Catalytic Hydroconversion of Model Compounds over Ni/NiO@NC Nanoparticles.

The conversion of lignite into aromatic compounds by highly active catalysts is a key strategy for lignite valorization. In this study, Ni/NiO@NC nanocomposites with a high specific surface area and a vesicular structure were successfully prepared via a facile sol-gel method. The Ni/NiO@NC catalysts exhibited excellent catalytic activity for the catalytic hydroconversion (CHC) of benzyloxybenzene (as lignite-related modeling compounds) under mild conditions (120 °C, 1.5 MPa H2, 60 min). The possible mechanism of the catalytic reaction was investigated by analyzing the type and content of CHC reaction products at different temperatures, pressures, and times. More importantly, the magnetic catalyst could be conveniently separated by a magnet after the reaction, and it maintained high catalytic efficiency after six reuses. This study provides an efficient and recyclable catalyst for the cleavage of >CH-O bonds in lignite, thereby offering another way for improved utilization of lignite.

Enhancement of Ni-NiO-CeO2 Interaction on Ni-CeO2/Al2O3-MgO Catalyst by Ammonia Vapor Diffusion Impregnation for CO2 Reforming of CH4.

Ni-based catalysts have been widely used for the CO2 reforming of methane (CRM) process, but deactivation is their main problem. This study created an alternative electronic Ni-NiO-CeO2 interaction on the surface of 5 wt% Ni-5 wt% CeO2/Al2O3-MgO (5Ni5Ce(xh)/MA) catalysts to enhance catalytic potential simultaneously with coke resistance for the CRM process. The Ni-NiO-CeO2 network was developed on Al2O3-MgO through layered double hydroxide synthesis via our ammonia vapor diffusion impregnation method. The physical properties of the fresh catalysts were analyzed employing FESEM, N2 physisorption, and XRD. The chemical properties on the catalyst surface were analyzed employing H2-TPR, XPS, H2-TPD, CO2-TPD, and O2-TPD. The CRM performances of reduced catalysts were evaluated at 600 °C under ambient pressure. Carbon deposits on spent catalysts were determined quantitatively and qualitatively by TPO, FESEM, and XRD. Compared to 5 wt% Ni-5 wt% CeO2/Al2O3-MgO prepared by the traditional impregnation method, the electronic interaction of the Ni-NiO-CeO2 network with the Al2O3-MgO support was constructed along the time of ammonia diffusion treatment. The electronic interaction in the Ni-NiO-CeO2 nanostructure of the treated catalyst develops surface hydroxyl sites with an efficient pathway of OH* and O* transfer that improves catalytic activities and coke oxidation.

Enhanced hydrogen production via urea electrolysis over Ni-NiO electrodeposited on Ti mesh.

The sluggish kinetics of anodic oxygen evolution reaction (OER) is regarded as the main bottleneck for ineffective hydrogen production efficiency, limiting the industrial application of electrochemical water splitting. Substituting the OER by urea electrooxidation reaction (UOR) and simultaneously developing highly active and economical bifunctional electrocatalyst for UOR and hydrogen evolution reaction (HER) is a promising method to realize energy-saving hydrogen production and urea-rich wastewater abatement. Herein, self-supporting Ni-NiO film grown on Ti mesh (Ni-NiO/TM) was successfully prepared by a facile cathodic electrodeposition method with using nickel acetate as the only raw material. Electrodeposition process was optimized by modulating the electrodeposition time and potential. x-ray diffraction, scanning electron microscopy, transmission electron microscopy, x-ray photoelectron spectroscopy and Raman characterization revealed the optimized Ni-NiO/TM was comprised of crystalline Ni and amorphous NiO and its morphology exhibited nanosphere structure, assembled by nanosheets. Ni-NiO/TM sample prepared under the potential of -1.5 V and deposition time of 10 min illustrated the lowest UOR potential of 1.34 V at 50 mA cm-2and robust stability, superior to the recently reported literatures. Furthermore, the HER potential was only -0.235 V to drive the current density of 50 mA cm-2. The cell voltage of urea-assisted electrolysis for hydrogen production in Ni-NiO/TM||Ni-NiO/TM two-electrode system only required 1.56 V to deliver 50 mA cm-2, obviously lower than that (>1.72 V) for overall water splitting. This work demonstrated the potential of Ni-based material as bifunctional electrocatalyst for energy-saving H2production by urea-rich wastewater electrolysis.

