Application Of Nanoporous Metals In Electrocatalysis And Biocatalysis

This paper is focusing on applications of nanoporous gold (NPG) in electrochemical catalysis, fuel cell and enmzy immobilization. Investigations are based on several aspects mainly including:electrochemical detection of hydrazine by NPG, direct N2H4/H2O2 fuel cell based on NPG, glucose fuel cell based on NPG and NPG-Pt, xylanase immobilized on nanoporous gold as a highlyefficient biocatalyst.1. An effective and rapid electrochemical detection of hydrazine by NPGNPG membranes prepared by dealloying AgAu alloys in concentrated nitric acid towards hydrazine electrochemical oxidation were studied. Compared with bulk gold, NPG shows not only the enhanced current but lower overpotential of hydrazine oxidation. The diffusion coefficient of hydrazine was examined to be 1.68×10-3 cm2 s-1 using chronoamperometry. In addition, it can be found that the behavior of hydrazine oxidation on NPG depends strongly on the pH value of the solution. A detection limit of 16.7 nM hydrazine can be determined by high sensitive NPG. These results indicate that NPG can be employed to be as an efficient electrode material of electrochemical sensors for hydrazine detection in solution.2. A platinum-free direct N2H4/H2O2 fuel cell based on NPGDealloyedNPG is found to exhibit high electrocatalytic properties toward both hydrazine (N2H4) oxidation and hydrogen peroxide (H2O2) reduction. This observation allows the implementation of a direct hydrazine-hydrogen peroxide fuel cell (DHHPFC) based on these novel membrane electrode materials. The effects of fuel and oxidizer flow rate, concentration and cell temperature on the performance of DHHPFC are systematically investigated. With a loading of 0.1 mg cm-2 Au on each side, an open circuit voltage of 1.2 V is obtained at 80℃with a maximum power density 195 mW cm-2, which is 22 times higher than that of commercial Pt/C as electrocatalysts at the same noble metal load. NPG thus holds great potential as an effective and stable platinum-free electrocatalyst for DHHPFCs.3. NPG and Pt-decorated NPG for DGFC(1)NPG for DGFC The NPG with 12 nm pore size was obtained by electrochemical dealloying under anodic potential, and using it as catalyst for DGFC performance studying. Activity of glucose electrocatalytic oxidation on NPG was investigated in neutral and alkaline solution. The results indicated that the activity in alkaline was higher than that in neutral solution for glucose oxidation. Then e plored the performance of DGFC on NPG, the results illustrated that the performance of DGFC was improved with the increasing of temperature.(2) NPG-Pt for GDFCPt-decorated nanoporous gold (NPG-Pt), created by depositing a thin layer of Pt on NPG surface, was proposed as an active electrode for GDFC in neutral and alkaline solutions. The structure and surface properties of NPG-Pt were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray powder diffraction (XRD). A direct glucose fuel cell (DGFC) was performed based on the novel membrane electrode materials. With a low precious metal load of less than 0.3 mg cm-2 Au and 60μg cm-2 Pt in anode and commercial Pt/C in cathode, the performance of DGFC in alkaline is much better than that in neutral condition.4. Xylanase immobilized nanoporous gold as a biocatalystNPG, a nanostructured metallic sponge with tunable porosity and excellent biocompatibility, was employed as an effective support material for xylanase immobilization. Structure analyses revealed that the immobilization of xyalanse was realized via chemical bonding of sulphur end-groups with gold surface atoms, suggesting a characteristic self-assembled monolayer type adsorption process. The activity and stability for the immobilized enzyme were investigated under different conditions. And the immobilized enzymes were found to keep as high as 80% of the activity of free ones. More importantly, these novel composite nanobiocatalysts showed quite impressive stability. Even after ten reaction cycles, this bio-nanocomposite could still retain76% of the initial activity.