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Methyl mercaptan (MM) is one kind of volatile sulfur compound (VSC) with odor and properties (inflammable, highly toxic, and corrosive) similar to H2S; therefore, the highly sensitive and selective monitoring of ambient MM by chemiresistors is strongly essential, but it remains a challenge owing to its relatively weak reducibility/response in comparison with H2S. In this study, a novel chemiresistor composed of hexahedral particles SBO-loaded CdS nanoparticles has been prepared via a facile chemical precipitation method for the super-sensitive and highly-selective recognition of MM. The heterostructural CdS/SBO (0.05%) chemiresistor exhibited an extremely high response (114.7) to 100 ppm MM at a relatively low operating temperature (100 °C) and was about 36- and 9-fold higher than pure SBO and CdS chemiresistor, respectively. Various characterizations suggested that the sulfurization–desulfurization reaction, the abundant oxygen vacancies, and the generation of n–n heterojunctions at the interface promote the redox reaction of surface-active substances, thereby, boosting the outstanding MM response characteristics. In addition, the heterostructural chemiresistor possesses good selectivity, weak humidity interference, a lower limit of detection (LoD) of 82 ppb, and long-term stability (∼6% decline of response after 120 days), which promises practical applications in air quality (odor) monitoring. [ABSTRACT FROM AUTHOR]

2D Ti3C2Tx MXene, possessing facile preparation, high electrical conductivity, flexibility, and solution processability, shows good application potential for enhancing device performance of perovskite solar cells (PVSCs). In this study, tetrabutylammonium bromide functionalized Ti3C2Tx (TBAB‐Ti3C2Tx) is developed as cathode buffer layer (CBL) to regulate the PCBM/Ag cathode interfacial property for the first time. By virtue of the charge transfer from TBAB to Ti3C2Tx demonstrated by electron paramagnetic resonance and density functional theory, the TBAB‐Ti3C2Tx CBL with high electrical conductivity exhibits significantly reduced work function of 3.9 eV, which enables optimization of energy level alignment and enhancement of charge extraction. Moreover, the TBAB‐Ti3C2Tx CBL can effectively inhibit the migration of iodine ions from perovskite layer to Ag cathode, which synergistically suppresses defect states and reduce charge recombination. Consequently, utilizing MAPbI3 perovskite without post‐treatment, the TBAB‐Ti3C2Tx based device exhibits a dramatically improved power conversion efficiency of 21.65% with significantly improved operational stability, which is one of the best efficiencies reported for the devices based on MAPbI3/PCBM with different CBLs. These results indicate that TBAB‐Ti3C2Tx shall be a promising CBL for high‐performance inverted PVSCs and inspire the further applications of quaternary ammonium functionalized MXenes in PVSCs. [ABSTRACT FROM AUTHOR]

The structural, electronic, optical, mechanical, lattice dynamics, and electronic transport properties of SrCu2O2 crystals were studied using first-principles calculations. The calculated band gap of SrCu2O2 using the HSE hybrid functional is about 3.33 eV, which is well consistent with the experimental value. The calculated optical parameters show a relatively strong response to the visible light region for SrCu2O2. The calculated elastic constants and phonon dispersion indicate that SrCu2O2 has strong stability in mechanical and lattice dynamics. The deep analysis of calculated mobilities of electrons and holes with their effective masses proves the high separation and low recombination efficiency of photoinduced carriers in SrCu2O2. [ABSTRACT FROM AUTHOR]

Antioxidants are molecules that can prevent the harmful effects of oxygen, help capture and neutralize free radicals, and thus eliminate the damage of free radicals to the human body. Persimmon tannin (PT) has excellent antioxidant activity, which is closely related to its molecular structure. We report here a comparative study of four characteristic structural units from PT (epicatechin gallate (ECG), epigallocatechin gallate (EGCG), A−type linked ECG dimer (A−ECG dimer), A−type linked EGCG dimer (A−EGCG dimer)) to explore the structure–activity relationship by using the density functional theory. Based on the antioxidation mechanism of hydrogen atom transfer, the most favorable active site for each molecule exerts antioxidant activity is determined. The structural parameters, molecular electrostatic potential, and frontier molecular orbital indicate that the key active sites are located on the phenolic hydroxyl group of the B ring for ECG and EGCG monomers, and the key active sites of the two dimers are located on the phenolic hydroxyl groups of the A and D' rings. The natural bond orbital and bond dissociation energy of the phenolic hydroxyl hydrogen atom show that the C11−OH in the ECG monomer and the C12−OH in the EGCG monomer are the most preferential sites, respectively. The most active site of the two A−linked dimers is likely located on the D' ring C20′ phenolic hydroxyl group. Based on computational analysis of quantum chemical parameters, the A−ECG dimer is a more potent antioxidant than the A−EGCG dimer, ECG, and EGCG. This computational analysis provides the structure–activity relationship of the four characteristic units which will contribute to the development of the application of PT antioxidants in the future. [ABSTRACT FROM AUTHOR]

