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Glycerol selective oxidation to dihydroxyacetone was investigated systematically in a semibatch reactor over Pt−Bi/C catalyst. Catalysts with different metal loadings, supports, and preparation methods were synthesized, characterized, and tested. The sequential impregnation of Pt and then Bi, followed by NaBH4reduction, was the optimum synthesis method for high glycerol oxidation rate and maximum DHA yield. The optimum catalyst composition was determined to be 3 wt % Pt, 0.6 wt % Bi, supported on Norit Darco 20-40 mesh activated carbon (BET surface area 600 m2/g, average pore size 4 nm, average pore volume 0.53 cm3/g). In addition to the catalyst, the reaction conditions were also optimized by conducting experiments in the range of temperature 30−90 °C, oxygen pressure 0−180 psig, and initial pH 2−12. The optimum reaction conditions were identified as 80 °C, 30 psig, and initial pH = 2. Under these conditions, a maximum DHA yield of 48% was obtained at 80% glycerol conversion. The catalysts were characterized by using BET, ICP-OES, TEM, XRD, and XPS techniques. [ABSTRACT FROM AUTHOR]

Exploring highly efficient single atom catalysts with defined active centers and tunable electronic structures is highly desirable. Herein, we developed an efficient hydrogen evolution reaction (HER) electrocatalyst through a self-gating phenomenon induced by Pt single atoms (SAs) supported on ultrathin NiO nanosheets (Pt SA -NiO). The Ni atoms in NiO are partially replaced by the atomically dispersed Pt atoms, leading to a transition from p-type NiO into n-type Pt SA -NiO. When the n-type Pt SA -NiO serves as HER electrocatalyst, the self-gating phenomenon occurs in the ultrathin nanosheets, resulting in a mixture of leakage ("active") and metal-insulator-semiconductor ("inert") regions. The "inert" region induced by the ionic gating and reverse potential is capable of accumulating relatively high surface charge carrier concentration with an ultrahigh electric field, making the Pt SA -NiO highly conductive; meanwhile, the HER process occurs at the Pt SAs sites (active region) in the Pt SA -NiO nanosheets. As a result, the Pt SA -NiO requires only 55 mV to deliver 10 mA/cm 2 in an alkaline solution with good stability.

Zinc-nickel batteries are promising competitors for next-generation power supply due to their benefits of high safety, high working voltage, and attractive rate performance. However, their practical applications are plagued by their poor cycling performance, stemming from uneven redistribution of zinc during cycling that results in dendrite formation and shape changes of the electrode. In this work, mesoporous Ti 4 O 7 microspheres are prepared and are employed as additives of a zinc anode. Notably, the presence of mesopores provides abundant chemisorption sites for Zn(OH) 4 2- ions, inhibiting severe zinc redistribution in the electrode. Moreover, due to the good electrical conductivity and mesopores that serve as ion diffusion channels, the reaction reactivity and reversibility of the zinc electrode are greatly facilitated. As a result, the fabricated zinc-nickel battery with mesoporous Ti 4 O 7 additives (ms-Ti 4 O 7 ) exhibits an enhanced discharge capacity and a significantly prolonged cycling life. Even at a current of 10 A (∼138 mA cm -2 ), the ms-Ti 4 O 7 -modified anode demonstrates stable operation for longer than 718 h (700 cycles) with a discharge voltage of 1.2 V, which is much longer than those of a ZnO anode (192 h, 117 cycles) and a Ti 4 O 7 -particle (p-Ti 4 O 7 )-modified battery (590 h, 443 cycles). Furthermore, due to the anchoring effect for Zn(OH) 4 2- and the uniform electric field, the effect of mesoporous Ti 4 O 7 on inhibiting dendrite formation and shape change of the zinc electrode is highlighted.

