Improvement in high-temperature thermoelectric properties of NaCo2O4 through partial substitution of Ni for Co

We have prepared polycrystalline Na(Co1−zNiz)2O4 (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 NaNiO2 content. On the other hand, the Ni substitution led to a significant increase in the Seebeck coefficient (α).The calculated power factor (σα2) was substantially improved by the partial substitution of Ni for Co in NaCo2O4. The highest power factor (2.36 × 10− 3Wm− 1K− 2) was obtained for Na(Co0.95Ni0.05)2O4 sample at 1073 K. It is demonstrated that the Ni substitution is highly effective for enhancing high-temperature thermoelectric properties.