Degradation of nickel anodes in alkaline fuel cells

Alkaline fuel cells (AFC) are an interesting alternative to polymer electrolyte fuel cells (PEFC), especially AFCs need neither expensive electrolytes nor expensive noble metal catalysts. For using of AFCs long-term stability of the components is decisive, in particular the stability of the electrodes, because the electrolyte can be easily exchanged. The long-term behavior of AFC anodes was investigated electrochemically by measuring U–i curves. The electrodes consisting of a mixture of a nickel catalyst, which is formed from an aluminium–nickel alloy by dissolving the aluminum, polytetrafluorethylene (PTFE) as organic binder and with added copper powder, rolled onto a metal web. In addition, these electrodes were characterized physically after different operation times by X-ray photoelectron spectroscopy (XPS), porosimetry measurements by nitrogen adsorption, scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The electrochemical performance decreases with operating time. The decrease of the electrochemical performance can be described by combination of two exponential functions with different time constants. The physical characterization shows that the PTFE in the electrodes partially decomposes and the nickel catalysts disintegrates. The changes of the physical characteristics can be correlated with the electrochemical performance.