Stability Studies And Lifetime Evaluation Of Gas Electrode In Brine Electrolysis By Ion-Exchange Membrane

Chlor-alkali industry is a high-energy-consumption industry which produces chorine and sodium hydroxide by brine electrolysis, therefore, more and more attention is paid to the development of low-energy-consumption technology in brine electrolysis. Although much progress has been made in the gas diffusion electrode in ion-exchange membrane brine electrolysis, there are many factors restrict the commercial application. The operating conditions of gas diffusion electrode is with high alkaline concentration, high temperature and high oxygen concentration, which may cause different degrees of corrosion on the matrix structure, precious metal catalysts, carbon support.This thesis aims to systematically study and evaluate the electro catalytic stability and durability of Ag/C gas diffusion electrode in the operating condition of brine electrolysis. First, the the stability and corrosion mechanism of Ag/C electrocatalytic materials was studied, consisting of the stability and corrosion mechanism of silver nanoparticles and carbon support in accelerated corrosion situation; then, the stability and corrosion mechanism of Ag/C electrode in corrosive medium and unstable operating conditions was also involved. At last, the lifetime of miniature Ag/C electrode was preliminary evaluated. This has the significant meaning in prolonging the lifetime and reducing cost of electrode.At first, after the accelerated anodic corrosion of electrode, we can conclude silver transfer into Ag2O film, Ag2O bulk, passivation film of AgO gradually with the increase of anodic potential, and the durability of electrode is well in different anodic potential. Then, we studied the anodic corrosion of carbon black, such as Vulcan XC-72, graphite carbon black and acidifying Vulcan XC-72 and acidifying graphite carbon black. We can make the conclusion that the corrosion resistance of graphite carbon black is well. The reason is graphite carbon black has high conductivity and it has low oxidation degree in the anodic oxidation.According to the experiment of weight loss in NaOH solution, we can find that the hydrophilic of electrode become more stronger as time goes on after dipping in NaOH solution. FT-IR result shows there are much more-COO and -C=O organic functional groups, which are in the ester or epoxide. Polarization curve shows the limited diffusion current density of oxygen reduction decrease slightly. EIS indicates radius of condensance arc increases, which means charge transfer resistance increases and oxygen reduction efficiency decreases. Simulating the unstable operating condition of brine electrolysis -repeatedly shutting down make the current reverse. We can find that the catalytic layer of electrode is serious etched, particle size also obviously increases, the stability obviously decreases, making the structure life greatly reduced.Using changes of oxygen concentration, we evaluate the structure lifetime of electrode and the fitting result is about 5.1 years. And we test the decay rate of electrocatalyst, which shows the failure life is 5.4 years. This indicates the stability and durability of electrocatalyt is well in the operating conditions of high alkaline concentration, high temperature and high oxygen concentration.