Insight into the photocatalytic properties of diatomite@Ni/NiO composite for effective photo-degradation of malachite green dye and photo-reduction of Cr (VI) under visible light.

Diatomite frustules decorated by nano Ni/NiO nanoparticles (Diatomite@Ni/NiO) were synthesized as a novel photocatalyst for effective degradation of malachite green cationic dye (M.G) and photocatalytic-reduction of Cr (VI) ions. The composite was characterized by different analytical techniques and revealed enhancing in the surface area (400 m2/g), 5.8 nm as average pore diameter and showed lower band gap energy (1.71 eV) than NiO as single phase. The photocatalytic activity of the composite in the removal of M.G and reduction of Cr (VI) was evaluated under visible light considering the pH, illumination time, catalyst mass, and the pollutants concentrations. The results revealed complete removal of 25 mg/L M.G can be achieved using 20 mg, 30 mg, 40 mg and 50 mg of the after 150 min, 90 min, 60 min, and 30 min, respectively. The complete degradation of 50 mg/L can be obtained after 240 min, 90 min, and 60 min using 20 mg, 40 mg, and 50 mg of the catalyst, respectively. This also was reported for the photocatlytic-reduction of 25 mg/L of Cr(VI) ions as the complete reduction was estimated after 180 min, 60 min and 30 min using 20 mg, 40 mg, and 50 mg, respectively. Also, 50 mg/L of Cr (VI) can be completely reduced after 240 min, 90 min, and 60 min using 20 mg, 40 mg, and 50 mg as catalyst dosage, respectively. The photocatalytic degradation of M.G controlled mainly by the generated electron-hole pairs and the superoxide species while the photocatalytic-reduction of Cr (VI) controlled mainly by the directly excited electrons of Ni/NiO and partially by the formed superoxide radicals. Hence, the synthetic diatomite@Ni/NiO composite can be considered as potential photocatalyst in the degradation of M.G dye and photoreduction of Cr (VI) ions.

Ni@NiO Nanowires on Nickel Foam Prepared via "Acid Hungry" Strategy: High Supercapacitor Performance and Robust Electrocatalysts for Water Splitting Reaction.

Ni/NiO core-shell nanowires on nickel foam (NF) are successfully synthesized using an "acid-hungry" strategy. The 3D electrode with large accessible active sites and improved conductivity, possesses an optimized ionic and electronic transport path during electrochemical processes. High areal capacitance of 1.65 F cm-2 is obtained at an ultrahigh current density of 100 mA cm-2 , which is 19.88 times higher than pristine NF. The direct growth of nanowires makes the present supercapacitor electrode robust for long-term cycling test. By virtue of the favorable hydrogen adsorption energies on Ni0 and OHads energy on NiO or NiOOH, the 3D electrode exhibits high performance in hydrogen evolution reaction with 146 mV at η10 mA cm-2 and Tafel value of 72 mV dec-1 , and oxygen evolution reaction with 382 mV at η10 mA cm-2 and Tafel value of 103 mV dec-1 in 1 m KOH. An electrolyzer using 3D electrodes as both anode and cathode can yield a current density of 10 mA cm-2 at 1.71 V, and possesses superior long-term stability to an electrolyzer consisting of Pt/C||Ir/C. The present work develops an effective and low-cost method for the large-scale fabrication of Ni/NiO core-shell nanowires on commercial NF, providing a promising candidate for supercapacitors, fuel cells, and electrocatalysis.

Modification of MgH2 hydrogen storage performance by nickel-based composite catalyst Ni/NiO.

