Modulating the Electrolyte Microenvironment in Electrical Double Layer for Boosting Electrocatalytic Nitrate Reduction to Ammonia.

Electrochemical nitrate reduction reaction (NO3RR) is a promising approach to achieve remediation of nitrate-polluted wastewater and sustainable production of ammonia. However, it is still restricted by the low activity, selectivity and Faraday efficiency for ammonia synthesis. Herein, we propose an effective strategy to modulate the electrolyte microenvironment in electrical double layer (EDL) by mediating alkali metal cations in the electrolyte to enhance the NO3RR performance. Taking bulk Cu as a model catalyst, the experimental study reveals that the NO3 --to-NH3 performance in different electrolytes follows the trend Li+

Dynamic Reconstructed RuO2 /NiFeOOH with Coherent Interface for Efficient Seawater Oxidation.

Developing efficient oxygen evolution reaction (OER) electrocatalysts for seawater electrolysis is still a big challenge. Herein, a facile one-pot approach is reported to synthesize RuO2 -incorporated NiFe-metal organic framework (RuO2 /NiFe-MOF) with unique nanobrick-nanosheet heterostructure as precatalyst. Driven by electric field, the RuO2 /NiFe-MOF dynamically reconstructs into RuO2 nanoparticles-anchored NiFe oxy/hydroxide nanosheets (RuO2 /NiFeOOH) with coherent interface, during which the dissolution and redeposition of RuO2 are witnessed. Owing to the synergistic interaction between RuO2 and NiFeOOH, the as-reconstructed RuO2 /NiFeOOH exhibits outstanding alkaline OER activity with an ultralow overpotential of 187.6 mV at 10 mA cm-2 and a small Tafel slope of 31.9 mV dec-1 and excellent durability at high current densities of 840 and 1040 mA cm-2 in 1 m potassium hydroxide (KOH). When evaluated for seawater oxidation, the RuO2 /NiFeOOH only needs a low overpotential of 326.2 mV to achieve 500 mA cm-2 and can continuously catalyze OER at 500 mA cm-2 for 100 h with negligible activity degradation. Density function theory calculations reveal that the presence of strong interaction and enhanced charge transfer along the coherent interface between RuO2 and NiFeOOH ensures improved OER activity and stability.

Oxygen Vacancy Engineering Synergistic with Surface Hydrophilicity Modification of Hollow Ru Doped CoNi-LDH Nanotube Arrays for Boosting Hydrogen Evolution.

With the development of clean hydrogen energy, the cost effective and high-performance hydrogen evolution reaction (HER) electrocatalysts are urgently required. Herein, a green, facile, and time-efficient Ru doping synergistic with air-plasma treatment strategy is reported to boost the HER performance of CoNi-layered double hydroxide (LDH) nanotube arrays (NTAs) derived from zeolitic imidazolate framework nanorods. The Ru doping and air-plasma treatment not only regulate the oxygen vacancy to optimize the electron structure but also increase the surface roughness to improve the hydrophilicity and hydrogen spillover efficiency. Therefore, the air plasma treated Ru doped CoNi-LDH (P-Ru-CoNi-LDH) nanotube arrays display superior HER performance with an overpotential of 29 mV at a current density of 10 mA cm-2 . Furthermore, by assembling P-Ru-CoNi-LDH as both cathode and anode for two-electrode urea-assisted water electrolysis, a small cell voltage of 1.36 V is needed at 10 mA cm-2 and can last for 100 h without any obvious activity attenuation that showing outstanding durability. In general, the P-Ru-CoNi-LDH can improve the HER performance from intrinsic electronic structure regulation cooperated with extrinsic surface wettability modification. These findings provide an effective intrinsic and extrinsic synergistic effect avenue to develop high performance HER electrocatalysts, which is potential to be applied to other research fields.

N2 plasma-activated NiO nanosheet arrays with enhanced water splitting performance.

