A Controllable Dual Interface Engineering Concept for Rational Design of Efficient Bifunctional Electrocatalyst for Zinc-Air Batteries.

Searching for bifunctional noble-free electrocatalysts with high activity and stability are urgently demanded for the commercial application of zinc-air batteries (ZABs). Herein, the authors propose a controllable dual interface engineering concept to design a noble-metal-free bifunctional catalyst with two well-designed interfaces (Ni3 FeN|MnO and MnO|CNTs) via a simple etching and wet chemical route. The heterointerface between MnO and Ni3 FeN facilitates the charge transfer rate during surface reaction, and heterointerface between MnO and carbon nanotubes (CNTs) support provides effective electron transfer path, while the CNTs matrix builds free diffusion channels for gas and electrolyte. Benefiting from the advantages of dual interfaces, Ni3 FeN/MnO-CNTs show superior oxygen reduction reaction and oxygen evolution reaction catalytic activity with an ultralow polarization gap (∆E) of 0.73 V, as well as preferable durability and rapid reaction kinetics. As proof of concept, the practical ZAB with Ni3 FeN/MnO-CNT exhibits high power density of 197 mW cm-2 and rate performance up to 40 mA cm-2 , as well as superior cycling stability over 600 cycles, outperforming the benchmark mixture of Pt/C and RuO2 . This work proposes a controllable dual interface engineering concept toward regulating the charge, electron, and gas transfer to achieve efficient bifunctional catalysts for ZABs.

Recent Advances in Emerging Metal- and Covalent-Organic Frameworks for Enzyme Encapsulation.

Enzyme catalysis enables complex biotransformation to be imitated. This biomimetic approach allows for the application of enzymes in a variety of catalytic processes. Nevertheless, enzymes need to be shielded by a support material under challenging catalytic conditions due to their intricate and delicate structures. Specifically, metal-organic frameworks and covalent-organic frameworks (MOFs and COFs) are increasingly popular for use as enzyme-carrier platforms because of their excellent tunability in structural design as well as remarkable surface modification. These porous organic framework capsules that host enzymes not only protect the enzymes against harsh catalytic conditions but also facilitate the selective diffusion of guest molecules through the carrier. This review summarizes recent progress in MOF-enzyme and COF-enzyme composites and highlights the pore structures tuned for enzyme encapsulation. Furthermore, the critical issues associated with interactions between enzymes and pore apertures on MOF- and COF-enzyme composites are emphasized, and perspectives regarding the development of high-quality MOF and COF capsules are presented.

Stabilizing Li Anodes in I2 Steam to Tackle the Shuttling-Induced Depletion of an Iodide/Triiodide Redox Mediator in Li-O2 Batteries with Suppressed Li Dendrite Growth.

Redox mediators (RMs) have become a significant point in the now-established Li-O2 battery system to reduce the charging overpotential in the oxygen evolution process. Nevertheless, a major inherent barrier of the RM is the redox shuttling between the Li metal anode and mobile RM, resulting in the corrosion of Li and depletion of RM. In this study, taking iodide/triiodide as a model RM, we propose an effective strategy by immersing the Li metal anode in I2 steam to create a 1.5 µm thick surface protective layer. The resultant ionic conductive LiI layer on the Li metal anode can not only suppress Li dendrite growth but also act as a buffer layer between the RM and bare Li. By combining the iodide/triiodide RM with the LiI protective layer, the Li-O2 battery shows low and steady charge voltage plateaus of ∼3.6 V over 70 cycles. Importantly, the symmetrical cell using the LiI-protected Li electrode exhibited small Li plating/stripping overpotentials (∼20 mV, 480 h), far superior to that of the bare Li electrode (∼70 mV, 300 h). The in situ interfacial observation shows that dendrite growth on the Li metal can be effectively suppressed by optimizing the LiI protective layer.

Photoelectrochemical response of Ag-graphene heterostructures: insight into the localized surface plasmon enhanced photocurrent generation process.

