Cobalt Phthalocyanine Catalyst Research Articles

Directed Electron Delivery from a Pb-Free Halide Perovskite to a Co(II) Molecular Catalyst Boosts CO2 Photoreduction Coupled with Water Oxidation.

The development of high-performance photocatalytic systems for CO2 reduction is appealing to address energy and environmental issues, while it is challenging to avoid using toxic metals and organic sacrificial reagents. We here immobilize a family of cobalt phthalocyanine catalysts on Pb-free halide perovskite Cs2AgBiBr6 nanosheets with delicate control on the anchors of the cobalt catalysts. Among them, the molecular hybrid photocatalyst assembled by carboxyl anchors achieves the optimal performance with an electron consumption rate of 300±13 μmol g-1 h-1 for visible-light-driven CO2-to-CO conversion coupled with water oxidation to O2, over 8 times of the unmodified Cs2AgBiBr6 (36±8 μmol g-1 h-1), also far surpassing the documented systems (<150 μmol g-1 h-1). Besides the improved intrinsic activity, electrochemical, computational, ex-/in situ X-ray photoelectron and X-ray absorption spectroscopic results indicate that the electrons photogenerated at the Bi atoms of Cs2AgBiBr6 can be directionally transferred to the cobalt catalyst via the carboxyl anchors which strongly bind to the Bi atoms, substantially facilitating the interfacial electron transfer kinetics and thereby the photocatalysis.

Directed Electron Delivery from a Pb‐Free Halide Perovskite to a Co(II) Molecular Catalyst Boosts CO2 Photoreduction Coupled with Water Oxidation

AbstractThe development of high‐performance photocatalytic systems for CO2 reduction is appealing to address energy and environmental issues, while it is challenging to avoid using toxic metals and organic sacrificial reagents. We here immobilize a family of cobalt phthalocyanine catalysts on Pb‐free halide perovskite Cs2AgBiBr6 nanosheets with delicate control on the anchors of the cobalt catalysts. Among them, the molecular hybrid photocatalyst assembled by carboxyl anchors achieves the optimal performance with an electron consumption rate of 300±13 μmol g−1 h−1 for visible‐light‐driven CO2‐to‐CO conversion coupled with water oxidation to O2, over 8 times of the unmodified Cs2AgBiBr6 (36±8 μmol g−1 h−1), also far surpassing the documented systems (&lt;150 μmol g−1 h−1). Besides the improved intrinsic activity, electrochemical, computational, ex‐/in situ X‐ray photoelectron and X‐ray absorption spectroscopic results indicate that the electrons photogenerated at the Bi atoms of Cs2AgBiBr6 can be directionally transferred to the cobalt catalyst via the carboxyl anchors which strongly bind to the Bi atoms, substantially facilitating the interfacial electron transfer kinetics and thereby the photocatalysis.

Closed-Loop Synthesis of Highly Dispersed Cobalt Phthalocyanine Catalysts for Efficient CO2 Electroreduction

Closed-Loop Synthesis of Highly Dispersed Cobalt Phthalocyanine Catalysts for Efficient CO₂ Electroreduction

Integrated capture and solar-driven utilization of CO2 from flue gas and air

Integrated capture and solar-driven utilization of CO2 from flue gas and air

“Substituents optimization” and “push effect” dual strategy for design of cobalt phthalocyanine catalyst on oxygen reduction reaction

