The fabrication of a new type of one-dimensional Au-Ag porous nanotube（NPT） structure was presented based on a facile combination of nanocrystal growth and surface modification.Ag nanowires with various diameters were firstly served as the chemical plating templates via a polyol-process.Then,one-dimensional（1D） Au-Ag porous nanostructures with tailored structural features could be prepared by controlling the individual steps involved in this process,such as nanowire growth,surface modification,thermal diffusion,and dealloying.Structural characterizations reveal these Au-Ag porous nanotubes,non-porous nanotubes and porous nanowires possess novel nano-architectures with multimodal open porosity and excellent structural continuity and integrity,which make them particularly desirable as novel 1D nanocarriers for biomedical,drug delivery and sensing applications.
The oxygen reduction reaction （ORR） and oxygen evolution reaction （OER） are crucial processes for energy conversion/storage systems, such as fuel cells, metal-air batteries, and water splitting. However, both reactions are severely restricted by their sluggish kinetics, thus requiring highly active, cost-effective, and durable electrocatalysts. Herein, we develop novel bifunctional nanocatalysts through surface nanoengineering of dealloying-driven nanoporous gold （NPG）. Pd overlayers were precisely deposited onto the NPG ligament surface by epitaxial layer-by-layer growth. More importantly, the obtained NPG-Pd overlayer nanocatalysts exhibit remarkably enhanced electrocatalytic activities toward both the ORR and OER in alkaline media, benchmarked against a state- of-the-art Pt/C catalyst. The improved electrocatalytic performance is rationalized by the unique three-dimensional nanoarchitecture of NPG, enhanced Pd utilization efficiency from precise control of the Pd overlayers, and change in electronic structure, as revealed by density functional theory calculations.
Yan WangWei HuangConghui SiJie ZhangXuejiao YanChuanhong JinYi DingZhonghua Zhang
Combined with air annealing, rutile-structured IrO 2 nanoparticles with various sizes were prepared using colloidal method. The nanoparticles were used as the electrocatalysts for the oxygen evolution reaction （OER） in acidic media, and their grain size effect was studied. The results show that with the increase in annealing temperature, the grain size of the catalyst increases, and the voltammetric charges （the electroactive areas） and apparent activity for the OER decrease. The relationship between the intrinsic activity and the annealing temperature exhibits a volcano-type curve and the catalyst annealed at 550 ℃ achieved the best result.
The nanostructure of the catalytic electrode has a great effect on the performance of direct metha- nol fuel cells （DMFCs）, including catalyst utilization, precious metal loading, water balance, and oxygen mass transfer. In this work, ordered arrays of platinum nanorods with different diameters were directly grown onto microporous layers by electrodeposition via a sacrificial template, and were used as the catalytic cathode for passive DMFCs. The use of these ordered electrodes led to a dramatic decrease in cathode polarization behavior. The maximum power density of passive DMFCs fabricated with catalytic electrodes of 200 and 100 am Pt nanorod arrays were 17.3 and 12.0 mW/cm2, respectively. The obtained improvement in performance was ascribed to the fact that the ordered nanostructured electrode not only increased the electrochemically active surface area and the catalyst utilization, but also enhanced oxygen mass transfer and water balance in the system.
Fe and Co porphyrins and phthalocyanines are excellent catalysts for the oxygen reduction reaction （ORR） and are promising alternatives to Pt in fuel cells. However, the stability of these molecular catalysts in acidic media is poor. This study explores whether demetalation through proton ex- change causes these metal macrocyclic catalysts to be unstable in acidic media. We first present a theoretical scheme for investigating exchange reactions of metal ions in metal macrocyclic com- pounds with protons in acidic media. The equilibrium concentrations of metal ions in solution when various metalloporphyrins （MPs） and metallophthalocyanines （MPcs） are brought into contact with a strongly acidic solution （pH = 1） were then estimated using density functional theory calculations; these values were used to evaluate the stability of these metal macrocyclic compounds against demetalation in acidic media, The results show that Fe, Co, Ni, and Cu phthalocyanines and porphy- rins have considerable resistance to exchange with protons, whereas Cr, Mn, and Zn phthalocya- nines and porphyrins easily undergo demetalation through ion exchange with protons, This sug- gests that the degradation in the ORR activity of Fe and Co macrocyclic molecular catalysts and of carbon materials doped with Fe（Co） and nitrogen, which are believed to have metal-nitrogen coor- dination structures similar to those of macrocyclic molecules as ORR catalytic centers, is not the result of replacement of metal ions by protons. The calculation results show that electron-donating substituents could enhance the stability of Fe and Co phthalocyanines.