Converting CO 2 into value-added chemicals and fuels is one of the promising approaches to alleviate CO 2 emissions, reduce the dependence on nonrenewable energy resources, and minimize the negative environmental effect of fossil fuels. This work used density functional theory (DFT) calculations combined with microkinetic modeling to provide fundamental insight into the mechanisms of CO 2 hydrogenation to hydrocarbons over the iron carbide catalyst, with a focus on understanding the energetically favorable pathways and kinetic controlling factors for selective hydrocarbon production. The crystal orbital Hamiltonian population analysis demonstrated that the transition states associated with O-H bond formation steps within the path are less stable than those of C-H bond formation, accounting for the observed higher barriers in O-H bond formation from DFT. Energetically favorable pathways for CO 2 hydrogenation to CH 4 and C 2 H 4 products were identified which go through an HCOO intermediate, while the CH* species was found to be the key C 1 intermediate over χ-Fe 5 C 2 (510). The microkinetic modeling results showed that the relative selectivity to CH 4 is higher than C 2 H 4 in CO 2 hydrogenation, but the trend is opposite under CO hydrogenation conditions. The major impact on C 2 hydrocarbon production is attributed to the high surface coverage of O* from CO 2 conversion, which occupies crucial active sites and impedes C-C couplings to C 2 species over χ-Fe 5 C 2 (510). The coexistence of iron oxide and carbide phases was proposed and the interfacial sites created between the two phases impact CO 2 surface chemistry. Adding potassium into the Fe 5 C 2 catalyst accelerates O* removal from the carbide surface, enhances the stability of the iron carbide catalyst, thus, promotes C-C couplings to hydrocarbons.

Acid recycling and arsenic recovery from strongly acidic wastewater are goals of the metallurgical industry to reduce carbon emissions. In this study, arsenic was recovered using a hydroxyl-enriched CeO 2 adsorbent, and the adsorption mechanism in a strongly acidic solution was investigated. The adsorption capacities of 88.59 mg/g for As(III) and 126.211 mg/g for As(V) at pH 1.0 are the highest reported values to date. It is revealed that the hydroxyl groups on the CeO 2 surface can buffer hydrogen ions, and the isoelectric point of the material can be reduced to pH 1.52. The binding energy of arsenic is -1.25 eV for the hydroxyl-enriched CeO 2 and -2.24 eV for CeO 2 without hydroxyl groups. Additionally, the protonated hydroxyl groups reduce the oxidation energy of As(III) and promote the adsorption of arsenic by forming new active sites in the strongly acidic solution. Nearly 98.11% of arsenic (initial concentration is 886.8 mg/L) is removed within 24 h without pH adjustment, indicating the feasibility of hydroxyl-enriched CeO 2 for recovering arsenic and acid. This work investigated the adsorption and proton-enhanced oxidation mechanism of arsenic by hydroxyl-enriched CeO 2 in strongly acidic wastewater.

Facilitating the efficient activation of N 2 molecules and inhibiting the competing hydrogen evolution reaction remain a challenge in the nitrogen reduction reaction (NRR). A heteroatom doping strategy is an effective way to optimize the energy barrier during the NRR process to improve the catalytic efficiency. Herein, we report Ni-doped Mo 2 C anchored on graphitized porous conductive carbon for regulating the electronic structure and catalytic properties of electrocatalysts toward NRR. Benefiting from the porous structure and graphitization features of the carbon matrix, more active sites and high electronic conductivity were achieved. Meanwhile, with the doping of Ni atoms, the electronic configuration near the Ni-Mo active sites was optimized and the adsorption of N 2 on them was also promoted due to the increased electron transfer. Moreover, the lowered energy barrier of the NRR process and the suppressed hydrogen adsorption on the active site all resulted in the high catalytic activity and selectivity of the catalyst. Therefore, a high NH 3 yield rate of 46.49 μg h -1 mg -1 and a faradic efficiency of 29.05% were achieved. This work not only validates the important role of heteroatom doping on the regulation of NRR catalytic activity but also provides a promising avenue for the green synthesis of NH 3 .

Exploring active materials with a high rate capability and long lifespan for sodium ion batteries attracts much more attention and plays an important role in realizing clean energy storage and conversion. The strategy of optimizing the electronic structure by atomic element substitution within MoS 2 layers was employed to change the inherent physical property. The enhanced electronic conductivity from a decreased bandgap and increased surface Na + adsorption energy can efficiently and dramatically optimize the electrochemical performance for sodium storage. Attempting to limit the large volume variation and avoid MoS 2 nanosheet stacking and restacking, numerous nanosheets are in situ grown into a designed hierarchical mesopore carbon matrix. This structure can tightly capture the nanosheets to prevent them from aggregating and offer a sufficient buffer zone for alleviating severe volume changes during the discharging/charging process, contributing remarkably to the structural integrity and superior rate performance of electrodes.

