The importance of phase purity in Ni–BaZr0.85Y0.15O3−δ cermet anodes – novel nitrate-free combustion route and electrochemical study

Abstract

A novel, nitrate-free, combustion method has been developed to prepare Ni–BaZr_0.85Y_0.15O_3−δ (Ni–BZY) cermet anodes for proton ceramic fuel cells. Nickel acetate and 30% H₂O₂ were used as starting precursors for the combustion reaction into which pre-prepared BZY powders were dispersed. The advantages of this nitrate-free combustion method have been demonstrated by comparison to a more common nitrate/glycine combustion route. The results demonstrate that use of the nitrate-free precursors is essential to avoid partial decomposition of the pre-prepared BZY phase. Employment of the more common nitrate-based precursors, due to their acidic nature, results in removal of Ba from the perovskite phase and formation of Ba(NO₃)₂, subsequently leading to the presence of BaY₂NiO₅ in the final product. The impact of Ni–BZY phase purity on resultant polarisation behaviour has been assessed as a function of water vapour and oxygen partial pressures for electrodes of comparable microstructure. Partial decomposition of the perovskite phase limits performance by increasing the higher frequency polarisation resistance and this phenomenon is suggested to be associated with impaired proton transport in the oxide cermet phase. The novel actetate–H₂O₂ combustion method here described may be of interest for the formation of other ceramic oxide materials, offering economical advantages over more classical nitrate-based combustion routes, as well as significant environmental benefits due to the avoidance of releasing NO_x gases.