Electrochemical behavior of Ir_xRu_(1-x)O_2 oxides as anodic electrocatalyst for electrosynthesis of dinitrogen pentoxide

摘要

The Ir_xRu_(1-x)O_2/Ti electrodes (x = 0-1) were prepared by thermal decomposition of non-aqueous solutions of H_2IrCl_6 and RuCl_3. The surface morphology and microstructure of the Ir_xRu_(1-x)O_2 coatings were characterized by XRD and SEM. The electrochemical characterization of the surface was carried out in a 0.5 mol L~(-1) H_2SO_4 solution. The Ir_xRu_(1-x)O_2 coating with x = 0.5 showed a minimal nanocrystalline particle size and a maximum surface charge (q~*). The electrochemical behaviors of the Ir_xRu_(1-x)O_2 coatings for oxidation of N_2O_4 were determined by cyclic voltammetry (CV), the open circuit potential (OCP) and Tafel plot in 1.7 mol L~(-1) N_2O_4/HNO_3 solutions. The open-circuit potential (E_(ocp)) in N_2O_4/HNO_3 solution was about 1.18 V and it was almost independent of the surface composition. Cyclic voltammetry showed a broad wave feature at 1.4-1.8 V in the anodic scan, which was attributed to the oxidation of NO_2 derived from N_2O_4 to NO_2~+. The redox couple of NO_2/NO_2~+ showed a quasi-reversible behavior and the process was under diffusion control. The electrocatalytic activities of various Ir_xRu_(1-x)O_2 coatings for oxidation of N_2O_4 were evaluated by potentiostatic polarization curves under the quasi-steady state conditions. The Ru_(0.5)Ir_(0.5)O_2 coating showed the lowest Tafel slope, 35.7 mV, in the low current densities, indicating that this coating had the highest electrocatalytic activity. The experiments of electrochemical synthesis of N_2O_5 from N_2O_4 in nitric acid also indicated that the Ru_(0.5)Ir_(0.5)O_2 coating had the best electrocatalytic performance.