We present Ag-graphene heterostructures by combining few layer graphene (FLG) with plasmonic silver nanoparticle (AgNP) arrays to boost the photoelectrochemical (PEC) efficiency of graphene-based nanostructures. AgNP arrays with controlled coverage and size distribution were fabricated on the graphene surface by means of gas phase cluster beam deposition. The photocurrent generation process in the FLG-based nanostructures was analyzed with a PEC amperometric measurement. A significant photocurrent enhancement was observed in the AgNPs-FLG heterostructures compared with bare FLG. It was found that the PEC performance was strongly related to the wavelength and power of the incident light, as well as the density and size of the AgNPs. The enhancement of the PEC response was attributed to the effect of the surface plasmon local fields of the AgNPs, which induce efficient generation and quick separation of the electron-hole pairs in FLG.

Ultralong Cycle Life Li-O2 Battery Enabled by a MOF-Derived Ruthenium-Carbon Composite Catalyst with a Durable Regenerative Surface.

The cycling performance of Li-O2 batteries (LOBs), which is an important parameter determining the practical use of this advanced energy technology with ultrahigh energy density, is strongly affected by the nature of the oxygen electrocatalyst. As a good oxygen electrode, it should possess good activity for both the oxygen evolution reaction and the oxygen reduction reaction and superior stability under operating conditions. During the past, oxygen electrodes for LOBs were generally fabricated by loading noble metal nanoparticles on the surface of a porous carbon support. However, the nanoparticles could easily lose contact with the carbon support during the reversible liquid-gas-solid reactions that involve lithium ions, oxygen gas, and Li2O2. Herein, we reported a novel Ru-metal-organic framework (MOF)-derived carbon composite, characterized by stereoscopic Ru nanoparticle distribution within the carbon matrix, as an alternative oxygen catalyst of LOBs, enabling superior operational stability and favorable activity. More specifically, the battery demonstrated stable charge-discharge cycling for up to 800 times (∼107 days) at a current density of 500 mA g-1 with low discharge/charge overpotentials (∼0.2/0.7 V vs Li). A mechanism of regenerative surface was further proposed to explain the excellent cycling stability of the LOBs through the use of the Ru-MOF-C catalyst. These encouraging results imply an accessible solution to address issues related to the oxygen catalyst for the realization of practical LOBs.

Developing a "Water-Defendable" and "Dendrite-Free" Lithium-Metal Anode Using a Simple and Promising GeCl4 Pretreatment Method.

Lithium metal is an ultimate anode in "next-generation" rechargeable batteries, such as Li-sulfur batteries and Li-air (Li-O2 ) batteries. However, uncontrollable dendritic Li growth and water attack have prevented its practical applications, especially for open-system Li-O2 batteries. Here, it is reported that the issues can be addressed via the facile process of immersing the Li metal in organic GeCl4 -THF steam for several minutes before battery assembly. This creates a 1.5 µm thick protection layer composed of Ge, GeOx , Li2 CO3 , LiOH, LiCl, and Li2 O on Li surface that allows stable cycling of Li electrodes both in Li-symmetrical cells and Li-O2 cells, especially in "moist" electrolytes (with 1000-10 000 ppm H2 O) and humid O2 atmosphere (relative humidity (RH) of 45%). This work illustrates a simple and effective way for the unfettered development of Li-metal-based batteries.

Flexible, Flame-Resistant, and Dendrite-Impermeable Gel-Polymer Electrolyte for Li-O2 /Air Batteries Workable Under Hurdle Conditions.

Gel-polymer electrolytes are considered as a promising candidate for replacing the liquid electrolytes to address the safety concerns in Li-O2 /air batteries. In this work, by taking advantage of the hydrogen bond between thermoplastic polyurethane and aerogel SiO2 in gel polymer, a highly crosslinked quasi-solid electrolyte (FST-GPE) with multifeatures of high ionic conductivity, high mechanical flexibility, favorable flame resistance, and excellent Li dendrite impermeability is developed. The resulting gel-polymer Li-O2 /air batteries possess high reaction kinetics and stabilities due to the unique electrode-electrolyte interface and fast O2 diffusion in cathode, which can achieve up to 250 discharge-charge cycles (over 1000 h) in oxygen gas. Under ambient air atmosphere, excellent performances are observed for coin-type cells over 20 days and for prototype cells working under extreme bending conditions. Moreover, the FST-GPE electrolyte also exhibits durability to protect against fire, dendritic Li, and H2 O attack, demonstrating great potential for the design of practical Li-O2 /air batteries.

