Active layer of fuel cell electrode with polymer electrolyte: Nature of proton and oxygen supply channels

Abstract

The nature of proton and oxygen supply channels in the active layer of a cathode of fuel cell with polymer electrolyte is discussed. There are three types of electron, proton, and oxygen carriers in the active layer: agglomerates of carbon particles with supported platinum (support grains), agglomerates of Nafion molecules (Nafion grains), and void grains. In computer simulation of the active layer structure, the three types of grains were assumed equal-sized, cube-shaped and arranged into a cubic node lattice (in the terms of the percolation theory). Impossibility of forming on the basis solely the above three grain types of three percolation clusters (“electron”, “proton”, and “gas”) that could supply all that is required for the electrochemical process is proved. But in this, the following question arises: how can satisfactory operation of the cathode with polymer electrolyte be provided? The required supply of protons and oxygen can be provided only if the support grains can feature not only electronic conductivity, but can also participate in transport of both protons and oxygen. As a result, the transport of protons and oxygen is carried out via special combined percolation clusters that must include apart from the support grains either Nafion grains (combined “proton” cluster) or void grains (combined “gas” cluster). The paper describes the technique of calculation of effective specific conductivity of a combined “proton” cluster. The effective specific diffusion coefficient of a combined “gas” cluster can also be calculated in a similar way.