Efficient mineralization of sulfanilamide over oxygen vacancy-rich NiFe-LDH nanosheets array during electro-fenton process.

Electrochemical degradation of toxic sulfanilamide with inexpensive approach is in urgent demand due to the harmful effects of sulfanilamide for both humans and aquatic environments. Here, we reported an efficient mineralization of sulfanilamide by using NiFe-layered double hydroxide (NiFe-LDH) nanosheets array with abundant oxygen vacancies that was in situ grown on exfoliated graphene (EG) by a simple hydrothermal treatment at different temperatures. The hydrothermal temperature was carefully analyzed for control synthesis of oxygen vacancy-rich NiFe-LDH/EG nanosheets array (NiFe-LDH/EG-OVr) for sulfanilamide degradation. Owing to the abundant oxygen vacancies, NiFe-LDH/EG-OVr rapidly generated hydrogen peroxide (H2O2) and hydroxyl radical (•OH) during electro-Fenton (EF) process, which resulted in the 98% mineralization of sulfanilamide in first 80 min. The radicals trapping experiments revealed that the •OH radicals was participated as the main active oxidation species in the efficient mineralization of sulfanilamide. The present results indicated that the oxidative attack by •OH radicals initiated the degradation process of sulfanilamide. During the total degradation of sulfanilamide, several organic compounds including aminophenol, hydroquinone, and oxalic acid, were identified as main intermediates by using gas chromatography-mass spectroscopy (GC-MS) and high-performance liquid chromatography-mass spectroscopy (HPLC-MS).

Strongly coupling of amorphous/crystalline reduced FeOOH/α-Ni(OH)2 heterostructure for extremely efficient water oxidation at ultra-high current density.

Development of Fe-Ni-based electrocatalysts with high efficiency and stability remains a foremost challenge in the research for oxygen evolution reaction (OER) under high-current-density. Herein, a fast reduction strategy is developed for synthesis of strongly coupled crystalline α-Ni(OH)2 with amorphous reduced FeOOH (r-FeOOH) heterostructure grown on Ni foam (r-FeOOH/α-Ni(OH)2/NF). The obtained r-FeOOH/α-Ni(OH)2 with particle sizes around ~ 10 nm is coated orderly on the 3D NF surface in this hybrid. Benefitting from the strong coupling effects between r-FeOOH and α-Ni(OH)2, low potentials of 1.62 and 1.66 V at ultra-high current densities of 1,000 and 1,500 mA cm-2, as well as a robust stability over 10 h at 1,500 mA cm-2 in alkaline electrolyte are achieved in 3D r-FeOOH/α-Ni(OH)2/NF. Such a high OER performance is almost the best among all previously reported Fe-Ni-based OER electrocatalysts. Experimental results revealed that the NiOOH species is the real OER active phase in the 3D r-FeOOH/α-Ni(OH)2/NF. Further, bifunctional 3D r-FeOOH/α-Ni(OH)2 in alkaline electrolyzer delivers low cell voltages of 2.32 and 2.78 V to attain 500 and 1,000 mA cm-2 toward the overall-water-splitting, surpassing the benchmark Pt/C-Ir/C/NF system.

Gas Diffusion Strategy for Inserting Atomic Iron Sites into Graphitized Carbon Supports for Unusually High-Efficient CO2 Electroreduction and High-Performance Zn-CO2 Batteries.

Emerging single-atom catalysts (SACs) hold great promise for CO2 electroreduction (CO2 ER), but the design of highly active and cost-efficient SACs is still challenging. Herein, a gas diffusion strategy, along with one-step thermal activation, for fabricating N-doped porous carbon polyhedrons with trace isolated Fe atoms (Fe1 NC) is developed. The optimized Fe1 NC/S1 -1000 with atomic Fe-N3 sites supported by N-doped graphitic carbons exhibits superior CO2 ER performance with the CO Faradaic efficiency up to 96% at -0.5 V, turnover frequency of 2225 h-1 , and outstanding stability, outperforming almost all previously reported SACs based on N-doped carbon supported nonprecious metals. The observed excellent CO2 ER performance is attributed to the greatly enhanced accessibility and intrinsic activity of active centers due to the increased electrochemical surface area through size modulation and the redistribution of doped N species by thermal activation. Experimental observations and theoretical calculations reveal that the Fe-N3 sites possess balanced adsorption energies of *COOH and *CO intermediates, facilitating CO formation. A universal gas diffusion strategy is used to exclusively yield a series of dimension-controlled carbon-supported SACs with single Fe atoms while a rechargeable Zn-CO2 battery with Fe1 NC/S1 -1000 as cathode is developed to deliver a maximal power density of 0.6 mW cm-2 .

