Reversing the Interfacial Electric Field in Metal Phosphide Heterojunction by Fe-Doping for Large-Current Oxygen Evolution Reaction.

Developing non-precious-metal electrocatalysts that can operate with a low overpotential at a high current density for industrial application is challenging. Heterogeneous bimetallic phosphides have attracted much interest. Despite high hydrogen evolution reaction (HER) performance, the ordinary oxygen evolution reaction (OER) performance hinders their practical use. Herein, it is shown that Fe-doping reverses and enlarges the interfacial electrical field at the heterojunction, turning the H intermediate favorable binding sites for HER into O intermediate favorable sites for OER. Specifically, the self-supported heterojunction catalysts on nickel foam (CoP@Ni2P/NF and Fe-CoP@Fe-Ni2P/NF) are readily synthesized. They only require the overpotentials of 266 and 274 mV to drive a large current density of 1000 mA cm-2 (j1000) for HER and OER, respectively. Furthermore, a water splitting cell equipped with these electrodes only requires a voltage of 1.724 V to drive j1000 with excellent durability, demonstrating the potential of industrial application. This work offers new insights on interfacial engineering for heterojunction catalysts.

Mn-single-atom nano-multizyme enabled NIR-II photoacoustically monitored, photothermally enhanced ROS storm for combined cancer therapy.

RATIONALE: To realize imaging-guided multi-modality cancer therapy with minimal side effects remains highly challenging. METHODS: We devised a bioinspired hollow nitrogen-doped carbon sphere anchored with individually dispersed Mn atoms (Mn/N-HCN) via oxidation polymerization with triton micelle as a soft template, followed by carbonization and annealing. Enzyme kinetic analysis and optical properties were performed to evaluate the imaging-guided photothermally synergized nanocatalytic therapy. RESULTS: Simultaneously mimicking several natural enzymes, namely peroxidase (POD), catalase (CAT), oxidase (OXD), and glutathione peroxidase (GPx), this nano-multizyme is able to produce highly cytotoxic hydroxyl radical (•OH) and singlet oxygen (1O2) without external energy input through parallel and series catalytic reactions and suppress the upregulated antioxidant (glutathione) in tumor. Furthermore, NIR-II absorbing Mn/N-HCN permits photothermal therapy (PTT), enhancement of CAT activity, and photoacoustic (PA) imaging to monitor the accumulation kinetics of the nanozyme and catalytic process in situ. Both in vitro and in vivo experiments demonstrate that near-infrared-II (NIR-II) PA-imaging guided, photothermally enhanced and synergized nanocatalytic therapy is efficient to induce apoptosis of cancerous cells and eradicate tumor tissue. CONCLUSIONS: This study not only demonstrates a new method for effective cancer diagnosis and therapy but also provides new insights into designing multi-functional nanozymes.

Highly Stereoselective Syntheses of α,α-Disubstituted (E)- and (Z)-Crotylboronates.

We report herein stereoselective syntheses of α,α-disubstituted (E)- and (Z)-crotylboronates. Starting from α-boryl (E)- or (Z)-crotylboronate, base-mediated alkylation occurred exclusively at the position α to the boryl groups to give targeted boronates while retaining the geometries of the alkenes in the starting crotylboronates. Under proper conditions, the resulting α,α-disubstituted crotylboronates underwent aldehyde addition to give allylated products with high stereoselectivities.

Starvation, Ferroptosis, and Prodrug Therapy Synergistically Enabled by a Cytochrome c Oxidase like Nanozyme.

Nanozymes, which are inorganic nanomaterials mimicking natural enzyme activities, are bringing enormous opportunities to theranostics. Herein, a cytochrome c oxidase-like nanozyme (copper-silver alloy nanoparticle, Cu-Ag NP) is demonstrated for nanocatalytic cancer therapy. Loaded with bioreductive predrug (AQ4N), this Cu-Ag nanozyme unprecedentedly enables simultaneous starvation, ferroptosis, and chemical therapy with high specificity, and is able to totally eliminate tumor and greatly prolong the survival rate for 4T1-tumor-bearing mice. The underlying working mechanism is revealed both experimentally and theoretically.