In this study, the Ni/NiO catalyst was demonstrated to enhance the hydrogen storage performance of MgH2. The dehydrogenation of MgH2+10 wt% Ni/NiO started at approximately 180 °C, achieving 5.83 wt% of dehydrogenation within 10 min at 300 °C. Completely dehydrogenated, MgH2 began to rehydrogenate at about 50 °C, absorbing about 4.56 wt% of hydrogen in 10 min at 150 °C. In addition, the activation energies of dehydrogenation and rehydrogenation of MgH2+10 wt% Ni/NiO were 87.21 and 34.84 kJ/mol. During the dehydrogenation/rehydrogenation cycle, Mg2Ni/Mg2NiH4 could promote hydrogen diffusion, thus enhancing the hydrogen storage performance of Mg/MgH2.

Simple Solution Plasma Synthesis of Ni@NiO as High-Performance Anode Material For Lithium-ion Batteries Application.

The pursuit of straightforward and cost-effective methods for synthesizing high-performance anode materials for lithium-ion batteries is a topic of significant interest. This study elucidates a one-step synthesis approach for a conversion composite using glow discharge in a nickel formate solution, yielding a composite precursor comprising metallic nickel, nickel hydroxide, and basic nickel salts. Subsequent annealing of the precursor facilitated the formation of the Ni@NiO composite, exhibiting exceptional electrochemical properties as anode material in Li-ion batteries: a capacity of approximately 1000 mAh·g-1, cyclic stability exceeding 100 cycles, and favorable rate performance (200 mAh·g-1 at 10 A·g-1). Comparative analysis across various methods for synthesizing NiO-based materials underscored the superiority of the Ni@NiO composite. Furthermore, an assessment of resource costs demonstrated the cost-effectiveness and scalability of the approach in terms of resource consumption per Ah. Lastly, the integration of a Ni@NiO anode with an NMC532 cathode in a full battery highlights Ni@NiO's potential for conversion anodes, achieving a practical gravimetric energy density of 92 Wh kg-1.

ZnIn2S4-based multi-interface coupled photocatalyst for efficient photothermal synergistic catalytic hydrogen evolution.

Photothermal synergistic catalysis is a novel technology that converts energy. In this study, ZnIn2S4 with S-vacancy (ZIS-Vs) is combined with Nickel, Nickle Oxide and Carbon Nanofiber aggregates (Ni-NiO@CNFs) to create a multi-interface coupled photocatalyst with double Schottky barrier, double channel and mixed photothermal conversion effect. Theoretical calculation confirms that the Gibbs free energy (ΔG*H) of the S-scheme heterojunction in the composite material is -0.07 eV, which is close to 0. This promotes the adsorption of H* and accelerates the formation of H2. Internal photothermal catalysis is achieved by visible-near infrared (Vis-NIR, RT) irradiation. The internal photothermal catalytic hydrogen production rate of the best sample (0.9Ni-NiO@CNFs/ZIS-Vs) is as high as 17.24 mmol·g-1·h-1, and its photothermal conversion efficiency (η) is as high as 61.42 %. Its hydrogen production efficiency is 20.52 times that of ZIS-Vs (0.84 mmol·g-1·h-1) under visible light (Vis, RT) conditions. When the Vis-NIR light source is combined with external heating (75 ℃), the hydrogen production efficiency is further improved, and the hydrogen production efficiency (29.16 mmol·g-1·h-1) is 26.75 times that of ZIS-Vs (1.09 mmol·g-1·h-1, Vis-NIR, RT). Further analysis shows that the increase in hydrogen production resulted from the apparent activation energy (Ea) of the catalyst decreasing from 16.7 kJ·mol-1 to 9.28 kJ·mol-1. This study provides a valuable prototype for the design of an efficient photothermal synergistic catalytic system.

Interface engineering of Ni/NiO heterostructures with abundant catalytic active sites for enhanced methanol oxidation electrocatalysis.

