CO2 Catalysis Research Articles

Modeling Adsorption of CO2 in Rutile Metallic Oxide Surfaces: Implications in CO2 Catalysis

CO2 is the most abundant greenhouse gas, and for this reason, it is the main target for finding solutions to climatic change. A strategy of environmental remediation is the transformation of CO2 to an aggregated value product to generate a carbon-neutral cycle. CO2 reduction is a great challenge because of the large C=O dissociation energy, ~179 kcal/mol. Heterogeneous photocatalysis is a strategy to address this issue, where the adsorption process is the fundamental step. The focus of this work is the role of adsorption in CO2 reduction by means of modeling the CO2 adsorption in rutile metallic oxides (TiO2, GeO2, SnO2, IrO2 and PbO2) using Density Functional Theory (DFT) and periodic DFT methods. The comparison of adsorption on different metal oxides forming the same type of crystal structure allowed us to observe the influence of the metal in the adsorption process. In the same way, we performed a comparison of the adsorption capability between two different surface planes, (001) and (110). Two CO2 configurations were observed, linear and folded: the folded conformations were observed in TiO2, GeO2 and SnO2, while the linear conformations were present in IrO2 and PbO2. The largest adsorption efficiency was displayed by the (001) surface planes. The CO2 linear and folded configurations were related to the interaction of the oxygen on the metallic surface with the adsorbate carbon, and the linear conformations were associated with the physisorption and folded configurations with chemisorption. TiO2 was the material with the best performance for CO2 interactions during the adsorption.

Aluminum Porphyrin-Based Ionic Porous Aromatic Frameworks Having High Surface Areas and Highly Dispersed Dual-Function Sites for Boosting the Catalytic Conversion of CO2 into Cyclic Carbonates.

Multifunctionalization of porous organic polymers toward synergistic CO2 catalysis has drawn much attention in recent decades, but it still faces many challenges. Herein, we develop a facile, simple, and efficient strategy to obtain a series of aluminum porphyrin-based ionic porous aromatic frameworks (iPAFs), which are considered excellent bifunctional catalysts for converting CO2 into cyclic carbonates without any cocatalyst under mild and solvent-free conditions. By increasing the amounts of tetraphenylmethane fragments in the porphyrin backbones, the cooperative effect between Lewis acidic metal centers and nucleophilic ionic sites has been enhanced and then the significant improvement of catalytic activity can be achieved owing to the high surface areas (up to 719 m2·g-1), abundant hierarchical micro-mesopores, and prominent CO2 adsorption capacities (up to 1.8 mmol·g-1 at 273 K) as well as highly dispersed dual-function sites. More fascinatingly, high-active AlPor-iPAF-3 enables CO2 cycloaddition to perform with diluted CO2 (15% CO2 in 85% N2, v/v) or under ambient conditions. Therefore, this postsynthetic modification procedure in combination with the framework dilution strategy provides a new approach to fabricating high-surface-area metalloporphyrin-based porous ionic polymers (PIPs) with hierarchical structures, which is conducive to improving the accessibility of multiple active sites around substrates.

High-Entropy Alloys FeCoNiCuX (X = Al, Mo)-Ce0.8Sm0.2O2 as High-Performance Solid Oxide Fuel Cell Anodes

High-entropy alloys (HEAs) have received a lot of attention in electrocatalysis due to their potent synergistic effects of uniformly mixing many elements. In this study, HEAs FeCoNiCuX (X = Al, Mo)-Ce0.8Sm0.2O2 (SDC) are considered as a prospective intermediate temperature solid oxide fuel cell (SOFC) anode. FeCoNiCuX-SDC as a SOFC anode shows comparable high conductivity with a Ni-based anode and exhibits outstanding catalytic capability for H2, CH4, and CO2. The LSGM electrolyte-supported single cell with FeCoNiCuAl-SDC as anode shows maximum power densities of 779 and 526 mW cm–2 with H2 and CH4 as fuel gases and testing at 850 °C, respectively. The distribution of relaxation time analysis shows that the prime speed-limiting steps for the FeCoNiCuX-SDC anode are the adsorption/dissociation of fuel gas. X-ray photoelectron spectroscopy results showed that FeCoNiCuX HEAs with the main constituents in different valence states created more active sites, which provided a synergistic effect for H2, CH4, and CO2 catalysis.