Molecular metallocycle electrocatalysts like metalloporphyrins and metallophthalocyanines were found to be effective for oxygen reduction reaction (ORR) due to their M–N4 active sites and large conjugated electronic molecular structures. Herein, the “substituents optimization” strategy combined with “push effect” modification was innovatively employed to target a single Co–N4 active site in three substituted phthalocyaninato cobalt complexes: tetranitrophthalocyaninato cobalt (CoTNPc), tetra(4-nitrophenoxy) phthalocyaninato cobalt (CoTPNPc), and tetraphenoxy phthalocyaninato cobalt (CoTPPc) electrocatalyst, also with 4-phenylpyridine axial coordination on Co–N4 unit. Through substituents screening, the half-wave potential (E1/2) for ORR increases in the order of CoTPNPc (0.75 V) < CoTPPc (0.80 V) < CoTNPc (0.83 V) along with decreased electron-withdrawing ability of their substituents from –OC6H4–NO2, –OC6H5 to –NO2 in the three cobalt phthalocyanine derivatives. CoTNPc with the weakest electron-withdrawing substituent exhibits the best ORR performance among the three compounds. This is attributed to its higher electron delocalization and lifted HOMO energy level with the lower energy barrier in the rate-determining step relative to the other two compounds, which facilitate the electron transfer and reduction of oxygen as evidenced by XPS, UPS, and DRS analysis combined with DFT calculations. Further coordination of 4-phenylpyridine shifts the E1/2 up to 0.78, 0.82, and 0.85 V for CoTPNPc, CoTPPc, and CoTNPc. DFT calculations demonstrate that the introduction of the electron-donating phenylpyridine ligand into the cobalt phthalocyanines breaks the symmetry of the Co–N4 center and also raises the electron density of Co sites, which promotes O2 adsorption and improves ORR performance. After comparing the two strategies, the substituents on metallophthalocyanine are more determined by the electroactivity than the axial group, which directly regulates the coordination environment and then the activation barrier of the ORR process. This work provides theoretical and experimental guidance by two coupling strategies for the design of highly active molecular CoPc-based ORR electrocatalysts in the practical application.

Efficient Pretreatment of Landfill Leachate by Loading Sulfonated Cobalt Phthalocyanine Catalyst: Optimization, Regeneration and Mechanisms

Efficient Pretreatment of Landfill Leachate by Loading Sulfonated Cobalt Phthalocyanine Catalyst: Optimization, Regeneration and Mechanisms

Syngas mediated microbial electrosynthesis for CO2 to acetate conversion using Clostridium ljungdahlii

Carbon dioxide valorization through microbial electrosynthesis (MES) is promising due to it's potential for mild operating conditions and stable long-term performance. Previous MES studies have typically shown poor organic production rates using direct electron transfer mechanisms, prompting the use of electrochemically generated H2 to provide reducing equivalents for improved carbon utilization via metabolisms like the Wood-Ljungdahal pathway. Still, CO is a more favorable electron donor than H2 as it provides more thermodynamic reducing power for conversion of CO2 into valuable products. Here, we incorporated highly selective cobalt phthalocyanine catalysts into new planar 2D and porous 3D MES cathodes to produce syngas rather than H2 and boost the overall bioconversion rates of CO2 into value-added products (i.e. acetate and ethanol). Both the 2D and 3D systems were able to consistently generate syngas for over 250 h using microbial media electrolyte, demonstrating excellent stability in challenging electrolyte conditions. However, the 2D planar cathodes required a larger potential to maintain similar current densities as the 3D porous cathodes (-1.8 V vs. -1.2 V vs. Ag/AgCl) and showed a slow decline in CO production (0.23 ml/min–0.09 ml/min) and increase in H2 (0.01 ml/min–0.13 ml/min) production after 250 h. In comparison, the 3D porous electrodes allowed for more stable CO (0.08–0.06 ml/min) and H2 (0.16–0.06 ml/min) generation that also led to higher maximum acetate (5.1 vs. 3.8 g/L) and ethanol (1.2 vs. 0.9 g/L) titers. Demonstration of these new cathode materials shows significant progress towards more stable and effective MES operations and delivers useful insight on syngas mediated electron transfer and utilization in bioelectrochemical systems.

Understanding the factors governing the water oxidation reaction pathway of mononuclear and binuclear cobalt phthalocyanine catalysts.

