Bridging Nickel-MOF and Copper Single Atoms/Clusters with H-Substituted Graphdiyne for the Tandem Catalysis of Nitrate to Ammonia.

Interfacial engineering of synergistic catalysts is one of the keys to achieving multiple proton-coupled electron transfer processes in nitrate-to-ammonia conversion. Herein, by joining ultrathin nickel-based metal-organic framework (denoted Ni-MOF) nanosheets with few-layered hydrogen-substituted graphdiyne-supported copper single atoms and clusters (denoted HsGDY@Cu), a tandem catalyst of Ni-MOFs@HsGDY@Cu with dual-active interfaces was developed for the concerted catalysis of nitrate-to-ammonia. In such a system, the sandwiched HsGDY layer could serve as a bridge to connect the coordinated unsaturated Ni2+ sites with Cu single atoms/clusters in a limited range of 0 to 3.6 nm. From Ni2+ to Cu, via the hydrogen spillover process, the hydrogen radicals (H⋅) generated at the unsaturated Ni2+ sites could migrate across HsGDY to the Cu sites to participate in the transformation of *HNO3 to NH3. From Cu to Ni2+, bypassing the higher reaction energy for *HNO3 formation on the Ni2+ sites, the NO2 - detached from the Cu sites could diffuse onto the unsaturated Ni2+ sites to form NH3 as well. The combined results make this hybrid a tandem catalyst with dual active sites for the catalysis of nitrate-to-ammonia conversion with improved Faradaic efficiency at lower overpotentials.

Hybrid nanoarrays of Cu-MOFs@H-substituted graphdiyne with various levels of Lewis acidity for nitrate electroreduction.

To mimic enzymes in nature, a set of hybrid nanoarrays of Cu-MOFs sealed in hydrogen-substituted graphdiyne has been developed in order to serve as Lewis-acid-promoted catalysts. By regulating the electron-withdrawing capability of the ligands bridging Cu2+ sites, these Cu-MOFs provided different levels of Lewis acidity toward nitrate affinity, a feature crucial for nitrate-to-ammonia conversion.

Interfacial Engineering of Bimetallic Ni/Co-MOFs with H-Substituted Graphdiyne for Ammonia Electrosynthesis from Nitrate.

The electrochemical synthesis of ammonia is highly dependent on the coupling reaction between nitrate and water, for which an electrocatalyst with a multifunctional interface is anticipated to promote the deoxygenation and hydrogenation of nitrate with water. Herein, by engineering the surface of bimetallic Ni/Co-MOFs (NiCoBDC) with hydrogen-substituted graphdiyne (HsGDY), a hybrid nanoarray of NiCoBDC@HsGDY with a multifunctional interface has been achieved toward scale-up of the nitrate-to-ammonia conversion. On the one hand, a partial electron transfers from Ni2+ to the coordinatively unsaturated Co2+ on the surface of NiCoBDC, which not only promotes the deoxygenation of *NO3 on Co2+ but also activates the water-dissociation to *H on Ni2+. On the other hand, the conformal coated HsGDY facilitates both electrons and NO3- ions gathering on the interface between NiCoBDC and HsGDY, which moves forward the rate-determining step from the deoxygenation of *NO3 to the hydrogenation of *N with both *H on Ni2+ and *H2O on Co2+. As a result, such a NiCoBDC@HsGDY nanoarray delivers high NH3 yield rates with Faradaic efficiency above 90% over both wide potential and pH windows. When assembled into a galvanic Zn-NO3- battery, a power density of 3.66 mW cm-2 is achieved, suggesting its potential in the area of aqueous Zn-based batteries.

Construction of Synergistic Ni3 S2 -MoS2 Nanoheterojunctions on Ni Foam as Bifunctional Electrocatalyst for Hydrogen Evolution Integrated with Biomass Valorization.

