Highly Active CoNi-CoN3 Composite Sites Synergistically Accelerate Oxygen Electrode Reactions in Rechargeable Zinc-Air Batteries.

Reaching rapid reaction kinetics of oxygen reduction (ORR) and oxygen evolution reactions (OER) is critical for realizing efficient rechargeable zinc-air batteries (ZABs). Herein, a novel CoNi-CoN3 composite site containing CoNi alloyed nanoparticles and CoN3 moieties is first constructed in N-doped carbon nanosheet matrix (CoNi-CoN3 /C). Benefiting from the high electroactivity of CoNi-CoN3 composite sites and large surface area, CoNi-CoN3 /C shows a superior half-wave potential (0.88 V versus RHE) for ORR and a small overpotential (360 mV) for OER at 10 mA cm-2 . Theoretical calculations have demonstrated that the introduction of CoNi alloys has modulated the electronic distributions near the CoN3 moiety, inducing the d-band center of CoNi-CoN3 composite site to shift down, thus stabilizing the valence state of Co active sites and balancing the adsorption of OER/ORR intermediates. Accordingly, the reaction energy trends exhibit optimized overpotentials for OER/ORR, leading to superior battery performances. For aqueous and flexible quasi-solid-state rechargeable ZABs with CoNi-CoN3 /C as catalyst, a large power density (250 mW cm-2 ) and high specific capacity (804 mAh g-1 ) are achieved. The in-depth understanding of the electroactivity enhancement mechanism of interactive metal nanoparticles and metal coordinated with nitrogen (MNx ) moieties is crucial for designing novel high-performance metal/nitrogen-doped carbon (M─N─C) catalysts.

Urchin-like PtNPs@Bi2S3: synthesis and application in electrochemical biosensor.

Efficient urchin-like Pt nanoparticles@Bi2S3 (PtNPs@Bi2S3) composite materials were prepared by a composite soft template synthesis of urchin-like Bi2S3 and then the microwave-assisted growth of PtNPs onto the Bi2S3 nanostructure. For the first time, an accurate electrochemical glucose biosensor was fabricated via immobilizing glucose oxidase (GOx) on PtNPs@Bi2S3. The PtNPs@Bi2S3 composite was investigated via scanning electron microscopy, electrochemical impedance spectroscopy, Fourier transform infrared spectroscopy, and cyclic voltammetry. The PtNPs@Bi2S3 composite provides a large surface area to load a large number of enzyme molecules, which maintains the biological activity. PtNPs loaded on Bi2S3 enhanced the conductivity and improved the direct electron transfer of the proposed biosensor with the synergistic effect. The fabricated electrochemical biosensor possesses high sensitivity, and a wide linear range from 0.003 mM to 0.1 mM and 0.1 mM to 1.9 mM. Moreover, the biosensor has outstanding stability, superior selectivity and good repeatability, which can be utilized to monitor the glucose level in practical human serum. The PtNPs@Bi2S3 composite supplies a special matrix for immobilizing proteins and potential for establishing other effective biosensors.

A MOF nanozyme-mediated acetylcholinesterase-free colorimetric strategy for direct detection of organophosphorus pesticides.

Although some simple and rapid colorimetric methods have been developed to detect organophosphorus pesticides (OPs), the difficult extraction and easy denaturation of acetylcholinesterase (AChE) are still drawbacks needing to be overcome. Here, we propose a MOF nanozyme-mediated AChE-free colorimetric strategy for the direct detection of OPs. In the presence of OPs (pirimiphos-methyl as a model), the intense blue of oxidized 3,3',5,5'-tetramethylbenzidine (TMB) becomes light due to the quenching effect of OPs towards hydroxyl radicals (˙OH) that are generated by the decomposition of H2O2 catalyzed by the Cu4Co6 ZIF nanozyme with excellent peroxidase (POD)-like activity. The developed colorimetric sensor exhibits assay performance and offers a universal and promising analysis strategy for detecting OPs in practical samples.

Interfacial Coupling Engineering Boosting Electrocatalytic Performance of CoFe Layered Double Hydroxide Assembled on N-Doped Porous Carbon Nanosheets for Water Splitting and Flexible Zinc-Air Batteries.

The disadvantages of layered double hydroxides (LDHs) such as easy stacking, poor inherent conductivity, and limited versatility hinder their application in splitting water and zinc-air batteries (ZABs). Interface engineering to regulate the electron distribution of LDHs by introducing another component is a way to compensate for the poor electron transport capacity of LDHs during catalysis. Herein, a hierarchical structure is synthesized by assembling CoFe-LDH nanosheets onto the surface of layered N-doped porous carbon (NPC), CoFe-LDH@NPC, by using an interface engineering strategy. CoFe-LDH@NPC has high catalytic activity for the oxygen/hydrogen evolution reaction (OER/HER) with overpotentials of 280/100 mV, respectively. The two-electrode water splitting catalyzed by CoFe-LDH@NPC only needs 1.61 V to drive a current density of 10 mA cm-2 for 60 h. The theoretical results show that there is an electron-deficient/electron-rich interface between the NPC substrate and the CoFe-LDH in CoFe-LDH@NPC. The electrons on the coupling interface are easily transferred, which results in a change of the adsorption behavior of the reaction intermediates and improves the catalytic activity for the OER and HER. In addition, CoFe-LDH@NPC-catalyzed rechargeable flexible ZABs have excellent performance with low charge-discharge polarization (0.87 V) and a long-term stability of 65 h.