The importance of phase purity in Ni–BaZr_0.85Y_0.15O_3−δcermet anodes – novel nitrate-free combustion route and electrochemical study

Abstract

A novel, nitrate-free, combustion method has been developed to prepare Ni-BaZr 0.85 Y 0.15 O 32d (Ni-BZY) cermet anodes for proton ceramic fuel cells. Nickel acetate and 30% H 2 O 2 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 nitratebased precursors, due to their acidic nature, results in removal of Ba from the perovskite phase and formation of Ba(NO 3 ) 2 , subsequently leading to the presence of BaY 2 NiO 5 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-H 2 O 2 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.

In-situ redox cycling behaviour of Ni–BaZr0.85Y0.15O3−δ cermet anodes for Protonic Ceramic Fuel Cells

“…NiO-BZY anodes (40 vol% Ni) were prepared by dispersing nickel in pre-made BZY by the method of microwave-assisted combustion, using a new acetate-H 2 O 2 based route [15]. The BaZr 0.85 Y 0.15 O 3-δ powder was pre-prepared by mechanosynthesis, as described in the literature [29].…”

“…As such, this factor may lead to lower performance degradation upon alteration of the microstructure (thus, three phase boundary length) during redox cycling. On the other hand, it has also been noted that lower porosity is desirable to obtain peak performance in PCFC anodes (as hydrogen is the only diffusing gas species), in contrast to that of an oxide-ion conducting anode in which water vapour must also counter-diffuse [8,15,27]. This second factor may produce a very serious negative effect on redox cycling stability, as it has been noted that a higher porosity is preferable to minimize bulk volume expansion upon Ni reoxidation in oxide-ion conducting cermets [28].…”

“…Recently, a novel synthesis route to form Ni-BZY cermets and their resultant electrochemical behavior has been documented by the current authors [15]. Our previous studies and further works in the literature, have shown the area specific resistance (ASR) of Ni-BZY to be within the suitable range <1.5 Ω cm 2 for efficient fuel cell operation [7,15].…”

“…Our previous studies and further works in the literature, have shown the area specific resistance (ASR) of Ni-BZY to be within the suitable range <1.5 Ω cm 2 for efficient fuel cell operation [7,15]. The performance of PCFC cermet anodes has been shown to be tailorable by changes in the Ni content, the proton conductivity of the ceramic matrix phase [7] and the porosity [8].…”

“…The content of 40vol%Ni was selected as it represented the lowest Ni content required to ensure percolation [15]. The redox cycles were performed on a Ni-BZY/BCZY/Ni-BZY symmetrical cell, cycling between a 10% H 2 /N 2 gas mixture and an air stream.…”