Quantitative Depth Profiling of Biporous Nickel Electrodes by Frequency-Domain Laser-Induced Photoacoustic Spectroscopy

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Abstract
Frequency-domain Photoacoustic Spectroscopy (PAS) was used with a He-Ne laser exciting beam to probe commercially available, powdered and pressed nickel electrodes with dual-porosity profiles. The frequency response of the electrodes was shown to be capable of providing quantitative information about the thermal conductivity and diffusivity of each of the two porous layers, provided the depth of the porosity junction in the electrode bulk is known. The reasonable agreement of the experimental data with a one-dimensional mathematical model of the photoacoustic response from a two-layer, photoacoustically saturated, continuous system indicates that powdered and pressed nickel electrodes behave photoacoustically approximately like a simple continuous composite-layer solid. This conclusion, together with experimental PAS results from uniporous electrodes, emphasizes the high potential of photoacoustic spectroscopy as a nondestructive, depth profiling, analytical technique for the determination of complex porosity profiles in electrodes manufactured for use in electrochemical energy conversion devices, such as fuel cells.