Designing efficient and stable non-noble metal electrocatalysts with good performance in reaction kinetics is desirable yet challenging for the study of methanol oxidation reaction (MOR). Herein, we have reported well-defined nanoscale nickel/nickel oxide (Ni/NiO) heterostructures supported by a three-dimensional (3D) porous graphene network (RG) via a delicate interface engineering technique. The as-prepared 3D Ni/NiO/RG composites achieve outstanding catalytic activity (79.5 mA cm-2/1262.1 mA mg-1) for MOR in alkaline solution, outperforming most reported non-precious catalysts. A combined experimental and computational investigation shows that such a good performance benefits from the specific Ni/NiO interface, which not only bears abundant accessible active sites but also improves the energetics of MOR. Moreover, this interface contributes to favorable kinetic and improved structural stability during electrocatalysis, ensuring superior catalytic performance after 1000 consecutive cyclic voltammetry tests for MOR. Our work demonstrates the potential of interface engineering in the rational design of efficient precious-metal-free electrocatalysts.

Regulable in-situ autoredox for anchoring synergistic Ni/NiO nanoparticles on reduced graphene oxide with boosted alkaline electrocatalytic oxygen evolution.

To develop ideal alternatives to noble metal catalysts, transition metal catalysts supported on graphene have been receiving extensive attention in the field of electrochemical energy. In this work, using graphene oxide (GO) and nickel formate as precursors, Ni/NiO synergistic nanoparticles with regulable composition are anchored on reduced graphene oxide (RGO) to prepare Ni/NiO/RGO composite electrocatalysts through in-situ autoredox. Thanks to the synergistic effect of Ni3+ active sites and Ni electron donors, the as-prepared Ni/NiO/RGO catalysts exhibit efficient electrocatalytic oxygen evolution performance in 1.0 M KOH electrolyte. The optimal sample has an overpotential of only 275 mV at a current density of 10 mA cm-2 and a small Tafel slope of 90 mV dec-1, which are very comparable to those of commercial RuO2 catalyst. Additionally, the catalytic capacity and structure remain stable after 2000 cyclic voltammetry cycles. For the electrolytic cell assembled with the best-performing sample as anode and commercial Pt/C as cathode, the current density can reach 10 mA cm-2 at a low potential of 1.57 V and remains stable after 30 h of continuous work. It would be expected that the as-developed Ni/NiO/RGO catalyst with high activity should have broad application prospects.

Pd Atomic Engineering of Nanoporous Ni/NiO for Efficient Nitrophenol Hydrogenation Reaction.

The catalytic hydrogenation of nitrophenols is widely utilized for both industrial synthesis and environmental protection, thus efficient and cost-effective catalysts are in urgent need. Still, the cost and scarcity of the materials still inhibit their application and the active sites are not well specified, especially in the complex catalysts. Herein, we developed an atomic Pd-doped nanoporous Ni/NiO (Pd1@np-Ni/NiO) catalyst via facial dealloying for efficient nitrophenol hydrogenation reaction under mild conditions. Pd1@np-Ni/NiO achieves an excellent specific activity (1301 min-1 mgPd-1, 35.2 times that of commercial Pd/C), nearly 100% selectivity, and continuous reproducibility. The catalytic performance is highly relevant to the Ni sites on the catalysts regarding the exposure sites and the intrinsic property. The metal/metal oxide interfacial structure could cooperatively accelerate the catalytic reaction kinetics. The atomic dopants could effectively modulate the electronic structure, facilitate the absorption of molecules, and reduce the energy barrier of catalytic hydrogenation reaction. Based on the efficient catalyst, the protype nitrophenol//NaBH4 battery is designed for efficient material conversion and power output, which is very attractive for green energy systems.

Hollow Ni/NiO/C composite derived from metal-organic frameworks as a high-efficiency electrocatalyst for the hydrogen evolution reaction.

