In the present work, we demonstrate crystallographically textured n-type BiTeSe nanomaterials with exceptional thermoelectric figures of merit produced by consolidating disk-shaped BiTeSe colloidal nanocrystals (NCs). Crystallographic texture was achieved by hot pressing the asymmetric NCs in the presence of an excess of tellurium. During the hot press, tellurium acted both as lubricant to facilitate the rotation of NCs lying close to normal to the pressure axis and as solvent to dissolve the NCs approximately aligned with the pressing direction, which afterward recrystallize with a preferential orientation. NC-based BiTeSe nanomaterials showed very high electrical conductivities associated with large charge carrier concentrations, n. We hypothesize that such large n resulted from the presence of an excess of tellurium during processing, which introduced a high density of donor Te antisites. Additionally, the presence in between grains of traces of elemental Te, a narrow band gap semiconductor with a work function well below BiTeSe , might further contribute to increase n through spillover of electrons, while at the same time blocking phonon propagation and hole transport through the nanomaterial. NC-based BiTeSe nanomaterials were characterized by very low thermal conductivities in the pressing direction, which resulted in ZT values up to 1.31 at 438 K in this direction. This corresponds to a ca. 40% ZT enhancement from commercial ingots. Additionally, high ZT values were extended over wider temperature ranges due to reduced bipolar contribution to the Seebeck coefficient and the thermal conductivity. Average ZT values up to 1.15 over a wide temperature range, 320 to 500 K, were measured, which corresponds to a ca. 50% increase over commercial materials in the same temperature range. Contrary to most previous works, highest ZT values were obtained in the pressing direction, corresponding to the c crystallographic axis, due to the predominance of the thermal conductivity reduction over the electrical conductivity difference when comparing the two crystal directions.

IntroductionCVD synthesis of graphene on catalytically-active substrates has emerged as the most promising approach for large-area production of graphene [1] . The self-limiting nature of CVD growth on metals such as copper (Cu) and platinum allows synthesis of large-scale homogeneous films of monolayer graphene. However, electrical characterization of polycrystalline samples of CVD graphene reveals that the presence of grain boundaries causes significant degradation of the electric performance, compared to pristine material obtained by mechanical exfoliation of flakes [2] . As demonstrated initially by Petrone et al [3] , samples fabricated using single-crystals of CVD graphene can have electrical performance comparable to that of exfoliated flakes [4] . Furthermore, recent reports have shown that by fully encapsulating CVD graphene with suitable materials such as hexagonal boron nitride (h-BN), low-temperature charge carrier mobility above 300 000 cm 2 / V s [5] or even 3 000 000 cm 2 / V s [6] can be achieved.Over the last few years the synthesis of large-crystal graphene has attracted a huge scientific interest, with significant advances in the achievable crystal size [7][8][9][10] . Recent work has reported single-crystals of graphene measuring 1 cm [10] and, using copper/nickel alloy as the growth substrate, even 4 cm [11] . Inevitably, these approaches still produce randomlydistributed crystals of graphene, which limits their applicability to scaled production of graphene devices. Furthermore, the commonly-used transfer methods either allow scalability while introducing significant performance degradation, or are limited to transferring areas of several tens of µm 2 [5] .For many applications the size of individual graphene devices is limited to tens or hundreds of microns, easily achievable by the current methods of single-crystal synthesis, however, ran-dom spatial distribution of graphene crystals in such samples makes polycrystalline graphene preferable for wafer-scale integration. This issue could be mitigated by selectively predetermining the nucleation sites for graphene crystals according to the target architecture, which could allow the fabrication of large and complex circuits utilising completely monocrystalline graphene. Patterned growth using polymer-based nucleation seeds was first reported by Wu et al [12] , however, only high-density arrays of 10-20 µm crystals were demonstrated. Arrays of similar dimensions were recently presented by Song et al, using poly(methyl methacrylate) (PMMA) seeds to nucleate graphene on top of CVD-grown h-BN [13] .In this work we present a method to selectively pattern the Cu growth substrate using chromium (Cr) nucleation seeds, which allows deterministic nucleation of large-crystal graphene, measuring several hundred microns. The nucleation density is highly-controlled by the combined use of natively oxidised Cu foils, non-reducing annealing and sample enclosure [14] , and measuring as low as 10 crystals per mm 2 . We also demonstrate a clean semi-dry tran...

Lithium–sulfur batteries (LSBs) are considered to be one of the most promising next generation energy storage systems due to their high energy density and low material cost. However, there are still some challenges for the commercialization of LSBs, such as the sluggish redox reaction kinetics and the shuttle effect of lithium polysulfides (LiPS). Here a 2D layered organic material, C2N, loaded with atomically dispersed iron as an effective sulfur host in LSBs is reported. X‐ray absorption fine spectroscopy and density functional theory calculations prove the structure of the atomically dispersed Fe/C2N catalyst. As a result, Fe/C2N‐based cathodes demonstrate significantly improved rate performance and long‐term cycling stability. Fe/C2N‐based cathodes display initial capacities up to 1540 mAh g−1 at 0.1 C and 678.7 mAh g−1 at 5 C, while retaining 496.5 mAh g−1 after 2600 cycles at 3 C with a decay rate as low as 0.013% per cycle. Even at a high sulfur loading of 3 mg cm−2, they deliver remarkable specific capacity retention of 587 mAh g−1 after 500 cycles at 1 C. This work provides a rational structural design strategy for the development of high‐performance cathodes based on atomically dispersed catalysts for LSBs.

SnSe has emerged as one of the most promising materials for thermoelectric energy conversion due to its extraordinary performance in its single-crystal form and its low-cost constituent elements. However, to achieve an economic impact, the polycrystalline counterpart needs to replicate the performance of the single crystal. Herein, we optimize the thermoelectric performance of polycrystalline SnSe produced by consolidating solution-processed and surface-engineered SnSe particles. In particular, the SnSe particles are coated with CdSe molecular complexes that crystallize during the sintering process, forming CdSe nanoparticles. The presence of CdSe nanoparticles inhibits SnSe grain growth during the consolidation step due to Zener pinning, yielding a material with a high density of grain boundaries. Moreover, the resulting SnSe–CdSe nanocomposites present a large number of defects at different length scales, which significantly reduce the thermal conductivity. The produced SnSe–CdSe nanocomposites exhibit thermoelectric figures of merit up to 2.2 at 786 K, which is among the highest reported for solution-processed SnSe.