Selective recovery of indium has been widely studied to improve the resource efficiency of critical metals. However, the interaction and selective adsorption mechanism of indium/iron ions with tannin-based adsorbents is still unclear and hinders further optimization of their selective adsorption performance. In this study, the epigallocatechin gallate (EGCG) monomer, which is the key functional unit of persimmon tannin, was chosen to explore the ability and mechanism of selective separation/extraction of indium from indium–iron mixture solutions. The density functional theory calculation results indicated that the deprotonated EGCG was easier to combine with indium/iron cations than those of un-deprotonated EGCG. Moreover, the interaction of the EGCG–Fe(III) complex was dominated by chelation and electrostatic interaction, while that of the EGCG–In(III) complex was controlled by electrostatic interactions and aromatic ring stacking effects. Furthermore, the calculation of binding energy verified that EGCG exhibited a stronger affinity for Fe(III) than that for In(III) and preferentially adsorbed iron ions in acidic or neutral solutions. Further experimental results were consistent with the theoretical study, which showed that the Freundlich equilibrium isotherm fit the In(III) and Fe(III) adsorption behavior very well, and the Fe(III) adsorption processes followed a pseudo-second-order model. Thermodynamics data revealed that the adsorption of In(III) and Fe(III) onto EGCG was feasible, spontaneous, and endothermic. The adsorption rate of the EGCG monomer for Fe(III) in neutral solution (1:1 mixed solution, pH = 3.0) was 45.7%, 4.3 times that of In(III) (10.7%). This study provides an in-depth understanding of the relationship between the structure of EGCG and the selective adsorption capacity at the molecular level and provides theoretical guidance for further optimization of the selective adsorption performance of structurally similar tannin-based adsorbents. [ABSTRACT FROM AUTHOR]

A highly efficient MgBi2O6 (MBO)/TiO2 heterostructured photocatalyst for the evolution of H2 was successfully prepared using a one-step hydrothermal method. The phase structure, microstructure and optical properties of the MBO/TiO2 composites were investigated by various experimental techniques. A series of H2 production experiments were performed under visible light. The measured results indicated that the nanostructured MBO/TiO2 composite, with a stoichiometric molar ratio of MBO:TiO2 = 0.2%, displayed the best H2 production rate of 3413 μmol h−1 g−1. The excellent photocatalytic performance of the obtained composite material was due to the heterojunction formed between MBO and TiO2, which reduced the charge transfer resistance and accelerated the separation efficiency of the photogenerated electron–hole pairs. The reaction mechanism was also discussed in detail. [ABSTRACT FROM AUTHOR]

To improve the ferroelectric photovoltaic characteristic of bismuth sodium titanate-based lead-free ceramics. The B-site Mo-doped Na0.5, Bi0.5 (Ti1-x Mox) O3 (BNT-Mox, the value of x is 0 to 0.02) lead-free ferroelectric ceramic was synthesized by the conventional solid state reaction method. The optical band gap of the ceramic was researched by XRD, Raman spectroscopy, absorption spectroscopy, combining the calculations based on first-principles density functional theory (DFT). The experiment results show that with the increase of the content, the optical band gap decreases firstly and then increases. The minimum value of band gap is 2.33 eV when x = 1% and the maximum value of light absorption intensity is 69%. The DFT calculation results of the band structure and density of states show that the band gap is shifted from indirect to direct mode by the Mo 4d orbit after the Mo doped, and led to the decrease of band gap. There is a competitive relationship between the impurity energy level caused by Mo doping and the Moss-Bolstein effect in band gap regulation, which could control the band structure of BNT effectively. [ABSTRACT FROM AUTHOR]