Highly Effective Electrochemical Exfoliation of Ultrathin Tantalum Disulfide Nanosheets for Energy-Efficient Hydrogen Evolution Electrocatalysis.

Developing highly efficient transition metal dichalcogenide electrocatalysts would be significantly beneficial for the electrocatalytic hydrogen evolution reaction (HER) from water splitting. Herein, we reported novel ultrathin tantalum disulfide nanosheets (TaS2 NSs) prepared by electrochemically exfoliating bulk TaS2 with an alternating voltage in an acidic electrolyte. The obtained TaS2 NS electrocatalyst possessed an ultrathin structure with a lateral size of 2 µm and a thickness of ∼3 nm. Owing to the unique 2D structure, the achieved TaS2 NSs displayed remarkable electrocatalytic activity toward the HER by a small overpotential of 197 mV at 10 mA cm-2 and a small Tafel slope of 100 mV dec-1 in acidic solution, much lower than those of TaS2 (>547 mV and 216 mV dec-1, respectively) and other reported TaS2-based HER electrocatalysts. Furthermore, highly efficient full water splitting could be realized with two electrodes in which TaS2 NSs acted as the cathode while Ir/C served as the anode, with help of two AA size batteries or solar cells. By replacing the oxygen evolution reaction with the urea oxidation reaction (UOR), bifunctional TaS2 NSs enabled an energy-effective HER process in the cathode and UOR process in the anode with decreased applied potential.

Nanoconfined Tin Oxide within N-Doped Nanocarbon Supported on Electrochemically Exfoliated Graphene for Efficient Electroreduction of CO2 to Formate and C1 Products.

Developing low-cost and effective electrocatalysts for electrochemical reduction of CO2 (CO2ER) is critical to CO2 conversion and utilization. Herein, we report a novel two-dimensional (2D) confined electrocatalyst composed of core-shell structured tin oxide nanoparticles (NPs) encapsulated into N-doped carbon (NC) supported on electrochemically exfoliated graphene (SnO2⊃NC@EEG) prepared by in situ carbonization of a 2-methylimidazole/SnO2 complex@poly(vinyl pyrrolidone) (PVP)-modified EEG precursor. The SnO2 NPs with an average size of ∼10 nm are confined in the NC shells with a thickness of 0.7 nm derived from 2-methylimidazole. The resulting 2D confined electrocatalyst significantly enhances the CO2ER performance with a small onset potential of -0.45 V, and high Faradic efficiencies of 81.2 and 93.2% for HCOO- and C1 products at -1.2 V, respectively, which is far superior to other reported SnO2/carbon-based CO2ER hybrids. The superb CO2ER catalytic activity of the SnO2⊃NC@EEG has resulted from the positive effect of N dopants and a strong confinement effect, which significantly expedites the CO2 adsorption associated with charge transfer from the NC to SnO2 NPs during CO2ER electrocatalysis.

A Superaerophobic Bimetallic Selenides Heterostructure for Efficient Industrial-Level Oxygen Evolution at Ultra-High Current Densities.

Cost-effective and stable electrocatalysts with ultra-high current densities for electrochemical oxygen evolution reaction (OER) are critical to the energy crisis and environmental pollution. Herein, we report a superaerophobic three dimensional (3D) heterostructured nanowrinkles of bimetallic selenides consisting of crystalline NiSe2 and NiFe2Se4 grown on NiFe alloy (NiSe2/NiFe2Se4@NiFe) prepared by a thermal selenization procedure. In this unique 3D heterostructure, numerous nanowrinkles of NiSe2/NiFe2Se4 hybrid with a thickness of ~ 100 nm are grown on NiFe alloy in a uniform manner. Profiting by the large active surface area and high electronic conductivity, the superaerophobic NiSe2/NiFe2Se4@NiFe heterostructure exhibits excellent electrocatalytic activity and durability towards OER in alkaline media, outputting the low potentials of 1.53 and 1.54 V to achieve ultra-high current densities of 500 and 1000 mA cm-2, respectively, which is among the most active Ni/Fe-based selenides, and even superior to the benchmark Ir/C catalyst. The in-situ derived FeOOH and NiOOH species from NiSe2/NiFe2Se4@NiFe are deemed to be efficient active sites for OER.

