以化学竞赛思维引领的基础化学实验教学改革

以化学竞赛思维为引领,对两个基础化学实验案例进行教学改革,拟解决教学改革中遇到的深层次问题。教学改革结果表明,相关课程教学目标与专业培养目标能够高度统一;不同任课教师能在同一教学主题中高度统一思想,从而进行深入交流;通过竞赛思维培养方式,可极大地激发学生学习动力,提高他们的学习效率。

1+1>2: Learning from the interfacial modulation on single-atom electrocatalysts to design dual-atom electrocatalysts for dinitrogen reduction

Developing efficient electrocatalysts for converting dinitrogen to ammonia through electrocatalysis is of significance to the decentralized ammonia production. Here, through high-throughput density functional theory calculations, we demonstrated that the interfacial modulation of hexagonal boron nitride/graphene(hBN-graphene) could sufficiently improve the catalytic activity of the single transition metal atom catalysts for nitrogen reduction reaction(NRR). It was revealed that Re@hBN-graphene and Os@hBN-graphene possessed remarkable NRR catalytic activity with low limiting potentials of 0.29 V and 0.33 V, respectively. Furthermore, the mechanism of the enhanced catalytic activity was investigated based on various descriptors of the adsorption energies of intermediates, where the synergistic effect of hBN and graphene in the hybrid substrate was found to play a key role. Motivated by the synergistic effect of hybrid substrate in single-atom catalysts, a novel strategy was proposed to efficiently design dual-atom catalysts by integrating the merits of both metal components. The as-designed dual-atom catalyst Fe-Mo@hBN exhibited more excellent NRR catalytic performance with a limiting potential of 0.17 V, manifesting the solidity of the design strategy. Our findings open new avenues for the search of heterostructure substrates for single-atom catalysts and the efficient design of dualatom catalysts for NRR.

Unusual tunability of multiferroicity in GdMn_2O_5 by electric field poling far above multiferroic ordering point

The multiferroicity in the RMn_2O_5 family remains unclear, and less attention has been paid to its dependence on high-temperature(high-T) polarized configuration. Moreover, no consensus on the high-T space group symmetry has been reached so far. In view of this consideration, one may argue that the multiferroicity of RMn_2O_5 in the low-T range depends on the poling sequence starting far above the multiferroic ordering temperature. In this work, we investigate in detail the variation of magnetically induced electric polarization in GdMn_2O_5 and its dependence on electric field poling routine in the high-T range. It is revealed that the multiferroicity does exhibit qualitatively different behaviors if the high-T poling routine changes, indicating the close correlation with the possible high-T polarized state. These emergent phenomena may be qualitatively explained by the co-existence of two low-T polarization components, a scenario that was proposed earlier.One is the component associated with the Mn^(3+)–Mn^(4+)–Mn^(3+) exchange striction that seems to be tightly clamped by the high-T polarized state, and the other is the component associated with the Gd Mn^(3+)–Mn^(4+)–Mn^(3+) exchange striction that is free of the clamping. The present findings may offer a different scheme for the electric control of the multiferroicity in RMn_2O_5.

Influence of reduction energy match among CuO species in CuO-CeO_2 catalysts on the catalytic performance for CO preferential oxidation in excess hydrogen

In the present study, we have investigated the reducibility of CuO species on CuO-CeO2 catalysts and the influence of CuO species on the catalytic performance for CO preferential oxidation （CO PROX） in excess hydrogen. It is revealed that the smaller the difference of reduction temperature （denoted as ？T） for two adjacent CuO species is, the higher the catalytic activity of CuO-CeO2 for the PROX in excess hydrogen may be obtained. It means that if the reduction energy of Cu0-Cu2＋ pairs matched better, the reduction-oxidation recycle of Cu0-Cu2＋ pairs would go on more easily, then the transferring energy of Cu0-Cu2＋ pairs would be lesser. Therefore, the CuO-CeO2 catalysts will be largely improved in their catalytic performance if the different CuO species on the catalysts have matched the reduction energy, which would allows them to cooperate effectively.

Incommensurate-commensurate magnetic phase transition in double tungstate Li_(2)Co(WO_4)_(2)

Magnetic susceptibility,specific heat,and neutron powder diffraction measurements have been performed on polycrystalline Li_(2)Co(WO_4)_(2)samples.Under zero magnetic field,two successive magnetic transitions at T_(N1)~9.4 K and T_(N2)~7.4 K are observed.The magnetic ordering temperatures gradually decrease as the magnetic field increases.Neutron diffraction reveals that Li_(2)Co(WO_4)_(2)enters an incommensurate magnetic state with a temperature dependent k between T_(N1)and T_(N2).The magnetic propagation vector locks-in to a commensurate value k=(1/2,1/4,1/4)below T_(N2).The antiferromagnetic structure is refined at 1.7 K with Co2+magnetic moment 2.8(1),μ_B,consistent with our first-principles calculations.

