Electrocatalytic Activity of Novel Ball-Type Metallophthalocyanines with Trifluoro Methyl Linkages in Oxygen Reduction Reaction and Application as Zn-Air Battery Cathode Catalyst

Fe-phthalocyanine derived highly conjugated 2D covalent organic framework as superior electrocatalyst for oxygen reduction reaction

Although porphyry systems like metallo-phthalocynine are recognized as promising molecular models for electrocatalytic oxygen reduction reaction (ORR), their poor durability and methanol tolerance are still challenges and need improvement before being considered for practical applications. Herein, we successfully designed and constructed a Fe-phthalocyanine-derived highly conjugated 2D covalent organic framework (2D FePc-COF), using octa-amino-Fe-phthalocyanine (OA-FePc) and cyclohexanone as precursors. The prepared 2D FePc-COF was characterized via multiple analytic techniques. The electrochemical studies indicated that prepared 2D FePc-COF was far more superior to OA-FePc and 20% Pt/C, displaying anodic shift of 100 and 50 mV (vs RHE) in formal potential, respectively. Moreover, this catalyst also demonstrated excellent methanol tolerance and durability (over 10,000 CV cycles). Theoretical investigations revealed that due to extended conjugation and elimination of electron donating groups (-NH2), the shifting of dz2-orbital (Fe) energy took nearer to π*-orbital (O2), allowing optimum coupling of both the orbitals, thereby enhancing 4e- ORR. This work demonstrates the art of molecular design, aiming at improving catalytic activity of macrocyclic molecular systems towards ORR.

Effects of MN4-Type Coordination Structure in Metallophthalocyanine for Bio-Inspired Oxidative Desulfurization Performance

Oxidative desulfurization (ODS) is the promising new method for super deep desulfurization of fuel oil. The oxidative desulfurization performance of the metal-N₄-chelates metallophthalocyanines (MPcs) is related to the chemical properties of conjugate structures and the central metal ions. Herein, a biomimetic catalytic system composed of metallophthalocyanines (MPcR₄, M = Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II); R = -H, -COOH, -NO₂, -NH₂) and molecular O₂ was performed to study the influence of MN₄-type coordination structure in metallophthalocyanines for the degradation of dibenzothiophene (DBT) in model oil containing n-octane. The results reveal that the conjugate structures and the center metal ions of metallophthalocyanines played key roles in oxidative desulfurization performance. The inductive effect of different R substituents strongly affected the electron cloud distribution of the conjugate structures and the catalytic performance. Moreover, the catalytic activity of MPcs, which is related to the d electronic configuration and ligand-field effects, does not sequentially increase with the increase in the d electron number of central metal ions.

Tellurium Triggered Formation of Te/Fe-NiOOH Nanocubes as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting

The electrocatalyzed oxygen and hydrogen evolution reactions (OER/HER) are the key constituents of water splitting toward hydrogen production over electrolysis. The development of stable non-noble nanomaterials as bifunctional OER/HER electrocatalysts is the foremost bottleneck to commercial applications. Herein, the fabrication of Te-modulated FeNiOOH nanocubes (NCs) by a novel tailoring approach is reported, and the doping of Te superbly modulated the local electronic structures of Fe and Ni. The Te/FeNiOOH-NC catalyst displays better mass and electron transfer ability, exposure of plentiful OER/HER edge active centers on the surface, and a modulated electronic structure. Accordingly, the as-made Te/FeNiOOH-NC catalyst reveals robust OER activity (overpotential of 0.22 V@10 mA cm^-2) and HER activity (overpotential of 0.167 V@10 mA cm^-2) in alkaline media. Considerably, this bifunctional catalyst facilitates a high-performance alkaline water electrolyzer with a cell voltage of 1.65 V at 10 mA cm^-2. This strategy opens up a new way for designing and advancing the tellurium dopant nanomaterials for various applications.

