Electrochemical performance of strontium-doped neodymium nickelate mixed ionic-electronic conductor for intermediate temperature solid oxide fuel cells

The Nd2 -aEuro parts per thousand x Sr (x) NiO4 + delta (x = 0.1-0.5) solid solutions prepared by combustion synthesis are of submicron/superfine crystallite size. The crystal structure estimated by Rietveld analysis reveals increase in space in the rock salt layer on partial replacement of Nd3+ by Sr2+. The transition from negative temperature coefficient to positive temperature coefficient of conductivity is observed at 913 K. The maximum dc conductivity (sigma = 1.3 +/- 0.02 S cm(-1) at 973 K) is obtained for x = 0.2 in Nd2 -aEuro parts per thousand x Sr (x) NiO4 + delta . The low dc conductivity compared with reported (a parts per thousand 100 S cm(-1)) is due to high porosity (low relative density) resulting from agglomeration of submicron crystallites. The variation in the conductivity with Sr content in Nd2 -aEuro parts per thousand x Sr (x) NiO4 + delta is understood on the basis of defect chemistry. The electrochemical properties of the cathode materials are studied using electrochemical impedance spectroscopy at various temperatures and oxygen partial pressures. Nd1.8Sr0.2NiO4 + delta cathode exhibits lowest-area-specific resistance = 0.52 +/- 0.015 Ohm cm(2) at 973 K. At low (< 1,000 Pa), oxygen ion transfer from Nd1.8Sr0.2NiO4 + delta cathode to gadolinium-doped ceria electrolyte is the rate-limiting step, whereas, charge-transfer reaction on the cathode becomes more important at high oxygen partial pressures and temperature (973 K).