Heteroatom-Induced Electronic Structure Modulation of Vertically Oriented Oxygen Vacancy-Rich NiFe Layered Double Oxide Nanoflakes To Boost Bifunctional Catalytic Activity in Li-O2 Battery

Phase regulation of Ni(OH)2 nanosheets induced by W doping as self-supporting electrodes for boosted water electrolysis

Developing high-performance and low-cost electrodes for hydrogen and oxygen evolution reactions (HER and OER, respectively) represents a pivotal challenge in the field of water electrolysis. Herein, W doped NiFe LDH nanosheets (NiFe-Wx/NF) were immobilized on nickel foam (NF) through one-step corrosion engineering, which induced the coexistence of α-Ni(OH)2 and β-Ni(OH)2. The doping of large atomic radius W influenced the growth of crystal planes of Ni(OH)2, promoting the formation of α-Ni(OH)2, which results in large layer spaces and neatly arranged nanosheets structure. The optimized NiFe-W0.5/NF catalyst require potentials of only 69 to attain 10 mA/cm2 for HER, and require overpotentials of 269 mV to reach 100 mA/cm2 current density for OER, respectively. The W6+ with high oxidation state can withdraw neighboring electrons from Ni, altering the adsorption energy of hydrogen intermediates, which improves the Volmer step and electrical conductivity in HER. And the large layer space of α-Ni(OH)2 in NiFe-W0.5/NF can be contributed to accelerating the formation of high valence γ-NiOOH, which can accelerate OER kinetics. In addition, the NiFe-W0.5/NF catalyst also provides an overall water splitting activity of 780 mA/cm2 current density at a cell voltage of only 1.90 V, and remains highly stable for over 70 h at 100 mA/cm2, which makes it a bifunctional efficient catalyst for water electrolysis.

Disinfection by-products of metformin in the environment: A systematic toxicity evaluation on gut-liver-brain axis homeostasis and establishment of a detection method based on NiFe-LDOs/N-BC composite

Metformin, a first-line drug used to treat type 2 diabetes, is not metabolised in the body and discharged into the environment in the form of prototype drugs. Compounds C (C4H6ClN3) and Y (C4H6ClN5) are the main disinfection byproducts of metformin in urban sewage treatment; however, their potential toxicity is unclear. In this study, absorption, distribution, metabolism, elimination, and toxicity (ADMET) prediction indicated that compounds C and Y had potential hepatotoxicity and could cross the blood-brain-barrier. Toxicity verification tests indicated a sex difference in the acute toxicity of compound C, with an LD50 value of 253.269 mg kg-1 for male mice and 728.908 mg kg-1 for female mice. The subacute toxicity of compounds C and Y was evaluated to study the toxicity mechanism via the gut-liver-brain axis, which indicated that they could cause damage to the liver and brain, change the composition of the gut microbiota, and disturb the levels of metabolites in mice. Neuron-like magnetic N-doped biochar (NiFe-LDOs/N-BC) was synthesised using hydrothermal and calcination methods, and the optimised d-MSPE-HPLC-UV method was proven to be applicable for the trace detection of compound C in real water samples. The simultaneous presentation of toxicity evaluation and trace detection of compound C is intended to make the monitoring system for compound C more comprehensive.

Hierarchically Interconnected 3D Catalyst Structure of Porous Multi-Metal Oxide Nanofibers for High-Performance Li-O2 Batteries

Non-aqueous lithium-oxygen batteries (LOBs) have emerged as a promising candidate due to their high theoretical energy density and eco-friendly cathode reaction materials. However, LOBs still suffer from high overpotential and poor cycling stability resulting from difficulties in the decomposition of discharge reaction Li2O2 products. Here, a 3D open network catalyst structure is proposed based on highly-thin and porous multi-metal oxide nanofibers (MMONFs) developed by a facile electrospinning approach coupled with a heat treatment process. The developed hierarchically interconnected 3D porous MMONFs catalyst structure with high specific surface area and porosity shows the enhanced electrochemical reaction kinetics associated with Li2O2 formation and decomposition on the cathode surface during the charge and discharge processes. The uniquely assembled cathode materials with MMONFs exhibit excellent electrochemical performance with energy efficiency of 82% at a current density of 50 mA g-1 and a long-term cycling stability over 100 cycles at 200 mA g-1 with a cut-off capacity of 500 mAh g-1. Moreover, the optimized cathode materials exhibit a remarkable energy density of 1013 Wh kg-1 at the 100th discharge and charge cycle, which is nearly four times higher than that of C/NMC721, which has the highest energy density among the cathode materials currently used in electric vehicles.