The intrinsic sluggish kinetics of the oxygen evolution reaction (OER) limit the improvement of hydrogen evolution reaction (HER) performance, and substituting the anodic oxidation of biomass materials is an alternative approach, given its lower oxidation potential and higher added value compared to those of OER. In this study, a Ni3 S2 -MoS2 nanoheterojunction catalyst with strong electronic interactions is prepared. It exhibits high efficiency for both the HER and the electrooxidation of 5-hydroxymethylfurfural (HMF). In a two-electrode cell with Ni3 S2 -MoS2 serving as both the anode and cathode, the potential is only 1.44 V at a current density of 10 mA cm-2 , which is much lower than that of pure water splitting. Density functional theory calculations confirm that the strong chemisorption of H and HMF at the interface leads to outstanding electrocatalytic activity. The findings not only provide a strategy for developing efficient electrocatalysts, but also provide an approach for the continuous production of high value-added products and H2 .

Hierarchical Nanocapsules of Cu-Doped MoS2@H-Substituted Graphdiyne for Magnesium Storage.

Hierarchical nanocomposites, which integrate electroactive materials into carbonaceous species, are significant in addressing the structural stability and electrical conductivity of electrode materials in post-lithium-ion batteries. Herein, a hierarchical nanocapsule that encapsulates Cu-doped MoS2 (Cu-MoS2) nanopetals with inner added skeletons in an organic-carbon-rich nanotube of hydrogen-substituted graphdiyne (HsGDY) has been developed for rechargeable magnesium batteries (RMB). Notably, both the incorporation of Cu in MoS2 and the generation of the inner added nanoboxes are developed from a dual-template of Cu-cysteine@HsGDY hybrid nanowire; the synthesis involves two morphology/composition evolutions by CuS@HsGDY intermediates both taking place sequentially in one continuous process. These Cu-doped MoS2 nanopetals with stress-release skeletons provide abundant active sites for Mg2+ storage. The microporous HsGDY enveloped with an extended π-conjugation system offers more effective electron and ion transfer channels. These advantages work together to make this nanocapsule an effective cathode material for RMB with a large reversible capacity and superior rate and cycling performance.

Solar Seawater Distillation by Flexible and Fully Passive Multistage Membrane Distillation.

Solar-assisted distillation is considered promising to solve the freshwater supply for off-grid communities. In this work, a passive and flexible multistage membrane distillation (F-MSMD) device is devised to produce freshwater via solar distillation with the latent heat of vapor condensation being recycled to enhance its energy efficiency. By designing a siphon effect, source water is continuously wicked into the evaporation layer and the concentrated brine flows out of the device before reaching saturation, which successfully solves the otherwise challenge of salt accumulation inside the device. To achieve such siphon flow, the recycled paper is prepared from spent copy paper and used as the evaporation layer for efficient water delivery owing to its large pore size and high hydrophilicity. An eight-stage F-MSMD device exhibits a stable clean water production rate at 3.61 kg m-2 h-1 in the newly designed siphon-flow mode. This work provides a green route for designing a solar-assisted distillation device.

Designing a next generation solar crystallizer for real seawater brine treatment with zero liquid discharge.

Proper disposal of industrial brine has been a critical environmental challenge. Zero liquid discharge (ZLD) brine treatment holds great promise to the brine disposal, but its application is limited by the intensive energy consumption of its crystallization process. Here we propose a new strategy that employs an advanced solar crystallizer coupled with a salt crystallization inhibitor to eliminate highly concentrated waste brine. The rationally designed solar crystallizer exhibited a high water evaporation rate of 2.42 kg m-2 h-1 under one sun illumination when treating real concentrated seawater reverse osmosis (SWRO) brine (21.6 wt%). The solar crystallizer array showed an even higher water evaporation rate of 48.0 kg m-2 per day in the outdoor field test, suggesting a great potential for practical application. The solar crystallizer design and the salt crystallization inhibition strategy proposed and confirmed in this work provide a low-cost and sustainable solution for industrial brine disposal with ZLD.

Iontronics Using V2CTx MXene-Derived Metal-Organic Framework Solid Electrolytes.

