state rechargeable Li-metal batteries.

Modulating Electronic Density of Single-Atom Ni Center by Heteroatoms for Efficient CO2 Electroreduction

Single-atom catalysts (SACs) with unique geometric and electronic configurations have triggered great interest in many important reactions. However, controllably modulating the electronic structure of metal centers to enhance catalytic performance remains a challenge. Here, the electronic structure of Ni centers over Ni1-NC SACs by introducing electron-rich phosphorus or electron-deficient boron for electrochemical CO2 reduction (CO2RR) is systematically tailored. It is found that the Ni1-PNC with Ni1-N3P site exhibits superior performance with a current density of 14.6 mA cm-2 and a Faradaic efficiency of 90.6% at -0.8 V versus RHE for CO production, far exceeding Ni1-NC and Ni1-BNC SACs. Detailed characterizations and theoretical calculations reveal a linear relationship between the valence state of Ni species and the CO2RR performance. The incorporation of P species facilitates the electronic localization around the Ni1 center, significantly promoting the adsorption of CO2 and the formation of key *COOH intermediate to enhance CO2RR. This work provides a feasible approach to quantitatively manipulate the electronic structure of single-atom metal sites and to rationally design highly efficient catalysts for boosted performance.

In Situ Modulated Nickel Single Atoms on Bicontinuous Porous Carbon Fibers and Sheets Networks for Acidic CO2 Reduction

Carbon-supported single-atom catalysts exhibit exceptional properties in acidic CO2 reduction. However, traditional carbon supports fall short in building high-site-utilization and CO2-rich interfacial environments, and the structural evolution of single-atom metals and catalytic mechanisms under realistic conditions remain ambiguous. Herein, an interconnected mesoporous carbon nanofiber and carbon nanosheet network (IPCF@CS) is reported, derived from microphase-separated block copolymer, to improve catalytic efficiency of isolated Ni. In IPCF@CS nanostructure, highly mesoporous IPCF hinders stacking of CS that provides additional fully exposed sites and abundant bicontinuous mesochannels of IPCF facilitate smooth CO2 transport. Such unique features enable enhanced Ni utilization and local CO2 enrichment, which cannot be achieved over conventional pore-deficient and discontinuous porous carbon fibers-based supports. In situ X-ray and Infrared spectroscopy coupling constant-potential calculations reveal the dynamic distortion of the planar Ni-N4 to an out-of-plane configuration with expanded Ni-N bond during operating CO2 electroreduction. The potential-driven low-valance-state Ni-N4 possesses enhanced intrinsic electrokinetics for CO2 activation and CO desorption yet inhibiting hydrogen evolution. The favorable electronic and interfacial reaction environments, resulted from the in situ tailored Ni site and IPCF@CS support, achieve an FE of near 100% at 540 mA cm-2, a TOF of 55.5 s-1, and a SPCE of 89.2% in acidic CO2-to-CO electrolysis.

CoTCNQ as a Catalyst for CO2 Electroreduction: A First Principles r2SCAN Meta-GGA Investigation

Using first principles calculations we investigate cobalt-coordinated tetracyanoquinodimethane (R-CoTCNQ) as a potential catalyst for the CO2 electroreduction reaction (CO2ERR). We determine that exchange-correlation functionals beyond the generalized gradient approximation (GGA) are required to accurately describe the spin properties of R-CoTCNQ, therefore, the meta-GGA r2SCAN functional is used in this study. The free energy CO2ERR reaction pathways are calculated for the reduced catalyst ([R-CoTCNQ]-1e) with reaction products HCOOH and HCHO predicted depending on our choice of electrode potential. Calculations are also performed for [R-CoTCNQ]-1e supported on a H-terminated diamond (1 1 0) surface with reaction pathways being qualitatively similar to the [R-CoTCNQ]-1e monolayer. The inclusion of boron-doping in the diamond support shows a slightly improved CO2ERR reaction pathway. Furthermore, structurally, supported R-CoTCNQ provide a high specific area of active Co active sites and could be promising catalysts for future experimental consideration.

Unique Oxygen-Bridged Nickel Atomic Pairs Efficiently Boost Electrochemical Reduction of Carbon Dioxide

Benefiting from the synergism between adjacent bimetallic atoms, in comparison with single atom catalysts, the dual atom catalysts have displayed great potential in electrocatalytic CO2 reduction reaction (CO2RR). However, the further modulation of the electronic structure of dual atom sites to enhance CO2RR performance still remains a challenge. Herein, an atomically dispersed oxygen-bridged Ni2N6O/NC catalyst with unique Ni-O-Ni sites is successfully synthesized through the microwave pyrolysis of the supported mixture containing the dinuclear nickel phthalocyanine and glucose on N-doped carbon nanosheets. Experiments and density functional theory calculation reveal that the Ni-O-Ni sites can adsorb H+ from the KHCO3 electrolyte to in situ-form the unique Ni-OH-Ni sites without Ni─Ni bonding interaction, which effectively lowers the energy barrier towards the formation of *COOH from CO2. As a result, the Ni2N6OH/NC catalyst exhibits a 99.4% of CO Faradaic efficiency with a 32.4 mA·cm-2 of CO partial current density at -0.7 V versus RHE in H-cell, much superior to the Ni2N6/NC with a Ni-Ni bonding interaction prepared by a similar procedure to that for Ni2N6O/NC but replacing microwave pyrolysis by a traditional heating process.