A nonchlorinated solvent-processed polymer semiconductor for high-performance ambipolar transistors.

Ambipolar polymer semiconductors are potentially serviceable for logic circuits, light-emitting field-effect transistors (LFETs) and polymer solar cells (PSCs). Although several high-performance ambipolar polymers have been developed, their optoelectronic devices are generally processed from toxic chlorinated solvents. To achieve the commercial applications of organic FETs (OFETs), the polymers should be processed from nonchlorinated solvents, instead of chlorinated solvents. However, most conjugated polymers show poor solubility in nonchlorinated solvents. It is of great importance to develop ambipolar polymers that can be processed from nonchlorinated solvents. Here, we develop a nonchlorinated solvent processed polymer named poly[7-fluoro-N, N'-di(4-decyltetradecyl)-7'-azaisoindigo-6',6″-(thieno[3,2-b]thiophene-2,5-diyl)-7‴-fluoro-N″, N‴-di(4-decyltetradecyl)-7″-azaisoindigo-6,6‴-([2,2″-bithiophene]-5,5″-diyl)] (PITTI-BT) by designing a monomer with a large molar mass. The polymer displays good solubility in p-xylene (PX). Well-aligned films of PITTI-BT are achieved by an off-center spin-coating (SC) method. Based on the high-quality films, the OFETs fabricated from PX solution achieve record ambipolar performance with hole and electron mobilities of 3.06 and 2.81 cm2 V-1 s-1, respectively. The combination of nonchlorinated solvents and good alignment process offers an effective and eco-friendly approach to obtain high-performance ambipolar transistors.

Template-Sacrificing Synthesis of Well-Defined Asymmetrically Coordinated Single-Atom Catalysts for Highly Efficient CO2 Electrocatalytic Reduction.

Although various single-atom catalysts have been designed, atomically engineering their coordination environment remains a great challenge. Herein, a one-pot template-sacrificing pyrolysis approach is developed to synthesize well-defined Ni-N4-O catalytic sites on highly porous graphitic carbon for electrocatalytic CO2 reduction to CO with high Faradaic efficiency (maximum of 97.2%) in a wide potential window (-0.56 to -1.06 V vs RHE) and with high stability. In-depth experimental and theoretical studies reveal that the axial Ni-O coordination introduces asymmetry to the catalytic center, leading to lower Gibbs free energy for the rate-limiting step, strengthened binding with *COOH, and a weaker association with *CO. The present results demonstrate the successful atomic-level coordination environment engineering of high-surface-area porous graphitic carbon-supported Ni single-atom catalysts (SACs), and the demonstrated method can be applied to synthesize an array of SACs (metal-N4-O) for various catalysis applications.

Substrate Engineering for CVD Growth of Single Crystal Graphene.

Single crystal graphene (SCG) has attracted enormous attention for its unique potential for next-generation high-performance optoelectronics. In the absence of grain boundaries, the exceptional intrinsic properties of graphene are preserved by SCG. Currently, chemical vapor deposition (CVD) has been recognized as an effective method for the large-scale synthesis of graphene films. However, polycrystalline films are usually obtained and the present grain boundaries compromise the carrier mobility, thermal conductivity, optical properties, and mechanical properties. The scalable and controllable synthesis of SCG is challenging. Recently, much attention has been attracted by the engineering of large-size single-crystal substrates for the epitaxial CVD growth of large-area and high-quality SCG films. In this article, a comprehensive and comparative review is provided on the selection and preparation of various single-crystal substrates for CVD growth of SCG under different conditions. The growth mechanisms, current challenges, and future development and perspectives are discussed.

Orbital coupling of hetero-diatomic nickel-iron site for bifunctional electrocatalysis of CO2 reduction and oxygen evolution.