Electronic applications of porous metal-organic frameworks (MOFs) have recently emerged as an important research area. However, there is still no report on using MOF solid electrolytes in iontronics, which could take advantage of the porous feature of MOFs in the ionic transport. In this article, MXene-derived two-dimensional porphyrinic MOF (MX-MOF) films are demonstrated as an electronic-grade proton-conducting electrolyte. Meanwhile, the MX-MOF film shows high quality, chemical stability, and capability of standard device patterning processes (e.g., dry etching and optical and electron beam lithography). Using the commercialized nanofabrication processes, an electric double-layer (EDL) transistor is demonstrated using the MX-MOF film (derived from V2CTx MXene) as an ionic gate and MoS2 film as a semiconducting channel layer. The EDL transistor, operated by applying an electric field to control the interaction between ions and electrons, is the core device platform in the emerging iontronics field. Therefore, The MX-MOF, confirmed as a solid electrolyte for EDL transistor devices, could have a significant impact on iontronics research and development.

Simultaneous production of fresh water and electricity via multistage solar photovoltaic membrane distillation.

The energy shortage and clean water scarcity are two key challenges for global sustainable development. Near half of the total global water withdrawals is consumed by power generation plants while water desalination consumes lots of electricity. Here, we demonstrate a photovoltaics-membrane distillation (PV-MD) device that can stably produce clean water (>1.64 kg·m-2·h-1) from seawater while simultaneously having uncompromised electricity generation performance (>11%) under one Sun irradiation. Its high clean water production rate is realized by constructing multi stage membrane distillation (MSMD) device at the backside of the solar cell to recycle the latent heat of water vapor condensation in each distillation stage. This composite device can significantly reduce capital investment costs by sharing the same land and the same mounting system and thus represents a potential possibility to transform an electricity power plant from otherwise a water consumer to a fresh water producer.

Solar Evaporator with Controlled Salt Precipitation for Zero Liquid Discharge Desalination.

A sustainable supply of clean water is essential for the development of modern society, which has become increasingly dependent on desalination technology since 96.5% of the water on Earth is salt water. Thousands of desalination plants are producing massive waste brine as byproduct, and the direct discharge of brine raises serious concerns about its ecological impact. The concept of zero liquid discharge (ZLD) desalination is regarded as the solution, but the current ZLD technologies are hampered by their intensive use of energy and high cost. In this work, a 3D cup shaped solar evaporator was fabricated to achieve ZLD desalination with high energy efficiency via solar distillation. It produces solid salt as the only byproduct and uses sunlight as the only energy source. By rationally separating the light absorbing surface from the salt precipitation surface, the light absorption of the 3D solar evaporator is no longer affected by the salt crust layer as in conventional 2D solar evaporators. Therefore, it can be operated at an extremely high salt concentration of 25 wt % without noticeable water evaporation rate decay in at least 120 h. This new solar evaporator design concept offers a promising technology especially for high salinity brine treatment in desalination plants to achieve greener ZLD desalination as well as for hypersaline industrial wastewater treatment.

Dual-template engineering of triple-layered nanoarray electrode of metal chalcogenides sandwiched with hydrogen-substituted graphdiyne.

Hybrid nanostructures integrating electroactive materials with functional species, such as metal-organic frameworks, covalent organic frameworks, graphdiyne etc., are of significance for both fundamental research and energy conversion/storage applications. Here, hierarchical triple-layered nanotube arrays, which consist of hydrogen-substituted graphdiyne frameworks seamlessly sandwiched between an outer layer of nickel-cobalt co-doped molybdenum disulfide nanosheets and an inner layer of mixed cobalt sulfide and nickel sulfide (Co9S8/Ni3S2), are directly fabricated on conductive carbon paper. The elaborate triple-layered structure emerges as a useful hybrid electrode for energy conversion and storage, in which the organic hydrogen-substituted graphdiyne middle layer, with an extended π-conjugated system between the electroactive nanomaterials, provides built-in electron and ion channels that are crucial for performance enhancement. This dual-template synthetic method, which makes use of microporous organic networks to confine a self-template, is shown to be versatile and thus provides a promising platform for advanced nanostructure-engineering of hierarchical multi-layered nanostructures towards a wide range of electrochemical applications.