Confined carburization-engineered synthesis of ultrathin nickel oxide/nickel heterostructured nanosheets for enhanced oxygen evolution reaction.

Low-cost and highly effective transition metal oxides are being widely researched as one of the most promising electrocatalysts for the oxygen evolution reaction (OER). However, traditional transition metal oxides suffer from sluggish reaction kinetics due to their intrinsically poor electronic conductivity. Herein, we demonstrate a facile polydopamine-assisted carburization strategy for the confined synthesis of novel NiOx/Ni ultrathin heterostructured nanosheets. Benefiting from the large exposed surface area and fast charge transfer, the obtained ultrathin NiOx/Ni heterostructured nanosheets exhibit an overpotential of 358 mV at a current density of 10 mA cm-2 and a small Tafel slope of 51 mV dec-1, outperforming other reported representative nickel oxide based materials and commercial Ir/C catalysts. In addition, a sustainable and efficient overall water-splitting electrolyzer integrated ultrathin NiOx/Ni nanosheets with commercial Pt/C can be effectively and stably driven by solar cells.

High-index faceted binary-metal selenide nanosheet arrays as efficient 3D electrodes for alkaline hydrogen evolution.

Exploring highly active and durable Earth-abundant electrocatalysts to replace the precious noble metals holds great promise for the hydrogen evolution reaction (HER) from water splitting. Herein, a novel (110) high-index faceted binary-metal selenide (FeNiSe) nanosheet array grown on electrochemically exfoliated graphene foil (FeNiSe-NS/EG) is developed from its vertically-oriented NiFe-LDH nanosheet/EG precursor through a low-temperature selenization reaction. Benefiting from its unique 3D configuration and enhanced electrical conductivity, the obtained FeNiSe-NS/EG electrode exhibits excellent electrocatalytic activity toward the HER with small overpotentials of -187 and -222 mV at current densities of 10 and 20 mA cm-2, a low Tafel slope of 65 mV dec-1, and remarkable long term stability in alkaline media, outperforming the recently reported NiFe-based non-precious metal HER catalysts. Theoretical calculations and experimental results reveal that the synergistic effects of the exposed (110) high-index facets and Fe dopants give rise to a greatly enhanced HER performance.

Strongly Coupled 3D N-Doped MoO2/Ni3S2 Hybrid for High Current Density Hydrogen Evolution Electrocatalysis and Biomass Upgrading.

Developing noble metal-free electrocatalysts toward hydrogen evolution reaction (HER) that can work well at ultrahigh current density are crucial components in renewable energy technologies. Herein, we have reported a strongly coupled 3D hybrid electrocatalyst, which consists of N-doped MoO2 with Ni3S2 grown on Ni foam (N-MoO2/Ni3S2 NF) through an annealing treatment, followed by a thermal ammonia reaction. This N-MoO2/Ni3S2 with a particle size of ∼50 nm was evenly grown on the Ni substrate in this 3D hybrid system. Benefiting from the strong coupling effect, the N-MoO2/Ni3S2 NF exhibited a high HER performance in basic media, with a small value of the Tafel slope (76 mV dec-1) and a low potential of 517 mV at 1000 mA cm-2, which was superior to that of Pt/C (631 mV at 1000 mA cm-2). Experimental results revealed that constructing a coupling interface between N-MoO2 and Ni3S2 facilitated the absorption and dissociation of water molecules, consequently boosting the HER activity. Additionally, the 3D N-MoO2/Ni3S2 NF hybrid could act as a bifunctional electrode for both anode (biomass upgrading) and cathode (HER), which only required a lower potential of 2.08 V at 100 mA cm-2 as compared to the overall water splitting (2.25 V) and achieved a high biomass conversion ratio of over 90%. Moreover, substituting oxygen evolution reaction by urea oxidation reaction also can assist energy-saving hydrogen evolution for 3D N-MoO2/Ni3S2 NF.

