氢氧原子平衡关系式的推导及应用

过去认为配平氧化数未发生变化的氢氧原子是配平氧化还原反应方程式的难点,对配平这类氢氧原子,很长时间一直是采用经验方法。近些年国内外出版的化学教材对配平这类氢氧原子的方法作了较好的改进,但如何用一个数学模型抽象、简约。

Electrocatalytic generation of hydrogen peroxide on cobalt nanoparticles embedded in nitrogen-doped carbon

Electrocatalytic reduction of oxygen is a growing synthetic technique for the sustainable production of hydrogen peroxide(H_(2)O_(2)).The current challenges concern seeking low-cost,highly active,and selective electrocatalysts.Cobalt-nitrogen-doped carbon containing catalytically active cobalt-nitrogen(Co-N_(x))sites is an emerging class of materials that can promote the electrochemical generation of H_(2)O_(2).Here,we report a straightforward method for the preparation of cobalt-nitrogen-doped carbon composed of a number of Co-N_(x)moieties using low-energy dry-state ball milling,followed by controlled pyrolysis.This scalable method uses inexpensive materials containing cobalt acetate,2-methylimidazole,and Ketjenblack EC-600JD as the metal,nitrogen,and carbon precursors,respectively.Electrochemical measurements in an acidic medium show the present material exhibits a significant increase in the oxygen reduction reaction current density,accompanied by shifting the onset potential into the positive direction.The current catalyst has also demonstrated an approximate 90%selectivity towards H_(2)O_(2)across a wide range of potential.The H_(2)O_(2)production rate,as measured by H_(2)O_(2)bulk electrolysis,has reached 100 mmol g_(cat).^(–1)h^(–1)with high H_(2)O_(2)faradaic efficiency close to 85%(for 2 h at 0.3 V vs.RHE).Lastly,the catalyst durability has been tested(for 6 h at 0.3 V vs.RHE).The catalyst has shown relatively consistent performance,while the overall faradic efficiency reaches approximate 85%throughout the test cycle indicating the promising catalyst durability for practical applications.The formed Co-N_(x)moieties,along with other parameters,including the acidic environment and the applied potential,likely are the primary reasons for such high activity and selectivity to H_(2)O_(2)production.

Exploring the Interactions of Atomic Oxygen on Silver Clusters with Hydrogen

The interactions between AgnO- （n=1-8） and H2 （or D2） were explored by combination of the mass spectroscopy experiments and density function theory （DFT） calculations. The experiments found that all oxygen atoms in AgnO- （n--1-8） are inert in the interactions with H2 or D2 at the low temperature of 150 K, which is in contrast to their high reactivity with CO under the same condition. These observations are parallel with the preferential oxidation （PROX） of CO in excess hydrogen catalyzed by dispersed silver species in the condensed phase. Possible reaction paths between AgnO- （n=1-8） and H2 were explored using DFT calculations. The results indicated that adsorption of H2 on any site of AgnO- （n=1-8） is extremely weak, and oxidation of H2 by any kind of oxygen in AgnO- （n=1-8） has an apparent barrier strongly dependent on the adsorption style of the ＂O＂. These experiments and theoretical results about cluster reactions provided molecule-level insights into the activity of atomic oxygen on real silver catalysts.

Recent progress in production and usage of hydrogen peroxide

Hydrogen peroxide has attracted increasing interest as an environmentally benign and green oxidant that can also be used as a solar fuel in fuel cells.This review focuses on recent progress in production of hydrogen peroxide by solar-light-driven oxidation of water by dioxygen and its usage as a green oxidant and fuel.The photocatalytic production of hydrogen peroxide is made possible by combining the e^(-)and 4e-oxidation of water with the e^(-)reduction of dioxygen using solar energy.The catalytic control of the selectivity of the e^(-)vs.4e-oxidation of water is discussed together with the selectivity of the e^(-)vs.4e-reduction of dioxygen.The combination of the photocatalytic e^(-)oxidation of water and the e^(-)reduction of dioxygen provides the best efficiency because both processes afford hydrogen peroxide.The solar-light-driven hydrogen peroxide production by oxidation of water and by reduction of dioxygen is combined with the catalytic oxidation of substrates with hydrogen peroxides,in which dioxygen is used as the greenest oxidant.

FeOx Coating on Pd/C Catalyst by Atomic Layer Deposition Enhances the Catalytic Activity in Dehydrogenation of Formic Acid

Hydrogen generation from formic acid （FA） has received significant attention. The challenge is to obtain a highly active catalyst under mild conditions for practical applications. Here atomic layer deposition （ALD） of FeOx was performed to deposit an ultrathin oxide coating layer to a Pd/C catalyst, therein the FeOx coverage was precisely controlled by ALD cycles. Transmission electron microscopy and powder X-ray diffraction measurements suggest that the FeOx coating layer improved the thermal stability of Pd nanoparticles （NPs）. X-ray photoelectron spectroscopy measurement showed that deposition of FeOx on the Pd NPs caused a positive shift of Pd3d binding energy. In the FA dehydrogenation reaction, the ultrathin FeOx layer on the Pd/C could considerably improve the catalytic activity, and Pd/C coated with 8 cycles of FeOx showed an optimized activity with turnover frequency being about 2 times higher than the uncoated one. shape as a function of the number of FeOx ALD The improved activities were in a volcanocycles, indicating the coverage of FeOx is critical for the optimized activity. In summary, simultaneous improvements of activity and thermal stability of Pd/C catalyst by ultra-thin FeOx overlayer suggest to be an effective way to design active catalysts for the FA dehydrogenation reaction.