Synthesis, characterization, third-order non-linear optical properties and DFT studies of novel SUBO bridged ball-type metallophthalocyanines

Novel 4,4'-(((2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diyl)bis(2-methylpropane-2,1-diyl))bis(oxy)) (SUBO) bridged ball-type metallophthalocyanines were synthesized starting from 4,4'-(((2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diyl)bis(2-methylpropane-2,1-diyl))bis(oxy))diphthalonitrile with convenient metal salts in 2-N,N-dimethylaminoethanol. A new bisphthalonitrile compound was obtained from 2,2'-(2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-diyl)bis(2-methylpropan-1-ol) and 4-nitrophthalonitrile in acetonitrile at reflux temperature in the presence of potassium carbonate as a catalyst. The structural characterization of the compounds was performed by elemental analysis, and infrared, ultraviolet-visible and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopic methods. Nonlinear absorptions of the phthalocyanine complexes were measured using the Z-scan technique with 7 ns pulse duration at a 532 nm wavelength. It is obvious that ball-type copperphthalocyanine has a high nonlinear absorption coeffıcient and imaginary component of the third-order susceptibility compared to other complexes. Therefore, ball-type copperphthalocyanine can be regarded as a very good candidate for optical limiting applications. Density functional theory was used for geometry optimizations and time-dependent density functional theory calculations of electronic transitions in order to compare with the experimental results. Molecular orbital and nonlinear optical analyses were also performed with density functional theory at the CAM-B3LYP/6-31G(d,p)/LANL2DZ level. The nonlinear optical analyses show that ball-type copperphthalocyanine has significantly better nonlinear optical properties in comparison to a common reference compound, urea.

Study on the Effects of a π Electron Conjugated Structure in Binuclear Metallophthalocyanines Graphene-Based Oxygen Reduction Reaction Catalysts

The high overpotentials for oxygen reduction reaction (ORR) create an extremely negative impact on the energy efficiency of the air-based battery systems. To overcome this problem, binuclear ball-type metallophthalocyanines containing methoxy substituents (M₂Pc₂(EP)₄, M = Fe(II), Co(II) and Zn(II)) were wrapped with polystyrene sodium sulfonate (PSS) modified graphene oxide (GO), using a facilely “solvothermal π-π assembly” method to prepare M₂Pc₂(EP)₄/PSS-Gr composites. Compared with the commercial Pt/C catalysts, the M₂Pc₂(EP)₄/PSS-Gr composites enhanced the catalytic activity of oxygen reduction reaction. The π electron conjugated structure of the MN₄-type phthalocyanine macrocyclic system strongly influenced the one-step four-electron electrocatalytic process of the M₂Pc₂(EP)₄/PSS-Gr composites. Moreover, the π-π interactions between the M₂Pc₂(EP)₄ and PSS-Gr dramatically enhanced the π electron density in the conjugated structure and oxygen could be reduced more easily. The electrocatalytic activity test was displayed in the order of Fe₂Pc₂(FP)₄/PSS-Gr > Co₂Pc₂(EP)₄/PSS-Gr > Zn₂Pc₂(EP)₄/PSS-Gr. The results indicated that the catalytic performance of M₂Pc₂R_n could be enhanced by the modification of π electron conjugated structure of M₂Pc₂(EP)₄ and carbon materials.

DUT-58 (Co) Derived Synthesis of Co Clusters as Efficient Oxygen Reduction Electrocatalyst for Zinc-Air Battery

To meet the requirement of fuel cells and metal-air batteries, non-noble metal catalysts have to be developed to replace precious platinum-based catalysts. Herein, Co nanoclusters (≈2 nm) are anchored on nitrogen-doped reduced graphene oxide (Co/N-r-GO) by using DUT-58 (Co) metal-organic framework and GO as precursors. Compared with single-atom catalysts usually with ultralow concentration (<0.5 wt%), Co nanoclusters are more beneficial to break the O-O bond to ensure four electronic way for oxygen reduction reaction (ORR), since they can provide more adsorption centers for reactants. Therefore, as expected, the sample with 6.67 wt% Co content (Co/N-r-GO-5%-850) exhibits better ORR activity with a higher half-wave potential of 0.831 V, a more positive onset potential of 0.921 V than Pt/C, and a comparable limiting current density in alkaline medium. The Co nanoclusters enhance the catalytic performance for ORR in three aspects: quantum size effects, metal-support interactions, and low-coordination environment of metal centers. Furthermore, the sample is assembled into a zinc-air battery as the outstanding durable ORR catalyst. It displays a higher specific capacity (795 mAh g-1 at the current density 50 mA cm-2) and power density (175 mW cm-2) than Pt/C (731 mAh g-1 and 164 mW cm-2, respectively).