Low Overpotential Electrochemical Reduction of CO2 to Ethanol Enabled by Cu/CuxO Nanoparticles Embedded in Nitrogen-Doped Carbon Cuboids.

The electrochemical conversion of CO2 into value-added chemicals is a promising approach for addressing environmental and energy supply problems. In this study, electrochemical CO2 catalysis to ethanol is achieved using incorporated Cu/CuxO nanoparticles into nitrogenous porous carbon cuboids. Pyrolysis of the coordinated Cu cations with nitrogen heterocycles allowed Cu nanoparticles to detach from the coordination complex but remain dispersed throughout the porous carbon cuboids. The heterogeneous composite Cu/CuxO-PCC-0h electrocatalyst reduced CO2 to ethanol at low overpotential in 0.5 M KHCO3, exhibiting maximum ethanol faradaic efficiency of 50% at -0.5 V vs. reversible hydrogen electrode. Such electrochemical performance can be ascribed to the synergy between pyridinic nitrogen species, Cu/CuxO nanoparticles, and porous carbon morphology, together providing efficient CO2 diffusion, activation, and intermediates stabilization. This was supported by the notably high electrochemically active surface area, rich porosity, and efficient charge transfer properties.

Control of CeO2 Defect Sites for Photo- and Thermal- Synergistic Catalysis of CO2 and Methanol to DMC

Control of CeO2 Defect Sites for Photo- and Thermal- Synergistic Catalysis of CO2 and Methanol to DMC

High-Surface-Area Metalloporphyrin-Based Porous Ionic Polymers by the Direct Condensation Strategy for Enhanced CO2 Capture and Catalytic Conversion into Cyclic Carbonates.

Metalloporphyrin-based porous organic polymers (POPs) that behave as advanced biomimetic nanoreactors have drawn continuous attention for heterogeneous CO2 catalysis in the past decades. Inspired by the double activation model of epoxides, the design and synthesis of metalloporphyrin-based porous ionic polymers (PIPs) are considered as one of the most promising approaches for converting CO2 to cyclic carbonates under cocatalyst- and solvent-free conditions. To overcome the obstacle of poor reaction activity of ionic monomers or highly irregular stacking architecture, in this paper, we have proposed and demonstrated a modular bottom-up approach for constructing a series of high-surface-area metalloporphyrin-based PIPs in high yields by the direct condensation strategy, thus boosting the close contact of multiple active sites and achieving the enhanced CO2 capture and catalytic conversion into cyclic carbonates with high turnover frequencies under mild conditions. These recyclable aluminum-porphyrin-based PIPs are featured with high surface areas, prominent CO2 adsorptive capacities, rigid porphyrin skeletons, and flexible ionic pendants, as well as the matched amounts and spatial positions of metal centers and ionic sites, in which is demonstrated to be one of the quite competitive catalysts. Therefore, this strategy of introducing ionic components into the porphyrin frameworks as flexible side chains rather than main chains and adjusting the reactivity ratios of comonomers by structure-oriented methods, provides feasible guidance for the multifunctionalization of metalloporphyrin-based POPs, thereby increasing the accessibility of multiple active sites and improving their synergistic catalytic behavior.

Comment on "CO2 Footprint of Thermal Versus Photothermal CO2 Catalysis".