NiO is a promising electrocatalyst for electrochemical energy conversion due to its rich redox sites, low cost, and ease of synthesis. However, hindered by low electrical conductivity and limited electrocatalytic active sites, bare NiO usually exhibits poor electrochemical performance towards hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we develop an N2 plasma activation approach to simultaneously improve both HER and OER activity of NiO by constructing heterostructured Ni/Ni3N/NiO nanosheet arrays on Ni foam. The optimized N2 plasma-activated NiO nanosheet arrays for HER and OER (denoted as P-NiO-HER and P-NiO-OER) only need an overpotential of 46 and 294 mV, respectively, to achieve 10 mA cm-2. Moreover, for overall water splitting, the assembled electrolysis cell with P-NiO-HER and P-NiO-OER as the cathode and anode, respectively, only requires a small voltage of 1.57 V to deliver 10 mA cm-2. Remarkably, the plasma-activated NiO nanosheet arrays exhibit excellent stability for up to 50 h for HER, OER, and full water electrolysis. The strategy developed here to activate the electrocatalytic performance of metal oxides opens a new door for water splitting.

Bullet-like Cu9 S5 Hollow Particles Coated with Nitrogen-Doped Carbon for Sodium-Ion Batteries.

Metal sulfides with excellent redox reversibility and high capacity are very promising electrode materials for sodium-ion batteries. However, their practical application is still hindered by the poor rate capability and limited cycle life. Herein, a template-based strategy is developed to synthesize nitrogen-doped carbon-coated Cu9 S5 bullet-like hollow particles starting from bullet-like ZnO particles. With the structural and compositional advantages, these unique nitrogen-doped carbon-coated Cu9 S5 bullet-like hollow particles manifest excellent sodium storage properties with superior rate capability and ultra-stable cycling performance.

Formation of Polypyrrole-Coated Sb2 Se3 Microclips with Enhanced Sodium-Storage Properties.

Antimony-based electrode materials with high specific capacity have aroused considerable interest as anode materials for sodium-ion batteries (SIBs). Herein, we develop a template-engaged ion-exchange method to synthesize Sb2 Se3 microclips, and the as-obtained Sb2 Se3 microclips are further in situ coated with polypyrrole (PPy). Benefiting from the structural and compositional merits, these PPy-coated Sb2 Se3 microclips exhibit enhanced sodium-storage properties in terms of high reversible capacity, superior rate capability, and stable cycling performance.

A Practical High-Energy Cathode for Sodium-Ion Batteries Based on Uniform P2-Na0.7 CoO2 Microspheres.

Layered metal oxides have attracted increasing attention as cathode materials for sodium-ion batteries (SIBs). However, the application of such cathode materials is still hindered by their poor rate capability and cycling stability. Here, a facile self-templated strategy is developed to synthesize uniform P2-Na0.7 CoO2 microspheres. Due to the unique microsphere structure, the contact area of the active material with electrolyte is minimized. As expected, the P2-Na0.7 CoO2 microspheres exhibit enhanced electrochemical performance for sodium storage in terms of high reversible capacity (125 mAh g-1 at 5 mA g-1 ), superior rate capability and long cycle life (86 % capacity retention over 300 cycles). Importantly, the synthesis method can be easily extended to synthesize other layered metal oxide (P2-Na0.7 MnO2 and O3-NaFeO2 ) microspheres.

Carbon-Incorporated Nickel-Cobalt Mixed Metal Phosphide Nanoboxes with Enhanced Electrocatalytic Activity for Oxygen Evolution.

Hollow nanostructures have attracted increasing research interest in electrochemical energy storage and conversion owing to their unique structural features. However, the synthesis of hollow nanostructured metal phosphides, especially nonspherical hollow nanostructures, is rarely reported. Herein, we develop a metal-organic framework (MOF)-based strategy to synthesize carbon incorporated Ni-Co mixed metal phosphide nanoboxes (denoted as NiCoP/C). The oxygen evolution reaction (OER) is selected as a demonstration to investigate the electrochemical performance of the NiCoP/C nanoboxes. For comparison, Ni-Co layered double hydroxide (Ni-Co LDH) and Ni-Co mixed metal phosphide (denoted as NiCoP) nanoboxes have also been synthesized. Benefiting from their structural and compositional merits, the as-synthesized NiCoP/C nanoboxes exhibit excellent electrocatalytic activity and long-term stability for OER.

