This work presents a novel approach of dramatically increasing the energy conversion efficiency of thermoelectric CaMnO 3−δ ceramics through the combination of lattice dopants substitution and secondary phase segregation at the grain boundaries. The oxide ceramic samples are with the nominal composition of Ca 1−x Bi x MnCu y O 3−δ (x = 0, 0.02, 0.03; y = 0.02, 0.04). When Cu is introduced into the Ca 1−x Bi x MnCu y O 3−δ samples, the grain growth from Bi-doped CaMnO 3−δ grains is accompanied by the limited solubility of Cu ions in the grain interior, whereas Cu mainly formed a CuO secondary phase at the grain boundaries. Cu nonstoichiometry addition subsequently resulted in the increase of the Seebeck coefficient and decrease of electrical resistivity simultaneously. The sample with designed chemistry of Ca 2.97 Bi 0.03 MnCu 0.04 O 3−δ exhibits the power factor of 2.4 mW m −1 K −2 at 337 K and figure of merit ZT of 0.67 at 773 K. This ZT of 0.67 is by far the highest ZT reported for various perovskites oxide ceramics. Such enhancements in electrical power factor and the overall ZT are attributed to the synergistic effect of decreasing the carrier concentration to increase the Seebeck coefficient and simultaneously increasing the carrier mobility through the existence of CuO phase at the grain boundaries.
The sluggish oxygen reduction reaction (ORR) in the cathode is hindering the power density of solid oxide fuel cells (SOFCs). Infiltration of catalyst into the cathode of SOFCs is promising to accelerate the ORR. However, the degradation associated with the coarsening of the nanocatalyst is intense. To stabilize the catalyst, atomic layer deposition (ALD) is employed to coat a dual electrocatalyst consisting of a superjacent 2 nm CoO x layer and superjacent 3 nm discrete Pt particles into the porous lanthanum strontium manganite (LSM)/yttria-stabilized zirconia (YSZ) cathode. After 504 h of operation at 750 °C, the ALD coating resulted in the peak power density enhancement by ∼200%, while CoO x becomes Mnenriched (MnCo)O x nanograins coupling with nano-Pt. The Pt/(MnCo)O x nanocouplings are uniformly distributed on the YSZ grain surface, triple-phase boundaries, and at LSM/LSM surface grain boundaries. This study demonstrates an effective approach of stabilizing the minute amount of catalyst for enhancing ORR activity at elevated temperatures.
The impact of the non-stoichiometric addition of potassium (K) on the nanostructure and thermoelectric performance of misfit layered calcium cobaltite (Ca3Co4O9) ceramics is reported.
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