While inheriting the exceptional merits of single atom catalysts, diatomic site catalysts (DASCs) utilize two adjacent atomic metal species for their complementary functionalities and synergistic actions. Herein, a DASC consisting of nickel-iron hetero-diatomic pairs anchored on nitrogen-doped graphene is synthesized. It exhibits extraordinary electrocatalytic activities and stability for both CO2 reduction reaction (CO2RR) and oxygen evolution reaction (OER). Furthermore, the rechargeable Zn-CO2 battery equipped with such bifunctional catalyst shows high Faradaic efficiency and outstanding rechargeability. The in-depth experimental and theoretical analyses reveal the orbital coupling between the catalytic iron center and the adjacent nickel atom, which leads to alteration in orbital energy level, unique electronic states, higher oxidation state of iron, and weakened binding strength to the reaction intermediates, thus boosted CO2RR and OER performance. This work provides critical insights to rational design, working mechanism, and application of hetero-DASCs.

Graphene quantum dots as full-color and stimulus responsive fluorescence ink for information encryption.

Developing anti-counterfeiting technique with rich information encrypted by cheap, eco-friendly and stable photoluminescent materials is useful yet challenging. Herein, we present the application of graphene quantum dots (GQDs) for full-color and stimuli-responsive information encryption. GQDs with red, green and blue (RGB) fluorescence or ion-responsiveness are prepared based on scalable bottom-up molecular fusion in one-step hydrothermal or solvothermal reaction. Printable fluorescent ink is easily prepared by dispersing GQDs homogeneously in glycerol-containing ethanol. Utilizing the color, pattern, characteristic fluorescence emission spectrum, or stimuli-responsive emission of GQDs, information encryption under daylight and information decryption under UV light are realized. Moreover, N and S co-doped GQDs (N, S-GQDs), which have Cu2+-quenchable and cysteine (Cys)-recoverable blue fluorescence, are mixed with lanthanide complex (Eu3+DP) to realize order-sensitive stimulus-responsive information encryption.

Naturally derived honeycomb-like N,S-codoped hierarchical porous carbon with MS2 (M = Co, Ni) decoration for high-performance Li-S battery.

Even though lithium-sulfur batteries have appealing advantages including a high theoretical capacity and energy density, their commercial implementation has been seriously hindered by some notorious reasons, particularly the severe shuttling effect, the insulating nature of sulfur, the large volumetric variation during cycling and the sluggish redox reaction kinetics. To tackle these issues, a biomass (ginkgo-nut) derived N,S-codoped porous carbon (GC) with an interconnected honeycomb-like hierarchical structure is synthesized by a templated carbonization method, followed by hydrothermal growth of transition metal sulfide MS2 (M = Co, Ni) nanocrystals, giving rise to a hybrid 3D electrocatalyst. The unique structure constructed by N,S-codoping can expose more active sites and polar surfaces to physically confine and chemically adsorb polysulfides. Meanwhile, the embedded MS2 polyhedral-like nanoparticles further enhance the interaction with polysulfides and improve conversion and redox kinetics of polysulfides. Remarkably, with 80 wt% sulfur loading (∼2.5 mg cm-2), GC-CoS2 exhibits a reversible capacity of 988.8 mA h g-1 after 500 cycles at 0.1 C and an excellent capacity of 610.3 mA h g-1 after 1000 cycles at 2 C, outperforming bare GC and GC-NiS2. Compared with the electrochemical performances of the representative reported biomass-derived sulfur host for Li-S batteries, evidently, both the discharge capacity and cycling stability of our GC-CoS2 sample are superior. Density functional theory (DFT) calculation results suggest that CoS2 exhibits a higher binding energy towards lithium polysulfides and a lower energy barrier for Li+ diffusion on the surface compared to the NiS2 counterpart, suggesting that CoS2 is a better choice for lithium-sulfur batteries than NiS2. This work provides a new avenue to rationally design a carbonaceous catalyst host for high-performance lithium-sulfur batteries.