Single Atom Catalysts Based on Earth-Abundant Metals for Energy-Related Applications

Anthropogenic activities related to population growth, economic development, technological advances, and changes in lifestyle and climate patterns result in a continuous increase in energy consumption. At the same time, the rare metal elements frequently deployed as catalysts in energy related processes are not only costly in view of their low natural abundance, but their availability is often further limited due to geopolitical reasons. Thus, electrochemical energy storage and conversion with earth-abundant metals, mainly in the form of single-atom catalysts (SACs), are highly relevant and timely technologies. In this review the application of earth-abundant SACs in electrochemical energy storage and electrocatalytic conversion of chemicals to fuels or products with high energy content is discussed. The oxygen reduction reaction is also appraised, which is primarily harnessed in fuel cell technologies and metal-air batteries. The coordination, active sites, and mechanistic aspects of transition metal SACs are analyzed for two-electron and four-electron reaction pathways. Further, the electrochemical water splitting with SACs toward green hydrogen fuel is discussed in terms of not only hydrogen evolution reaction but also oxygen evolution reaction. Similarly, the production of ammonia as a clean fuel via electrocatalytic nitrogen reduction reaction is portrayed, highlighting the potential of earth-abundant single metal species.

Synthesis and Structure-Property Relationship of meso-Substituted Porphyrin- and Benzoporphyrin-Thiophene Conjugates toward Electrochemical Reduction of Carbon Dioxide

A novel series of ZnII-trans-A2B2 porphyrins and benzoporphyrins bearing phenyl and thiophene-based meso-substituents was successfully synthesized and characterized by spectroscopic and electrochemical techniques. Systematic comparison among the compounds in this series, together with the corresponding A4 analogs previously studied by our group, led to the understanding of the effects of π-conjugated system extension of a porphyrin core through β-fused rings, replacement of the phenyl with the thiophene-based meso-groups, and introduction of additional thiophene rings on thienyl substituents on photophysical and electrochemical properties. Oxidative electropolymerization through bithiophenyl units of both A4 and trans-A2B2 analogs was achieved, resulting in porphyrin- and benzoporphyrin-oligothiophene conjugated polymers, which were characterized by cyclic voltammetry and absorption spectrophotometry. Preliminary studies on catalytic performance toward electrochemical reduction of carbon dioxide (CO2) was described herein to demonstrate the potential of the selected compounds for serving as homogeneous and heterogeneous electrocatalysts for the conversion of CO2 to carbon monoxide (CO).

Single-Pd-Site Catalyst Induced by Different Dimensional Nitrogen of N-Doping Carbon for Efficient Hydroaminocarbonylation of Alkynes

The unsaturated amides are traditionally synthesized by acylation of carboxylic acids or hydration of nitrile compounds but are rarely investigated by hydroaminocarbonylation of alkynes using heterogeneous single-metal-site catalysts (HSMSCs). Herein, single-Pd-site catalysts supported on N-doping carbon (NC) with different nitrogen dimensions inherited from corresponding metal-organic-framework precursors are successfully synthesized. 2D NC-supported single-Pd-site (Pd1/NC-2D) exhibited the best performance with near 100% selectivity and 76% yield of acrylamide for acetylene hydroaminocarbonylation with better stability, superior to those of Pd1/NC-3D, single-metal-site/nanoparticle coexisting catalyst, and nanoparticle catalyst. The coordination environment and molecular evolution of the single-Pd-site during the process of acetylene hydroaminocarbonylation on Pd1/NC-2D are detailly illuminated by various characterizations and density functional theoretical calculations (DFT). DFT also showed the energy barrier of rate-determining step on Pd1/NC-2D is lower than that of Pd1/NC-3D. Furthermore, Pd1/NC-2D catalyst illustrated the general applicability of the hydroaminocarbonylation for various alkynes.

Approaching Splendid Catalysts for Li-CO2 Battery from the Theory to Practical Designing: A Review

Lithium carbon dioxide (Li-CO2) batteries, noted for their high discharge voltage of approximately 2.8 V and substantial theoretical specific energy of 1876 Wh kg-1, represent a promising avenue for new energy sources and CO2 emission reduction. However, the practical application of these batteries faces significant hurdles, particularly at high current densities and over extended cycle lives, due to their complex reaction mechanisms and slow kinetics. This paper delves into the recent advancements in cathode catalysts for Li-CO2 batteries, with a specific focus on the designing philosophy from composition, geometry, and homogeneity of the catalysts to the proper test conditions and real-world application. It surveys the possible catalytic mechanisms, giving readers a brief introduction of how the energy is stored and released as well as the critical exploration of the relationship between material properties and performances. Specifically, optimization and standardization of test conditions for Li-CO2 battery research is highlighted to enhance data comparability, which is also critical to facilitate the practical application of Li-CO2 batteries. This review aims to bring up inspiration from previous work to advance the design of more effective and sustainable cathode catalysts, tailored to meet the practical demands of Li-CO2 batteries.

Graphite conjugated nickel phthalocyanine for efficient CO2 electroreduction and Zn-CO2 batteries

The linking chemistry between molecular catalysts and substrates is a crucial challenge for enhancing electrocatalytic performance. Herein, we elucidate the influence of various immobilization methods of amino-substituted Ni phthalocyanine catalysts on their electrocatalytic CO2 reduction reaction (eCO2RR) activity. A graphite-conjugated Ni phthalocyanine, Ni(NH2)8Pc-GC, demonstrates remarkable electrocatalytic performance both in H-type and flow cells. In situ infrared spectroscopy and theoretical calculations reveal that the graphite conjugation, through strong electronic coupling, increases the electron density of the active site, reduces the adsorption energy barrier of *COOH, and enhances the catalytic performance. As the cathode catalyst, Ni(NH2)8Pc-GC also displays remarkable charge-discharge cycle stability of over 50 hours in a Zn-CO2 battery. These findings underscore the significance of immobilization methods and highlight the potential for further advancements in eCO2RR.