The previously published report by Wang et al. provides universal equations for evaluating the net CO2 emission via photothermal/thermal CO2 hydrogenation reactions in batch and flow reactors, respectively. However, it remains to be discussed whether the original feed amount or feed rate of H2 should be changed accordingly when the CO2 reduction rate is selected as the variable to investigate the net CO2 emission rate of the system. If not, the reaction would not be in accordance with the stoichiometric ratio, which is inconsistent with reality, bringing about the optimistic scenario in the assessment of CO2 footprint. This work has taken the potential relationship between the original feed amount or feed rate of H2 and CO2 conversion rate into account. The effects of CO2 conversion rate on the net CO2 emission rate in the photothermal catalytic system are re-examined, the obtained trends exhibit more challenging preconditions to achieve net-zero carbon emission than those in the work by Wang etal. The quantitative results indicate that green hydrogen source is indeed vital for carbon neutrality in photothermal CO2 catalysis. Here, the viewpoints will be worth considering and be seen as complementary to the proposed carbon emission assessment equations.

Photothermal Catalytic CO2 Hydrogenation with High Activity and Tailored Selectivity Over Monodispersed Pd-Ni Nanoalloys.

Bimetallic nanomaterials exhibit excellent catalytic performance in photothermal CO2 hydrogenation due to the synergistic effect between the two metal components. However, the component-performance relationship remains unclear, which hinders the design of efficient bimetallic catalysts and the investigation of catalytic reaction mechanism. Here we illustrate the influence of the composition of binary alloy on their performance of photothermal catalytic CO2 hydrogenation by using monodispersed Pd-Ni nanocrystal as an example. Our study reveals that Ni and Pd play a significantly different role in the catalytic processes. Higher Ni component in the catalysts could lead to stronger light absorption, higher activity, and lower CO selectivity. The optimized Pd4 Ni1 -SiO2 catalyst exhibited a near-unity and stable CO production rate of 230 mmol ⋅ g-1 ⋅ h-1 under 25-sun illumination. This study paves the way for the usage of bimetal in photothermal CO2 catalysis towards more efficient solar-to-chemical energy conversions, and sheds light on some general design principles of bimetallic catalysts to balance the intrinsic properties of individual components.

Design, Synthesis, Kinetic Analysis and Pharmacophore-Directed Discovery of 3-Ethylaniline Hybrid Imino-Thiazolidinone as Potential Inhibitor of Carbonic Anhydrase II: An Emerging Biological Target for Treatment of Cancer.

Carbonic anhydrases (CA), having Zn2+ metal atoms, are responsible for the catalysis of CO2 and water to bicarbonate and protons. Any abnormality in the functioning of these enzymes may lead to morbidities such as glaucoma and different types of cancers including brain, renal and pancreatic carcinomas. To cope with the lack of presence of a promising therapeutic agent against these cancers, searching for an efficient and suitable carbonic anhydrase inhibitor is crucial. In the current study, ten novel 3-ethylaniline hybrid imino-thiazolidinones were synthesized and characterized by FTIR, NMR (1H, 13C), and mass spectrometry. Synthesis was carried out by diethyl but-2-ynedioate cyclization and different acyl thiourea substitutions of 3-ethyl amine. The CA (II) enzyme inhibition profile for all synthesized derivatives was determined. It was observed that compound 6e demonstrated highest inhibition of CA-II with an IC50 value of 1.545 ± 0.016 µM. In order to explore the pharmacophoric properties and develop structure activity relationship, in silico screening was performed. In silico investigations included density functional theory (DFT) studies, pharmacophore-guided model development, molecular docking, molecular dynamic (MD) simulations, and prediction of drug likeness scores. DFT investigations provided insight into the electronic characteristics of compounds, while molecular docking determined the binding orientation of derivatives within the CA-II active site. Compounds 6a, 6e, and 6g had a reactive profile and generated stable protein-ligand interactions with respective docking scores of -6.12, -6.99, and -6.76 kcal/mol. MD simulations were used to evaluate the stability of the top-ranked complex. In addition, pharmacophore-guided modeling demonstrated that compound 6e produced the best pharmacophore model (HHAAARR) compared to standard brinzolamide. In vitro and in silico investigations anticipated that compound 6e would be an inhibitor of carbonic anhydrase II with high efficacy. Compound 6e may serve as a potential lead for future synthesis that can be investigated at the molecular level, and additional in vivo studies are strongly encouraged.

