Recent progress and future challenges on thermoelectric Zintl materials

Photoreduction of N₂ is among the most interesting and challenging methods for N₂ fixation under mild conditions. In this study, we determined that nitrogen vacancies (NVs) could endow graphitic carbon nitride (g-C₃N₄) with the photocatalytic N₂ fixation ability. Photocatalytic N₂ fixation induced by NVs is free from the interference of other gases. The reason is that NVs could selectively adsorb and activate N₂ because NVs have the same shape and size as the nitrogen atom in N₂. In addition to this, NVs could also improve many other properties of g-C₃N₄ to support photocatalytic N₂ fixation. These new findings could elucidate the design of efficient photocatalysts for photocatalytic N₂ fixation.

Selective photocatalytic N₂ fixation dependent on g-C₃N₄ induced by nitrogen vacancies

Carbon nitride polymers have emerged as a new class of materials for a wide range of applications such as photo- and electro-catalysis, sensors, bioimaging and more due to their chemical, photophysical and catalytic properties as well as their low-price, facile synthesis and high stability under harsh chemical conditions. In this review we begin with a broad overview of carbon-based materials, arriving at the focus of this review, polymeric carbon nitrides (CNs). After a brief overview of applications, we delve into their various synthetic methods, with an emphasis on achieving control on the nanoscale features of this intriguing polymeric semiconductor. The main synthetic pathways include co-polymerization at various stages, templating, an ionothermal pathway and harnessing of supramolecular pre-organization, which are discussed in detail along with CN growth and deposition on substrates. Finally, we give our perspectives on the evolution of this field, the current limitations, and elaboration of achievable control over the chemical composition, the electronic structure and the morphology of this family of materials.

/pdf/polymeric-carbon-nitrides-and-related-metal-free-materials-3koxy773bj.pdf

Polymeric carbon nitrides and related metal-free materials for energy and environmental applications

Facing the increasingly serious energy and environmental crisis, the development of heteronuclear metal-free double-atom catalysts is a potential strategy to realize efficient catalytic nitrogen reduction with low energy consumption and no pollution because it could combine the advantages of flexible active sites in double-atom catalysts while also being pollution-free and have high Faraday efficiency in metal-free catalysts simultaneously. However, according to the existing mechanism, the finite orbits of other nonmetallic atoms, except the boron atom, reduce the possibility of metal-free catalysis and hinder the development of heteronuclear metal-free double-atom catalysts. Herein, we propose a new "capture-backdonation-recapture" mechanism, which skillfully uses the electron capture-backdonation-recapture between boron, the substrate, and other nonmetallic elements to solve the above problems. Based on this mechanism, by means of the first-principle calculations, the material structure, adsorption energy, catalytic activity, and selectivity of 36 catalysts are systematically investigated to evaluate their catalytic performance. B-Si@BP1 and B-Si@BP3 are selected for their good catalytic performance and low limiting potentials of -0.14 and -0.10 V, respectively. Meanwhile, the "capture-backdonation-recapture" mechanism is also verified by analyzing the results of adsorption energy and electron transfer. Our work broadens the ideas and lays the theoretical foundation for the development of heteronuclear metal-free double-atom catalysts in the future.

"Capture-Backdonation-Recapture" Mechanism for Promoting N2 Reduction by Heteronuclear Metal-Free Double-Atom Catalysts.

MBenes, an emerging family of two-dimensional (2D) transition metal borides, have recently been synthesized in experiment and hold great promise for 2D ferromagnets and metal ion batteries. With a well-defined layered structure and outstanding electrical conductivity, MBenes provide an ideal platform for exploring the catalytic behavior of boride surfaces at the atomic level. Herein, we exploit ten kinds of MBenes for electrocatalysis of the N2 reduction reaction (NRR). By comprehensive first-principles calculations, we show that MBenes have high stability in aqueous environments and excellent selectivity toward the NRR against the hydrogen evolution reaction (HER). Intriguingly, both the surface boron and metal atoms of MBenes can serve as the active sites owing to the co-existence of occupied and unoccupied p (d) states for the boron (metal) atoms, while the boron reaction centers provide even superior activity compared to the metal atoms. Moreover, the activity of these 2D borides can be tuned by engineering their work function. Our theoretical results shine light on utilizing metal borides as a new category of non-precious catalysts for nitrogen fixation, and illuminate the fundamental principles for controlling their catalytic performance.

