In situ synthesis of Co_(3)O_(4)nanoparticles confined in 3D nitrogendoped porous carbon as an efficient bifunctional oxygen electrocatalyst

The rational exploitation of non-precious metal catalyst with high activity,strong durability and low cost for the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)is of vital importance for metalair batteries.Herein,a composite of Co_(3)O_(4)nanoparticles confined in three-dimensional(3 D)N-doped porous carbon(Co-NpCs)was prepared by a simple freeze-drying and in situ pyrolysis method.The effect of different dosages of Co(NO_(3))_(2)on the catalytic performance was discussed.The Co-NpC-12%exhibits the best catalytic performance(E_(1/2)=0.78 V,better stability than 20%Pt/C)in ORR and in OER among all the as-synthesized samples.Furthermore,it also exhibits the best bifunctional activity(ΔE=0.849 V).The excellent properties of Co-NpCs are mainly due to the synergy between Co_(3)O_(4)and carbon.Firstly,a high Co_(3)O_(4)loading amount can boost the defect level of the N-doped hierarchical porous carbon and expose more active sites.Secondly,the unique in situ pyrolysis guarantees a largearea contact between Co_(3)O_(4)and carbon as well as a strong C-O-Co bonding,which promotes charge transfer,avoids the peeling of Co_(3)O_(4)nanoparticles and effectively improves the stability of the material.This work is expected to offer a feasible strategy to produce metal oxide/carbon nanocomposite and push forward the development of bifunctional electrocatalyst with high activity and stability.

Solvothermal Synthesis of Visible Light Responsive Titania Nanocrystals at Moderate Temperature

Visible light responsive nitrogen-doped titania nanocrystals were prepared by "Homogeneous Precipitation-Solvothermal Process" in TiCl3-hexamethylenetetramine (C6Hi2N4) mixed solution. The phase composition, crystallinity, microstructure and specific surface area of titania greatly changed depending on pH,solvent and temperature. The titania powders prepared in TiCl3-hexamethylenetetramine aqueous solutions at pH 1～6 and 190℃ for 2 h consisted of single phase of brookite and that prepared at pH 9 was single phase of rutile. On the other hand, the sample prepared in the presence of methanol at pH 9 consisted of single phase of anatase. All titania powders prepared in the present study were yellow and showed excellent visible light absorption property and photocatalytic ability for NO destruction under irradiation of the visible light (λ＞510nm). The photocatalytic activity of the sample possessing similar specific surface area was in the order anatase ＞ brookite ＞ rutile. The photocatalytic activity of nitrogen doped titania under irradiation of visible light (λ＞510 nm) slightly decreased with increasing calcination temperature up to 600℃ and then greatly decreased at 800 C. The visible light responsive photocatalytic activity of rutile titania nanoparticles could be improved by forming nanocomposite with layered tetratitanate possessing high specific surface area via a delamination-reassembly process of K2Ti4O9 combined with planetary ball-milling.

Efficient CO_(2) adsorption and mechanism on nitrogen-doped porous carbons

In this work,nitrogen-doped porous carbons(NACs)were fabricated as an adsorbent by urea modification and KOH activation.The CO_(2) adsorption mechanism for the NACs was then explored.The NACs are found to present a large specific surface area(1920.72-3078.99 m2·g^(-1))and high micropore percentage(61.60%-76.23%).Under a pressure of 1 bar,sample NAC-650-650 shows the highest CO_(2) adsorption capacity up to 5.96 and 3.92 mmol·g^(-1) at 0 and 25℃,respectively.In addition,the CO_(2)/N_(2) selectivity of NAC-650-650 is 79.93,much higher than the value of 49.77 obtained for the nonnitrogen-doped carbon AC-650-650.The CO_(2) adsorption capacity of the NAC-650-650 sample maintains over 97% after ten cycles.Analysis of the results show that the CO_(2) capacity of the NACs has a linear correlation(R^(2)=0.9633)with the cumulative pore volume for a pore size less than 1.02 nm.The presence of nitrogen and oxygen enhances the CO_(2)/N_(2) selectivity,and pyrrole-N and hydroxy groups contribute more to the CO_(2) adsorption.In situ Fourier transform infrared spectra analysis indicates that CO_(2) is adsorbed onto the NACs as a gas.Furthermore,the physical adsorption mechanism is confirmed by adsorption kinetic models and the isosteric heat,and it is found to be controlled by CO_(2) diffusion.The CO_(2) adsorption kinetics for NACs at room temperature and in pure CO_(2) is in accordance with the pseudo-first-order model and Avramís fractional-order kinetic model.

Nitrogen-doped Zn–Ni oxide for electrochemical reduction of carbon dioxide in sea water

Nitrogen-doped Zn-Ni oxide nanoparticles prepared by ammonia treatment are efficient electrocatalysts for CO_(2) reduction to CO.The single-phase nanostructures of N-Zn-Ni oxide nanoparticles exhibited high electrocatalytic CO_(2) reduction activity with CO Faradaic efficiency of 91.5% and partial current density of 3.2 mA·cm^(-2) at-0.95 V(vs.reversible hydrogen electrode’RHE) in NaCl aqueous solution.Furthermore’ N-Zn-Ni oxides catalyst achieved CO Faradaic efficiency over 89%at—0.8 V(vs.RHE) in natural seawater’ much better than the CO_(2) reduction activity of benchmark Ag/C catalysts in seawater’ and demonstrated strong tolerance to several metal ion impurities with retained CO selectivity.The notable reactivity toward CO_(2) reduction and contamination-tolerance is attributed to peculiar synergistic effect from binary Zn-Ni oxide and nitrogen doping.