In situ growth of Fe(ii)-MOF-74 nanoarrays on nickel foam as an efficient electrocatalytic electrode for water oxidation: a mechanistic study on valence engineering.

In this work, our theoretical results first demonstrate that varying the metal valence in MOFs plays a significant role in tuning their stable intrinsic electronic structure. Different valence Fe(ii) and Fe(iii) based pristine MOF-74 nanoarrays on nickel foam are further synthesized as electrodes for highly efficient electrocatalytic water oxidation.

Self-Supported Biocarbon-Fiber Electrode Decorated with Molybdenum Carbide Nanoparticles for Highly Active Hydrogen-Evolution Reaction.

Devising and facilely synthesizing an efficient noble metal-free electrocatalyst for the acceleration of the sluggish kinetics in the hydrogen-evolution reaction (HER) is still a big challenge for electrolytic water splitting. Herein, we present a simple one-step approach for constructing self-supported biocarbon-fiber cloth decorated with molybdenum carbide nanoparticles (BCF/Mo2C) electrodes by a direct annealing treatment of the Mo oxyanions loaded cotton T-shirt. The Mo2C nanoparticles not only serve as the catalytic active sites toward the HER but also enhance the hydrophilicity and conductivity of resultant electrodes. As an integrated three-dimensional HER cathode catalyst, the BCF/Mo2C exhibits outstanding electrocatalytic performance with extremely low overpotentials of 88 and 115 mV to drive a current density of 20 mA cm-2 in alkaline and acidic media, respectively. In addition, it can continuously work for 50 h with little decrease in the cathodic current density in both alkaline and acidic solutions. Even better, self-supported tungsten carbide and vanadium carbide based electrodes also can be prepared by a similar synthesis process. This work will illuminate an entirely new avenue for the preparation of various self-supported three-dimensional electrodes made of transition-metal carbides for various applications.

Well-Ordered Oxygen-Deficient CoMoO4 and Fe2O3 Nanoplate Arrays on 3D Graphene Foam: Toward Flexible Asymmetric Supercapacitors with Enhanced Capacitive Properties.

In this work, we report the development of well-ordered hydrogenated CoMoO4 (H-CoMoO4) and hydrogenated Fe2O3 (H-Fe2O3) nanoplate arrays on 3D graphene foam (GF) and explore their practice application as binder-free electrodes in assembling flexible all-solid-state asymmetric supercapacitor (ASC) devices. Our results show that the monolithic 3D porous GF prepared by solution casting method using Ni foam template possesses large surface area, superior electrical conductivity, and sufficient surface functional groups, which not only facilitate in situ growth of CoMoO4 and Fe2O3 nanoplates but also contribute the double-layer capacitance of the resultant supercapacitor. The well-ordered pseudocapacitive metal oxide nanoplate arrays standing up on 3D GF scaffold can provide efficient space and shorten the length for electrolyte diffusion from the outer to the inner region of the electrode material for Faradaic energy storage. Furthermore, one of our major findings is that the introduction of oxygen vacancies in CoMoO4 and Fe2O3 nanoplates by hydrogenation treatment can increase their electronic conductivity as well as improve their donor density and surface properties, which gives rise to a substantially improved electrochemical performance. Benefiting from the synergistic contributions of different components in the nanohybrid electrode, the resultant flexible ASC device with GF/H-CoMoO4 as the positive electrode and GF/H-Fe2O3 as the negative electrode achieves a wide operation voltage of 1.5 V and a maximum volumetric specific capacitance of 3.6 F cm-3, which is two times larger than that of the Ni/GF/CoMoO4//Ni/GF/Fe2O3 device (1.8 F cm-3), and the rate capability is up to 70% as the current density increases from 2 to 200 mA cm-3. Moreover, the Ni/GF/H-CoMoO4//Ni/GF/H-Fe2O3 device also exhibits a high energy density of 1.13 mWh cm-3 and a high power density of 150 mW cm-3, good mechanical flexibility with the decrease in capacitance of less than 4% after being bent inward to different angles and inward to 90° 200 times, and good cycling stability of 93.1% capacitance retention after 5000 cycles.