MBenes: emerging 2D materials as efficient electrocatalysts for the nitrogen reduction reaction

The electrocatalytic N2 reduction reaction (NRR) is a very attractive yet challenging route for sustainable NH3 synthesis under ambient conditions, for which efficient catalysts are required due to the highly strong NN bond. In this work, B decorated C9N4 monolayer (B-C9N4) for NRR is studied by using first-principles calculations. It is found that the inert N2 can be sufficiently activated through the electron “acceptance-donation” pattern between N2 and the B dopant. The subsequent N2 reduction prefers the alternating mechanism, and the reduction of *N2 to *N2H is the potential-limiting step with an overpotential of 0.56 V. Furthermore, B-C9N4 exhibits a metallic nature, which can promote charge transfer during the reduction process. The stability of B-C9N4 can be confirmed by the calculated B adsorption energies and the ab initio molecular dynamic simulation. Consequently, owing to its high activity, good electrical conductivity, and excellent stability, B-C9N4 is a promising metal-free N2 reduction catalyst. Our work not only provides an efficient electrocatalyst for NH3 production, but also opens up a promising avenue to develop highly active and robust metal-free catalysts for other applications.

Boron-decorated C9N4 monolayers as promising metal-free catalysts for electrocatalytic nitrogen reduction reaction: a first-principles study

Modulating electronic and optical properties of black phosphorous carbide monolayers by molecular doping

Based on first-principles calculations, the adsorption behaviors of H2, O2, CO, CO2, NH3, NO, and NO2 molecules on the Ge-, As- and Br-doped PtSe2 monolayers are theoretically investigated. The results indicate that it is viable for the dopant atoms to be filled into the Se vacancies under Pt-rich conditions. Ge and As act as p-type dopants, while Br acts as n-type dopant. For the adsorption of molecules, the geometrical structures, adsorption energies, charge transfers and the electronic and magnetic properties of the most stable configurations are presented and discussed. It is found that the Ge-doped PtSe2 monolayers exhibit greatly enhanced sensitivity toward O2, CO, NH3, NO and NO2 molecules and the As-doped PtSe2 monolayers are more sensitive toward O2, NH3, NO and NO2 molecules than the pristine ones. This is evident from large adsorption energies, charge transfers, and obvious changes of the electronic states due to the molecule adsorption. However, Br doping cannot enhance the sensing sensitivity of the PtSe2 monolayer. The possible reason is that when substituting for the Se atom, the doped Br with more 4p electrons and less empty orbitals are already chemically saturated by the two of the three neighboring Pt atoms, and thus lose the ability of charge exchange with the adsorbed molecules. On the contrary, the Ge and As as p-type dopants have sizable empty 4p orbitals near the Fermi level to exchange the electrons with the adsorbed molecules, and thus form strong bonds with them.

https://iopscience.iop.org/article/10.1088/2053-1591/aab4e3/pdf

First-principles study on the gas sensing property of the Ge, As, and Br doped PtSe2

Electronic structure and high thermoelectric properties of a new material Ba3Cu20Te13

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Papers

Boron-decorated C9N4 monolayers as promising metal-free catalysts for electrocatalytic nitrogen reduction reaction: a first-principles study

Modulating electronic and optical properties of black phosphorous carbide monolayers by molecular doping

First-principles study on the gas sensing property of the Ge, As, and Br doped PtSe2

Electronic structure and high thermoelectric properties of a new material Ba3Cu20Te13