Considering the environmental problems caused by a large amount of cotton textile waste and its possible applications in flexible electrodes, it is very promising to reuse the cotton textile waste as an electrode material, reducing the cost of flexible electrodes and alleviating environmental problems. In this work, we present a rechargeable flexible Zn-air battery based on cotton textile waste, which employs Ni-metallized cotton textile waste (NMCTW) as a flexible substrate for Zn anodes and air cathodes. The transparent NiFe hydroxide thin film horizontally grown on the surface of the NMCTW substrate was synthesized in situ by the electrodeposition method, which exhibits excellent catalytic activity because of the high surface area of the two-dimensional (2D) thin film, large contact area between the thin film and substrate, and fast charge transport of the 2D thin-film structure. In view of the high catalytic performance of the NiFe hydroxide thin film, it was used as the catalytic material of the air cathode for the flexible Zn-air battery. The assembled Zn-air battery based on cotton textile waste demonstrated a good rate performance and outstanding charge and discharge cycling stability. The assembled Zn-air battery was applied to power the light-emitting diode, which exhibits exceptional flexibility and stable output power even under severe mechanical bending deformation, proving the feasibility for its application in flexible electronics., Competing Interests: The authors declare no competing financial interest., (Copyright © 2019 American Chemical Society.)

Exploring efficient bifunctional oxygen electrocatalysts is a critical element for developing high-power-density metal-air batteries. Here, we propose an interface and oxygen vacancy engineering strategy to integrate subtle lattice distortions, oxygen vacancies, and nanopores on the surface of Ni x Co 1- x Se 2 -O interface nanocrystals, which exhibit efficient bifunctional catalytic performances for oxygen evolution and reduction. The results from X-ray absorption spectroscopy and electron spin resonance spectroscopy demonstrate that the defect structure can enlarge the number of active sites for electrocatalytic performances. Flexible Zn-air battery using Ni x Co 1- x Se 2 -O as a cathode displays large specific capacity and remarkable stability even after twisting at any angle, thus showing potential for wearable and portable electronic device application. The implementation of our method provides a powerful strategy for preparing advanced catalysts for energy utilization.

As one of the advanced cobalt-based materials, cobalt sulfides with novel architecture have attracted huge interest due to the low cost, easy availability, and promising bifunctional activity for both the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which is essential for next-generation energy storage devices. Herein, we demonstrated a facile and clean electrochemical technique to directly synthesize CoS nanosheets with high purity onto the surface of carbon cloth, and a quick thermal treatment was performed to further improve the catalytic performance (CoS-A). This novel electrochemical technique avoids the use of the binder, surfactant, and other organic additives, which may cause poor electric conductivity as well as undesirable surface wettability, exhibiting great potential of the large-scale applications. The obtained CoS-A exhibits a superior electrocatalytic performance for the OER and ORR, with a high ORR current density (-1.51 mA cm -2 at 0.2 V), considerable OER current density (148 mA cm -2 at 1.9 V), and excellent durability in continuous measurement for over 12 h. The approach offers a powerful yet simple method to control the phase, composition, and morphology of a highly active CoS catalyst, which provides a new idea for the design of high-performance catalysts.

With the aid of X-ray microcomputed tomography and digital image processing technology, the three-dimensional structure of foam zinc prepared by the electrodeposition process is reconstructed. Furthermore, a simplified finite-element model of foam zinc, which can more accurately reflect its structure, is proposed. Based on the Brinkman-Forchheimer-extended-Darcy law, the finite-element method is used for the numerical simulation of the percolation performance of the foam zinc. The results indicate that for high-porosity foam zinc, the pore density is the main factor affecting its percolation performance. A function is established to describe the relationship between the pore density and pressure drop. To obtain an optimum structure, a tetrakaidecahedron cylinder model is established and compared to a previously built model, and the comparison demonstrates that the optimized model performs better in the field of percolation performance., Competing Interests: The authors declare no competing financial interest.