Preparation of Shaped Binder‐Free SSZ‐13 Zeolite and Its Application in CO2 Adsorption and Catalysis

AbstractSSZ‐13, small‐pore zeolite with chabazite (CHA) topology, exhibits outstanding performance in gas adsorption‐separation and catalysis. However, most of the studies on SSZ‐13 zeolite are limited to the powder form. In practical application, the SSZ‐13 zeolite should be shaped with a certain amount of inert binder into technical form resulting in reduced performance. Herein, shaped binder‐free SSZ‐13 zeolite was prepared by treating the extruded SSZ‐13/SiO2 sample with amantadine solution under hydrothermal conditions, to crystallize the SiO2 binder into the zeolite phase. The characterization and DFT calculation results point out that the recrystallization of SiO2 binder in shaped SSZ‐13 into zeolite crystal could improve the physical and chemical properties. Enhanced CO2 adsorption capacity and catalysis performance in CO2‐assisted oxidative dehydrogenation of ethane and propane were also found on the shaped binder‐free SSZ‐13 zeolite.

Multifunctional Mesoporous Hollow Cobalt Sulfide Nanoreactors for Synergistic Chemodynamic/Photodynamic/Photothermal Therapy with Enhanced Efficacy.

The unique tumor microenvironment (TME) characteristic of severe hypoxia, overexpressed intracellular glutathione (GSH), and elevated hydrogen peroxide (H2O2) concentration limit the anticancer effect by monotherapy. In this report, glucose oxidase (GOx)-encapsulated mesoporous hollow Co9S8 nanoreactors are constructed with the coverage of polyphenol diblock polymers containing poly(oligo(ethylene glycol) methacrylate) and dopamine moieties containing methacrylate polymeric block, which are termed as GOx@PCoS. After intravenous injection, tumor accumulation, and cellular uptake, GOx@PCoS deplete GSH by Co3+ ions. GOx inside the nanoreactors produce H2O2 via oxidation of glucose to enhance •OH-based chemodynamic therapy (CDT) through the Fenton-like reaction under the catalysis of Co2+. Moreover, Co3+ ions possess catalase activity to catalyze production of O2 from H2O2 to relieve tumor hypoxia. Upon 808 nm laser irradiation, GOx@PCoS exhibit photothermal and photodynamic effects with a high photothermal conversion efficiency (45.06%) and generation capacity of the toxic superoxide anion (•O2-) for photothermal therapy (PTT) and photodynamic therapy (PDT). The synergetic antitumor effects can be realized by GSH depletion, starvation, and combined CDT, PTT, and PDT with enhanced efficacy. Notably, GOx@PCoS can also be used as a magnetic resonance imaging (MRI) contrast agent to monitor the antitumor performance. Thus, GOx@PCoS show great potentials to effectively modulate TME and perform synergistic multimodal therapy.

Uniting Heat and Light in Heterogeneous CO2 Photocatalysis: Optochemical Materials and Reactor Engineering