Orthogonal-Channel, Low-Tortuosity Carbon Nanotube Platforms for High-Performance Li-O2 Batteries

Aerogels and foams are promising electrode materials owing to their lightweight, high porosity, and large surface area for creating abundant active/catalytic sites. Tailoring their porous structure is essential toward maximum electrode performance yet remains challenging in the field. Here, by modifying a pristine carbon nanotube (CNT) sponge with random internal distribution, we present a CNT platform consisting of regular, orthogonally intercrossed through-channels centered at a suitable lateral size (around 5 μm), with low tortuosity and enhanced electrochemical kinetics under predefined compression. Our CNT platforms, grafted by bifunctional transitional metal hydroxide catalyst, overcome considerable challenges of both long cycle life and high rates simultaneously, serving as Li-O2 cathodes and achieving lifetime of 500 cycles at 0.5 mA cm-2 (275 cycles even at 1 mA cm-2) and also displaying high areal capacity (27 mA h cm-2), which are superior to most of the recently reported porous electrodes based on various materials. The mechanism involving fast triple-phase transport and reversible discharge product deposition, enabled by catalyst-loaded orthogonal channels, has been disclosed. Such structure-tailored robust CNT platforms could find many applications in electrochemical catalysis and energy storage systems.

Vanadium-Doped Porous Cobalt Oxide for Its Superior Peroxidase-like Activity in Simultaneous Total Cholesterol and Glucose Determination in Whole Blood Based on a Simple Two-Dimensional Paper-Based Analytical Device

Vanadium-doped porous Co₃O₄ (V-porous Co₃O₄) was synthesized via a simple soft-templating method and used as a superior peroxidase mimic for the simultaneous colorimetric determination of glucose and total cholesterol (TC) in whole blood samples on a two-dimensional microfluidic paper-based analytical device (2D-μPAD). The large surface area and the presence of two metals in V-porous Co₃O₄ contributed to its excellent catalytic activity toward 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and 3,3',5,5'- tetramethylbenzidine (TMB) with Michaelis-Menten constants (K_M) of 0.1301 and 0.0141 mM, respectively. The 2D-μPAD was fabricated using simple wax screen-printing and cutting techniques. The colorimetric reactions of both glucose and TC on 2D-μPAD were simultaneously performed by adding a single drop of a whole blood sample on the sample zone made of the LF1 membrane. After the enzymatic reactions, the generated hydrogen peroxide (H₂O₂) was oxidized by V-porous Co₃O₄ to produce hydroxy radicals (^•OH), inducing ABTS and TMB to generate colored products. The generated H₂O₂ was proportional to the intensities of the green and blue products of the glucose and TC systems, respectively. The developed 2D-μPAD required a short analysis time (∼5 min) with small volumes of samples (15 μL of whole blood) whereby no sample preparation was needed. Owing to several advantages including simplicity, low cost, long-term stability, and simultaneous readout, the novel V-porous Co₃O₄ coupled with 2D-μPAD proved to be promising for practical uses as a pioneering portable device for the determination of glucose, TC, and other important biomarkers without the need of technical supports.

Plasma Surface Engineering of NiCo2S4@rGO Electrocatalysts Enables High-Performance Li-O2 Batteries

The sluggish redox reaction kinetics for aprotic Li-O₂ batteries (LOBs) caused by the insulating discharge product of Li₂O₂ could result in the poor round-trip efficiency, low rate capability, and cyclic stability. To address these challenges, we herein fabricated NiCo₂S₄ supported on reduced graphene oxide (NiCo₂S₄@rGO), the surface of which is further modified via a unique low-pressure capacitive-coupled nitrogen plasma (CCPN-NiCo₂S₄@rGO). The high ionization environment of the plasma could etch the surface of NiCo₂S₄@rGO, introducing effective nitrogen doping. The as-prepared CCPN-NiCo₂S₄@rGO has been employed as an efficient catalyst for advanced LOBs. The electrochemical analysis, combined with theoretical calculations, reveals that the N-doping can effectively improve the thermodynamics and kinetics for LiO₂ adsorption, giving rise to a well-knit Li₂O₂ formation on CCPN-NiCo₂S₄@rGO. The LOBs based on the CCPN-NiCo₂S₄@rGO oxygen electrode deliver a low overpotential of 0.75 V, a high discharge capacity of 10,490 mA h g^-1, and an improved cyclic stability (more than 110 cycles). This contribution may pave a promising avenue for facile surface engineering of the electrocatalyst in LOBs and other energy storage systems.