The rational design of efficient catalysts for electrochemical water oxidation highly depends on the understanding of reaction pathways, which still remains a challenge. Herein, mononuclear and binuclear cobalt phthalocyanine (mono-CoPc and bi-CoPc) with a well-defined molecular structure are selected as model electrocatalysts to study the water oxidation mechanism. We found that bi-CoPc on a carbon support (bi-CoPc/carbon) shows an overpotential of 357 mV at 10 mA cm−2, much lower than that of mono-CoPc/carbon (>450 mV). Kinetic analysis reveals that the rate-determining step (RDS) of the oxygen evolution reaction (OER) over both electrocatalysts is a nucleophilic attack process involving a hydroxy anion (OH−). However, the substrate nucleophilically attacked by OH− for bi-CoPc is the phthalocyanine cation-radical species (CoII–Pc–Pc˙+–CoII–OH) that is formed from the oxidation of the phthalocyanine ring, while cobalt oxidized species (Pc–CoIII–OH) is involved in mono-CoPc as evidenced by the operando UV-vis spectroelectrochemistry technique. DFT calculations show that the reaction barrier for the nucleophilic attack of OH− on CoII–Pc–Pc˙+–CoII–OH is 1.67 eV, lower than that of mono-CoPc with Pc–CoIII–OH nucleophilically attacked by OH− (1.78 eV). The good agreement between the experimental and theoretical results suggests that bi-CoPc can effectively stabilize the accumulated oxidative charges in the phthalocyanine ring, and is thus bestowed with a higher OER performance.

Enhanced CO2 electroreduction on Co active site of cobalt phthalocyanine by electronic effect

Metal phthalocyanines molecular catalysts exhibit the unique ability of CO2 electrochemical reduction reaction (CO2ERR) thanks to their well-defined macrocycle structure. In this work, we introduced different substituting functional groups at the phthalocyanine ring of cobalt phthalocyanine to study the relationship of molecular structure optimization and CO2ERR activity. An optimal nitro-substituted cobalt phthalocyanine catalyst can mediate CO2 to CO in a H-cell with maximum selectivity of ∼94% together with a current density of 12.6 mA cm−2 at −0.877 V vs. RHE. The insights of this work on designing and optimizing of the molecular catalysts contribute to lower energy as well as cost-effective CO2ERR.

Elimination characteristics of sulfonated cobalt phthalocyanine catalyst (Europhtal) from wastewater in natural gas refineries by adsorption using modified natural zeolite

The present research introduces adsorption of sulfonated cobalt phthalocyanine catalyst (Europhtal) from the real wastewater that is produced in the mercaptan removal unit (Merox) of the third refinery, South Pars Gas Complex (SPGC), Assaluyeh, Iran. Therefore, novel low-cost natural zeolite modified with polyaluminium chloride (PAC) was investigated as an adsorbent for the treatment of Europhtal wastewater. Central composite design (CCD), as a set of response surface methodology (RSM), was applied to acquire optimum operational conditions such as contact time, pH, adsorbent dosage, and Europhtal concentration. Results showed that the removal percentage of Europhtal in the real wastewater was 93.4% at best operating condition consisting of a pH of 6.7, sonication time of 8 min, 0.035 g of adsorbent. The obtained results were evaluated by adsorption isotherms and kinetic parameters. It was found that the equilibrium data matched the Freundlich model acceptably, with the maximum experimental adsorption capacity of this model was 687.51 mg g-1 at 301.15 K. From the kinetic data, it was revealed that the adsorption process followed the pseudo-second-order kinetic model. Furthermore, the obtained thermodynamic parameters such as ∆H°, ∆S°, and ∆G° imply the endothermic essence of adsorption proceeding spontaneously.

