Improvement in high-temperature thermoelectric properties of NaCo 2O 4 through partial substitution of Ni for Co

Abstract

We have prepared polycrystalline Na(Co 1−zNi z) 2O 4 (0 ≤ z ≤ 0.25) samples using a solid-state reaction process and investigated the Ni substitution effect on the high-temperature thermoelectric properties. With the Ni substitution, the electrical conductivity ( σ) decreased mainly because of a decrease in both density and grain size as well as an increase in NaNiO 2 content. On the other hand, the Ni substitution led to a significant increase in the Seebeck coefficient ( α).The calculated power factor ( σα 2) was substantially improved by the partial substitution of Ni for Co in NaCo 2O 4. The highest power factor (2.36 × 10 − 3 Wm − 1 K − 2 ) was obtained for Na(Co 0.95Ni 0.05) 2O 4 sample at 1073 K. It is demonstrated that the Ni substitution is highly effective for enhancing high-temperature thermoelectric properties.