No abstract

It has been shown previously that the thermoelectric properties of the Zintl phase compound, YbZn2Sb2 can be finely tuned via substitution at the cationic Yb-site. Here we report the results of the investigation of isoelectronic substitution of Zn by Mn in the anionic (Zn2Sb2)2− framework. The p-type YbZn2−xMnxSb2 (0.0⩽x⩽0.4) samples have been synthesized via a solid-state reaction followed by suitable cooling, annealing, grounding, and hot-pressing densification processes. In samples with x=0.0, 0.05, 0.10, 0.15, 0.2, 0.3, and 0.4, the electrical conductivity, Seebeck coefficient, and thermal conductivity measurements have been performed as a function of temperature from 300to750K. It is found that the Mn substitution effectively lowers the thermal conductivity for all samples, while it significantly increases the power factor for x⩽0.15. As a result, a dimensionless figure of merit ZT of ∼0.61–0.65 has been attained at 726K for x=0.05–0.15 as compared to the ZT of ∼0.48 in the unsubstituted YbZn2Sb2.

Self-assembled and well-aligned nanowires (NWs) of poly­(3-hexyl­thiophenes) (P3HT) embedded within insulating polystyrene (PS) matrix were found to have a high field-effect carrier mobility. We demonstrate that solution shear coating of P3HT-NWs/PS nanocomposites is an effective strategy in aligning P3HT NWs in the presence of PS and has a significant impact on the molecular order, morphology, and consequently charge transport. Shear-coated P3HT-NWs/PS nanocomposites consistently exhibited higher carrier mobilities compared to P3HT NWs or pristine P3HT/PS films by up to 10.2-fold. P3HT-NWs/PS nanocomposites containing only 3 wt % P3HT exhibit a mobility of ∼0.053 cm2 V–1 s–1, which is comparable to that of the 30 wt % P3HT (∼0.064 cm2 V–1 s–1) and even higher than that of 100 wt % P3HT (∼0.024 cm2 V–1 s–1).

Electrocatalytic water splitting is an emerging technique to produce sustainable hydrogen energy. However, it is still challengeable to fabricate a stable, efficient, and cost-effective electrocatalyst that can overcome the sluggish reaction kinetics of water electrolysis. In order to reduce the energy barrier, for the first time, metal−organic framework (MOF)-derived nickel (Ni) and nickel sulfide (NiS) heteronanoparticleembedded semi-MOFs are prepared by a partial sulfurization strategy. These semi-MOF electrocatalysts inherit the advantages associated with MOF architecture and nanoparticles, unlike the traditional OER catalysts such as pristine MOFs or completely pyrolyzed MOFs. Due to the unique nanoarchitecture fabricated by Ni/NiS heteronanoparticles within semi-MOF nanosheets and a carbon nanotube (CNT) network (Ni-M@C-130), it displays exceptional bifunctional activity over the other transition metalbased electrocatalysts ever reported. It requires very small overpotentials for both oxygen evolution reaction (OER; η 10 = 244 mV) and hydrogen evolution reaction (HER; η 10 = 123 mV), with low Tafel slopes of 47.2 and 50.8 mV/dec, respectively. Furthermore, it exhibits overpotential as low as 1.565 V (η 10 ) on nickel foam (1 mg/cm 2 ) substrates for overall water splitting. The outstanding catalytic performance of Ni-M@C-130 is attributed to the combined benefits of MOF nanosheets, synergistic interactions, and improved electrical conductivity and mechanical stability. This study describes the advantages of partial sulfurization of CNT-integrated MOFs in attaining electrochemically active heteronanoparticles within MOF nanosheets to accomplish improved bifunctional activity.