Failure Mechanism And Life Time Evaluation Of Gas Diffusion Electrode

The application of gas diffusion electrode (GDE) in the chlor-alkali technology resulted in a significant cut of more than30%of the energy consumption. Evaluation of the running life of the electrode and the explanation of the failure mechanism are significant for lengthening the service life of the electrode, reducing the electrode cost and ensuring the safe operation of electrolysis equipments. This article mainly focused on the accelerated degradation procedure (ADP) of the life time and the failure mechanism of a gas diffusion electrode for chlor-alkali industry.Silver-based gas-diffusion electrodes were prepared, characterized and tested during chlor-alkali electrolysis with oxygen depolarized cathodes. The gas diffusion electrode was accelerated using electrochemical methods under different low oxygen concentrations and elevated current density. The relationship between the logarithm of the life and the operating start potential was linear. Using this relation, the life of a possible electrode was assumed to be five years or more. Meanwhile, the electrodes were used in the real chlor-alkali process and the results indicated that the lifetime of electrodes can reach five years as well. The electrochemical test and Physico-chemical characterizations of the GDEs are applied after ADP, whose results showed significant changes in the composition and structural properties after APD, including an increase in crystallite sizes, the content of oxygen element in the catalysts and the cracks by the physico-chemical characterizations of XRD, XPS, SEM respectively, and the functional groups can be observed by infrared detection. Polarization curves denoted electrodes performance loss after the ADP, which suggests that the kinetics of the degradation process occurring in the catalysts follow the Ostwald ripening mechanism. As seen from the impedance results, this leads to an increase in charge-transfer resistance, which is another proof of performance loss of the half-cell after the degradation procedure. Structural properties of the electrode before and after the ADP are obtained through mercury intrusion, whose results indicated that the porosity of secondary pores and the ratio of them to total pore volume and their average pore diameter decreased, resulting the fall of gas permeability coefficient.The result indicated that the lower the oxygen concentration and higher current density, the larger of overvpotential, resulting in more byproduct of peroxide during an electrode operation.The loss of hydrophobicity in the electrode was caused by the oxidation of surface carbon. The degradation of the electrode was caused by submerge of three boundary phase. So the performance decay of electrodes could be attributed to a combination of the following causes:(a) the increase of the electrode internal resistance originated by the oxidation of carbon and the accumulation of Ag crystallites contributing to reduce to the electrode conductivity, and (b) hydrophobicity loss contributing to electrode flooding.