The development of earth-abundant, highly active, and corrosion-resistant electrocatalysts to promote the oxygen reduction reaction (ORR) and oxygen and hydrogen evolution reactions (OER/HER) for rechargeable metal-air batteries and water-splitting devices is urgently needed. In this work, Ni x Se (0.5 ≤ x ≤ 1) nanocrystals with different crystal structures and compositions have been controllably synthesized and investigated as potential electrocatalysts for multifunctional ORR, OER, and HER in alkaline conditions. A novel hot-injection process at ambient pressure was developed to control the phase and composition of a series of Ni x Se by simply adjusting the added molar ratio of the nickel resource to triethylenetetramine. Electrochemical analysis reveals that Ni 0.5 Se nanocrystalline exhibits superior OER activity compared to its counterparts and is comparable to RuO 2 in terms of the low overpotential required to reach a current density of 10 mA cm -2 (330 mV), which may benefit from the pyrite-type crystal structure and Se enrichment in Ni 0.5 Se. For the ORR and HER, Ni 0.75 Se nanoparticles achieve the best performance including lower overpotentials and larger apparent current densities. Further investigations demonstrate that Ni 0.75 Se could not only provide an enhanced electrochemical active area but also facilitate electron transfer during the electrocatalytic process, thus contributing to the remarkable catalytic activity. As a practical application, the Ni 0.75 Se electrode enables rechargeable Zn-air battery with a considerable performance including a long cycling lifetime (200 cycles), high specific capacity (609 mA h g -1 based on the consumed Zn), and low overpotential (0.75 V) at 10 mA cm -2 . Meanwhile, the water-splitting cell setup with an anode of Ni 0.5 Se for the HER and a cathode of Ni 0.75 Se for the OER exhibits a considerable performance with low decay in activity of 12.9% under continuous polarization for 10 h. These results suggest the promising potential of nickel selenide nanocrystals as earth-abundant and high-performance electrocatalysts for metal-air batteries and alkaline water splitting.

Cu has recently received great interest as a potential candidate for glucose sensing to overcome the problems with noble metals. In this work, reduced graphene oxide-encapsulated Cu nanoparticles (Cu@RGO) have been prepared via an electrostatic self-assembly method. This core/shell composites were found to be more stable than conventional Cu-decorated graphene composites and bare copper nanoparticles in an air atmosphere because the graphene shell can effectively protect the Cu nanoparticles from oxidation. In addition, the obtained Cu@RGO composites also showed an outstanding electrocatalytic activity toward glucose oxidation with a wide linear detection range of 1 μM to 2 mM, low detection limit of 0.34 μM (S/N = 3), and a sensitivity of 150 μA mM -1 cm -2 . Moreover, Cu@RGO composites exhibited a satisfactory reproducibility, selectivity, and long effective performance. These excellent properties indicated that Cu@RGO nanoparticles have great potential application in glucose detection., Competing Interests: The authors declare no competing financial interest.

The primary challenge of developing clean energy conversion/storage systems is to exploit an efficient bifunctional electrocatalyst both for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with low cost and good durability. Here, we synthesized chlorine-doped Co(OH) 2 in situ grown on carbon cloth (Cl-doped Co(OH) 2 ) as an integrated electrode by a facial electrodeposition method. The anodic potential was then applied to the Cl-doped Co(OH) 2 in an alkaline solution to remove chlorine atoms (electro-oxidation (EO)/Cl-doped Co(OH) 2 ), which can further enhance the electrocatalytic activity without any thermal treatment. EO/Cl-doped Co(OH) 2 exhibits a better performance both for ORR and OER in terms of activity and durability because of the formation of a defective structure with a larger electrochemically active surface area after the electrochemical oxidation. This approach provides a new idea for introducing defects and developing active electrocatalyst.

