Influence of partial substitution of Cu for Co on the thermoelectric properties of NaCo2O4

Cu-substituted Na(Co1−yCuy)2O4 (0 ≤ y ≤ 0.2) polycrystalline samples have been prepared using a solid-state reaction method and their thermoelectric properties studied. The electrical conductivity of Na(Co1−yCuy)2O4 decreased with increasing temperature, indicating metallic behavior. The electrical conductivity (σ) of Cu-substituted Na(Co1−yCuy)2O4 was much higher than that of Cu-free NaCo2O4. In addition, the Seebeck coefficient (α) of Na(Co1−yCuy)2O4 increased with increasing temperature and the Cu substitution led to an increase in the Seebeck coefficient. The power factor (σα2) increased with an increase in temperature and the highest value of power factor (3.08 × 10−3 W m−1 K−2) was attained for Na(Co0.9Cu0.1)2O4 at 1073 K. We demonstrate that the Cu substitution is effective for enhancing thermoelectric properties.