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Optimizing the electronic transport properties of thermoelectric compounds is commonly achieved by either donor or acceptor atom doping to increase the conduction of the appropriate carrier type, electrons or holes, respectively. Enhancing carrier mobility and carrier concentration will both lead to optimized electronic properties. In this work the effect of various dopants on the electronic properties of TiNiSn was explored, by modeling the doping of an ideal compound on the Ti-sublattice with acceptor or donor elements. Using ab initio DFT calculations and a set of analytical expressions of transport properties, the temperature dependencies of the electronic properties were calculated, to examine possible n-type or p-type dopants to be used in further experimental studies. [ABSTRACT FROM AUTHOR]

Solid oxide fuel cells are characterized by a high efficiency for converting chemical energy into electricity and fuel flexibility. This research work focuses on developing durable and efficient anodes for solid oxide fuel cells (SOFCs) based on exsolving nickel from the perovskite structure. A-site-deficient La- and Ni-doped strontium titanates (La0.2Sr0.7Ti0.95Ni0.05O3−δ, LSTN) were synthesized using four different techniques and mixed with Ce0.8Gd0.2O2−δ (GDC) to form the SOFC anode. The synthesis routes of interest for comparison included solid-state, sol-gel, hydrothermal, and co-precipitation methods. LSTN powders were characterized via XRD, SEM, TPR, BET and XPS. In situ XRD during reduction was measured and the reduced powders were analyzed using TEM. The impact of synthesis route on SOFC performance was investigated. All samples were highly durable when kept at 0.5 V for 48 h at 800 °C with H2 fuel. Interestingly, the best performance was observed for the cell with the LSTN anode prepared via co-precipitation, while the conventional solid-state synthesis method only achieved the second-best results. [ABSTRACT FROM AUTHOR]

Thermoelectrics enabling a direct conversion of waste heat into useful electricity is widely investigated for renewable energy applications. n-type half-Heusler (HH) MNiSn (M = Ti,Zr,Hf) thermoelectric (TE) elements are known as attractive semiconducting candidates for such purposes. Yet, both electronic and phonon scattering optimization are still required for fulfilling their full potential. In the current research, Ti0.3Zr0.35Hf0.35Ni1.005Sn separating into a main Ti0.3Zr0.35Hf0.35NiSn HH matrix and a minority full-Heusler (FH) Ti0.3Zr0.35Hf0.35Ni2Sn phase is reported. Adverse electronic effects of the metallic FH phase are nearly avoided by its small relative amount and dimension, while maintaining nearly optimal electronic TE performance along with large phonon scattering, minimizing the lattice thermal conductivity. Consequently, a very high maximal TE figure of merit, ZT, of ∼1.04 is obtained, which is among the highest ever reported for n-type MNiSn HH compounds. [ABSTRACT FROM AUTHOR]

Most high-performance thermoelectric materials require either expensive, rare, or toxic elements. By doping TiNiSn, a low-cost, abundant thermoelectric compound, with copper as an n-type donor, some optimization can be performed for such materials. Ti(Ni1-xCux)Sn was synthesized by arc melting followed by heat treatment and hot pressing. The resulting material was analyzed for its phases using XRD and SEM and its transport properties. Cu undoped and 0.05/0.1% doped samples showed no additional phases in addition to the matrix half-Heusler phase, while the 1% copper doping initiated some Ti6Sn5 and Ti5Sn3 precipitation. The transport properties showed that copper acts as an n-type donor while also lowing the lattice thermal conductivity of the materials. the sample containing 0.1% copper showed the best figure of merit, ZT, with a maximal value of 0.75 and an average value of 0.5 through 325–750 K showing a 125% improvement over the undoped sample of TiNiSn. [ABSTRACT FROM AUTHOR]