Metal-organic frameworks (MOFs) constitute a class of crystalline porous materials employed in storage and energy conversion applications. MOFs possess characteristics that render them ideal in the preparation of electrocatalysts, and exhibit excellent performance for the hydrogen evolution reaction (HER). Herein, H-Ni/NiO/C catalysts were synthesized from a Ni-based MOF hollow structure via a two-step process involving carbonization and oxidation. Interestingly, the performance of the H-Ni/NiO/C catalyst was superior to those of H-Ni/C, H-NiO/C, and NH-Ni/NiO/C catalysts for the HER. Notably, H-Ni/NiO/C exhibited the best electrocatalytic activity for the HER, with a low overpotential of 87 mV for 10 mA cm-2 and a Tafel slope of 91.7 mV dec-1. The high performance is ascribed to the synergistic effect of the metal/metal oxide and hollow architecture, which is favorable for breaking the H-OH bond, forming hydrogen atoms, and enabling charge transport. These results indicate that the employed approach is promising for fabricating cost-effective catalysts for hydrogen production in alkaline media.

Highly Efficient Enzyme-Free Glutamate Sensors Using Porous Network Metal-Organic Framework-Ni-NiO-Ni-Carbon Nanocomposites.

This study introduces an innovative electrochemical sensor designed to detect glutamate using a nonenzymatic approach. The sensor utilizes a porous network metal-organic framework (Ni-MOF)-NiO-Ni-Carbon nanocomposite (PNM-NiO-Ni-Carbon) as an electrode modifier, which was synthesized and assessed for its effectiveness. Cyclic voltammetry measurements demonstrated that the PNM-NiO-Ni-Carbon nanocomposite, synthesized at 450 °C, displayed remarkable electrocatalytic activity for glutamate oxidation. The linear range for detection spanned from 5 to 960 µmol/L, and the sensor achieved a low detection limit of 320 nmol/L (S/N = 3), which was comparable to previously reported data. Moreover, the sensor exhibited high accuracy and favorable recovery rates when tested with real samples, thus, demonstrating its potential for rapid glutamate detection. The real samples were analyzed using both electrochemical and high-performance liquid chromatography methods, and the results obtained from the two methods did not differ significantly, validating the sensor's excellent practical performance. Based on our findings, the PNM-NiO-Ni-Carbon system exhibits potential for a wide range of biomedical applications.

Facile synthesis of mesoporous nano Ni/NiO and its synergistic role as super adsorbent and photocatalyst under sunlight irradiation.

Tailoring a material that has a synergistic role as an adsorbent and a photocatalyst for environmental application is an attractive field for research. This article presents a study of facile synthesis of NiO and Ni/NiO with a synergistic role as super adsorbents in the lake of light and photocatalysts under light irradiation. Nano flower-like mesoporous NiO and Ni/NiO were synthesized by the co-precipitation method. XRD, SEM, EDAX, XPS, BET, and DR/UV-Vis spectroscopy techniques were employed for samples' analysis. The point of zero surface charge of prepared samples was detected by the batch equilibrium method. The adsorption efficiency was investigated in the absence of light using aniline blue as a pollutant model dye. The synergistic effect as an adsorbent and a photocatalyst was investigated under UV and sunlight irradiation. Different parameters affecting the adsorption in the dark have been optimized. The results showed that in the absence of light, the prepared samples are super adsorbents with a maximum adsorption capacity ranging from 210 to 230 mg g-1 and a removal % ranging from 95 to 100% within 2 h. Under UV or sunlight irradiation, the adsorbent/photocatalyst attained a dye removal % of 99.8% within 30 min. The adsorption data matched the pseudo-second-order model, and the equilibrium adsorption data showed compatibility with Langmuir model. The findings of experiments revealed that the adsorption is spontaneous, exothermic, and results in less entropy. Under sunlight irradiation, the dye removal efficiency increased by 19% in the case of Ni/NiO hybrid; it showed a removal efficiency of 99.5% within 30 min under sunlight irradiation versus 80% after 120 min in the dark.

Self-templating hydrothermal synthesis of carbon-confined double-shelled Ni/NiO hollow microspheres for diphenylamine detection in fruit samples.