ConspectusThe rapid increase in atmospheric CO2 concentration (∼420 ppm) has become one of the significant issues threatening human survival. As an effective measure to solve this major problem, renewable energy-powered catalytic CO2 conversion technologies have received vast attention in both academia and industry. Among these techniques, photothermal catalysis is a rising star with promising potential for CO2 conversion even under milder conditions. Indium oxide was among the first to be used in photothermal CO2 catalysis, and through its various forms, stoichiometries, and surface chemistry, it has become one of the most well-studied photothermal catalyst systems. Indium oxide is a highly tunable semiconductor for CO2 photocatalysis, which can be driven by both light photochemically and heat photothermally, thereby serving as an archetype for understanding how to optimize its performance for storing solar as chemical energy, through creative materials chemistry.Our solar fuel cluster discovered photothermal CO2 catalysis over indium oxide in 2014 and has long been committed to the study of this field. Photothermal catalysis by semiconductors like indium oxide can be deconstructed into three key processes: photochemistry, thermochemistry, and surface chemistry. To be specific, photoexcited electron–hole pairs can enable redox and acid–base surface chemical reactions. Phonons and plasmons can drive these reactions photothermally. Surface active sites, such as surface frustrated Lewis pairs and oxygen vacancies, can amplify product activity and selectivity. Designer synergism between all of these effects ultimately determines the overall performance metrics of photothermal CO2 catalysis. Thus, to design and optimize a photothermal catalyst, the three aforementioned key processes should be considered synergistically.In this Account, indium oxide-based catalysts are selected as an archetype to introduce the process of photothermal CO2 catalysis and the advancements of indium oxide-based catalysts mainly from our solar fuel cluster are summarized. In detail, the strategies of material design are introduced systematically with the three key processes: photochemistry, thermochemistry, and surface chemistry. Moreover, a foreseeable future of the emerging field of optochemical engineering of photothermal catalysis, ranging from potential reactions to reactor design, is included as the perspective as well. In other words, this Account is dedicated to exploring how chemically tailored indium oxide-based catalyst has served as a platform material for understanding photothermal CO2 catalysis and how this know-how is enabling the design of high quantum efficiency photocatalysts and photoreactors. A comprehensive understanding of these points is the key to the development of the emerging field of optochemical materials and reactor engineering of heterogeneous CO2 photocatalysis.

Cobalt-Molybdenum Oxides for Effective Coupling of Ethane Activation and Carbon Dioxide Reduction Catalysis

This study reports the discovery of CoMoOx moieties with synergistic catalytic roles in C2H6–CO2 catalysis. C2H6–CO2 catalysis occurs through multiple, concomitant catalytic cycles, initiated by the dual cycles of C2H6 activation and CO2 activation, together with an undesired coke deposition cycle. C2H6 activation requires reactive oxygen species that assist with the kinetically relevant C–H bond activation; these oxygen species are generated from the CO2 activation cycle within the reverse water-gas shift (RWGS) reaction. An efficient CO2 activation in the RWGS reaction would retain higher O contents in CoMoOx moieties, leading to more effective kinetically relevant C–H bond activation of C2H6 and oxidation of coke precursors and thus increasing turnovers while mitigating deactivation. This mechanistic insight led us to design CoMoOx moieties, where the Co cation acts as a Lewis acid. Together with a vicinal oxygen vacancy, the Co cation activates CO2 via a Vacancy route through the formation of a kinetically relevant [Co···C(O) ═ O··· □vacancy···Mo]‡ transition state, at which the Co interacts with the C and the oxygen vacancy (□vacancy) abstracts the leaving O of CO2. The kinetically coupled cycles lead the ethane conversion rates in dehydrogenation and reforming reactions to both depend directly on the RWGS reaction rates. This mechanistic understanding of rate coupling has led to the design of CoMoOx moieties with dual functionality for effective C2H6–CO2 catalysis.

Grave-to-cradle upcycling of Ni from electroplating wastewater to photothermal CO2 catalysis

Treating hazardous waste Ni from the electroplating industry is mandated world-wide, is exceptionally expensive, and carries a very high CO2 footprint. Rather than regarding Ni as a disposable waste, the chemicals and petrochemicals industries could instead consider it a huge resource. In the work described herein, we present a strategy for upcycling waste Ni from electroplating wastewater into a photothermal catalyst for converting CO2 to CO. Specifically, magnetic nanoparticles encapsulated in amine functionalized porous SiO2, is demonstrated to efficiently scavenge Ni from electroplating wastewater for utilization in photothermal CO2 catalysis. The core-shell catalyst architecture produces CO at a rate of 1.9 mol·gNi−1·h−1 (44.1 mmol·gcat−1·h−1), a selectivity close to 100%, and notable long-term stability. This strategy of upcycling metal waste into functional, catalytic materials offers a multi-pronged approach for clean and renewable energy technologies.