GFP Chromophore Integrated Conjugated Microporous Polymers toward Bioinspired Photocatalytic CO2 Reduction to CO

The development of highly active, durable, and low-cost metal-free catalysts for the photocatalytic CO2 reduction reaction (CO2RR) is an efficient and environmentally friendly solution to address significant problems like global warming and high energy demand. In the present study, we have demonstrated the design and synthesis of a donor-acceptor based conjugated microporous polymer (CMP), TPA-GFP, by integrating an electron donor, tris(4-ethynylphenyl)amine (TPA), with a green fluorescent protein chromophore analogue (Z)-4-(2-hydroxy-3,5-diiodobenzylidene)-1-(4-iodophenyl)-2-methyl-1H-imidazol-5(4H)-one (o-HBDI-I3) (GFP). In comparison to nondonor 1,3,5-triethynylbenzene (TEB) based TEB-GFP CMP, photocatalytic CO2 reduction using donor-acceptor based TPA-GFP CMP displays a 3-fold increment of CO production yield with a maximum CO yield of 1666 μmol g-1 at 12 h. Further, the CO selectivity increases significantly from a mere 54% in TEB-GFP to an impressive 95% in TPA-GFP. The impressive CO2 reduction efficiency and selectivity for TPA-GFP can be attributed to the efficient light-harvesting capability and facile charge separation and migration through donor-acceptor building units of the CMP. The mechanistic aspect of the photocatalytic CO2 reduction process is explored using in situ DRIFTS and DFT calculation, and a plausible photocatalytic mechanism is proposed.

Pressure-Dependent CO2 Electroreduction to Methane over Asymmetric Cu-N2 Single-Atom Sites

Single-atom catalysts (SACs) with unitary active sites hold great promise for realizing high selectivity toward a single product in the CO2 electroreduction reaction (CO2RR). However, achieving high Faradaic efficiency (FE) of multielectron products like methane on SACs is still challenging. Herein, we report a pressure-regulating strategy that achieves 83.5 ± 4% FE for the CO2-to-CH4 conversion on the asymmetric Cu-N2 sites, representing one of the best CO2-to-CH4 performances. Elevated CO2 pressure was demonstrated as an efficient way to inhibit the hydrogen evolution reaction via promoting the competing adsorption of reactant CO2, regardless of the nature of the active sites. Meanwhile, the asymmetric Cu-N2 structure could endow the Cu sites with stronger electronic coupling with *CO, thus suppressing the desorption of *CO and facilitating the following hydrogenation of *CO to *CHO. This work provides a synergetic strategy of the pressure-induced reaction environment regulating and the electronic structure modulating for selective CO2RR toward targeted products.

Synergistic Effects of Amine Functional Groups and Enriched-Atomic-Iron Sites in Carbon Dots for Industrial-Current-Density CO2 Electroreduction

Metal phthalocyanine molecules with Me-N4 centers have shown promise in electrocatalytic CO2 reduction (eCO2R) for CO generation. However, iron phthalocyanine (FePc) is an exception, exhibiting negligible eCO2R activity due to a higher CO2 to *COOH conversion barrier and stronger *CO binding energy. Here, amine functional groups onto atomic-Fe-rich carbon dots (Af-Fe-CDs) are introduced via a one-step solvothermal molecule fusion approach. Af-Fe-CDs feature well-defined Fe-N4 active sites and an impressive Fe loading (up to 8.5 wt%). The synergistic effect between Fe-N4 active centers and electron-donating amine functional groups in Af-Fe-CDs yielded outstanding CO2-to-CO conversion performance. At industrial-relevant current densities exceeding 400 mA cm-2 in a flow cell, Af-Fe-CDs achieved >92% selectivity, surpassing state-of-the-art CO2-to-CO electrocatalysts. The in situ electrochemical FTIR characterization combined with theoretical calculations elucidated that Fe-N4 integration with amine functional groups in Af-Fe-CDs significantly reduced energy barriers for *COOH intermediate formation and *CO desorption, enhancing eCO2R efficiency. The proposed synergistic effect offers a promising avenue for high-efficiency catalysts with elevated atomic-metal loadings.

Robust Electrocatalytic CO2 Reduction in Acid Enabled by "Molecularly Charged" Cobalt Phthalocyanine: A Profound Understanding from Electric Double Layer

Electrocatalytic CO2 reduction (eCO2R) in acid holds promise in renewable electricity-powered CO2 utilization with high efficiency, but the hydrogen evolution reaction (HER) often prevails and results in a low eCO2R selectivity. Here, using cobalt phthalocyanine/Ketjen black (CoPc/KB) as the model catalysts, we systematically study the effect of active site density, operational current density, and hydrated cations on the acidic eCO2R selectivity and decipher it through the componential dynamics of electric double layer (EDL). The optimal CoPc-4/KB demonstrates a near-unity CO Faradaic efficiency from 50 to 400 mA cm-2 and superb operational stability (>120 h) at 100 mA cm-2. Aided by in situ Raman and infrared spectroscopies, we reveal that the proper cations establish an electrostatic shield for mitigating bulk H+ penetration and mediate the interfacial water structure for suppressing HER. This study should elicit further profound thinking on robust eCO2R system design from the perspective of multiphasic and dynamic EDL.

Molecular Engineering of Hydrogen-Bonded Organic Framework for Enhanced Nitrate Electroreduction to Ammonia

Electrocatalytic nitrate reduction is an efficient way to produce ammonia sustainably. Herein, we rationally designed a copper metalloporphyrin-based hydrogen-bonded organic framework (HOF-Cu) through molecular engineering strategies for electrochemical nitrate reduction. As a result, the state-of-the-art HOF-Cu catalyst exhibits high NH3 Faradaic efficiency of 93.8%, and the NH3 production rate achieves a superior activity of 0.65 mmol h-1 cm-2. The in situ electrochemical spectroscopic combined with density functional theory calculations reveals that the dispersed Cu promotes the adsorption of NO3- and the mechanism is followed by deoxidation of NO3- to *NO and accompanied by deep hydrogenation. The generated *H participates in the deep hydrogenation of intermediate with fast kinetics as revealed by operando electrochemical impedance spectroscopy, and the competing hydrogen evolution reaction is suppressed. This research provides a promising approach to the conversion of nitrate to ammonia, maintaining the nitrogen balance in the atmosphere.

