Optimisation of electroless co-deposited solid oxide fuel cell electrodes

Nwosu, Nkem O. E.

Abstract

Research already carried out on the use of the recently patented electroless nickel ceramic codeposition technique as a method of manufacturing solid oxide fuel cell (SOFC) electrodes has thus far indicated that, while functional electrodes can be manufactured by the technique, for optimum performance of the cell, amplification of the ceramic content of the coatings is still required.
By mainly employing external agents such as surface active agents (surfactants) and magnetic fields (in a bid to aid ceramic particle stability), this research focused on the prospect of increasing the ceramic content of cermets co-deposited for use as SOFC electrodes. A total of 137 co-deposited samples were produced from different bath compositions.
As a prelude to the study, the interactions between the ceramic powders used (yttria stabilised zirconia (YSZ) / lanthanum strontium manganate (LSM)) and the medium for the deposition process – the electroless nickel solution, were investigated by zeta potentiometry and ultraviolet-visible spectroscopy techniques. The results obtained from the studies led to a variation of a series of fundamental plating factors such as the ceramic bath loading and particle size of the powders. While the former was found to yield the highest ceramic content in the coating at a bath loading of 50 g/l, variation of latter notably produced mixed results.
With the introduction of surfactants, it was noted that above the surfactant’s (sodium dodecyl sulphate) critical micelle concentration, the incorporation of ceramic particles (YSZ) into the nickel matrix steadily increased to as much as 60 volume %. An inverse relationship was though found to exist between the coating thickness and the surfactant’s bath concentration.
Uniform coatings were found to be associated with low magnetic field strengths while although increased magnetic field strengths positively resulted in the amplification of particle incorporation into the coating, a lack of cohesion between the coating and the substrate – as indicated by coating flake-off, was observed at such strengths. It is suggested that because the magnetic flux was more dominant than the normally ionic plating mechanism, the particles co-deposited under the influence of a high magnetic field were relatively unstable after the coating process.
Since LSM is alkaline in nature this work confirms that future research on the application of electroless nickel ceramic co-deposition as a method of manufacturing SOFC cathodes, be focused on the use of alkaline electroless nickel baths rather than the acidic solutions, which better suite YSZ particles.

Citation

Nwosu, N. O. E. Optimisation of electroless co-deposited solid oxide fuel cell electrodes. (Thesis). Edinburgh Napier University. Retrieved from http://researchrepository.napier.ac.uk/id/eprint/6448

• Thesis Type: Thesis
• Deposit Date: Oct 15, 2013
• Peer Reviewed: Not Peer Reviewed
• Keywords: electroless nickel ceramic codeposition technique; solid oxide fuel cell (SOFC); electrodes; ceramic content; optimal performance; SOFC cathodes
• Public URL: http://researchrepository.napier.ac.uk/id/eprint/6448
• Contract Date: Oct 15, 2013
• Award Date: 2013-06