Electrochemical exfoliation of ultrathin ternary molybdenum sulfoselenide nanosheets to boost the energy-efficient hydrogen evolution reaction.

Developing low-cost and highly efficient transition metal dichalcogenides as alternative electrocatalysts has become an urgent need for the hydrogen evolution reaction (HER). However, the inert basal planes of transition metal dichalcogenides severely suppress their practical applications. Herein, we developed ultrathin ternary molybdenum sulfoselenide (MoSexS2-x) nanosheets by using the cathodic electrochemical exfoliation approach in non-aqueous electrolytes. The exfoliated MoSexS2-x nanosheets demonstrated high structural integrity with lateral dimensions up to ∼1.5 µm and an average thickness of about 3 nm. Owing to the unique ultrathin structure and immensely exposed active sites, the ternary MoSexS2-x nanosheets supported on Ni foam demonstrated a greatly enhanced electrocatalytic activity for the HER in 1.0 M KOH with an overpotential of 123 mV at a current density of 10 mA cm-2 and high stability, superior to majority of the previously published MoS2-based electrocatalysts. Furthermore, the ternary MoSexS2-x nanosheets as a highly active bifunctional electrocatalyst contributed to enhanced energy-efficient hydrogen production and electrocatalytic synthesis of ammonia.

Hollow black TiAlOx nanocomposites for solar thermal desalination.

Although a solar-thermal conversion technique shows great potential for seawater desalination, there remains a grand challenge in exploring low-cost and high-efficiency photothermal materials. We report here a molten salt assisted galvanic replacement method for preparing a hollow black TiAlOx composite, which features a high solar absorptivity with up to 90.2% and has a high efficiency of 71.1% in a high salinity solution containing 15.3 wt% NaCl (∼5 times more concentrated than seawater). We exemplify the practical application of such hollow black TiAlOx composites as photothermal composites by setting up the automatic and manual tracking of solar desalination devices with a photic area of ∼1.0 m2, which can produce purified water with a rate of above 4.0 L m-2 day-1 in high-salinity water under natural light irradiation, and maintains good stability upon 5 days of continuous running. The advantages of the as-developed hollow black TiAlOx composites, including scalability, low cost, and high photothermal conversion efficiency, may open up a promising avenue practical application in seawater desalination.

Scalable Production of Few-Layer Niobium Disulfide Nanosheets via Electrochemical Exfoliation for Energy-Efficient Hydrogen Evolution Reaction.

Two-dimensional (2D) niobium disulfide (NbS2) materials feature unique physical and chemical properties leading to highly promising energy conversion applications. Herein, we developed a robust synthesis technique consisting of electrochemical exfoliation under alternating currents and subsequent liquid-phase exfoliation to prepare highly uniform few-layer NbS2 nanosheets. The obtained few-layer NbS2 material has a 2D nanosheet structure with an ultrathin thickness of ∼3 nm and a lateral size of ∼2 µm. Benefiting from their unique 2D structure and highly exposed active sites, the few-layer NbS2 nanosheets drop-casted on carbon paper exhibited excellent catalytic activity for the hydrogen evolution reaction (HER) in acid with an overpotential of 90 mV at a current density of 10 mA cm-2 and a low Tafel slope of 83 mV dec-1, which are superior to those reported for other NbS2-based HER electrocatalysts. Furthermore, few-layer NbS2 nanosheets are effective as bifunctional electrocatalysts for hydrogen production by overall water splitting, where the urea and hydrazine oxidation reactions replace the oxygen evolution reaction.

Nitrogen-Doped Carbon-Encased Bimetallic Selenide for High-Performance Water Electrolysis.