The windmill, the dragon, and the frog: geometry control over the spectral, magnetic, and electrochemical properties of cobalt phthalocyanine regioisomers

For the first time, we have prepared non-aggregating phthalocyanine cobalt complexes as a set of resolved positional isomers. These compounds comprise a unique test bed for the structure-properties studies, as their optical and electrochemical properties are influenced by the planarity of the phthalocyanine macrocycle, which can be controlled by the positional isomerism of the bulky aromatic substituents at the α-phthalo sites. We support our conclusions with molecular modelling studies, which show a perfect match between the calculated and experimentally determined spectral/electrochemical values. We challenge a common perception that the NMR spectra of cobalt phthalocyanines cannot be measured due to the paramagnetic nature of Co(II). We suggest instead that the key factors affecting the NMR spectral resolution are molecular aggregation and π-π stacking. These interactions are suppressed by the bulky peripheral substituents on the cobalt phthalocyanines prepared, making these isomeric compounds an excellent tool for paramagnetic NMR studies.

Multi-atomic loaded C2N1 catalysts for CO2 reduction to CO or formic acid

In recent years, the development of highly active and selective electrocatalysts for the electrochemical reduction of CO2 to produce CO and formic acid has aroused great interest, and can reduce environmental pollution and greenhouse gas emissions. Due to the high utilization of atoms, atom-dispersed catalysts are widely used in CO2 reduction reactions (CO2RRs). Compared with single-atom catalysts (SACs), multi-atom catalysts have more flexible active sites, unique electronic structures and synergistic interatomic interactions, which have great potential in improving the catalytic performance. In this study, we established a single-layer nitrogen-graphene-supported transition metal catalyst (TM-C2N1) based on density functional theory, facilitating the reduction of CO2 to CO or HCOOH with single-atom and multi-atomic catalysts. For the first time, the TM-C2N1 monolayer was systematically screened for its catalytic activity with ab initio molecular dynamics, density of states, and charge density, confirming the stability of the TM-C2N1 catalyst structure. Furthermore, the Gibbs free energy and electronic structure analysis of 3TM-C2N1 revealed excellent catalytic performance for CO and HCOOH in the CO2RR with a lower limiting potential. Importantly, this work highlights the moderate adsorption energy of the intermediate on 3TM-C2N1. It is particularly noteworthy that 3Mo-C2N1 exhibited the best catalytic performance for CO, with a limiting potential (UL) of -0.62 V, while 3Ti-C2N1 showed the best performance for HCOOH, with a corresponding UL of -0.18 V. Additionally, 3TM-C2N1 significantly inhibited competitive hydrogen evolution reactions. We emphasize the crucial role of the d-band center in determining products, as well as the activity and selectivity of triple-atom catalysts in the CO2RR. This theoretical research not only advances our understanding of multi-atomic catalysts, but also offers new avenues for promoting sustainable CO2 conversion.

Ultrasensitive cortisol electrochemical immunosensor amplifying by Au single-atom nanozymes and HRP enzymes

Cortisol, a corticosteroid hormone as a primary stress hormone response to internal and external stress, has been regarded as a gold standard reliable biomarker to evaluate human mental stress. The double enzymes strategy, using nanozyme and enzyme amplifying the electrochemical signal, has been widely used to improve the performance of electrochemical biosensors. An ultra-sensitive electrochemical cortisol sensor based on Au single-atom nanozymes had been fabricated through HRP labeled anti-cortisol antibody binding with Au by Au-S bond. Based on the high catalytic activity of Au single-atom nanozymes and the high selectivity of HRP-labeled anti-cortisol antibodies, the cortisol electrochemical sensor-based Au single-atom nanozymes had an excellent response to cortisol, such as high electrochemical activity, high sensitivity, high selectivity, and wide linear range (0.15-300 ng mL-1) and low detection (0.48 pg mL-1) through the four-parameter logistic model with 95% confidence. The electrochemical cortisol sensor was used to determine the cortisol concentration of human saliva at different times.

Insight into Impacts of π-π Assembly on Phthalocyanine Based Heterogeneous Molecular Electrocatalysis

Electrochemical CO2 reduction (CO2R) to feedstocks competes with the hydrogen evolution reaction (HER). Cobalt phthalocyanine (CoPc) immobilized onto carbon driven by π-π interaction represents a classical type of heterogeneous molecular catalyst for CO2R. However, the impacts of π conjugation on the electrocatalysis have not been clarified. Herein, the electrochemical properties of CoPc were investigated by comparison of its analogue to 2,3-naphthalocyanine cobalt (NapCo) having extended π conjugation. It is found that CoPc is redox-active on carbon to provide low oxidized Co sites for improving the CO2R activity and selectivity, while NapCo on carbon turned out to be redox-inert leading to lower performance. In addition, the redox-mediated mechanism for CO2R on CoPc tends to operate with increasing electrolyte alkalinity, which further enhances the reaction selectivity. We speculated that moderate π conjugation allows the redox-mediated mechanism on CoPc, which is critical to promote CO2R performance while depressing the competing HER.

Kinetic isotope effect offers selectivity in CO2 reduction

A binuclear Ni complex with N,O donors catalyzes CO2 reduction via its Ni(I) state. The product distribution when H2O is used as a proton source shows similar yields for CO, HCOOH and H2. However, when D2O is used, the product distribution shows a ∼65% selectivity for HCOOH. In situ FTIR indicates that the reaction involves a Ni-COO* and a Ni-CO intermediate. Differences in H/D KIEs on different protonation pathways determine the selectivity of CO2 reduction.

