Synergistic effect of Polydopamine incorporated Copper electrocatalyst by dopamine oxidation for efficient hydrogen production.

Tuning the metal-support interaction in electrocatalysts has been proposed as a viable method for manipulating the electronic structure and catalytic activity. In this work, inspired by natural hydrogenase enzyme, electrocatalysts with a hybrid metal-matrix complex using polydopamine (PDA) as a supporting matrix were synthesized for efficient green hydrogen production. Among the various Metal-PDA electrocatalysts, Cu-PDA shows outstanding catalytic activity (low overpotential (ƞ) of 104 mV at 10 mA cm-2 and small Tafel slope of 60.67 mV dec-1) with high stability at neutral pH. Also, the electrochemical impedance spectroscopy analysis verified the fast charge transfer properties of Cu-PDA (2.8 Ω cm2) than PDA (26 Ω cm2), indicating a faster proton-coupled electron transfer process in Cu-PDA electrocatalyst. Therefore, emerging nature inspired organic ligand-transition metal ion complexes can be extensively encouraged as a prospective HER electrocatalyst under neutral conditions.

Cofactor-Assisted Artificial Enzyme with Multiple Li-Bond Networks for Sustainable Polysulfide Conversion in Lithium-Sulfur Batteries.

Lithium-sulfur batteries possess high theoretical energy density but suffer from rapid capacity fade due to the shuttling and sluggish conversion of polysulfides. Aiming at these problems, a biomimetic design of cofactor-assisted artificial enzyme catalyst, melamine (MM) crosslinked hemin on carboxylated carbon nanotubes (CNTs) (i.e., [CNTs-MM-hemin]), is presented to efficiently convert polysulfides. The MM cofactors bind with the hemin artificial enzymes and CNT conductive substrates through FeN5 coordination and/or covalent amide bonds to provide high and durable catalytic activity for polysulfide conversions, while π-π conjugations between hemin and CNTs and multiple Li-bond networks offered by MM endow the cathode with good electronic/Li+ transmission ability. This synergistic mechanism enables rapid sulfur reaction kinetics, alleviated polysulfide shuttling, and an ultralow (<1.3%) loss of hemin active sites in electrolyte, which is ≈60 times lower than those of noncovalent crosslinked samples. As a result, the Li-S battery using [CNTs-MM-hemin] cathode retains a capacity of 571 mAh g-1 after 900 cycles at 1C with an ultralow capacity decay rate of 0.046% per cycle. Even under raising sulfur loadings up to 7.5 mg cm-2 , the cathode still can steadily run 110 cycles with a capacity retention of 83%.

Nanozyme-Modified Metal-Organic Frameworks with Multienzymes Activity as Biomimetic Catalysts and Electrocatalytic Interfaces.

Many metal-organic frameworks have been designed and synthesized for biosensors because of high surface area and porosity, suitable size, and good biocompatibility. Despite recent advances, however, most of them are only used as a nanocarrier. In this work, a new artificial nanozyme was constructed on a metalloporphyrinic metal-organic framework (PMOF(Fe)), which was formed by Fe porphyrin and Zr4+ ions. Then, ultrasmall Pt nanoparticles (Pt NPs) were loaded on the surface of PMOF(Fe) to form Pt@PMOF(Fe). Because of the high surface area and exposed Fe activity center, PMOF(Fe) works as a nanocarrier to hinder the Pt NP aggregation and exhibits high peroxidase-mimicking activity. Hence, Pt NPs decorated on the surface of PMOF(Fe) possessed high stability and exhibited high activity. Due to the synergistic effect between PMOF(Fe) and Pt NPs, Pt@PMOF(Fe) exhibits superior catalase- and peroxidase-like activities. Moreover, Pt@PMOF(Fe) possesses high electrocatalytic activity toward the reduction of H2O2 and the oxygen reduction reaction (ORR). This strategy may serve as a strong foundation to design MOF-based artificial nanozymes and develop an ideal platform for MOFs and nanozymes toward artificial enzymatic catalytic systems, fuel cells and new analytical applications.

Direct Spectroscopic Detection of Key Intermediates and the Turnover Process in Catalytic H2 Formation by a Biomimetic Diiron Catalyst.

[FeFe(Cl2 -bdt)(CO)6 ] (1; Cl2 -bdt=3,6-dichlorobenzene-1,2-dithiolate), inspired by the active site of FeFe-hydrogenase, shows a chemically reversible 2 e- reduction at -1.20 V versus the ferrocene/ferrocenium couple. The rigid and aromatic bdt bridging ligand lowers the reduction potential and stabilizes the reduced forms, compared with analogous complexes with aliphatic dithiolates; thus allowing details of the catalytic process to be characterized. Herein, time-resolved IR spectroscopy is used to provide kinetic and structural information on key catalytic intermediates. This includes the doubly reduced, protonated complex 1H- , which has not been previously identified experimentally. In addition, the first direct spectroscopic observation of the turnover process for a molecular H2 evolving catalyst is reported, allowing for straightforward determination of the turnover frequency.

Cucurbit[7]uril as a Supramolecular Artificial Enzyme for Diels-Alder Reactions.

The ability to mimic the activity of natural enzymes using supramolecular constructs (artificial enzymes) is a vibrant scientific research field. Herein, we demonstrate that cucurbit[7]uril (CB[7]) can catalyse Diels-Alder reactions for a number of substituted and unreactive N-allyl-2-furfurylamines under biomimetic conditions, without the need for protecting groups, yielding powerful synthons in previously unreported mild conditions. CB[7] rearranges the substrate in a highly reactive conformation and shields it from the aqueous environment, thereby mimicking the mode of action of a natural Diels-Alderase. These findings can be directly applied to the phenomenon of product inhibition observed in natural Diels-Alderase enzymes, and pave the way toward the development of novel, supramolecular-based green catalysts.

Growth of Au Nanoparticles on 2D Metalloporphyrinic Metal-Organic Framework Nanosheets Used as Biomimetic Catalysts for Cascade Reactions.

Inspired by the multiple functions of natural multienzyme systems, a new kind of hybrid nanosheet is designed and synthesized, i.e., ultrasmall Au nanoparticles (NPs) grown on 2D metalloporphyrinic metal-organic framework (MOF) nanosheets. Since 2D metalloporphyrinic MOF nanosheets can act as the peroxidase mimics and Au NPs can serve as artificial glucose oxidase, the hybrid nanosheets are used to mimic the natural enzymes and catalyze the cascade reactions. Furthermore, the synthesized hybrid nanosheets are used to detect biomolecules, such as glucose. This study paves a new avenue to design nanomaterial-based biomimetic catalysts with multiple complex functions.