Annealing temperature effects on photoelectrochemical performance of bismuth vanadate thin film photoelectrodes.

The effects of annealing treatment between 400 °C and 540 °C on crystallization behavior, grain size, electrochemical (EC) and photoelectrochemical (PEC) oxygen evolution reaction (OER) performances of bismuth vanadate (BiVO4) thin films are investigated in this work. The results show that higher temperature leads to larger grain size, improved crystallinity, and better crystal orientation for the BiVO4 thin film electrodes. Under air-mass 1.5 global (AM 1.5) solar light illumination, the BiVO4 thin film prepared at a higher annealing temperature (500-540 °C) shows better PEC OER performance. Also, the OER photocurrent density increased from 0.25 mA cm-2 to 1.27 mA cm-2 and that of the oxidation of sulfite, a hole scavenger, increased from 1.39 to 2.53 mA cm-2 for the samples prepared from 400 °C to 540 °C. Open-circuit photovoltage decay (OCPVD) measurement indicates that BiVO4 samples prepared at the higher annealing temperature have less charge recombination and longer electron lifetime. However, the BiVO4 samples prepared at lower annealing temperature have better EC performance in the absence of light illumination and more electrochemically active surface sites, which are negatively related to electrochemical double-layer capacitance (C dl). C dl was 0.0074 mF cm-2 at 400 °C and it decreased to 0.0006 mF cm-2 at 540 °C. The OER and sulfide oxidation are carefully compared and these show that the efficiency of charge transport in the bulk (η bulk) and on the surface (η surface) of the BiVO4 thin film electrode are improved with the increase in the annealing temperature. The mechanism behind the light-condition-dependent role of the annealing treatment is also discussed.

Sub-1.1 nm ultrathin porous CoP nanosheets with dominant reactive {200} facets: a high mass activity and efficient electrocatalyst for the hydrogen evolution reaction.

The exploration of a facile strategy to synthesize porous ultrathin nanosheets of non-layered materials, especially with exposed reactive facets, as highly efficient electrocatalysts for the hydrogen evolution reaction (HER), remains challenging. Herein we demonstrate a chemical transformation strategy to synthesize porous CoP ultrathin nanosheets with sub-1.1 nm thickness and exposed {200} facets via phosphidation of Co3O4 precursors. The resultant samples exhibit outstanding electrochemical HER performance: a low overpotential (only 56 and 131 mV are required for current densities of 10 and 100 mA cm-2, respectively), a small Tafel slope of 44 mV per decade, a good stability of over 20 h, and a high mass activity of 151 A g-1 at an overpotential of 100 mV. The latter is about 80 times higher than that of CoP nanoparticles. Experimental data and density functional theory calculations reveal that a high proportion of reactive {200} facets, high utilization efficiency of active sites, metallic nature, appropriate structural disorder, facile electron/mass transfer and rich active sites benefiting from the unique ultrathin and porous structure are the key factors for the greatly improved activity. Additionally, this facile chemical conversion strategy can be developed to a generalized method for preparing porous ultrathin nanosheets of CoSe2 and CoS that cannot be obtained using other methods.

General Self-Template Synthesis of Transition-Metal Oxide and Chalcogenide Mesoporous Nanotubes with Enhanced Electrochemical Performances.

The development of a general strategy for synthesizing hierarchical porous transition-metal oxide and chalcogenide mesoporous nanotubes, is still highly challenging. Herein we present a facile self-template strategy to synthesize Co3 O4 mesoporous nanotubes with outstanding performances in both the electrocatalytic oxygen-evolution reaction (OER) and Li-ion battery via the thermal-oxidation-induced transformation of cheap and easily-prepared Co-Asp(cobalt-aspartic acid) nanowires. The initially formed thin layers on the precursor surfaces, oxygen-induced outward diffusion of interior precursors, the gas release of organic oxidation, and subsequent Kirkendall effect are important for the appearance of the mesoporous nanotubes. This self-template strategy of low-cost precursors is found to be a versatile method to prepare other functional mesoporous nanotubes of transition-metal oxides and chalcogenides, such as NiO, NiCo2 O4 , Mn5 O8 , CoS2 and CoSe2 .

