Life tests of a skutterudites thermoelectric unicouple (MAR-03)

Life tests of a skutterudites unicouple (MAR-03) comprised of CeFe_3.5Co_0.5Sb₁₂ P-leg and CoSb₃ N-leg are performed. The tests, which are performed in argon at 0.051-0.068 MPa to suppress the antimony (Sb) sublimation from the N- and P-legs near the hot shoe, lasted for 450 hours, of which 261 hours at constant hot and cold junction temperatures of 973 K and 300 K, respectively. The open-circuit voltage, V_oc (or Seebeck coefficient), and peak electric power, P_e,peak, decreased linearly from 203.6 mV and 671 mWe to 183.9 mV and 502 mWe, respectively, in 261 hours of cumulative testing. While the peak efficiency, η_peak based on the measured voltage-current (V-I) characteristics and assuming zero side heat losses also decreased linearly from 10.3% after 24 hrs to 9.35% after 259 hrs of commutative testing. The estimated actual efficiency is lower, 7.32% and 3.83%, respectively, due to side heat losses. Ongoing tests confirmed present results and showed that the decrease in Seebeck coefficient of P-Leg levels off after 460-500 hours of testing, while that of the N-leg experiences little change. Post-tests examination showed only minimal losses of Sb from the N- and P-legs.