Electrocatalytic and Solar-Driven Reduction of Aqueous CO2 with Molecular Cobalt Phthalocyanine–Metal Oxide Hybrid Materials

Electrolytic and solar-driven reduction of CO2 to CO using heterogenized molecular catalysts are promising approaches toward the production of a key chemical feedstock, as well as mitigating CO2 emissions. Here, we report a molecular cobalt phthalocyanine catalyst bearing four phosphonic acid anchoring groups (CoPcP) that can be immobilized on metal oxide electrodes. A hybrid electrode with CoPcP on mesoporous TiO2 (mesoTiO2) converts CO2 to CO in aqueous electrolyte solution at a near-neutral pH (7.3) with high selectivity and a turnover number for CO (TONCO) of 1949 ± 5 after 2 h of controlled-potential electrolysis at −1.09 V against the standard hydrogen electrode (∼550 mV overpotential). In situ UV–visible spectroelectrochemical investigations alluded to a catalytic mechanism that involves non-rate-limiting CO2 binding to the doubly reduced catalyst. Finally, the integration of the mesoTiO2|CoPcP assembly with a p-type silicon (Si) photoelectrode allowed the construction of a benchmark precious-metal-free molecular photocathode that achieves a TONCO of 939 ± 132 with 66% selectivity for CO (CO/H2 = 1.9) under fully aqueous conditions. The electrocatalytic and photoelectrochemical (PEC) activities of CoPcP were compared to those of state of the art synthetic and enzymatic CO2 reduction catalysts, demonstrating the excellent performance of CoPcP and its suitability for integration in tandem PEC devices.

Electrochemical CO2 reduction on heterogeneous cobalt phthalocyanine catalysts with different carbon supports

Supporting materials have a significant impact on heterogeneous molecular catalysts. Herein, we have studied the electrochemical CO2 reduction on cobalt phthalocyanine (CoPc) with Vulcan XC-72 and carbon nanotubes (CNTs) supports, respectively. Compared with pure CoPc, the resulting CoPc/XC-72 and CoPc/CNTs exhibits a notable improvement in catalytic activity. The CoPc/XC-72 maintains a stable polarization just for 15 h with a turnover number (TON) of 48,600, whereas the CoPc/CNTs lasts over 45 h with a high TON of 180,000 and CO Faraday efficiency of 88%. The excellent catalytic stability of CoPc/CNTs is attributed to a strong π-π interaction between CoPc and CNTs.

Visible-Light-Driven CO2 Reduction by Mesoporous Carbon Nitride Modified with Polymeric Cobalt Phthalocyanine.

The integration of molecular catalysts with low‐cost, solid light absorbers presents a promising strategy to construct catalysts for the generation of solar fuels. Here, we report a photocatalyst for CO2 reduction that consists of a polymeric cobalt phthalocyanine catalyst (CoPPc) coupled with mesoporous carbon nitride (mpg‐CNx) as the photosensitizer. This precious‐metal‐free hybrid catalyst selectively converts CO2 to CO in organic solvents under UV/Vis light (AM 1.5G, 100 mW cm−2, λ>300 nm) with a cobalt‐based turnover number of 90 for CO after 60 h. Notably, the photocatalyst retains 60 % CO evolution activity under visible light irradiation (λ>400 nm) and displays moderate water tolerance. The in situ polymerization of the phthalocyanine allows control of catalyst loading and is key for achieving photocatalytic CO2 conversion.

Visible‐Light‐Driven CO2 Reduction by Mesoporous Carbon Nitride Modified with Polymeric Cobalt Phthalocyanine

AbstractThe integration of molecular catalysts with low‐cost, solid light absorbers presents a promising strategy to construct catalysts for the generation of solar fuels. Here, we report a photocatalyst for CO2 reduction that consists of a polymeric cobalt phthalocyanine catalyst (CoPPc) coupled with mesoporous carbon nitride (mpg‐CNx) as the photosensitizer. This precious‐metal‐free hybrid catalyst selectively converts CO2 to CO in organic solvents under UV/Vis light (AM 1.5G, 100 mW cm−2, λ&gt;300 nm) with a cobalt‐based turnover number of 90 for CO after 60 h. Notably, the photocatalyst retains 60 % CO evolution activity under visible light irradiation (λ&gt;400 nm) and displays moderate water tolerance. The in situ polymerization of the phthalocyanine allows control of catalyst loading and is key for achieving photocatalytic CO2 conversion.