Hierarchical Nanotubes Constructed by Carbon-Coated Ultrathin SnS Nanosheets for Fast Capacitive Sodium Storage.

Tin(II) sulfide (SnS) has been an attractive anode material for sodium ion batteries. Herein, an elegant templating method has been developed for the rational design and synthesis of hierarchical SnS nanotubes composed of ultrathin nanosheets. In order to enhance the electrochemical performance, carbon coated hierarchical SnS nanotubes (denoted as SnS@C nanotubes) have also been obtained by simply adding glucose into the reaction system. Benefiting from their unique structural merits, the SnS@C nanotubes exhibit enhanced sodium storage properties in terms of good cycling performance and superior rate capability.

Ultrathin MoS2 Nanosheets Supported on N-doped Carbon Nanoboxes with Enhanced Lithium Storage and Electrocatalytic Properties.

Molybdenum disulfide (MoS2) has received considerable interest for electrochemical energy storage and conversion. In this work, we have designed and synthesized a unique hybrid hollow structure by growing ultrathin MoS2 nanosheets on N-doped carbon shells (denoted as C@MoS2 nanoboxes). The N-doped carbon shells can greatly improve the conductivity of the hybrid structure and effectively prevent the aggregation of MoS2 nanosheets. The ultrathin MoS2 nanosheets could provide more active sites for electrochemical reactions. When evaluated as an anode material for lithium-ion batteries, these C@MoS2 nanoboxes show high specific capacity of around 1000 mAh g(-1), excellent cycling stability up to 200 cycles, and superior rate performance. Moreover, they also show enhanced electrocatalytic activity for the electrochemical hydrogen evolution.

Formation of nickel sulfide nanoframes from metal-organic frameworks with enhanced pseudocapacitive and electrocatalytic properties.

Nanoframe-like hollow structures with unique three-dimensional (3D) open architecture hold great promise for various applications. Current research efforts mainly focus on frame-like noble metals and metal oxides. However, metal sulfides with frame-like nanostructures have been rarely reported. Starting from metal-organic frameworks (MOFs), we demonstrate a novel structure-induced anisotropic chemical etching/anion exchange method to transform Ni-Co Prussian blue analogue (PBA) nanocubes into NiS nanoframes with tunable size. The reaction between Ni-Co PBA nanocube templates and Na2 S in solution leads to the formation of well-defined NiS nanoframes. The different reactivity between the edges and the plane surface of the Ni-Co PBA nanocubes is found to be the key factor for the formation of NiS nanoframes. Benefitting from their structural merits including 3D open structure, small size of primary nanoparticles, high specific surface area, and good structural robustness, the as-derived NiS nanoframes manifest excellent electrochemical performance for electrochemical capacitors and hydrogen evolution reaction in alkaline electrolyte.

Self-templated formation of uniform NiCo2O4 hollow spheres with complex interior structures for lithium-ion batteries and supercapacitors.

Despite the significant advancement in preparing metal oxide hollow structures, most approaches rely on template-based multistep procedures for tailoring the interior structure. In this work, we develop a new generally applicable strategy toward the synthesis of mixed-metal-oxide complex hollow spheres. Starting with metal glycerate solid spheres, we show that subsequent thermal annealing in air leads to the formation of complex hollow spheres of the resulting metal oxide. We demonstrate the concept by synthesizing highly uniform NiCo2O4 hollow spheres with a complex interior structure. With the small primary building nanoparticles, high structural integrity, complex interior architectures, and enlarged surface area, these unique NiCo2O4 hollow spheres exhibit superior electrochemical performances as advanced electrode materials for both lithium-ion batteries and supercapacitors. This approach can be an efficient self-templated strategy for the preparation of mixed-metal-oxide hollow spheres with complex interior structures and functionalities.

Rutile TiO2 submicroboxes with superior lithium storage properties.

Hollow structures of rutile TiO2 , and especially with non-spherical shape, have rarely been reported. Herein, high-quality rutile TiO2 submicroboxes have been synthesized by a facile templating method using Fe2 O3 submicrocubes as removable templates. Compared to other rutile TiO2 nanomaterials, the as-prepared rutile TiO2 submicroboxes manifest superior lithium storage properties in terms of high specific capacity, long-term cycling stability, and excellent rate capability.