Weak Bimetal Coupling-Assisted MN4 Catalyst for Enhanced Carbon Dioxide Reduction Reaction

The design of multimetal catalysts holds immense significance for efficient CO2 capture and its conversion into economically valuable chemicals. Herein, heterobimetallic catalysts (MiMo)L were exploited for the CO2 reduction reactions (CO2RR) using relativistic density functional theory (DFT). The octadentate Pacman-like polypyrrolic ligand (H4L) accommodates two metal ions (Mo, W, Nd, and U) inside (Mi) and outside (Mo) its month, rendering a weak bimetal coupling-assisted MN4 catalytically active site. Adsorption reactions have access to energetically stable coordination modes of -OCO, -OOC, and -(OCO)2, where the donor atom(s) are marked in bold. Among all of the species, (UiMoo)L releases the most energy. Along CO2RR, it favors to produce CO. The high-efficiency CO2 reduction is attributed to the size matching of U with the ligand mouth and the effective manipulation of the electron density of both ligand and bimetals. The mechanism in which heterobimetals synergetically capture and reduce CO2 has been postulated. This establishes a reference in elaborating on the complicated heterogeneous catalysis.

Structural engineering of atomic catalysts for electrocatalysis

As a burgeoning category of heterogeneous catalysts, atomic catalysts have been extensively researched in the field of electrocatalysis. To satisfy different electrocatalytic reactions, single-atom catalysts (SACs), diatomic catalysts (DACs) and triatomic catalysts (TACs) have been successfully designed and synthesized, in which microenvironment structure regulation is the core to achieve high-efficiency catalytic activity and selectivity. In this review, the effect of the geometric and electronic structure of metal active centers on catalytic performance is systematically introduced, including substrates, central metal atoms, and the coordination environment. Then theoretical understanding of atomic catalysts for electrocatalysis is innovatively discussed, including synergistic effects, defect coupled spin state change and crystal field distortion spin state change. In addition, we propose the challenges to optimize atomic catalysts for electrocatalysis applications, including controlled synthesis, increasing the density of active sites, enhancing intrinsic activity, and improving the stability. Moreover, the structure-function relationships of atomic catalysts in the CO2 reduction reaction, nitrogen reduction reaction, oxygen reduction reaction, hydrogen evolution reaction, and oxygen evolution reaction are highlighted. To facilitate the development of high-performance atomic catalysts, several technical challenges and research orientations are put forward.

Mono-, bi- and tri-metallic Fe-based platinum group metal-free electrocatalysts derived from phthalocyanine for oxygen reduction reaction in alkaline media

In this manuscript, a comprehensive study is presented on Fe-based electrocatalysts with mono, bi, and tri-metallic compositions, emphasizing the influence of processing-structure correlations on the electrocatalytic activity for the oxygen reduction reaction (ORR) in the alkaline medium. These electrocatalysts were synthesized through the mixing of transition metal phthalocyanines (TM-Pc) with conductive carbon support, followed by controlled thermal treatment at specific temperatures (600 °C and 900 °C). An extensive analysis was conducted, employing various techniques, including X-ray Absorption Spectroscopy (XAS), Transmission Electron Microscopy (TEM), and X-ray Diffraction (XRD), providing valuable insights into the structural characteristics of the synthesized nanoparticles. Importantly, an increase in the Fe-Pc weight percentage from 10% to 30% enhanced the ORR activity, although not proportionally. Furthermore, a comparative analysis between mono, bi, and tri-metallic samples subjected to different functionalization temperatures highlighted the superior electrocatalytic activity of electrocatalysts functionalized at 600 °C, particularly Fe 600 and Fe-Ni-Cu 600. These electrocatalysts featured Eon values of 0.96 V vs. RHE and E1/2 values of 0.9 V vs. RHE, with the added benefit of reduced anionic peroxide production. The potential of these Fe-based electrocatalysts to enhance ORR efficiency is underscored by this research, contributing to the development of more effective and sustainable electrocatalysts for energy conversion technologies.

Molecular Engineering of Copper Phthalocyanine for CO2 Electroreduction to Methane

Efficient electrochemical CO2 reduction reaction (ECO2RR) to multi-electron reductive products remains a great challenge. Herein, molecular engineering of copper phthalocyanines (CuPc) was explored by modifying electron-withdrawing groups (EWGs) (cyano, sulfonate anion) and electron-donating groups (EDGs) (methoxy, amino) to CuPc, then supporting onto carbon paper or carbon cloth by means of droplet coating, loading with carbon nanotubes and coating in polypyrrole (PPy). The results showed that the PPy-coated CuPc effectively catalysed ECO2RR to CH4. Interestingly, experimental results and DFT calculations indicated EWGs markedly improved the selectivity of methane for the reason that the introduction of EWGs reduces electron density of catalytic active center, resulting in a positive move to initial reduction potential. Otherwise, the modification of EDGs significantly reduces the selectivity towards methane. This electronic effect and heterogenization of CuPc are facile and effective molecular engineering, benefitting the preparation of electrocatalysts for further reduction of CO2.

Identification of Synergies in Fe, Co-Coordinated Polyphthalocyanines Scaffolds for Electrochemical CO2 Reduction Reaction

The synergistic interaction between the isolated metal sites promoted the electrocatalytic activity of the catalysts. However, the structural heterogeneity of the isolated sites makes it challenging to evaluate this effect accurately. In this work, metal-coordinated polyphthalocyanine molecules (Fe-PPc, Co-PPc, FeCo-PPc) with long-range ordered and precise coordination structures are used as a platform to study the synergies of different isolated metal sites in the electrochemical CO2 reduction reaction. The combination means of experimental and theoretical calculation clearly reveal that the coexistence of Fe and Co sites in PPc significantly enhances the conjugation effect of the macrocycle. This enhancement subsequently causes the metal sites to lose more electrons, thereby improving their adsorption of CO2 and facilitating the formation of intermediate *COOH on them. As a result, FeCo-PPc achieves a CO partial current density of about 57.4 mA/cm2 with a high turnover frequency of over 49000 site-1 h-1 at -0.9 V (vs RHE).

