Li effects on layer-structured oxide Li_xNi_0.8Co_0.15Al_0.05O_2-δ: Improving cell performance via on-line reaction

Li⁺ plays a critically important role in layer-structured LiNiO₂ family oxides in that it affects the oxidant state of Ni and catalyst's function. Layer-structured Li_xNi_0.8Co_0.15Al_0.05O_2-δ (L_xNCA, x = 1, 1.2, 1.4) with different lithium content was prepared and applicated as both cathode and anode catalysts in symmetrical solid oxide fuel cell (SSOFC) that using samarium doped ceria (SDC) as electrolyte. Excess Li precursor resulted in the formation of Li₂CO₃ in L_1.2NCA and L_1.4NCA materials, whose influence on the performance of L_xNCA was studied. Oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) of L_xNCA as well as its catalytic stability were investigated by impedance spectroscopy. Its ORR process was found to be greatly influenced by the amount of Li in L_xNCA while HOR was less related to Li content. Accompanying the on-line reduction and oxidation of L_xNCA, fuel cells tested under reverse operation condition revealed enormous improvement in P_max, which was due to the significant improvement of ORR process and the reduction of interface resistance.