Demand of highly efficient earth-abundant transition metal-based electrocatalysts to replace noble metal materials for boosting oxygen evolution reaction (OER) is rapidly growing. Herein, an electrochemically exfoliated graphite (EG) foil supported bimetallic selenide encased in N-doped carbon (EG/(Co, Ni)Se2-NC) hybrid is developed and synthesized by a vapor-phase hydrothermal strategy and subsequent selenization process. The as-prepared EG/(Co, Ni)Se2-NC hybrid exhibits a core-shell structure where the particle diameter of (Co, Ni)Se2 core is about 70 nm and the thickness of N-doped carbon shell is approximately 5 nm. Benefitting from the synergistic effects between the combination of highly active Co species and improved electron transfer from Ni species, and N-doped carbon, the EG/(Co, Ni)Se2-NC hybrid shows remarkable electrocatalytic activity toward OER with a comparatively low overpotential of 258 mV at an current density of 10 mA cm-2 and a small Tafel slope of 73.3 mV dec-1. The excellent OER catalysis performance of EG/(Co, Ni)Se2-NC hybrid is much better than that of commercial Ir/C (343 mV at 10 mA cm-2 and 98.1 mV dec-1), and even almost the best among all previously reported binary CoNi selenide-based OER electrocatalysts. Furthermore, in situ electrochemical Raman spectroscopy combined with ex situ X-ray photoelectron spectroscopy analysis indicates that the superb OER catalysis activity can be attributed to the highly active Co-OOH species and modified electron transfer process from Ni element.

Electrochemical activation of sulfate by BDD anode in basic medium for efficient removal of organic pollutants.

Electrochemical advanced oxidation processes (EAOPs) based on hydroxyl radicals (OH) have some limitations when they are applied to real wastewater treatment, such like strict requirements on pH (acidic electrolyte) and high energy consumption. Compared to OH, Sulfate radicals (SO4-) have high redox potential in wider range of pH (2-9). In this study, SO4- were efficiently produced by electrochemical activation of SO42- at boron doped diamond (BDD) anode. The degradation rate of 2,4-DCP (k = 0.828 ±â€¯0.05 h-1) in the presence of Na2SO4 was approximately 4 times than that without Na2SO4 (k = 0.219 ±â€¯0.01 h-1), indicating that SO4- exhibited higher reactivity than OH at initial pH = 9. Moreover, the amount of O2 decreased by 65% after 100 min during electro-oxidation of 2,4-DCP and the specific energy consumption per unit TOC (ECTOC) was reduced by 70% when the concentration of Na2SO4 increased from 0.01 to 0.1 M. The impact of sulfate ions in the electrochemical advanced oxidation were investigated. Electron spin resonance (ESR) measurements were conducted to identify the formation of SO4-. Electrolysis of 2,4-DCP with specific radical scavengers (ethanol and tert-Butanol) were conducted and the results revealed that SO4- were mainly produced by one-electron loss of sulfate at basic condition. Electro-generation persulfate was measured and participation of non-radical activation of persulfate was investigated. O2 production was quantified and we found electrochemical activation of sulfate could inhibit water dissociation. Taken all findings, a mechanism of electrochemical activation of sulfate at BDD anode was summarized. This technology eliminates the requirement for pH adjustment for wastewater treatment and makes EAOPs more effective and economic as well.

Porous Cobalt Oxynitride Nanosheets for Efficient Electrocatalytic Water Oxidation.

Exploring efficient and cheap oxygen evolution reaction (OER) electrocatalysts is of great significance for electrochemical water splitting. Herein, we successfully prepared an efficient ternary electrocatalyst of porous cobalt oxynitride (Co3 Ox Ny ) nanosheets by a simple nitridation strategy. Specifically, CoON PNS-400 (cobalt oxynitride with porous nanosheet structure obtained at 400 o C) offered a low OER overpotential of 0.23 V to achieve the catalytic current density of 10 mA cm-2 and a small Tafel slope of 48 mV dec-1 in alkali media, outperforming most of the first-row transition-metal-based OER electrocatalysts. The calculated density of states (DOS) analysis and electron spin resonance (ESR) measurements revealed that the introduction of foreign N atoms into pristine Co3 O4 nanosheets can optimize the electronic structure and create more oxygen vacancies, thus leading to enhanced electrical conductivity. Density functional theory (DFT) calculations demonstrated that the foreign N atoms can also improve the energetics for OER by modulating the free energy for adsorbed intermediates (OOH*, OH*, O*), further improving the OER electrocatalytic activity of CoON PNS-400. This work provides a possibility for rationally designing ternary transition-metal compounds as advanced OER electrocatalysts.