Hydrogen solubility and diffusivity are the key features of hydrogen permeable membrane materials. To characterize the hydrogen permeation performance of NbTM (TM = W, Ru) phases, their hydrogen diffusion coefficient and solution coefficient, thermodynamic stability and chemical bonding are studied by a series of first principles calculations. The phonon spectra and elastic constants show that NbTM is dynamically stable. The TM–H chemical bonds have an ionic/covalent mixed character and are stronger than the Nb–H bond. The preferential diffusion paths of H in both Nb16H and Nb15TMH are from a tetrahedral interstitial site (TIS) to another TIS. The TM doping in Nb16H lowers the solubility and energy barrier of H diffusion and enhances the H diffusion coefficient (D), with Nb16RuH exhibiting the highest D value for TIS to TIS diffusion (2.14 × 10−8 m2 s−1) at 600 K. This study shows that alloying and temperature could significantly affect the solubility and diffusivity of hydrogen in Nb. Moreover, TM doping could greatly improve the hydrogen diffusion performance with good control of hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

Electronic structure, optical, mechanical, and lattice dynamical properties of the tetragonal MgBi2O6 are studied using a first-principles method. The band gap of MgBi2O6 calculated from the PBE0 hybrid functional method is about 1.62 eV and agrees well with the experimental value. The calculations on elastic constants show that MgBi2O6 exhibits mechanical stability and strong elastic anisotropy. The detailed analysis of calculated optical parameters and effective masses clearly indicate that MgBi2O6 has strong optical response in the visible light region and high separation efficiency of photoinduced electrons and holes. [ABSTRACT FROM AUTHOR]

To investigate Mo doping effects on the hydrogen permeation performance of Nb membranes, we study the most likely process of atomic hydrogen adsorption and diffusion on/into Mo-doped Nb (100) surface/subsurface (in the Nb12Mo4 case) via first-principles calculations. Our results reveal that the (100) surface is the most stable Mo-doped Nb surface with the smallest surface energy (2.75 J/m2). Hollow sites (HSs) in the Mo-doped Nb (100) surface are H-adsorption-favorable mainly due to their large adsorption energy (−4.27 eV), and the H-diffusion path should preferentially be HS→TIS (tetrahedral interstitial site) over HS→OIS (octahedral interstitial site) because of the correspondingly lower H-diffusion energy barrier. With respect to a pure Nb (100) surface, the Mo-doped Nb (100) surface has a smaller energy barrier along the HS→TIS pathway (0.31 eV). [ABSTRACT FROM AUTHOR]

In this paper, we report a careful study of the properties and mechanisms of a 2LiBH4–MgH2 composite with a niobium oxide (Nb2O5) additive. It was found that directly milling with a small amount of the Nb2O5 additive exerted a negligible effect on the dehydrogenation kinetics of the 2LiBH4–MgH2 composite in the first cycle. However the recycled sample showed notable property advantages over the neat 2LiBH4–MgH2 composite. Phase/chemical state analyses and control experiments were conducted to gain insight into the chemical transformation of the Nb-containing species. It was found that the Nb2O5 additive reacted with LiBH4 to form a niobium boride (NbB2) heterogeneous nucleation agent, via a niobium hydride (NbH2) intermediate, in the dehydrogenation process of the composite sample. The retarded formation of the NbB2 is a major mechanistic reason for the observed drastic property change of the composite upon cycling. As a solution, we employed a novel three-step method to controllably promote the formation of the targeted NbB2 species and improve its dispersion state. As expected, the 2LiBH4–MgH2–0.08Nb2O5 composite sample, prepared using the new method, exhibits rapid dehydrogenation kinetics and high cyclic stability, which compare favorably with the literature results of the 2LiBH4–MgH2 composites with transition metal additives. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement causes deterioration of materials used in metal–hydrogen systems. Alloying is a good option for overcoming this issue. In the present work, first-principles calculations were performed to systematically study the effects of adding Ni on the stability, dissolution, trapping, and diffusion behaviour of interstitial/vacancy H atoms of pure V. The results of lattice dynamics and solution energy analyses showed that the V–Ni solid solutions are dynamically and thermodynamically stable, and adding Ni to pure V can reduce the structural stability of various VHx phases and enhance their resistance to H embrittlement. H atoms preferentially occupy the characteristic tetrahedral interstitial site (TIS) and the octahedral interstitial site (OIS), which are composed by different metal atoms, and rapidly diffuse along both the energetically favourable TIS → TIS and OIS → OIS paths. The trapping energy of monovacancy H atoms revealed that Ni addition could help minimise the H trapping ability of the vacancies and suppress the retention of H in V. Monovacancy defects block the diffusion of H atoms more than the interstitials, as determined from the calculated H-diffusion barrier energy data, whereas Ni doping contributes negligibly toward improving the H-diffusion coefficient. [ABSTRACT FROM AUTHOR]