Red phosphorus (P) is considered to be one of the most attractive anodic materials for lithium-ion batteries (LIBs) due to its high theoretical capacity of 2596 mAh g -1 . However, intrinsic characteristics such as the poor electronic conductivity and large volume expansion at lithiation impede the development of red P. Here, we design a new strategy to embed red P particles into a cross-link-structural carbon film (P-C film), in order to improve the electronic conductivity and accommodate the volume expansion. The red P/carbon film is synthesized via vapor phase polymerization (VPP) followed by the pyrolysis process, working as a flexible binder-free anode for LIBs. High cycle stability and good rate capability are achieved by the P-C film anode. With 21% P content in the film, it displays a capacity of 903 mAh g -1 after 640 cycles at a current density of 100 mA g -1 and a capacity of 460 mAh g -1 after 1000 cycles at 2.0 A g -1 . Additionally, the Coulombic efficiency reaches almost 100% for each cycle. The superior properties of the P-C films together with their facile fabrication make this material attractive for further flexible and high energy density LIB applications.

Pulse potential electrodeposition was successfully utilized to electrochemically fabricate platinum (Pt) nanoparticles on indium tin oxide (ITO) conductive glass substrates for catalysis toward ammonia electro-oxidation. The effect of deposition parameters (lower potential E l , lower potential duration t l , and upper potential duration t u ) on the size and number density of Pt nanoparticles was investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrocatalytic activity of the Pt nanoparticle/ITO electrode for ammonia oxidation was characterized by the cyclic voltammetry (CV) method. The results showed that lower E l and longer t l accelerate the formation of Pt nuclei while longer t u favors the growth of grain size to some extent, as E l mainly tunes electrochemical overpotential while t l and t u affect the activation and mass transfer process. By the tuning of the deposition parameters, Pt nanoparticle/ITO electrodes with a polycrystalline nature and 5 nm-scale primary particles, could be easily modified in Pt particle size and number density. Furthermore, the Pt nanoparticle/ITO electrode shows high mass specific catalytic activity (MA) toward ammonia oxidation (1.65 mC μg -1 ), much higher than that of the commercial Pt/C electrode (0.32 mC μg -1 ). Additionally, the high catalytic performance results not only from the nanosize effect of Pt nanoparticles, but also from the special morphology formed during the electrodeposition process.

Cobalt-based nanomaterials have been widely studied as catalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) due to their remarkable bifunctional catalytic activity, low cost, and easy availability. However, controversial results concerning OER/ORR performance exist between different types of cobalt-based catalysts, especially for Co(OH) 2 and Co 3 O 4 . To address this issue, we develop a facile electrochemical deposition method to grow Co(OH) 2 directly on the skeleton of carbon cloth, and further Co 3 O 4 was obtained by post thermal treatment. The entire synthesis strategy removes the use of any binders and also avoids the additional preparation process (e.g., transfer and slurry coating) of final electrodes. This leads to a true comparison of the ORR/OER catalytic performance between Co(OH) 2 and Co 3 O 4 , eliminating uncertainties arising from the electrode preparation procedures. The surface morphologies, microstructures, and electrochemical behaviors of prepared Co(OH) 2 and Co 3 O 4 catalysts were systemically investigated by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and electrochemical characterization methods. The results revealed that the electrochemically deposited Co(OH) 2 was in the form of vertically aligned nanosheets with average thickness of about 4.5 nm. After the thermal treatment in an air atmosphere, Co(OH) 2 nanosheets were converted into mesoporous Co 3 O 4 nanosheets with remarkably increased electrochemical active surface area (ECSA). Although the ORR/OER activity normalized by the geometric surface area of mesoporous Co 3 O 4 nanosheets is higher than that of Co(OH) 2 nanosheets, the performance normalized by the ECSA of the former is lower than that of the latter. Considering the superior apparent overall activity and durability, the Co 3 O 4 catalyst has been further evaluated by integrating it into a Zn-air battery prototype. The Co 3 O 4 nanosheets in situ supported on carbon cloth cathode enable the assembled Zn-air cells with large peak power density of 106.6 mW cm -2 , low charge and discharge overpotentials (0.67 V), high discharge rate capability (1.18 V at 20 mA cm -2 ), and long cycling stability (400 cycles), which are comparable or even superior to the mixture of state-of-the-art Pt/C and RuO 2 cathode.