Enhanced the synergistic degradation effect between active hydroxyl and reactive oxygen species for indoor formaldehyde based on platinum atoms modified MnOOH/MnO2 catalyst

Maintaining high activity during prolonged catalysis is always the pursuit in catalytic degradation of organic pollutants. For indoor formaldehyde (HCHO) degradation, the accumulation of intermediates is the major factor limiting the conversion of HCHO to final product CO2 (HCHO-to-CO2 conversion) and long-lasting catalysis. Herein, a three-dimensional radialized nanostructure catalyst self-assembled by MnOOH/MnO2 nanosheets anchored with Pt single atoms (PtSA-MnOOH/MnO2 with a trace platinum loading amount of 0.09%) is developed by thermally assisted two-step electrochemical method, which achieves enhanced CO2 production in catalytic HCHO degradation at the room temperature by the collaborative action of active hydroxyl (OH*) and active oxygen species (O2*). By boosting intermediates’ decomposing, the catalyst implements real-time HCHO-to-CO2 conversion (∼85.7%) and long-term continuous HCHO removal (∼98%) during 100 h in a 15 ppm HCHO atmosphere at 25 °C under a weight hourly space velocity of 30000 mL/gcat∙h. Density functional theory calculation shows that the formation energy of O2* from O2 over PtSA-MnOOH/MnO2 is nearly half lower than that over Pt-MnO2 catalyst. And decomposing accumulated intermediates gives the credit to OH* species sustainably generated by the combined action of MnOOH and O2*. The synergistic action between PtSA and MnOOH contributes to the continuous production of O2* and OH* for enhancing CO2 production in indoor catalytic formaldehyde degradation.

Ru/HxMoO3-y with plasmonic effect for boosting photothermal catalytic CO2 methanation

Utilizing localized surface plasmon resonance (LSPR) effect of catalysts to facilitate photothermal catalysis of CO2 to CH4 is an attractive strategy for mitigating CO2 emissions. Herein, we demonstrate that Ru/HxMoO3-y synthesized via H-spillover exhibits plasmonic absorption in the visible-near-infrared (Vis-NIR) region, achieving a CH4 yield of 20.8 mmol/gcat/h (520 mmol/gRu/h) with 100 % selectivity in the CO2 methanation under Vis-NIR light irradiation at 140 °C. Irradiation with Vis-NIR light substantialy increases the CH4 yield (~ 4.7 fold) compared with that under dark conditions. The abundant surface oxygen vacancies provide active sites for CO2 adsorption and activation. In situ infrared spectroscopic analysis reveals that photothermal catalytic CO2 methanation follows *CO pathway. This work represents a simple strategy for developing a plasmonic catalyst for efficient photothermal catalytic CO2 methanation.

Efficient homogenous catalysis of CO2 to generate cyclic carbonates by heterogenous and recyclable polypyrazoles

The high active catalyst, polypyrazoles, is designed and synthesized for the cycloaddition of CO 2 with epoxides to give a high yield of cyclic carbonates under mild conditions. Notably, the easy transition between the solid phase and liquid phase of polypyrazole can be realized by temperature adjustment, providing a novel guideline for the design of catalyst. The cycloaddition between CO 2 and epoxides to produce cyclic carbonate is an attractive and efficiency pathway for the utilization of CO 2 as C1 source. The development of catalyst to mediate cycloaddition between CO 2 and epoxides at low temperature and pressure is still a challenge. Herein, a series of polypyrazoles with glass transition temperature ( T g ) in the range of 42.3–52.5 °C were synthesized and served as catalyst to mediate the cycloaddition of CO 2 and epoxides by the assistant of tetrabutylammonium bromide. The catalytic behaviors of polypyrazole on the model cycloaddition of CO 2 to epichlorohydrin, including the reaction parameters optimization and versatility were investigated in detail, and excellent yield (99.9%) and selectivity (99%) were obtained under the optimized reaction conditions of 70 °C and 1.0 MPa for 6.0 h. Noteworthily, the polypyrazole acts as homogeneous catalyst during reaction (higher than T g ). And under room temperature, polypyrazoles can be easily separated and recovered, which is a promising feature of a heterogeneous catalyst. Furthermore, the reaction mechanism was proposed. The DFT calculation suggested that the formation of hydrogen bond between pyrazole and epoxide greatly reduced the energy barrier, which play an important role in promoting CO 2 cycloaddition.