The pyrochlore-type (Sr0.6Bi0.305)2Bi2O7 (SBO), containing Bi3+ and Bi5+ mixed valent states, was recently found to be used as a new visible light responsive photocatalyst. Novel SBO/SnO2 heterostructured composites were synthesized through a facile one-step hydrothermal method. The phase structure, morphology, chemical composition, and optical properties of the obtained samples were characterized by XRD, SEM, TEM, XPS, and UV-vis DRS. Compared to pure SBO and SnO2, the synthesized SBO/SnO2 composites exhibited significantly enhanced photocatalytic efficiency. The results indicated that the photoinduced holes and superoxide radicals play a dominant role and are the main reactive species during the degradation of Methylene Blue (MB) solution under visible light irradiation. Heterojunctions, formed in samples, directly contribute to the improvement of photocatalytic efficiency of SBO/SnO2 composites, since it not only broadens the light response range, but also accelerates the separation of photogenerated carriers. [ABSTRACT FROM AUTHOR]

The pyrochlore-type (Sr0.6Bi0.305)2Bi2O7 (SBO) containing Bi3+ and Bi5+ mixed valent states was first investigated as a photocatalyst in our very recent work. To further improve the photocatalytic performance, AgBr/SBO heterostructured composites were synthesized by using a deposition-precipitation method. The characterization of phase structure, morphology, microstructure, elemental composition, and optical properties of the obtained products were performed using X-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM)TEM, X-ray photoelectron spectroscopy (XPS), UV-visible diffuse reflectance spectroscopy (UV-vis DRS). The photocatalytic activity of samples was evaluated by degrading methylene blue under visible light illumination. AgBr/SBO composites possess high stability and significantly enhanced photocatalytic performance. The improvement of photocatalytic activity is due to the enhanced light absorption and the separation of photoinduced electrons and holes on the interface of AgBr/SBO heterostructured composites. [ABSTRACT FROM AUTHOR]

The group VB metals (V, Nb, Ta) are referred to as one of the most valuable hydrogen separation membrane materials because of their advantages over Pd. To evaluate the hydrogen-permeation performance of the three metals, their structure stability, H-solubility, H-diffusivity, H-permeability, and elastic stiffness tensors have been investigated using the first-principles method. Our results reveal that the tetrahedral interstitial site (TIS) is favorable position for H-occupying, but mainly because H-solution enthalpy is the lowest. H-diffusion coefficient follows the order of V > Nb > Ta, H-permeability and H-permeation flux follow the order of Nb > V > Ta. The attractive interactions between H atoms are weak, so it is impossible to form H 2 molecules inside the metals, and all metal hydride phases present good ductility. The calculated Debye temperature is basically consistent with the experimental value. These results provide fundamental data for the further design of alloy membranes based on VB metals. • H-permeation in VB metals (V, Nb, Ta) was systematically studied and compared. • Zero point energy was considered to ensure the accuracy of the calculations. • The preferred adsorption site and diffusion path of H atom was determined. • The calculated results agreed well with literature data. [ABSTRACT FROM AUTHOR]