One-Pot Synthesis of Three-Dimensional Graphene/Carbon Nanotube/SnO2 Hybrid Architectures with Enhanced Lithium Storage Properties.

Three-dimensional (3D) graphene/carbon nanotube (CNT)/SnO2 (GCS) hybrid architectures were constructed by a facile and cost-effective self-assembly method through hydrothermal treatment of a mixture of Sn(2+), CNTs, and graphene oxide (GO). The resultant GCS displayed a 3D hierarchically porous structure with large surface area and excellent electrical conductivity, which could effectively prevent the aggregation and volume variation of SnO2 and accelerate the transport of ions and electrons through 3D pathways. Benefiting from the unique structure and the synergistic effect of different components in the hybrid architectures, the GCS exhibited a remarkably improved reversible capacity of 842 mAh g(-1) after 100 cycles at 0.2 A g(-1) and excellent rate performance for lithium storage compared with that of graphene/SnO2 (GS) hybrid architectures. Hence, the impressive results presented here could provide a universal platform for fabricating graphene/CNT-based hybrid architectures with promising applications in various fields.

Scalable synthesis of a Pd nanoparticle loaded hierarchically porous graphene network through multiple synergistic interactions.

A unique Pd nanoparticle loaded hierarchically porous graphene network was successfully prepared through multiple synergistic interactions. The obtained architectures as electrocatalysts exhibit significantly higher activity and durability for ethanol oxidation than commercial Pd/C catalysts.

Scalable synthesis of freestanding sandwich-structured graphene/polyaniline/graphene nanocomposite paper for flexible all-solid-state supercapacitor.

We reported a scalable and modular method to prepare a new type of sandwich-structured graphene-based nanohybrid paper and explore its practical application as high-performance electrode in flexible supercapacitor. The freestanding and flexible graphene paper was firstly fabricated by highly reproducible printing technique and bubbling delamination method, by which the area and thickness of the graphene paper can be freely adjusted in a wide range. The as-prepared graphene paper possesses a collection of unique properties of highly electrical conductivity (340 S cm(-1)), light weight (1 mg cm(-2)) and excellent mechanical properties. In order to improve its supercapacitive properties, we have prepared a unique sandwich-structured graphene/polyaniline/graphene paper by in situ electropolymerization of porous polyaniline nanomaterials on graphene paper, followed by wrapping an ultrathin graphene layer on its surface. This unique design strategy not only circumvents the low energy storage capacity resulting from the double-layer capacitor of graphene paper, but also enhances the rate performance and cycling stability of porous polyaniline. The as-obtained all-solid-state symmetric supercapacitor exhibits high energy density, high power density, excellent cycling stability and exceptional mechanical flexibility, demonstrative of its extensive potential applications for flexible energy-related devices and wearable electronics.

An ultra-low Pd loading nanocatalyst with efficient catalytic activity.

An ultra-low Pd loading nanocatalyst is synthesized by a convenient solution route of photochemical reduction and aqueous chemical growth. The modification of nanocatalyst structures is investigated through changing morphologies of Pd nanoclusters on the surface of ZnO nanorods. A significant enhancement in photocatalytic properties has been achieved by decorating a trace amount of Pd clusters (0.05 at%) on the surface of ZnO nanorods. The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) is applied to demonstrate multiple catalytic activities in the Pd-ZnO hybrid nanocatalyst, which also provides a better understanding of the relationship between the unique nanoconfigured structure and catalytic performance.

Ultrafine Pd nanoparticles encapsulated in microporous Co3O4 hollow nanospheres for in situ molecular detection of living cells.