石墨烯对镁基复合材料抗压性能影响的分子动力学研究

镁(Mg)作为轻质金属材料,因其塑性不足及高温下力学性能下降等缺点限制了其应用.石墨烯(Gr)因其比表面积大、强度高等优点可以作为一种理想增强材料与金属镁复合,从而提升材料的力学性能.本文采用分子动力学(MD)方法对石墨烯/镁(Gr/Mg)复合材料在不同压缩条件下的力学性能进行研究.结果表明,单晶Mg在不同晶向下压缩表现出强烈的各向异性特征.引入Gr使得Mg基体中难以启动的滑移系因晶粒细化作用而被激活,应力得到释放,孪生变形机制难以开启.位错和孪生等缺陷在Gr界面附近形核增殖,载荷有效传递至Gr,提升了复合材料塑性阶段的平均流动应力.此外,Mg基体对Gr的约束限制了Gr的褶皱和弯曲,使材料韧性增强,Gr/Mg复合材料沿Z轴[0 0 0 1]晶向压缩的应变达0.35时,Gr仍未断裂.Gr/Mg复合材料中位错运动到Gr表面无法继续贯穿,抑制了Mg基体的破坏.压缩荷载作用下,Gr/Mg复合材料中位错线的增加有助于抵抗压缩塑性变形.Gr/Mg复合材料的屈服应力、屈服应变及塑性变形阶段的平均流动应力随着Gr层数增加而增大,且Gr处于分离状态时,Gr/Mg复合材料的屈服应变更大.在10K~600K温度范围内,Gr/Mg复合材料的弹性模量和屈服应力随着温度升高而降低.而应变率对Gr/Mg复合材料的弹性模量和塑性变形阶段的平均流动应力影响不明显,但增大应变率可以提高复合材料的屈服应力和屈服应变.

One-step,in situ formation of WN-W_(2)C heterojunctions implanted on N doped carbon nanorods as efficient oxygen reduction catalyst for metal-air battery

Transition metal nitrides and carbides have attracted intensive attentions in metal-air battery application due to their metallic electron transport behavior and high chemical stability toward the oxygen reduction reaction(ORR).Herein,the polyoxometalate@polyaniline composite derived WN-W_(2)C heterostructured composite(WN-W_(2)C@pDC)has been fabricated through an in situ nitriding-carbonization strategy,with WN-W_(2)C nanoparticles implanted on N doped carbon nanorods.Asfabricated WN-W_(2)C@pDC demonstrates prominent electrocatalytic performance towards ORR and excellent cycling stability in metal-air battery,which possesses positive half-wave potential and large diffusion limiting current density(0.81 V and 5.8 mA·cm^(-2)).Moreover,it demonstrates high peak power density of 157.4 mW·cm^(-2)as Al-air primary cathode and excellent stability at the discharge-charge test(>500 h)of Zn-air secondary battery.The excellent activity and durability of WNW_(2)C@pDC catalyst should be attributed to the combined effect of intimate WN-W_(2)C heterointerfaces,unique embedded nanoparticles structure,and excellent electrical media of N doped carbon,confirmed by a series of contrast experiments.

Control of large linear magnetoelectricity in Co_(3)NiNb_(2)O_(9)

Magnetoelectric(ME)materials have caught worldwide attentions owing to their potential technological applications in ME switching devices or high-density data storage.However,realizing a sufficiently strong ME effect in one single material is always the key issue.Herein,we systematically investigate the Co_(3)NiNb_(2)O_(9),including the characterization of its crystalline structure,magnetism,specific heat,and pyroelectric properties.It is revealed that Co_(3)NiNb_(2)O_(9) exhibits a remarkable ME response below the magnetic phase transition temperature of TN-32 K.On one hand,the magnetic field-induced electric polarization is observed below TN while it is non-ferroelectric at no magnetic field.The evaluated ME coefficient is as large as 21.2 ps/m.On the other hand,the magnetization is significantly modulated by the applied electric field,with the inverse ME coefficient being 14.1 ps/m.The observed ME responses suggest a stable ME mutual control by the magnetic or electric field in Co_(3)NiNb_(2)O_(9).