Unraveling Valence Electron Number Dependent Excitonic Effects over M1-N3C1 Sites in Single-Atom Catalysts

Excitonic effects significantly influence the selective generation of reactive oxygen species and photothermal conversion efficiency in photocatalytic reactions; however, the intrinsic factors governing excitonic effects remain elusive. Herein, a series of single-atom catalysts with well-defined M1-N3C1 (M = Mn, Fe, Co, and Ni) active sites are designed and synthesized to investigate the structure-activity relationship between photocatalytic materials and excitonic effects. Comprehensive characterization and theoretical calculations unveil that excitonic effects are positively correlated with the number of valence electrons in single metal atoms. The single Mn atom with 5.93 valence electrons exhibits the weakest excitonic effects, which dominate superoxide radical (O2•-) generation through charge transfer and enhance photothermal conversion efficiency. Conversely, the single Ni atom with 9.27 valence electrons exhibits the strongest excitonic effects, dominating singlet oxygen (1O2) generation via energy transfer while suppressing photothermal conversion efficiency. Based on the valence electron number dependent excitonic effects, a reaction environment with hyperthermia and abundant cytotoxic O2•- is designed, achieving efficient and stable water disinfection. This work reveals single metal atom dependent excitonic effects and presents an atomic-level methodology for catalytic application targeted reaction environment tailoring.

Materials descriptors of machine learning to boost development of lithium-ion batteries

Traditional methods for developing new materials are no longer sufficient to meet the needs of the human energy transition. Machine learning (ML) artificial intelligence (AI) and advancements have caused materials scientists to realize that using AI/ML to accelerate the development of new materials for batteries is a powerful potential tool. Although the use of certain fixed properties of materials as descriptors to act as a bridge between the two separate disciplines of AI and materials chemistry has been widely investigated, many of the descriptors lack universality and accuracy due to a lack of understanding of the mechanisms by which AI/ML operates. Therefore, understanding the underlying operational mechanisms and learning logic of AI/ML has become mandatory for materials scientists to develop more accurate descriptors. To address those challenges, this paper reviews previous work on AI, machine learning and materials descriptors and introduces the basic logic of AI and machine learning to help materials developers understand their operational mechanisms. Meanwhile, the paper also compares the accuracy of different descriptors and their advantages and disadvantages and highlights the great potential value of accurate descriptors in AI/machine learning applications for battery research, as well as the challenges of developing accurate material descriptors.

Carbon Catalysts Empowering Sustainable Chemical Synthesis via Electrochemical CO2 Conversion and Two-Electron Oxygen Reduction Reaction

Carbon materials hold significant promise in electrocatalysis, particularly in electrochemical CO2 reduction reaction (eCO2 RR) and two-electron oxygen reduction reaction (2e- ORR). The pivotal factor in achieving exceptional overall catalytic performance in carbon catalysts is the strategic design of specific active sites and nanostructures. This work presents a comprehensive overview of recent developments in carbon electrocatalysts for eCO2 RR and 2e- ORR. The creation of active sites through single/dual heteroatom doping, functional group decoration, topological defect, and micro-nano structuring, along with their synergistic effects, is thoroughly examined. Elaboration on the catalytic mechanisms and structure-activity relationships of these active sites is provided. In addition to directly serving as electrocatalysts, this review explores the role of carbon matrix as a support in finely adjusting the reactivity of single-atom molecular catalysts. Finally, the work addresses the challenges and prospects associated with designing and fabricating carbon electrocatalysts, providing valuable insights into the future trajectory of this dynamic field.

N and OH-Immobilized Cu3 Clusters In Situ Reconstructed from Single-Metal Sites for Efficient CO2 Electromethanation in Bicontinuous Mesochannels

Cu-based catalysts hold promise for electrifying CO2 to produce methane, an extensively used fuel. However, the activity and selectivity remain insufficient due to the lack of catalyst design principles to steer complex CO2 reduction pathways. Herein, we develop a concept to design carbon-supported Cu catalysts by regulating Cu active sites' atomic-scale structures and engineering the carbon support's mesoscale architecture. This aims to provide a favorable local reaction microenvironment for a selective CO2 reduction pathway to methane. In situ X-ray absorption and Raman spectroscopy analyses reveal the dynamic reconstruction of nitrogen and hydroxyl-immobilized Cu3 (N,OH-Cu3) clusters derived from atomically dispersed Cu-N3 sites under realistic CO2 reduction conditions. The N,OH-Cu3 sites possess moderate *CO adsorption affinity and a low barrier for *CO hydrogenation, enabling intrinsically selective CO2-to-CH4 reduction compared to the C-C coupling with a high energy barrier. Importantly, a block copolymer-derived carbon fiber support with interconnected mesopores is constructed. The unique long-range mesochannels offer an H2O-deficient microenvironment and prolong the transport path for the CO intermediate, which could suppress the hydrogen evolution reaction and favor deep CO2 reduction toward methane formation. Thus, the newly developed catalyst consisting of in situ constructed N,OH-Cu3 active sites embedded into bicontinuous carbon mesochannels achieved an unprecedented Faradaic efficiency of 74.2% for the CO2 reduction to methane at an industry-level current density of 300 mA cm-2. This work explores effective concepts for steering desirable reaction pathways in complex interfacial catalytic systems via modulating active site structures at the atomic level and engineering pore architectures of supports on the mesoscale to create favorable microenvironments.