MOF Encapsulated AuPt Bimetallic Nanoparticles for Improved Plasmonic-induced Photothermal Catalysis of CO2 Hydrogenation.

Exploring new catalytic strategies for achieving efficient CO2 hydrogenation under mild conditions is of great significance for environmental remediation. Herein, a composite photocatalyst Zr-based MOF encapsulated plasmonic AuPt alloy nanoparticles (AuPt@UiO-66-NH2 ) was successfully constructed for the efficient photothermal catalysis of CO2 hydrogenation. Under light irradiation at 150 °C, AuPt@UiO-66-NH2 achieved a CO production rate of 1451 μmol gmetal -1 h-1 with 91 % selectivity, which far exceeded those obtained by Au@Pt@UiO-66-NH2 with Pt shell on Au (599 μmol gmetal -1 h-1 ) and Au@UiO-66-NH2 (218 μmol gmetal -1 h-1 ). The outstanding performances of AuPt@UiO-66-NH2 were attributed to the synergetic effect originating from the plasmonic metal Au, doped active metal Pt, and encapsulation structure of UiO-66-NH2 shell. This work provides a new way for photothermal catalysis of CO2 and a reference for the design of high-performance plasmonic catalysts.

Edge-enriched Ni-N4 atomic sites embedded enoki-mushroom-like carbon nanotubes assembling hollow fibers for CO2 conversion and flexible Zn-air battery

Explorations of multifunctional catalysts for electrochemical reactions, such as oxygen electrocatalysis and CO2 electroreduction, are key issues for energy crisis and global warming. Herein, the hollow fiber stitched by enoki-mushroom-like carbon nanotube with enriched Ni-N4 single-atomic edge-sites (Ni/N-ESC) is constructed. The nickel clusters are introduced to catalyze in-situ growth of carbon nanotubes and preferentially anchor single-atomic Ni-N sites. These hairy units stitch together similar to enoki-mushroom and constitute the highly porous matrix for hollow fibers. After self-sacrifice of nickel clusters, hollow fibers assembled by carbon nanotubes with edge-enriched single-atomic Ni-N4 sites are constructed. Both theoretical and experimental results demonstrate the edge-rich single-atomic sites manifest superior activities on both oxygen and CO2 catalysis. Meanwhile, the highly porous and conductive framework favors the fast kinetics and gives abundant active sites. Taking above advantages, the Ni/N-ESC hollow fiber manifests the outstanding activities towards both oxygen catalysis and CO2 conversions. Moreover, the flexible Zn-air battery assembled with Ni/N-ESC hollow fiber delivers the good flexibility, high power/energy density and stable property during long-term cycling at both ambient (25 °C) and freezing (-20 °C) temperatures. Therefore, this work not only provides a new platform to design high efficient catalysts for multifarious electrochemical reactions, but also promotes the development of flexible Zn-air battery working in broadened temperature range.

Applications of Carbon Dots for the Photocatalytic and Electrocatalytic Reduction of CO2.

The photocatalytic and electrocatalytic conversion of CO2 has the potential to provide valuable products, such as chemicals or fuels of interest, at low cost while maintaining a circular carbon cycle. In this context, carbon dots possess optical and electrochemical properties that make them suitable candidates to participate in the reaction, either as a single component or forming part of more elaborate catalytic systems. In this review, we describe several strategies where the carbon dots participate, both with amorphous and graphitic structures, in the photocatalysis or electrochemical catalysis of CO2 to provide different carbon-containing products of interest. The role of the carbon dots is analyzed as a function of their redox and light absorption characteristics and their complementarity with other known catalytic systems. Moreover, detailed information about synthetic procedures is also reviewed.