Low efficiency and poor stability are two major challenges we encounter in the exploration of non-noble metal electrocatalysts for the hydrogen evolution reaction (HER) in both acidic and alkaline environment. Herein, the hybrid of cobalt encapsulated by N, B codoped ultrathin carbon cages (Co@BCN) is first introduced as a highly active and durable nonprecious metal electrocatalysts for HER, which is constructed by a bottom-up approach using metal organic frameworks (MOFs) as precursor and self-sacrificing template. The optimized catalyst exhibited remarkable electrocatalytic performance for hydrogen production from both both acidic and alkaline media. Stability investigation reveals the overcoating of carbon cages can effectively avoid the corrosion and oxidation of the catalyst under extreme acidic and alkaline environment. Electrochemical active surface area (EASA) evaluation and density functional theory (DFT) calculations revealed that the synergetic effect between the encapsulated cobalt nanoparticle and the N, B codoped carbon shell played the fundamental role in the superior HER catalytic performance.

Thermoelectrics interconvert heat to electricity and are of great interest in waste heat recovery, solid-state cooling and so on. Here we assessed the potential of SnS2 and SnSe2 as thermoelectric materials at the temperature gradient from 300 to 800 K. Reflecting the crystal structure, the transport coefficients are highly anisotropic between a and c directions, in particular for the electrical conductivity. The preferred direction for both materials is the a direction in TE application. Most strikingly, when 800 K is reached, SnS2 can show a peak power factor (PF) of 15.50 μW cm(-1) K(-2) along the a direction, while a relatively low value (11.72 μW cm(-1) K(-2)) is obtained in the same direction of SnSe2. These values are comparable to those observed in thermoelectrics such as SnSe and SnS. At 300 K, the minimum lattice thermal conductivity (κmin) along the a direction is estimated to be about 0.67 and 0.55 W m(-1) K(-1) for SnS2 and SnSe2, respectively, even lower than the measured lattice thermal conductivity of Bi2Te3 (1.28 W m(-1) K(-1) at 300 K). The reasonable PF and κmin suggest that both SnS2 and SnSe2 are potential thermoelectric materials. Indeed, the estimated peak ZT can approach 0.88 for SnSe2 and a higher value of 0.96 for SnS2 along the a direction at a carrier concentration of 1.94 × 10(19) (SnSe2) vs. 2.87 × 10(19) cm(-3) (SnS2). The best ZT values in SnX2 (X = S, Se) are comparable to that in Bi2Te3 (0.8), a typical thermoelectric material. We hope that this theoretical investigation will provide useful information for further experimental and theoretical studies on optimizing the thermoelectric properties of SnX2 materials.

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Infrared nonlinear optical (IR-NLO) crystals possessing excellent comprehensive performance are highly desirable, yet their preparation remains extremely challenging. Particularly, inorganic chalcogenides with diamond-like (DL) structures provide a tunable material platform for their structural design and functional control. In this work, a strategy involving the construction of chalcogenides with DL structures using the strong polarizability of metal cations has been put forward; thus, a quaternary Hg-containing metal sulfide HgCuPS 4 has been successfully discovered by the high-temperature solid-state technology. A remarkable structural characteristic of HgCuPS 4 is the three-dimensional (3D) defect DL framework constructed by vertex-sharing alignments of asymmetric building motifs (ABMs). The combination of the unique defect DL structure and the strong polarizability of the Hg 2+ cations enables such compound to achieve phase matchability in the IR range with a high laser-induced damage threshold (4.2 × AgGaS 2 ) and a strong second harmonic generation response (d ij = 6.5 × AgGaS 2 ), the best among the quaternary DL chalcogenides reported so far. Moreover, the detailed local dipole moment calculations and the theoretical results based on the length-gauge formalism elucidate that the very high d ij value of HgCuPS 4 originates from the combined effects of distorted [HgS 4 ], [CuS 4 ], and [PS 4 ] ABMs, that is, the 3D defect DL structure. This discovery can effectively help understand and design other promising defect DL metal chalcogenides toward future high-performing IR-NLO applications.

A novel niobium oxyiodate sulfate, Nb2O3(IO3)2 (SO4), was fabricated by a rational multi‐component design under moderate hydrothermal conditions. This multi‐component design is inspired by an interesting niobium oxysulfate reaction, which opens a new door for synthetic method to effectively introduce refractory metals such as Nb into crystal structures by hydrothermal synthesis. Nb2O3(IO3)2(SO4) features a cube‐like topological structure with a large phase‐matching second harmonic generation (SHG) response (6×KDP), a wide transparency window (0.38–8 μm), and a high laser damage threshold (LDT) (20×AgGaS2). It has the highest thermostability (stable up to 580 °C under air) among reported non‐centrosymmetric (NCS) iodates and sulfates and is stable in water and even concentrated H2SO4. Furthermore, Nb2O3(IO3)2(SO4) is a unique nonlinear optical (NLO) material among iodates and sulfates, because its SHG effect is mainly caused by the MO6 units rather than the IO3 or SO4 units, which is demonstrated by density functional theory (DFT) calculations.

The generation of clean and sustainable hydrogen fuel through water splitting demands efficient and robust earth-abundant catalysts for the hydrogen evolution reaction (HER). A new hybrid, which was fabricated by incorporating molybdenum carbide (Mo x C) nanoparticles into a nitrogen-implanted three-dimensional carbon matrix (MoCN-3D), was developed as a highly active and durable nonprecious metal electrocatalyst for HER. The porous architecture of MoCN-3D can provide continuous mass transportation with a minimal diffusion resistance and thus produce effective electrocatalytic kinetics in both acidic and alkaline media. Experimental observations in combination with density functional theory calculations reveal that the effective coupling between molybdenum carbide nanoparticles and the carbon matrix, as well as N hybrid coordination, can modify the electronic Fermi level of the final hybrid, which synergistically reduces the proton adsorption and the reduction barrier during electrocatalytic HER.

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Nonlinear optical (NLO) materials have received unprecedented attention owing to their capability of frequency conversion in the photoelectric fields. Yet, how to acquire a crystal with a noncentrosymmetric (NCS) structure is still a grand challenge for the NLO material. Herein, a new quaternary NCS oxychalcogenide, SrGeOSe 2 , was successfully designed and synthesized using the known centrosymmetric SrGeO 3 as a maternal structure through a generic partial isovalent anion substitution (PIAS) strategy. SrGeOSe 2 belongs to the NCS space group P2 1 2 1 2 1 (no.19) and features a one-dimensional (1D) chain made by heteroligand [GeO 2 Se 2 ] asymmetric building units. Such a new compound exhibits desirable comprehensive performance, which suggests a promising IR-NLO material: type-I phase-matching feature, strong powder second-harmonic generation intensity (d ij = 1.3 × commercial AgGaS 2 ), and giant powder laser-induced damage threshold (36 × commercial AgGaS 2 ). Furthermore, the systematic theoretical investigations have been performed for the deep understanding of the correlation between the NCS structure and the NLO property. More importantly, this work pioneers a new molecular engineering strategy for NCS compounds that could be extended to other NLO materials.