Active Sites of Cobalt Phthalocyanine in Electrocatalytic CO2 Reduction to Methanol

Many metal coordination compounds catalyze CO2 electroreduction to CO, but cobalt phthalocyanine hybridized with conductive carbon such as carbon nanotubes is currently the only one that can generate methanol. The underlying structure-reactivity correlation and reaction mechanism desperately demand elucidation. Here we report the first in situ X-ray absorption spectroscopy characterization, combined with ex situ spectroscopic and electrocatalytic measurements, to study CoPc-catalyzed CO2 reduction to methanol. Molecular dispersion of CoPc on CNT surfaces, as evidenced by the observed electronic interaction between the two, is crucial to fast electron transfer to the active sites and multi-electron CO2 reduction. CO, the key intermediate in the CO2 -to-methanol pathway, is found to be labile on the active site, which necessitates a high local concentration in the microenvironment to compete with CO2 for active sites and promote methanol production. A comparison of the electrocatalytic performance of structurally related porphyrins indicates that the bridging aza-N atoms of the Pc macrocycle are critical components of the CoPc active site that produces methanol. In situ X-ray absorption spectroscopy identifies the active site as Co(I) and supports an increasingly non-centrosymmetric Co coordination environment at negative applied potential, likely due to the formation of a Co-CO adduct during the catalysis.

Electrochemical C-N Bond Formation within Boron Imidazolate Cages Featuring Single Copper Sites

Electrocatalysis expands the ability to generate industrially relevant chemicals locally and on-demand with intermittent renewable energy, thereby improving grid resiliency and reducing supply logistics. Herein, we report the feasibility of using molecular copper boron-imidazolate cages, BIF-29(Cu), to enable coupling between the electroreduction reaction of CO2 (CO2RR) with NO3- reduction (NO3RR) to produce urea with high selectivity of 68.5% and activity of 424 μA cm-2. Remarkably, BIF-29(Cu) is among the most selective systems for this multistep C-N coupling to-date, despite possessing isolated single-metal sites. The mechanism for C-N bond formation was probed with a combination of electrochemical analysis, in situ spectroscopy, and atomic-scale simulations. We found that NO3RR and CO2RR occur in tandem at separate copper sites with the most favorable C-N coupling pathway following the condensation between *CO and NH2OH to produce urea. This work highlights the utility of supramolecular metal-organic cages with atomically discrete active sites to enable highly efficient coupling reactions.

Chlorine-Coordinated Unsaturated Ni-N2 Sites for Efficient Electrochemical Carbon Dioxide Reduction

Heteroatom-doping is an effective method for modifying the geometric symmetry of metal-nitrogen-carbon (M-N-C) single-atom catalysts and thereby tuning the electronic structure. Up to now, most of the current reports have concentrated on introducing heteroatoms into the highly symmetrical M-N4 structure. The coordination-unsaturated M-N2 structure is more sterically favorable for the insertion of alien atoms to optimize the electronic structure. Herein, a Ni-N2 catalyst with out-of-plane coordinated chlorine (Cl) atoms (Ni-N2 Cl/C) is successfully constructed on chlorine-functionalized carbon supports (C-Cl) for an efficient carbon dioxide reduction reaction (CO2 RR). Density functional theory calculations demonstrate that the prepared Ni-N2 Cl/C catalyst exhibits a higher capability in balancing COOH* formation and CO* desorption. In addition, in situ Raman spectra confirm that the lower CO binding energy on the Ni-N2 Cl/C facilitates CO escape, leading to excellent CO2 RR performance. A high CO Faradaic efficiency (FECO ) of more than 80% is achieved from -0.6 to -1.2 V versus reversible hydrogen electrode on the Ni-N2 Cl/C and it exhibits negligible FECO and current declination over a 40-h stability test. Furthermore, a high turnover frequency (TOF) value of 15 808 h-1 is obtained, which is more than ten times that of Ni-N2 /C (1476 h-1 ) without coordinated Cl atoms.

Boron-Doped Nickel-Nitrogen-Carbon Single-Atom Catalyst for Boosting Electrochemical CO2 Reduction

Tuning the coordination environment of the metal center in metal-nitrogen-carbon (M-N-C) single-atom catalysts via heteroatom-doping (oxygen, phosphorus, sulfur, etc.) is effective for promoting electrocatalytic CO2 reduction reaction (CO2 RR). However, few studies are investigated establishing efficient CO2 reduction by introducing boron (B) atoms to regulate the M-N-C structure. Herein, a B-C3 N4 self-sacrifice strategy is developed to synthesize B, N co-coordinated Ni single atom catalyst (Ni-BNC). X-ray absorption spectroscopy and high-angle annular dark field scanning transmission electron microscopy confirm the structure (Ni-N3 B/C). The Ni-BNC catalyst presents a maximum CO Faradaic efficiency (FECO ) of 98.8% and a large CO current density (jCO ) of -62.9 mA cm-2 at -0.75 and -1.05 V versus reversible hydrogen electrode, respectively. Furthermore, FECO could be maintained above 95% in a wide range of potential windows from -0.65 to -1.05 V. In situ experiments and density functional theory calculations demonstrate the Ni-BNC catalyst with B atoms coordinated to the central Ni atoms could significantly reduce the energy barrier for the conversion of *CO2 to *COOH, leading to excellent CO2 RR performance.

Catalytic ozonation mechanism over M1-N3C1 active sites

The structure-activity relationship in catalytic ozonation remains unclear, hindering the understanding of activity origins. Here, we report activity trends in catalytic ozonation using a series of single-atom catalysts with well-defined M1-N3C1 (M: manganese, ferrum, cobalt, and nickel) active sites. The M1-N3C1 units induce locally polarized M - C bonds to capture ozone molecules onto M atoms and serve as electron shuttles for catalytic ozonation, exhibiting excellent catalytic activities (at least 527 times higher than commercial manganese dioxide). The combined in situ characterization and theoretical calculations reveal single metal atom-dependent catalytic activity, with surface atomic oxygen reactivity identified as a descriptor for the structure-activity relationship in catalytic ozonation. Additionally, the dissociation barrier of surface peroxide species is proposed as a descriptor for the structure-activity relationship in ozone decomposition. These findings provide guidelines for designing high-performance catalytic ozonation catalysts and enhance the atomic-level mechanistic understanding of the integral control of ozone and methyl mercaptan.