Nitrogen-doped carbon dots/Ni-MnFe-layered double hydroxides (N-CDs/Ni-MnFe-LDHs) hybrid nanomaterials as immunoassay label for low-density lipoprotein detection

Nitrogen-doped carbon dots/Ni-MnFe-layered double hydroxides (N-CDs/Ni-MnFe-LDHs) are demonstrated as superior peroxidase mimic antibody labels alternative to horseradish peroxidase (HRP) in an immunoassay, potentially overcoming some of the inherent disadvantages of HRP and other enzyme mimicking nanomaterials. They revealed efficient peroxidase-like activity and catalyzed the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to form the intense blue product (at 620 nm) in the presence of hydrogen peroxide (H₂O₂). Using low-density lipoprotein (LDL) as a model target, an ultra-low limit of detection (0.0051 mg/dL) and a linear range of 0.0625-0.750 mg/dL were achieved, exhibiting higher sensitivity than the HRP-based immunoassay. Thus, the proposed N-CDs/Ni-MnFe-LDHs can be used as HRP mimicking analogs for developing highly sensitive colorimetric immunosensors for detection of biomarkers, as well as trace chemical analysis.

Rationalizing Surface Electronic Configuration of Ni-Fe LDO by Introducing Cationic Nickel Vacancies as Highly Efficient Electrocatalysts for Lithium-Oxygen Batteries

Cationic defect engineering is an effective strategy to optimize the electronic structure of active sites and boost the oxygen electrode reactions in lithium-oxygen batteries (LOBs). Herein, Ni-Fe layered double oxides enriched with cationic nickel vacancies (Ni-Fe LDO-V_Ni ) are first designed and studied as the electrocatalysts for LOBs. Based on the density functional theory calculation, the existence of nickel vacancy in Ni-Fe LDO-V_Ni significantly improves its intrinsic affinity toward intermediates, thereby fundamentally optimizing the formation and decomposition pathway of Li₂ O₂ . In addition, the number of e_g electrons on each nickel site is 1.19 for Ni-Fe LDO-V_Ni , which is much closer to 1 than 1.49 for Ni-Fe LDO. The near-unity occupation of e_g orbital enhances the covalency of transition metal-oxygen bonds and thus improves the electrocatalytic activity of Ni-Fe LDO-V_Ni toward oxygen electrode reactions. The experimental results show that the LOBs with Ni-Fe LDO-V_Ni electrode deliver low overpotentials of 0.11/0.29 V during the oxygen reduction reaction/oxygen evolution reaction, respectively, large specific capacities of 13 933 mA h g^-1 and superior cycling stability of over 826 h. This study provides a novel approach to optimize the electrocatalytic activity of LDO through reasonable defect engineering.

Surface chemical functionality of carbon dots: influence on the structure and energy storage performance of the layered double hydroxide

As a kind of zero-dimensional material, carbon dots (CDs) have become a kind of promising novel material due to their incomparable unique physical and chemical properties. Despite the optical properties of CDs being widely studied, their surface chemical functions are rarely reported. Here we propose an interesting insight into the important role of surface chemical properties of CDs in adjusting the structure of the layered double hydroxide (LDH) and its energy storage performance. It was demonstrated that CDs with positive charge (p-CDs) not only reduce the size of the flower-like LDH through affecting the growth of LDH sheets, but also act as a structure stabilizer. After calcination, the layered double oxide (LDO) maintained the morphology of the LDH and prevented the stacking of layers. And the superiority of the composite in lithium-ion batteries (LIBs) was demonstrated. When used as an anode of LIBs, composites possess outstanding specific capacity, cycle stability and rate performance. It presents the discharge capacity of 1182 mA h g-1 and capacity retention of 94% at the current density of 100 mA g-1 after 100 cycles. Our work demonstrates the important chemical functions of CDs and expands their future applications.