Bowl-like SnO2 @carbon hollow particles as an advanced anode material for lithium-ion batteries.

Despite the great advantages of hollow structures as electrodes for lithium-ion batteries, one apparent common drawback which is often criticized is their compromised volumetric energy density due to the introduced hollow interior. Here, we design and synthesize bowl-like SnO2 @carbon hollow particles to reduce the excessive hollow interior space while retaining the general advantages of hollow structures. As a result, the tap density can be increased about 30 %. The as-prepared bowl-like SnO2 @carbon hollow particles with conformal carbon support exhibit excellent lithium storage properties in terms of high capacity, stable cyclability and excellent rate capability.

Phase engineering of ZnSe by small molecules as a high-performance protective layer for Zn anode.

The practical application of aqueous zinc ion batteries is still hampered by the side reactions and dendrite growth on Zn anode. Herein, phase engineering of ZnSe coating layer by incorporating small molecules is developed to enhance the performance of Zn anode. The unique electronic structure of ZnSe·0.5N2H4 promises strong adsorption for Zn atoms and enhanced ability to inhibit hydrogen evolution, thereby promoting uniform Zn deposition and preventing by-product and dendrite growth. Meanwhile, fast Zn2+ transfer and deposition kinetics are also demonstrated by ZnSe·0.5N2H4. As a result, the ZnSe·0.5N2H4@Zn symmetric cell achieves long-term cycling stability up to 1900 h and 300 h at high current densities of 5 mA cm-2 and 20 mA cm-2, respectively. The assembled ZnSe·0.5N2H4@Zn||NVO full cell presents outstanding cycling stability and rate capability. This work highlights the key role of crystal phase control of protective layer for high-performance zinc anode.

Electrochemical detection of arsenic(III) completely free from noble metal: Fe3O4 microspheres-room temperature ionic liquid composite showing better performance than gold.

In recent decades, electrochemical detection of arsenic(III) has been undergoing revolutionary developments with higher sensitivity and lower detection limit. Despite great success, electrochemical detection of As(III) still depends heavily on noble metals (predominantly Au) in a strong acid condition, thus increasing the cost and hampering the widespread application. Here, we report a disposable platform completely free from noble metals for electrochemical detection of As(III) in drinking water under nearly neutral condition by square wave anodic stripping voltammetry. By combining the high adsorptivity of Fe3O4 microspheres toward As(III) and the advantages of room temperature ionic liquid (RTIL), the Fe3O4-RTIL composite modified screen-printed carbon electrode (SPCE) showed even better electrochemical performance than commonly used noble metals. Several ionic liquids with different viscosities and surface tensions were found to have a different effect on the voltammetric behavior toward As(III). Under the optimized conditions, the Fe3O4-RTIL composites offered direct detection of As(III) within the desirable range (10 ppb) in drinking water as specified by the World Health Organization (WHO), with a detection limit (3σ method) of 8 × 10(-4) ppb. The obtained sensitivity was 4.91 µA ppb(-1), which is the highest as far as we know. In addition, a possible mechanism for As(III) preconcentration based on adsorption has been proposed and supported by designed experiments. Finally, this platform was successfully applied to analyzing a real sample collected from Inner Mongolia, China.

Enhancing selectivity in stripping voltammetry by different adsorption behaviors: the use of nanostructured Mg-Al-layered double hydroxides to detect Cd(II).

We report the use of nanostructured layered double hydroxides (LDHs) for the highly selective and sensitive detection of Cd(2+) using anodic stripping voltammetry (ASV). In particular, the modification of a glassy carbon electrode promotes the sensitivity and selectivity towards Cd(2+) in the presence of Pb(2+), Hg(2+), Cu(2+) and Zn(2+). The electrochemical characterization and anodic stripping voltammetric performance of Cd(2+) were evaluated using cyclic voltammetry (CV) and square wave anodic stripping voltammetry (SWASV) analysis. Operational parameters, including supporting electrolytes, pH value, deposition potential and deposition time were optimized. In addition, the selectivity, interference and stability were also investigated under the optimized conditions. The results showed that the fabricated electrode possessed good selectivity, stability and reproducibility. The proposed electrochemical sensing strategy is thus expected to open new opportunities to broaden the use of ASV in analysis for detecting heavy metal ions in the environment.

