Electrocatalytic Reduction Of Concentrated Nitric Acid By Electro-deposited Pt And Pt-Ir Nanoparticles

In some civil and defense industries,such as nuclear industry,steel industry and nitrification industry,the wastes containing concentrated nitric acid is the major sources of environmental pollution.Electrocatalytic reduction of concentrated nitric acid is considered one of the most promising methods to eliminate the contamination of nitric acid.The development of low-cost and high-reactive electrodes is a research hotspot for this electrochemistry method.One of the main research directions in this method is to synthesize a high-performance Pt electrode with ultralow usage.In this work,Pt electrode and Pt-Ir bimetallic electrode with different morphologies were prepared by electrodeposit method on the carbon fiber paper?CFP?.The electrocatalytic activity of these electrodes for concentrated nitric acid reduction and reaction process were investigated.First of all,the Pt nanoparticles with different morphologies were prepared by cyclic voltammetry and square wave voltammetry,using glassy carbon electrode as the substrate.The Pt nanoparticles prepared by cyclic voltammetry were nanopolyhedron,while the square wave voltammetry produced the nanothorn Pt nanoparticles.Although both kinds of the electrodes exposed the same?110?and?100?lattice plane,the ratio was different.Comparing the electrochemical reduction activity of Pt nanoparticles for concentrated nitric acid,it can be found that?100?surface had higher electrocatalytic activity than?110?plane.For the reduction of different concentration of nitric acid by Pt nanothorn electrode,it can be found that the 4.0 M HNO₃ was the critical concentration.Meawhile,the higher concentration of hydrogen ions there was in the solution,the more beneficial there was to the autocatalytic reaction of nitric acid.Then the nano-Pt-loaded electrodes were prepared by electrodeposition of Pt nanoparticles onto CFP.Compared with traditional bulk Pt electrodes,the nano-Pt/CFP electrodes show remarkable electrocatalytic activity at room temperature.The maximum current densities of Pt nanopolyhedron electrode?Pt-NP/CFP?and Pt nanothorn electrode?Pt-NT/CFP?were 488.6 mA mg^-1 and 384.9 mA mg^-1,respectively,while 0.3667 mA mg^-1 for Pt mesh and 288.5 mA mg^-1 for commercial Pt/C.Furthermore,combined with the results of gaseous products,reaction mechanism and the effect of H⁺and NO₃^-on the reduction pathway was discussed.The nitric acid reduction was an autocatalytic reaction with nitrous acid as the electroactive species.The high concentration of H⁺and NO₃^-were beneficial to the generation of HNO₂,which would promote the autocatalytic reaction.Finally,using Pt-NP/CFP electrode as the substrate,two kinds of Pt-Ir bimetallic electrodes were prepared by cyclic voltammetry at different potential ranges.the electrocatalytic activity for concentrated nitric acid reduction was also investigated.Based on the SEM,TEM,XPS and electrochemical characterization,the electrodeposition process of Ir and the effect of deposited Ir on the morphology of Pt nanoparticles were discussed.When the electrodeposition potential was-0.85⁰.20V_SCE,the metallic Ir was deposited,while oxidized Ir was deposited during-0.85¹.0V_SCE.Then these electrodes were used for electrocatalytic reduction of concentrated nitric acid.The oxidized Ir showed greatly enhanced catalytic activity of nano-Pt/CFP electrode.