Toxic substances, such as heavy metals, toxins, pesticides, pathogens, and veterinary drug residues in food are hazardous to consumer health. The variety and quantity of food consumption have increased owing to developments in the agricultural and food industries. Food safety has a substantial socioeconomic impact, and an increasing number of consumers have become aware of its importance. Therefore, simple and cost-effective analytical methods are required to quantify the safety of preservatives. Herein, we report an electrochemical method using double-shelled carbon-confined Ni/NiO (C@Ni/NiO) hollow microspheres to detect diphenylamine (DPA). The microspheres were synthesized by a self-templating hydrothermal method followed by calcination. The hydrothermal temperature and precursor ratio were optimized systematically to prepare double-shelled C@Ni/NiO hollow microspheres. The excellent electrocatalytic activity and electron transport properties of a C@Ni/NiO-modified glassy carbon electrode (GCE) were exploited in the electrochemical oxidation of DPA. Interestingly, the engineered C@Ni/NiO/GCE has a wide dynamic linear range (0.02-473 µM) and a DPA detection limit of 0.007 µM. In addition, the DPA sensor exhibited good selectivity, reproducibility, repeatability, and stability. The practical feasibility of the DPA sensor was evaluated in fruit samples (sweet tomatoes, apples, and red grapes), with considerable recovery.

Anchoring Ni/NiO heterojunction on freestanding carbon nanofibers for efficient electrochemical water oxidation.

Rational design of low-cost and efficient electrocatalyst for the anodic oxygen evolution reaction (OER) to replace noble-metal-based catalysts is greatly desired for the large-scale application of water electrocatalysis. And compared with the conventional powdery catalysts, the freestanding electrode architecture is more attractive owing to the enhanced kinetics and stability. In this work, we report an electrospinning-carbonization-post oxidation strategy to develop the freestanding N-doped carbon nanofibers anchored with Ni/NiO nanoparticles (denoted as Ni/NiO-NCNFs) as efficient OER electrocatalyst. In the synthesized Ni/NiO-NCNFs, the conductive ultrathin carbon layer could promote electron transfer and thus improve the electrocatalytic activity. Meanwhile, the ratio between Ni and NiO could be regulated by tuning the oxidation duration, so as to optimize the adsorption energy of intermediates and improve the OER activity. The Ni/NiO-NCNFs prepared with the oxidation time of 3 h exhibit a promising OER activity and long-term operation durability in 0.1 M KOH solution, requiring an overpotential as small as 153 mV to achieve a current density of 10 mA cm-2. Its overpotential is far lower than that of the reported OER catalysts. This work offers an efficient pathway to develop low-cost and highly active freestanding transitional metal-based OER electrocatalyst for potential renewable electrochemical energy conversion.

Flowerlike Ni-NiO composite as magnetic solid-phase extraction sorbent for analysis of carbendazim and thiabendazole in edible vegetable oils by liquid chromatography-mass spectrometry.

A rapid, selective, and sensitive method was developed for the detection of carbendazim and thiabendazole in edible vegetable oil. Two benzimidazole analytes were pre-concentrated by magnetic solid phase extraction (MSPE) using flowerlike Ni-NiO composite as sorbents and followed by LC-MS/MS analysis. The flowerlike Ni-NiO composite sorbent displayed a high affinity towards benzimidazole analytes due to the reversible coordination interaction between the Ni(Ⅱ) ion and the electron-donating imidazole group. In comparison to the previous methods, this procedure is less time-consuming and simpler during sample preparation. The parameters affecting the extraction efficiency were optimized in detail. The method was validated according to SANTE/12682/2019. The limits of detection were in the range of 0.001-0.003 mg•kg-1. The recoveries ranged from 89.3% to 110.7% with inter-day and inter-day precision less than 10.9%. The results indicate that flowerlike Ni-NiO composite might be a promising alternative for MSPE of benzimidazole compounds in foods.