Pd nanoparticle-modified electrodes for nonenzymatic hydrogen peroxide detection.

A hydrogen peroxide (H2O2) sensor based on Pd nanoparticles (NPs) and glassy carbon electrodes (GCEs) is fabricated. Pd NPs are deposited on GCEs by using a gas phase cluster beam deposition technique. The NP-deposited electrodes show enhanced electrocatalytic activity in reduction of H2O2. The electrode with an optimized NP coverage of 85 % has a high selective and stable nonenzymatic sensing ability of H2O2 with a low detection limit (3.4 × 10(-7) M), high sensitivity (50.9 µA mM(-1)), and a wide linear range (from 1.0 × 10(-6) to 6.0 × 10(-3) M). The reduction peak potential of the electrode is close to -0.12 V, which enables high selective amperometric detection of H2O2 at a low applied potential.

Facile in Situ Preparation of Graphitic-C3N4@carbon Paper As an Efficient Metal-Free Cathode for Nonaqueous Li-O2 Battery.

The rechargeable Li-O2 batteries with high theoretical specific energy are considered to be a promising energy storage system for electric vehicle application. Because of the prohibitive cost, limited supply, and weak durability of precious metals, the developments of novel metal-free catalysts become significant. Herein, the graphitic-carbon nitride@carbon papers have been produced by a facile in situ method and explored as cathodes for Li-O2 batteries, which manifest considerable electrocatalytic activity toward oxygen reduction reaction and oxygen evolution reaction in nonaqueous electrolytes because of their improved electronic conductivity and high nitrogen content. The assembled Li-O2 batteries using graphitic-carbon nitride@carbon papers as cathodes deliver good rate capability and cycling stability with a capacity retention of more than 100 cycles.

Nanoporous Ru as a carbon- and binder-free cathode for Li-O2 batteries.

Porous carbon-free cathodes are critical to achieve a high discharge capacity and efficient cycling for rechargeable Li-O2 battery. Herein, we present a very simple method to directly grow nanoporous Ru (composed of polycrystalline particles of ∼5 nm) on one side of a current collector of Ni foam via a galvanic replacement reaction. The resulting Ru@Ni can be employed as a carbon- and binder-free cathode for Li-O2 batteries and delivers a specific capacity of 3720 mAh gRu (-1) at a current density of 200 mA gRu (-1) . 100 cycles of continuous discharge and charge are obtained at a very narrow terminal voltage window of 2.75∼3.75 V with a limited capacity of 1000 mAh gRu (-1) . The good performance of the nanoporous Ru@Ni cathode can be mainly attributed to the effective suppression of the by-products related to carbon or binder, the good adhesion of the catalyst to the current collector, and the good permeation of O2 and electrolyte into the active sites of the nanoporous Ru with the open pore system. This new type electrode provides a snapshot toward developing high-performance carbon- and binder-free Li-O2 batteries.

Hydrothermal synthesis of Ni(12)P(5) hollow microspheres, characterization and photocatalytic degradation property.

In this paper, we report the successful synthesis of Ni(12)P(5) hollow spheres via a facile hydrothermal route, employing white phosphorus (WP) and nickel nitrate as the reactants in the presence of hexamethylenetetramine (HMT) and polyethylene glycol 10000 (PEG-10000). The phase and morphology of the product were characterized by means of powder X-ray diffraction (XRD), energy dispersive spectrometry (EDS), transmission electron microscopy (TEM), and scanning electron microscopy (SEM). HMT and surfactant (PEG-10000) played important roles in the formation of Ni(12)P(5) hollow microspheres. Furthermore, research also showed that the as-prepared Ni(12)P(5) hollow spheres could photocatalytically degrade some organic dyes such as Safranine T and Pyronine B under irradiation of 365 nm UV light.