The 2LiBH 4 –MgH 2 reactive hydride composite is a promising hydrogen storage system due to the combined high hydrogen capacity and relatively moderate reaction enthalpy. However, the sluggish de/rehydrogenation kinetics severely impedes its practical applications. In this study, graphitic carbon nitride (C 3 N 4 ) as a metal-free additive was added to the 2LiBH 4 –MgH 2 composite and examined with respect to the promoting effect on the hydrogen storage properties of the composite. Our study found that mechanically milling with small amount of C 3 N 4 additive can eliminate the incubation period between two dehydrogenation steps and thus markedly enhance the dehydrogenation kinetics of the LiBH 4 –MgH 2 composite. Further cyclic study found that the composite with C 3 N 4 additive exhibits improved cyclic dehydrogenation property although it also shows capacity loss upon cycling, particularly in the second cycle. Combined dehydrogenation property, phase analysis and a series of designed experiments suggested that the C 3 N 4 additive could react with both LiBH 4 and MgH 2 in heating process, and the resulting products may improve the reversible dehydrogenation property of the composite system. [ABSTRACT FROM AUTHOR]

Abstract: In this study, activated carbon (AC) was added to the 2LiBH4–MgH2 composite and examined with respect to its effect on the hydrogen storage properties of the system. Our study found that AC is an effective additive for promoting the reversible dehydrogenation of the 2LiBH4–MgH2 composite. A series of control experiments were carried out to optimize the sample preparation method, milling time and addition amount of AC. In comparison with the neat LiBH4–MgH2 system, the LiBH4–MgH2–AC composite prepared under optimized conditions exhibits enhanced dehydrogenation kinetics, improved cyclic stability and particularly, eliminated incubation period between the two dehydrogenation stages. A combination of phase/microstructure/chemical state analyses has been conducted to gain insight into the promoting effect of AC on the reversible dehydrogenation of the 2LiBH4–MgH2 system. Our study found that AC exerts its promoting effect via tailoring nanophase structure of the 2LiBH4–MgH2 composite. [Copyright &y& Elsevier]

To improve the resistance to hydrogen embrittlement and hydrogen permeation performance of vanadium (V) membranes, first-principles calculations were employed to study the stability, dissolution, and diffusion properties of H in transition metal (M = Mo, W)-doped V membranes, as well as their mechanical and thermodynamic properties, as alternative candidates for H 2 separation. Our results revealed that the doping percentage of Mo/W alloying can significantly improve the mechanical and thermodynamic properties of pure V. The most stable location for adsorbed H atoms is the tetrahedral interstitial site (TIS) in the body-centered cubic structure of the V 1- x M x (x = 0.0625, 0.125, 0.1875, and 0.25) alloys. Additionally, the hydrogen migration path should preferentially follow TIS → nearest-neighbor TIS. An M content of 0.25 yields the best anti-hydrogen embrittlement and the highest hydrogen-diffusion properties. The addition of individual Mo or W as doping elements into the V-based system greatly enhanced the hydrogen diffusion coefficient, and the addition of both Mo and W significantly improved the anti-hydrogen embrittlement of V-based alloys. Our results also showed that hydrogen concentration markedly influenced the solubility and diffusivity of hydrogen in V-based alloy membranes. These results provide a basis for the design of V-based alloy hydrogen permeation membranes. Image 1 • Mo/W-doped V solid solutions present a better mechanical strength. • H-diffusion coefficient of V metal is greatly improved by 25 at.% Mo/W doping. • V 0.5 Mo 0.25 W 0.25 solid solution has a better resistance to H-embrittlement. [ABSTRACT FROM AUTHOR]

The electrochemical performances of Ti 3 C 2 T x MXene are severely restricted by the easy oxidation and restacking. Herein, tannic acid (TA) is introduced into Ti 3 C 2 T x dispersion, and the mixed dispersion is further subjected to a simple hydrothermal treatment to prepare the hydrothermal Ti 3 C 2 T x and TA composite (h-Ti 3 C 2 T x @h-TA). Due to the decomposition of TA into gallic acid (GA), hydrothermal TA (h-TA) is a mixture of TA and GA. The strong interaction between h-TA and MXene mainly involves chemical interaction between the hydroxyl groups in h-TA and the surface/edge Ti atoms, along with numerous hydrogen bonds. The h-TA intercalation weakens MXene restacking and increases interlayer spacing, thereby improving ion transport pathways and accessibility. The chemical interaction between the hydroxyl groups of GA and the Ti atoms significantly enhances oxidation resistance and pseudocapacitive active sites. Therefore, the h-Ti 3 C 2 T x @h-TA film electrode shows significantly enhanced capacitance (848 F·g -1 at 1 A g -1 ) and cycling stability (100% retention after 20 000 cycles). Moreover, flexible sandwiched supercapacitors with symmetrical h-Ti 3 C 2 T x @h-TA electrodes exhibit a high energy density of 30.1 Wh kg -1 at a high power density of 300 W kg -1 , outperforming those of Ti 3 C 2 T x -based film electrodes and sandwiched supercapacitors reported so far. The extrusion-printed microsupercapacitors with h-Ti 3 C 2 T x @h-TA electrodes demonstrate high areal capacitance (135 mF cm -2 at 5 mV s -1 ) along with energy storage performance (6.74 μWh cm -2 at 506 μW cm -2 ) and cycling stability (98.8% retention after 41 460 cycles), all while maintaining excellent flexibility. These impressive results indicate the great application potential of the hydrothermal Ti 3 C 2 T x MXene and tannic acid composite in flexible energy storage devices.