Recent progress in the in situ molecular detection of living cells has attracted tremendous research interests due to its great significance in biochemical, physiological, and pathological investigation. Especially for the electrochemical detection of hydrogen peroxide (H2O2) released by living cells, the highly efficient and cost-effective electrocatalysts are highly desirable. In this work, we develop a novel type of microporous Co3O4 hollow nanospheres containing encapsulated Pd nanoparticles (Pd@Co3O4). Owing to the synergy effect between the permeable microporous Co3O4 shell and the ultrafine Pd nanoparticles that encapsulated in it, the resultant Pd@Co3O4 based electrode exhibits excellent electrochemical sensor performance toward H2O2, even when the content of Pd in Pd@Co3O4 hollow nanospheres is as low as 1.14 wt %, which enable it be used for real-time tracking of the secretion of H2O2 in different types of living human cells.

Bifunctional nanocatalyst based on three-dimensional carbon nanotube-graphene hydrogel supported Pd nanoparticles: one-pot synthesis and its catalytic properties.

We reported the development of a new type of bifunctional nanocatalyst based on three-dimensional (3D) macroscopic carbon nanotube (CNT)-graphene hydrogel (GH) supported Pd nanoparticles (i.e., Pd-CNT-GH) and explored its practical application in catalytic reduction of p-nitrophenol to p-aminophenol. The 3D Pd-CNT-GH was synthesized by a facile one-pot self-assembled approach through hydrothermal treatment of a mixed aqueous precursor solution of PdCl4(2-), CNT, and graphene oxide (GO). Under the appropriate condition, the spontaneous redox reaction between precursor PdCl4(2-) and CNT-GO as well as the self-assembly of macroscopic CNT-GH occurs simultaneously, leading to the formation of 3D Pd-CNT-GH. Because of the unique structural and functional properties of different components in the nanocatalyst and the synergistic effect between them, the as-prepared Pd-CNT-GH exhibits superior catalytic performance toward the reduction of p-nitrophenol to p-aminophenol, with 100% conversion within 30 s, even when the content of Pd in it is as low as 2.98 wt %. Moreover, after 20 successive cycles of reactions, the reaction time still keeps within 46 s. Therefore, the rational design of 3D macroscopic graphene-based nanohybrid material supported highly catalytically active nanoparticles, combined with the facile one-pot self-assembled strategy, provide a universal platform to fabricate desired 3D multifunctional nanomaterials that can be used in a broad range of catalysis, environmental protection, energy storage and conversation, drug delivery, chemical and biological sensing, and so forth.

Freestanding graphene paper supported three-dimensional porous graphene-polyaniline nanocomposite synthesized by inkjet printing and in flexible all-solid-state supercapacitor.

Freestanding paper-like electrode materials have trigged significant research interest for their practical application in flexible and lightweight energy storage devices. In this work, we reported a new type of flexible nanohybrid paper electrode based on full inkjet printing synthesis of a freestanding graphene paper (GP) supported three-dimensional (3D) porous graphene hydrogel (GH)-polyaniline (PANI) nanocomposite, and explored its practical application in flexible all-solid-state supercapacitor (SC). The utilization of 3D porous GH scaffold to load nanostructured PANI dramatically enhances the electrical conductivity, the specific capacitance and the cycle stability of the GH-PANI nanocomposite. Additionally, GP can intimately interact with GH-PANI through π-π stacking to form a unique freestanding GP supported GH-PANI nanocomposite (GH-PANI/GP) with distinguishing mechanical, electrochemical and capacitive properties. These exceptional attributes, coupled with the merits of full inkjet printing strategy, lead to the formation of a high-performance binder-free paper electrode for flexible and lightweight SC application. The flexible all-solid-state symmetric SC based on GH-PANI/GP electrode and gel electrolyte exhibits remarkable mechanical flexibility, high cycling performance and acceptable energy density of 24.02 Wh kg(-1) at a power density of 400.33 W kg(-1). More importantly, the proposed simple and scale-up full inkjet printing procedure for the preparation of freestanding GP supported 3D porous GH-PANI nanocomposite is a modular approach to fabricate other graphene-based nanohybrid papers with tailorable properties and optimal components.