Power factor enhancement in NaxCoO2 doped by Bi

• Na0.74−xBixCoO2(0 ⩽ x ⩽ 0.3) have been synthesized and measured.
• Electrical conductivity and Seebeck coefficient increase simultaneously when x ⩽ 0.15.
• The electrical conductivity dramatically increased two times when x = 0.15.
• The Seebeck coefficient dramatically increased 24.6% when x = 0.15.
• The PF at the optimal doping level (x = 0.15) is 3.6 times as large as that of x = 0.00.

Polycrystalline materials of Na0.74−xBixCoO2 (0 ⩽ x ⩽ 0.3) have been prepared by combining solid state reaction with sintering process. The effects of partial substitution of Bi for Na-site on the thermoelectric performance of Na0.74CoO2 have been investigated. The optimal doping level was achieved when x = 0.15, at which the power factor is 3.6 times as large as that of the non-substituted one. The results indicate that the electrical conductivity and Seebeck coefficient of Bi-doped sample (x = 0.15) increase dramatically (two times and 24.6%, respectively) compared with the free-doped sample, which may be attributed to the adjustment of crystal structure and carrier mobility.