Experimental and Theoretical Study of Hydrogen Atom Abstraction from Ethylene by Stoichiometric Zirconium Oxide Clusters

The reactions of cationic zirconium oxide clusters （ZrxOy^＋） with ethylene （C2H4） were investigated by using a time-of-flight mass spectrometer coupled with a laser ablation/supersonic expansion cluster source. Some hydrogen containing products （ZrO2）xH^＋（x=-1-4） were observed after the reaction. The density functional theory calculations indicate that apart from the common oxygen transfer reaction channel, the hydrogen abstraction channel can also occur in （ZrO2）x^＋＋C2H4, which supports that the observed （ZrO2）xH^＋ may be due to （ZrO2）x^＋＋C2H4→（ZrO2）xH^＋＋C2H3. The rate constants of different reaction channels were also calculated by Rice-Rarnsberger-Kassel-Marcus theory.

华北四省市禽蛋和牛奶中硒含量调查

为了调查华北四省市禽蛋和牛奶中的硒含量,试验采用氢化物-原子荧光光度法对华北四省市禽蛋和牛奶样品进行测定调查。结果表明:牛奶中的硒含量显著低于禽蛋中的硒含量(P<0.05),而禽蛋中鸭蛋硒含量最高,与鸡蛋相比差异不显著(P>0.05),硒含量大小顺序为鸭蛋(0.186 0 mg/kg)>红皮鸡蛋(0.170 9 mg/kg)>白皮鸡蛋(0.162 7 mg/kg)>牛奶(0.031 7 mg/kg)。天津市蛋奶中的硒含量显著高于其他省市(P<0.05),顺序为天津市(0.211 7 mg/kg)>山西省(0.108 4 mg/kg)>北京市(0.108 3 mg/kg)>河北省(0.092 0 mg/kg)。

Recycling synthesis of single-atom Zn-nitrogen-carbon catalyst for electrocatalytic reduction of O_(2)to H_(2)O_(2)

Portable electrochemical synthesis of H_(2)O_(2),which is widely used for disinfection,sterilization,and waste treatment,has attracted increasing attention.However,low atomic utilization efficiency and by-product disposal during the synthesis of electrocatalysts are inevitable.Based on the advantages of single-atom catalysts(SACs)towards H_(2)O_(2)synthesis via a 2e−transfer oxygen reduction reaction,this work presents the synthesis of ZnNC SACs as excellent oxygen reduction catalysts with high atomic use efficiency and almost no generated waste by using formamide and metal powder as precursors.The ZnNC SACs exhibit H_(2)O_(2)selectivity exceeding 80%when working continuously for 10,000 s.The synthetic strategy described in this paper is intended to be used as a supplement to the synthesis of metal-nitrogen-carbon SACs with high atomic utilization efficiency and low waste generation for environmental and chemical applications.

Atomic-scale Pt clusters decorated on porousα-Ni(OH)_2 nanowires as highly efficient electrocatalyst for hydrogen evolution reaction

The synthesis of atomic-scale metal catalysts is a promising but very challenging project. In this work, we successfully fabricated a hybrid catalyst of PL/Ni（OH）2 with atomic-scale Pt clusters uniformly decorated on porous Ni（OH）2 nanowires （NWs） via a facile room-temperature synthesis strategy. The as-obtained Ptc/Ni（OH）2 catalyst exhibits highly efficient hydrogen evolution reaction （HER） performance under basic conditions. In 0.1moll-1 KOH, the Ptc/Ni（OH）2 has an onset overpotential of -0 mV vs. RHE, and a significantly low overpotential of 32 mV at a current density of 10mAcm-2, lower than that of the com- mercial 20% Pt/C （58 mV）. The mass current density data illustrated that the PL/Ni（OH）2 reached a high current den- sity of 6.34Amg^-1i at an overpotential of 50 mV, which was approximately 28 times higher than that of the commercial Pt/C （0.223Amg^-1i） at the same overpotential, proving the high-efficiency electrocatalytic activity of the as-obtained Ptc/Ni（OH）2 for HER under alkaline conditions.

Semi-polar GaN LEDs on Si substrate

Growth of semi-polar （1-101）GaN has been attempted on a patterned （001） silicon substrate adopting selective area MOVPE. The growth was initiated on （111） facets of the Si, which had been prepared by anisotropy etching in a KOH solution. A uni- form semi-polar layer was achieved by coalescence of stripes. Since the growth was performed on facets, the surface was atomically fiat in AFM surface analyses. By using a high temperature grown A1N nucleation layer, we achieved low threading dislocation density at the top most surface. Moreover, by tilting the c-axis of the GaN on the Si substrate, the effect of the thermal expansion coefficient mismatch was much reduced. As the result, we achieved a crack free （1-101）GaN template on （001）Si. On the thus prepared （1-101）GaN, a GalnN/GaN LED was fabricated, which showed excellent performance with weak quantum confined Stark effect.

First-principles study of hydrogen diffusion mechanism in Cr_2O_3

The system energy of H atom occupying different positions in Cr2O3 crystal lattice is calculated by adopting the first-principles calculation method based on density functional theory in this paper. The results indicate that the most stable position of H atom in Cr2O3 crystal lattice locates at the bilateral positions of the center of the unoccupied O octahedral interstice. The reason resulting in this situation is analyzed by comparing the change of Cr2O3 lattice distortion and density of states in Cr2O3_H system when H atom locates at different positions in octahedral interstice. The diffusion activation energy of H atom is 0.73 eV,which is determined by seeking the diffusion path and transition state of H atom in Cr2O3 crystal lattice. The effective attempt frequency of H atom in Cr2O3 crystal lattice is also calculated by using molecular dynamics. Combining with diffusion activation energy data,the diffusion coefficient of H atom in Cr2O3 crystal is determined.