Yolk-shell Ni/NiO anchored on N-doped graphene synthesized as dual-ion MALDI matrix for detecting and imaging bioactive small molecules.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is an attractive tool to analyze the bioactive small molecules but remains a great challenge owing to the serious background interference from conventional matrix with m/z < 1000. Herein, we reported a dual-ion MALDI matrix of yolk-shell Ni/NiO nanoparticles anchored on nitrogen-doped graphene (Ni/NiO/N-Gr) to enhance MALDI performance. The Ni/NiO/N-Gr was synthesized via the pyrolysis and controllable oxidation strategy based on the nanoscale regulation of Kirkendall effect. The novel matrix showed the superior behavior for the analysis of various small molecular metabolites (amino acids, saccharides, spermidine, creatinine, hippuric acid, dopamine, and ascorbic acid) with high sensitivity, excellent salt tolerance, and favorable reproducibility in dual-ion modes compared to the traditional α-cyano-4-hydroxycinnamic acid (CHCA) and control substances (Ni/N-Gr and NiO/N-Gr). Meanwhile, we have realized accurate quantitation of blood glucose in mice with a linearity concentration range of 0.2-7.5 mM and qualitative detection of various endogenous small molecular metabolites in mice serum and urine samples. Especially, the Ni/NiO/N-Gr assisted LDI MS imaging (MSI) has exhibited the excellent spatial distribution of lipids in hippocampus region of mice brain. These results may provide an approach to explore the MALDI MS and MSI applications in clinical diagnosis.

Phase-Controlled NiO Nanoparticles on Reduced Graphene Oxide as Electrocatalysts for Overall Water Splitting.

Efficient water electrolysis is one of the key issues in realizing a clean and renewable energy society based on hydrogen fuel. However, several obstacles remain to be solved for electrochemical water splitting catalysts, which are the high cost of noble metals and the high overpotential of alternative catalysts. Herein, we suggest Ni-based alternative catalysts that have comparable performances with precious metal-based catalysts and could be applied to both cathode and anode by precise phase control of the pristine catalyst. A facile microwave-assisted procedure was used for NiO nanoparticles anchored on reduced graphene oxide (NiO NPs/rGO) with uniform size distribution in ~1.8 nm. Subsequently, the Ni-NiO dual phase of the NPs (A-NiO NPs/rGO) could be obtained via tailored partial reduction of the NiO NPs/rGO. Moreover, we demonstrate from systematic HADDF-EDS and XPS analyses that metallic Ni could be formed in a local area of the NiO NP after the reductive annealing procedure. Indeed, the synergistic catalytic performance of the Ni-NiO phase of the A-NiO NPs/rGO promoted hydrogen evolution reaction activity with an overpotential as 201 mV at 10 mA cm-2, whereas the NiO NPs/rGO showed 353 mV. Meanwhile, the NiO NPs/rGO exhibited the most excellent oxygen evolution reaction performance among all of the Ni-based catalysts, with an overpotential of 369 mV at 10 mA cm-2, indicating that they could be selectively utilized in the overall water splitting. Furthermore, both catalysts retained their activities over 12 h with constant voltage and 1000 cycles under cyclic redox reaction, proving their high durability. Finally, the full cell capability for the overall water electrolysis system was confirmed by observing the generation of hydrogen and oxygen on the surface of the cathode and anode.

Electronegativity Assisted Synthesis of Magnetically Recyclable Ni/NiO/g-C3N4 for Significant Boosting H2 Evolution.

A magnetically recyclable Ni/NiO/g-C3N4 photocatalyst with significantly enhanced H2 evolution efficiency was successfully synthesized by a simple ethanol-solvothermal treatment. The presence of electronegative g-C3N4 is found to be the key factor for Ni0 formation in ternary Ni/NiO/g-C3N4, which provides anchoring sites for Ni2+ absorption and assembling sites for Ni0 nanoparticle formation. The metallic Ni0, on one side, could act as an electron acceptor enhancing carrier separation and transfer efficiency, and on the other side, it could act as active sites for H2 evolution. The NiO forms a p-n heterojunction with g-C3N4, which also promotes carrier separation and transfer efficiency. The strong magnetic property of Ni/NiO/g-C3N4 allows a good recyclability of catalyst from aqueous solution. The optimal Ni/NiO/g-C3N4 showed a full-spectrum efficiency of 2310 µmol·h-1·g-1 for hydrogen evolution, which is 210 times higher than that of pure g-C3N4. This ethanol solvothermal strategy provides a facile and low-cost synthesis of metal/metal oxide/g-C3N4 for large-scale application.