Self-template-directed synthesis of porous perovskite nanowires at room temperature for high-performance visible-light photodetectors.

The unique optoelectronic properties and promising photovoltaic applications of organolead halide perovskites have driven the exploration of facile strategies to synthesize organometal halide perovskites and corresponding hybrid materials and devices. Currently, the preparation of CH3 NH3 PbBr3 perovskite nanowires, especially those with porous features, is still a great challenge. An efficient self-template-directed synthesis of high-quality porous CH3 NH3 PbBr3 perovskite nanowires in solution at room temperature using the Pb-containing precursor nanowires as both the sacrificial template and the Pb(2+) source in the presence of CH3 NH3 Br and HBr is now presented. The initial formation of CH3 NH3 PbBr3 perovskite layers on the surface of the precursor nanowires and the following dissolution of the organic component of the latter led to the formation of mesopores and the preservation of the 1D morphology. Furthermore, the perovskite nanowires are potential materials for visible-light photodetectors with high sensitivity and stability.

Ni2P nanosheets/Ni foam composite electrode for long-lived and pH-tolerable electrochemical hydrogen generation.

The continuous consumption of fossil fuels and accompanying environmental problems are driving the exploration of low-cost and effective electrocatalysts to produce clean hydrogen. A Ni2P nanosheets/Ni foam composite, as a non-noble metal electrocatalyst, has been prepared through a facile chemical conversion pathway using surface oxidized Ni foam as precursor and low concentration of trioctylphosphine (TOP) as a phosphorus source. Further investigation shows the oxidized layer of Ni foam can orient the formation of Ni2P nanosheets and facilitate the reaction with TOP. The Ni2P/Ni, acting as a robust 3D self-supported superaerophobic hydrogen-evolving cathode, shows superior catalytic performance, stability, and durability in aqueous media over a wide pH value of 0-14, making it a versatile catalyst system for hydrogen generation. Such highly active, stable, abundant, and low-cost materials hold enormously promising potential applications in the fields of catalysis, energy conversion, and storage.

A water-soluble glucose-functionalized cobalt(III) complex as an efficient electrocatalyst for hydrogen evolution under neutral conditions.

A water-soluble glucose-functionalized cobalt(III) complex [Co(III)(dmgH)2(py-glucose)Cl] is active and stable for electrocatalytic hydrogen production in neutral aqueous solution.

Nanoporous hollow transition metal chalcogenide nanosheets synthesized via the anion-exchange reaction of metal hydroxides with chalcogenide ions.

Nanoporous hollow transition metal chalcogenides are of special interest for a variety of promising applications. Although some advanced synthetic methods have been reported, the development of a facile and general strategy to fabricate porous hollow nanostructures of transition metal chalcogenides, especially with enhanced electrocatalytic performance, still remains highly challenged. Herein, we report a facile chemical transformation strategy to prepare nanoporous hollow Co3S4 nanosheets via the anion exchange reaction of Co(OH)2 with sulfide ions. The chemical transformation mechanism involves the as-formed layer of nanoporous cobalt sulfide on Co(OH)2 driven by the anion-exchange-reaction and lattice mismatch induced quick strain release, a following diffusion-effect-dominated core-shell hollow intermediate with hollow interiors, and subsequent Ostwald ripening growth of hollow nanosheets at elevated temperatures. This anion-exchange strategy of transition metal hydroxides with chalcogenide ions is also suitable for fabricating nanoporous hollow nanosheets of other metal chalcogenides (e.g., CoSe2, CoTe2, CdS, and NiS). The as-prepared nanoporous hollow Co3S4 nanosheets are found to be highly active and stable for electrocatalytic oxygen evolution reaction.

Sulfur copolymer nanowires with enhanced visible-light photoresponse.

Sulfur copolymer nanowires have been reported for the first time as highly stable visible-light-active photocatalysts for photoelectrochemical water splitting depending on their size and sulfur content. The as-prepared sulfur copolymer nanowires can serve as a sulfur source and templates to create metal sulfide/copolymer heterocatalysts.