Electronic, optical and thermoelectric properties of boron-doped nitrogenated holey graphene

Biotene: Earth-Abundant 2D Material as Sustainable Anode for Li/Na-Ion Battery

Natural ores are abundant, cost-effective, and environmentally friendly. Ultrathin (2D) layers of a naturally abundant van der Waals mineral, Biotite, have been prepared in bulk via exfoliation. We report here that this 2D Biotene material has shown extraordinary Li-Na-ion battery anode properties with ultralong cycling stability. Biotene shows 302 and 141 mAh g-1 first cycle-specific charge capacity for Li- and Na-ion battery applications with ∼90% initial Coulombic efficiency. The electrode exhibits significantly extended cycling stability with ∼75% capacity retention after 4000 cycles even at higher current densities (500-2000 mA g-1). Further, density functional theory studies show the possible Li intercalation mechanism between the 2D Biotene layers. Our work brings new directions toward designing the next generation of metal-ion battery anodes.

Lattice thermal conductivity of 2D nanomaterials: a simple semi-empirical approach

Extracting reliable information on certain physical properties of materials, such as thermal transport, can be computationally very demanding. Aiming to overcome such difficulties in the particular case of lattice thermal conductivity (LTC) of 2D nanomaterials, we propose a simple, fast, and accurate semi-empirical approach for LTC calculation. The approach is based on parameterized thermochemical equations and Arrhenius-like fitting procedures, thus avoiding molecular dynamics or ab initio protocols, which frequently require computationally expensive simulations. As a proof of concept, we obtain the LTC of some prototypical physical systems, such as graphene (and other 2D carbon allotropes), hexagonal boron nitride (hBN), silicene, germanene, binary, and ternary BNC lattices and two examples of the fullerene network family. Our obtained values are in good agreement with other theoretical and experimental estimations, nonetheless, being derived in a rather straightforward way, at a fraction of the usual computational cost.

Progress of Nonmetallic Electrocatalysts for Oxygen Reduction Reactions

As a key role in hindering the large-scale application of fuel cells, oxygen reduction reaction has always been a hot issue and nodus. Aiming to explore state-of-art electrocatalysts, this paper reviews the latest development of nonmetallic catalysts in oxygen reduction reactions, including single atoms doped with carbon materials such as N, B, P or S and multi-doped carbon materials. Afterward, the remaining challenges and research directions of carbon-based nonmetallic catalysts are prospected.

First principles study of thermoelectric performance in pristine and binary alloyed monolayers of noble metals

In search of novel thermoelectric materials, we have investigated the thermoelectric performance of freestanding pristine and binary alloyed monolayers of noble metals (viz. Au, Ag, Cu, Pt) in honeycomb morphology using first principles methods based on density functional theory (DFT) and the non-equilibrium Green's function (NEGF) approach. The requisite electron transmission function is calculated using the TranSIESTA code - a module of the SIESTA package, while its phonon counterpart is obtained using the Phonons module of the python package along with the NEGF utility - PHtrans. Transport is explored along both the armchair (ac) and zigzag (zz) directions. Due to greater transverse length of the unit cell, electron and phonon transport is found to be more in the zz-direction. Among the pristine monolayers, Pt is found to exhibit ferromagnetism as well as the highest thermoelectric efficiency ZT ∼ 8 with an external bias of μ = 0.795 eV. However, alloying brings in a characteristic energy gap in the phononic transmission function, which diminishes the (room-temperature) relative phononic conductance to less than 5% in Pt-containing alloys. Also, monolayers of AuAg and AuCu turn semiconducting, with the former yielding a high Seebeck coefficient of 1264.96 μV K^-1 at μ ∼ -0.055 eV. Moreover, they exhibit an enhanced ZT near the edges of the band gap, with ZT_max as high as 3.74 and 3.05, respectively. Interestingly, the Pt-containing alloyed monolayers also show a ferromagnetic character and hence, a spin-dependent Seebeck effect. In the CuPt monolayer, the bias μ can be tuned to attain an appreciable charge figure of merit Z_cT = 4.80 at μ = 0.58 eV, while a decent spin figure of merit Z_sT = 1.43 at μ = 0.56 eV. Instead, the pristine Pt monolayer shows a much better Z_sT = 5.45 for a bias of μ = 0.785 eV. Nevertheless, the predicted ZT remains smaller than the corresponding alloyed atomic chains in double zigzag topology.

Thermoelectric Properties of Pristine Graphyne and the BN-Doped Graphyne Family

In this paper, we have investigated the thermoelectric properties of BN-doped graphynes and compared them with respect to their pristine counterpart using first-principles calculations. The effect of temperature on the thermoelectric properties has also been explored. Pristine γ-graphyne is an intrinsic band gap semiconductor and the band gap significantly increases due to the incorporation of boron and nitrogen atoms into the system, which simultaneously results in high electrical conductivity, a large Seebeck coefficient, and low thermal conductivity. The Seebeck coefficient for all these systems is significantly higher than that of conventional thermoelectric materials, suggesting their potential in thermoelectric applications. Among all the considered systems, the "graphyne-like BN sheet" has the highest electrical conductance and lowest thermal conductance, ensuring its superiority in thermoelectric properties over the other studied systems. We find that a maximum full ZT of ∼6 at room temperature is accessible in the "graphyne-like BN sheet".

Vacancy tuned thermoelectric properties and high spin filtering performance in graphene/silicene heterostructures

The main contribution of this paper is to study the spin caloritronic effects in defected graphene/silicene nanoribbon (GSNR) junctions. Each step-like GSNR is subjected to the ferromagnetic exchange and local external electric fields, and their responses are determined using the nonequilibrium Green's function (NEGF) approach. To further study the thermoelectric (TE) properties of the GSNRs, three defect arrangements of divacancies (DVs) are also considered for a larger system, and their responses are re-evaluated. The results demonstrate that the defected GSNRs with the DVs can provide an almost perfect thermal spin filtering effect (SFE), and spin switching. A negative differential thermoelectric resistance (NDTR) effect and high spin polarization efficiency (SPE) larger than 99.99% are obtained. The system with the DV defects can show a large spin-dependent Seebeck coefficient, equal to S_s ⁓ 1.2 mV/K, which is relatively large and acceptable. Appropriate thermal and electronic properties of the GSNRs can also be obtained by tuning up the DV orientation in the device region. Accordingly, the step-like GSNRs can be employed to produce high efficiency spin caloritronic devices with various features in practical applications.