Pronounced retention of stereoconfiguration upon sp3 C[sbnd]H bonds hydroxylation of dimethylcyclohexanes and decahydronaphthalenes with m-CPBA oxidant and a Co-phthalocyanine catalyst

A series of phthalocyanine (Pc) complexes of general formula [M(Pc)] (M = Mg, V, Mn, Fe, Co, Ni, Cu, Zn) was tested as catalysts for functionalization of sp3 CH bonds, namely in the mild stereoselective oxidation of cyclic alkanes (isomers of dimethylcyclohexane and decahydronaphthalene) using peroxides as oxidants. A high catalytic activity (yield of products up to 75% based on the oxidant) and outstanding retention of stereoconfiguration of substrates (>95% for isomers of dimethylcyclohexane) was disclosed for the cobalt phthalocyanine catalyst [Co(Pc)] using m-chloroperbenzoic acid (m-CPBA) as oxidant and nitric acid as promoter. The phthalocyanine complexes other than Co are much less active with yields of products <10% and low stereo- and bond selectivities. The main reaction mechanism is proposed not to involve high-valent metal species, as evidenced by 18O-labeling and selectivity studies. The [Co(Pc)]/HNO3/m-CPBA system also catalyses chlorination and bromination of cyclohexane with HCl and N-bromosuccinimide as halogen sources.

Effect of Nitrogen-Containing Functional Groups of Cobalt Phthalocyanine Catalyst on the Oxygen Reduction Performance in Fuel Cells

Effect of Nitrogen-Containing Functional Groups of Cobalt Phthalocyanine Catalyst on the Oxygen Reduction Performance in Fuel Cells

One step growth of GaN/SiO2 core/shell nanowire in vapor-liquid-solid route by chemical vapor deposition technique

GaN/SiO2 core/shell nanowires are grown by cobalt phthalocyanine catalyst assisted vapor-liquid-solid route, in which Si wafer coated with a mixture of gallium and indium is used as the source for Ga and Si and ammonia is used as the precursor for nitrogen and hydrogen. Gallium in the presence of indium and hydrogen, which results from the dissociation of ammonia, forms Si-Ga-In alloy at the growth temperature ∼910°C. This alloy acts as the source of Si, Ga and In. A detailed study using a variety of characterization tools reveals that these wires, which are several tens of micron long, has a diameter distribution of the core ranging from 20 to 50nm, while the thickness of the amorphous SiO2 shell layer is about 10nm. These wires grow along [101¯0] direction. It has also been observed that the average diameter of these wires decreases, while their density increases as the gallium proportion in the Ga-In mixture is increased.

Simple Graphite and Thermoplastic Mixtures for Complicated Electrochemical Systems