In situ reconstructed AgZn3 nanoparticles supported on zinc nanoplates for efficient CO2 electroreduction to tunable syngas.

Developing efficient electrocatalysts for CO2 reduction to syngas with tunable H2/CO ratios and high total faradaic efficiency is challenging. Herein, we report an effective catalyst composed of in situ reconstructed AgZn3 nanoparticles and Zn nanoplates for syngas synthesis, showing nearly 100% Faraday efficiency to syngas with a tunable H2/CO ratio from 2 : 1 to 1 : 2. Moreover, the in situ electrochemical measurements coupled with theoretical calculations disclose that the Zn site in AgZn3 nanoparticles and the hollow site between Ag and Zn in AgZn3 are the possible active sites for CO and H2 generation, respectively. This work has guiding significance for designing dual site catalysts for CO2 electroreduction to tunable syngas.

Highly sensitive determination of L-glutamic acid in pig serum with an enzyme-free molecularly imprinted polymer on a carbon-nanotube modified electrode.

Through electrochemical polymerization using L-glutamic acid (L-Glu) as a template and 4,6-diaminoresorcinol as a functional monomer, an enzyme-free molecularly imprinted polymer (MIP) based L-Glu sensor with multi-walled carbon nanotubes (MWCNTs) decorated on a glassy carbon electrode (GCE), namely G-MIP/MWCNTs/GCE, was developed in this work. The reaction conditions were optimized as follows: electrochemical polymerization of 23 cycles, pH of 3.0, molar ratio of template/monomer of 1 : 4, volume ratio of elution reagents of acetonitrile/formic acid of 1 : 1, and elution time of 2 min. The prepared materials and molecularly imprinted polymer were characterized by using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) as well as electrochemical methods. The electrochemical properties of different electrodes were investigated via differential pulse voltammetry (DPV), showing that the electrode of G-MIP/MWCNTs/GCE exhibited excellent catalytic oxidation activity towards L-Glu. A good linear relationship between peak-currents and L-Glu concentrations in a range from 1.00 × 10-8 to 1.00 × 10-5 mol L-1 was observed, with a detection limit of 5.13 × 10-9 mol L-1 (S/N = 3). The imprinted sensor possesses excellent selectivity, high sensitivity, and good stability, which have been successfully applied for the detection of L-Glu in pig serum samples with a recovery rate of 97.4-105.5%, being comparable to commercial high-performance liquid chromatography, demonstrating a simple, rapid, and accurate way for the determination of L-Glu in the fields of animal nutrition and biomedical engineering.

Stripping voltammetry study of ultra-trace toxic metal ions on highly selectively adsorptive porous magnesium oxide nanoflowers.

We have demonstrated highly selective and sensitive detection of Pb(II) and Cd(II) using a highly selective adsorptive porous magnesium oxide (MgO) nanoflowers. The MgO nanoflower-modified glassy carbon electrode was electrochemically characterized using cyclic voltammetry; and the anodic stripping voltammetric performance of bound Pb(II) and Cd(II) was evaluated using square wave anodic stripping voltammetry (SWASV) analysis. The MgO nanoflower-modified electrode exhibited excellent sensing performance toward Pb(II) and Cd(II) that was never observed previously at bismuth (Bi)-based electrodes. Simultaneous additions of Pb(II) and Cd(II) were investigated in the linear range from 3.3 to 22 nM for Pb(II) and 40 to 140 nM for Cd(II), and detection limits of 2.1 pM and 81 pM were obtained, respectively. Some foreign ions, such as Cu(II), Zn(II) and Cr(III) do not interfere with the detection of Pb(II) and Cd(II). To the best of our knowledge, this is the first example of a highly adsorptive metal oxide with hierarchical micro/nanostructure that allows the detection of both Pb(II) and Cd(II) ions.