Macrokinetic analysis of polarisation characteristics of gas-diffusion electrodes in contact with liquid electrolytes, Part II: Oxygen reduction as example for a higher order reaction

Abstract

Classical partial oxidation processes often suffer from low selectivities. Promising alternatives are electrochemical processes where the oxidation takes place at a packed-bed anode while an oxygen-consuming gas-liquid membrane is used as cathode. As a basis for the reliable design of such a process, the performance of oxygen-consuming gasdiffusion electrodes (GDE) is investigated experimentally and is analysed based on a rigorous model accounting for the reaction microkinetics and all relevant mass and charge transport phenomena. The results indicate that oxygen is transported in the gas-filled pores by Knudsen diffusion and that the cathodic oxygen reduction follows a parallel reaction scheme forming hydrogen peroxide at the carbon black support and water at the applied platinum catalyst particles.

Electrosynthesis of >20 g/L H2O2 from Air

“…In theory, the flux of electrons ( i.e ., current density) should be proportional to the oxygen flux diffused across the GDE. Thus, the limiting current ( I limt ) can be calculated as follows 25 where n = 2 is the number of electrons in the ORR-HP reaction, F is the Faraday constant (96 485 C/mol), D O 2 (1.90 × 10 –5 m 2 /s) is the oxygen diffusion coefficient in the gas diffusion layer, 26 H is the thickness of the gas diffusion layer (measured as 3.15 × 10 –4 m), P O 2 (21 278 Pa) is the oxygen partial pressure in the air, R is the universal gas constant (8.314 J/(mol·K)), and T (298 K) is the gas temperature.…”

“…In theory, the flux of electrons (i.e., current density) should be proportional to the oxygen flux diffused across the GDE. Thus, the limiting current (I limt ) can be calculated as follows 25 I nF D…”

Oxidation-assisted alkaline precipitation of nanoparticles using gas-diffusion electrodes

“…This accumulation would then cause a high pH in the electrode pores. 31 The built-up of these species slows down the flux of these species into the bulk of the electrolyte, which is registered as a delay of the measured pH during GDEx compared to during AT. This explanation is currently under investigation, with preliminary results that are in line with the hypothesis.…”