Self-Accelerating Effect in a Covalent-Organic Framework with Imidazole Groups Boosts Electroreduction of CO2 to CO

Solvent effect plays an important role in catalytic reaction, but there is little research and attention on it in electrochemical CO2 reduction reaction (eCO2 RR). Herein, we report a stable covalent-organic framework (denoted as PcNi-im) with imidazole groups as a new electrocatalyst for eCO2 RR to CO. Interestingly, compared with neutral conditions, PcNi-im not only showed high Faraday efficiency of CO product (≈100 %) under acidic conditions (pH ≈ 1), but also the partial current density was increased from 258 to 320 mA cm-2 . No obvious degradation was observed over 10 hours of continuous operation at the current density of 250 mA cm-2 . The mechanism study shows that the imidazole group on the framework can be protonated to form an imidazole cation in acidic media, hence reducing the surface work function and charge density of the active metal center. As a result, CO poisoning effect is weakened and the key intermediate *COOH is also stabilized, thus accelerating the catalytic reaction rate.

Amphiphilic Cobalt Phthalocyanine Boosts Carbon Dioxide Reduction

Due to the easy accessibility, chemical stability, and structural tunability of the macrocyclic skeleton, cobalt phthalocyanines immobilized on carbon supports offer an ideal research model for advanced electrochemical carbon dioxide reduction reaction (eCO2 RR). In this work, an amphiphilic cobalt phthalocyanine (TC-CoPc) is loaded on multiwalled carbon nanotubes to reveal the roles of hydrophilic/hydrophobic properties on catalytic efficiency. Surprisingly, the resultant electrode exhibits a CO Faradaic efficiency (FECO ) of 95% for CO2 RR with turnover frequency (TOF) of 29.4 s-1 at an overpotential of 0.585 V over long-term electrolysis in a H-type cell. In the membrane electrode assembly (MEA) device, the boosted transport of water vapor to the catalyst layer slows down carbonate crystallization and enhances the stability of the electrode, with FECO value of >99% over 27 h at -0.25 A, representing the best selectivity and stability among reported molecular catalysts in MEA devices. The amphiphilic cobalt phthalocyanine, which decreases interfacial charge and mass transfer resistance and maintains effective contact between active sites and the electrolyte, highlights the exceptional CO2 conversion from a molecular perspective.

Intermetallic Compound with CuNi Sites for Enhancing the Selectivity of Electrochemical CO2 Conversion

Although single-metal-site (SMS) catalysts have long been explored for the electrochemical CO2 reduction reaction (EC-CO2RR), the reactivity and selectivity of SMS catalysts remain rather low due to the competing hydrogen evolution reaction (HER). To improve the selectivity, in this work, a novel intermetallic particle of CuNi is decorated on the N-doped carbon substrate, which was first precisely fabricated by scarifying the bimetal-doped metal-organic framework (MOF). Thanks to the neighboring synergistic functions of Cu and Ni sites, CuNi/NC prominently boosts the electroreduction of CO2, far more than the SMS catalysts of Cu/NC and Ni/NC. Further, CuNi/NC presents superior selectivity toward CO with faradaic efficiency over a wide range of potentials (surpassing 90% at 0.6-1.0 V vs RHE, up to 98% at 0.6 V vs RHE) and excellent durability. The experimental results and theoretical calculations reveal that the Ni species can be highly activated due to the neighboring Cu species, which considerably facilitates the formation of an intermediate of COOH* and consequently enhances the selectivity of the reduction of CO2 to CO. This work paves a general way to precisely fabricate catalysts with multiple metal species and also demonstrates the significant synergetic efficiency between the neighboring sites to improve the catalytic performance.

Non-Covalent Interactions Mimic the Covalent: An Electrode-Orthogonal Self-Assembled Layer

Charge-transfer events central to energy conversion and storage and molecular sensing occur at electrified interfaces. Synthetic control over the interface is traditionally accessed through electrode-specific covalent tethering of molecules. Covalent linkages inherently limit the scope and the potential stability window of molecularly tunable electrodes. Here, we report a synthetic strategy that is agnostic to the electrode's surface chemistry to molecularly define electrified interfaces. We append ferrocene redox reporters to amphiphiles, utilizing non-covalent electrostatic and van der Waals interactions to prepare a self-assembled layer stable over a 2.9 V range. The layer's voltammetric response and in situ infrared spectra mimic those reported for analogous covalently bound ferrocene. This design is electrode-orthogonal; layer self-assembly is reversible and independent of the underlying electrode material's surface chemistry. We demonstrate that the design can be utilized across a wide range of electrode material classes (transition metal, carbon, carbon composites) and morphologies (nanostructured, planar). Merging atomically precise organic synthesis of amphiphiles with in situ non-covalent self-assembly at polarized electrodes, our work sets the stage for predictive and non-fouling synthetic control over electrified interfaces.

Contemporary Strategies for Immobilizing Metallophthalocyanines for Electrochemical Transformations of Carbon Dioxide

Metallophthalocyanine (PcM) coordination complexes are well-known mediators of the electrochemical reduction of carbon dioxide (CO2). They have many properties that show promise for practical applications in the energy sector. Such properties include synthetic flexibility, a high stability, and good efficiencies for the reduction of CO2 to useful feedstocks, such as carbon monoxide (CO). One of the ongoing challenges that needs to be met is the incorporation of PcM into the heterogeneous materials that are used in a great many CO2-reduction devices. Much progress has been made in the last decade and there are now several promising approaches to incorporate PcM into a range of materials, from simple carbon-adsorbed preparations to extended polymer networks. These approaches all have important advantages and drawbacks. In addition, investigations have led to new proposals regarding CO2 reduction catalytic cycles and other operational features that are crucial to function. Here, we describe developments in the immobilization of PcM CO2 reduction catalysts in the last decade (2013 to 2023) and propose promising avenues and strategies for future research.