A new carbon composite electrode will be presented. The advantages of composite electrodes include low cost, ease of catalyst incorporation, and facile fabrication. Persistent common problems with composite electrodes include low conductivity, sluggish electron transfer, difficulty in patterning, and complications with incorporation into advanced sensors such as microfluidics. To overcome these issues a solvent assisted process was developed to fabricate thermoplastic electrodes (TPEs) using polymethylmethacrylate (PMMA) combined with graphite. After fabrication, we tested the ability to pattern these electrodes using common manufacturing processes. It was discovered that these materials maintained the properties of the thermoplastic binder, enabling the electrodes to be patterned with channels and pillars of micron dimensions using hot embossing. The “chewing gum” like consistency of the semi-dried electrode material lends itself to simple templating techniques, were the shape and arrangement of the electrode is fully customizable. In this work, a CO2 laser used for templating electrode dimensions of ~150 µm, the resolution limit of the laser. The CO2 laser allowed for easy fabrication of wall-jet, band, and individually addressable microelectrode arrays. The entire process is easily scaled up and can create tens to hundreds of working electrodes in a single batch, or very large centimeter to meter sized electrodes. Electrode characterization was performed with electrochemistry, conductivity measurements, and various forms of spectroscopy (XPS, SEM/EDS, Raman, XRD). Emphasis was placed on understanding the relationship between particle loading and particle size. The particle loadings ranged from 20 to 85 mass % graphite, using graphite particle sizes of 0.5 to 100 µm. Interestingly, adjusting these simple parameters had an enormous impact on both electrochemical performance and conductivity. High conductivities of ~800 S/m were achieved with 11µm particles, as well as stable and enhanced electrode kinetics, while 0.5 and 100 mm particles generated lower conductivity and somewhat slower electron transfer. Initial experiments with the Fe(CN)6 3-/4- redox couple using impedance spectroscopy and cyclic voltammetry show that the TPE electrode out performs a DropSens commercial screen printed electrode as well as glassy carbon. The low charge transfer resistance of the TPE (<5 Ωcm2) more resembles the kinetics of a platinum electrode. The capacitance and solvent window were also measured, as they are critical parameters of the performance of electrochemical sensors. Both properties were highly dependent on the particle size, graphite purity, and graphite mass loading. An in-depth electrochemical investigation of the electrode surface following the redox mediator flow chart of McCreery was performed to give insight into the chemical composition of the electrode surface. Evidence for surface oxides (quinones), metallic impurities, and both basal and edge character from the graphite lattice were observed. The enhanced electrochemical reactivity of TPEs towards common analytes of dopamine, ascorbic acid, urate, NADH, thiols, and hydrazine is similar to that of carbon nanotubes and graphene. A major finding of this work is that electrochemical activity of the TPE can be tuned when the surface is activated through sanding, polishing or plasma cleaning. Finally, as a proof of concept, electrochemical cells were fabricated to analyze the oxidative load of aerosol particles through the use of the dithiothreitol(DTT) assay. The TPE devices enable ultralow volume sampling (~300 µL) by utilizing a microelectrode array. The high activity of the electrodes realized electrochemical sensing without the need for the commonly used cobalt phthalocyanine catalyst. This unique TPE sensing system achieved unprecedented resolution of the DTT Assay, allowing for measurements to be taken at ~10 second intervals. The rugged, reusable, complex sensor required less than one man hour to fabricate, with a materials cost of <$1. Figure 1

Kinetics and feasibility studies of thiol oxidation using magnetically separable Mg-Al layered double hydroxide supported cobalt phthalocyanine catalyst

This work describes kinetic studies of the catalytic oxidation of thiols (RSHs) found in kerosene to disulphides using a magnetically separable iron oxide coated Mg-Al layered double hydroxide supported tetra-sulphonated cobalt phthalocyanine (CoPcS/LDH@Fe3O4) catalyst in an alkali-free environment. Using 1-octanethiol as a representative RSH, we investigated the effects of different experimental parameters on RSH oxidation kinetics, including catalyst concentration, temperature (30–60°C), and initial thiol concentration ([RSH]0, 100–300ppm). The catalyst concentration was varied so that the [RSH]0/[Co]tot molar ratio ranged from 45 to 180. Based on the results, we propose a mechanistic rate expression to explain the observed oxidation of RSH in the presence of the CoPcS/LDH@Fe3O4 catalyst. The proposed rate law resembles double substrate Michaelis-Menten kinetics, however, for commonly encountered industrial conditions, we were able to simplify it to a linear form. This rate law for RSH oxidation can be used to design industrial reactors for an alkali-free sweetening process.

A two in one approach: renewable support and enhanced catalysis for sweetening using chicken feather bound cobalt(ii) phthalocyanine under alkali free environment

Poultry waste chicken feathers, an inexpensive and abundantly available material has been used as a renewable support for immobilizing a cobalt phthalocyanine catalyst.