Ni-Co-S/CA composite aerogels were prepared by hydrothermal method using bacterial cellulose-derived carbon aerogels (CA) as support. The microstructure and properties of the composites were adjusted via adding trace vanadium. The characterization results show that the main phase of Ni-Co-S is NiCo₂S₄ with the secondary phase of NiS₂. With the increment of the nickel-cobalt salt concentration, the load amount increases, and the peak current density of electrocatalysis firstly upgraded and then degraded. After being doped with a small amount of vanadium at lower nickel-cobalt salt concentration, Ni-Co-S transforms from spherical particles with high crystallinity to square particles with low crystallinity, and its electrocatalytic activity and stability are improved. Under the preparative conditions of 0.01 mol/L total concentration of nickel-cobalt salt and 3mol% vanadium salt, the as-obtained electrode exhibits the optimal catalytic performance for methanol oxidation. Compared with the sample without V doping, its peak current density (78.1 mA/cm ²) enhanced by 45.7% at least. The Ni-Co-S/CA composite aerogel electrodes with the advantages of light weight and high porosity, is expected to be applied in portable direct methanol fuel cell.

Proton conducting oxide BaCe_0.7Zr_0.1Y_0.2O_3-d (BCZY7) was synthesized by high temperature solid-state reaction method, which crystal structure and microstructure morphology were characterized. The anode-supported button solid oxide fuel cell (SOFC), NiO-BCZY7/BCZY7/La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ(LSCF)-BCZY7, was fabricated by combining the dip-coating and co-sintering processes. It operated by using H₂ (containing 3vol% H₂O) as fuel and ambient air as oxidant. The maximum power density of the cell reaches 203, 123 and 92 mW×cm^-2 at 600, 550 and 500 ℃, respectively. However, traditional SOFCs based on (ZrO₂)_0.92(Y₂O₃)_0.08 electrolyte usually display only tens of milliwatts output per unit area at 600 ℃. Proton conducting electrolyte greatly improves the low and medium temperature performance of SOFCs and provides a promising solution to reduce SOFCs’ operating temperature.

Flexible thermoelectric devices have received a great deal of interest due to their capability of direct convert human body heat into electrical energy. In this work, we synthesized the tellurium nanowires by using hydrothermal method. The effects of hydrothermal temperature and reducibility of the reaction solution (with or without ascorbic acid) on morphology and thermoelectric properties of tellurium nanowires were investigated. Compared to the nanowires prepared in strong reducing solution, those prepared in relatively weak reducing solution (without ascorbic acid) reveal a higher aspect ratio up to 200 and the as-assembled film exhibits better electrical conductivity up to 26 S·m^-1. It is also found that the wet-press method can enhance the micro-densification of the film, resulting in a tighter connection among the micro-nanowires. Therefore, the carrier mobility and carrier concentration of the tellurium nanowire film are significantly increased. As a result, its electrical conductivity is improved by 18.3 times, reached 476 S?m^-1. Simultaneously the optimal tellurium nanowire film exhibits good performances including Seebeck coefficient (282.9 μV?K^-1) and power factor (38 μW?m^-1?K^-2).

Solid solutions forming and doping is an effective approach to optimize the transport properties of thermoelectric materials. In this study, a series of single-phase Mo_1-xW_xSeTe (0≤x≤0.5) solid solutions and their Nb-doped products were successfully synthesized with solid-state reaction followed by rapid sintering utilizing a Plasma Assisted Sintering apparatus. Thermoelectric transport studies showed that the carrier concentration, carrier mobility, electrical conductivity and power factor of the Nb_2yMo_0.5-yW_0.5-ySeTe solid solutions were significantly increased by W substitution and Nb doping, while their lattice thermal conductivity was reduced, leading to remarkably enhanced dimensionless figure of merit ZT. The simultaneous increment of carrier density and carrier mobility with the increasing Nb content is due to the transition from discrete energy levels to continuous impurity band through Nb doping. The study of anisotropy indicated that, Nb_2yMo_0.5-yW_0.5-ySeTe solid solutions owned a higher ZT value along the //P direction as a result of the lower lattice thermal conductivity. The Nb_0.03Mo_0.485W_0.485SeTe compound presented the highest ZT values among all samples, which were 0.31 and 0.36 (@823 K) along the ⊥p and //P directions, respectively, representing one of the best results based on MoSe₂-based materials. The enhancement of the Seebeck coefficient and the power factor is expected to further improve the ZT values of MoSe₂-based compounds by optimizing the doping elements.

As a new promising thermoelectrical material in the range of intermediate temperature, BiCuSeO attracts much attention due to the combination of low intrinsic thermal conductivity and relatively high Seebeck coefficient. In this study, the effects of substituting variable-valence rare-earth element Eu for Bi site on the microstructure and thermoelectric performance of BiCuSeO-based material were investigated. The results indicate that ions of two valence states, Eu²⁺ and Eu³⁺, coexist in the doped BiCuSeO samples. The doping of Eu not only improves the concentration of the carriers, but also modifies the band structure of BiCuSeO matrix, resulting in effective improvement of electrical transport properties. The electrical conductivity of Bi_0.85Eu_0.15CuSeO reaches 98 S·cm^-1 at 823 K, which is 6 times as high as that of the undoped sample. The power factor of 0.32 mW·m^-1·K^-2 and ZT of 0.49 can be achieved at 823 K for Bi_0.975Eu_0.025CuSeO sample. This study shows that the doping of variable-valence rare-earth elements can effectively improve the thermoelectric properties of BiCuSeO.

The resonant levels can be introduced into GeTe by In element, however, the effect of its microstructure on thermoelectric properties still remained unclear. In this study, a series of Ge_1-xIn_xTe samples were prepared by smelting-quenching-annealing combined with spark plasma sintering (SPS). The XRD, SEM, laser thermal conductivity instrument and thermoelectric performance analysis system (ZEM-3) were applied to study the microstructure and thermoelectric properties. Results show that, with the incorporation of In content, the unit cell volume decreases, and Herringbone structure has become smaller and grain boundaries increase, which result in a decrease in the lattice thermal conductivity. Thereby, a minimum thermal conductivity of 2.16 W·m ^-1·K ^-1 is obtained. Meanwhile, In doping introduces the resonant levels and decreases the carrier concentration, so the Seebeck coefficient and the power factor increase. Consequently, the maximum ZT value of 1.15 is obtained in the 0.03 sample at 600 K, which is 26.4% higher than that of GeTe. This indicates that the thermoelectric properties of Ge_1-xIn_xTe can be effectively improved by the microstructure regulation.