Understanding the mechanism of the insulator-metal transition (IMT) in VO2 is a necessary step in optimising this material's properties for a range of functional applications. Here, Rietveld refinement of synchrotron X-ray powder diffraction patterns is performed on thermochromic V1-xWxO2 (0.0 ≤ x ≤ 0.02) nanorod aggregates over the temperature range 100 ≤ T ≤ 400 K to examine the effect of doping on the structure and properties of the insulating monoclinic (M1) phase and metallic rutile (R) phase. Precise measurement of the lattice constants of the M1 and R phases enabled the onset (Ton) and endset (Tend) temperatures of the IMT to be determined accurately for different dopant levels. First-principles calculations reveal that the observed decrease in both Ton and Tend with increasing W content is a result of Peierls type V-O-V dimers being replaced by linear W-O-V dimers with a narrowing of the band gap. The results are interpreted in terms of the bandwidth-controlled Mott-Hubbard IMT model, providing a more detailed understanding of the underlying physical mechanisms driving the IMT as well as a guide to optimising properties of VO2-based materials for specific applications.

First-principles calculations and the method of climbing-image nudged elastic band were used to investigate the effects of Mo alloying on the structural stability, mechanical properties, and hydrogen-diffusion behavior in the Nb 16 H phase. The Nb 12 Mo 4 H phase (26.5 at% Mo) was found to be the most thermodynamically stable structure, with a low Δ H f value (-0.26 eV) and high elastic modulus. Calculations revealed that the tetrahedral interstitial site (TIS) was the predominant location of H in both Nb 16 H and Nb 12 Mo 4 H phases. The calculated H-diffusion energy barrier and the diffusion coefficient of the Nb 12 Mo 4 H phase were 0.153 eV and 5.65 × 10 -6 cm 2 s -1 (300 K), respectively, which suggest that the addition of Mo would lead to a lower energy barrier and high diffusion coefficients for the Nb 16 H phase, thus improving the hydrogen-permeation properties of Nb metal., Competing Interests: None., (This journal is © The Royal Society of Chemistry.)

Changes in the stability, hydrogen diffusion, and mechanical properties of the NbH phases from Ni-doping was studied by using first-principles methods. The calculation results reveal that the single H atom adsorption is energetically favorable at the tetrahedral interstitial site (TIS) and octahedral interstitial site (OIS). The preferred path of H diffusion is TIS-to-TIS, followed by TIS-to-OIS in both Nb 16 H and Nb 15 NiH. Ni-doping in the Nb 15 NiH alloy lowers the energy barrier of H diffusion, enhances the H-diffusion coefficient (D) and mechanical properties of the Nb 16 H phase. The value of D increases with increasing temperature, and this trend due to Ni doping clearly becomes weaker at higher temperatures. At the typical operating temperature of 400 K, the D value of Nb 15 NiH (TIS) is about 1.90 × 10 -8  m 2 /s, which is about 80 times higher than that of Nb 16 H (TIS) (2.15 × 10 -10  m 2 /s). Our calculations indicated that Ni-doping can greatly improve the diffusion of H in Nb.

Optical and synchrotron x-ray diffraction diamond anvil cell experiments have been combined with first-principles theoretical structure predictions to investigate mixtures of N2 and H2 up to 55 GPa. Our experiments show the formation of structurally complex van der Waals compounds [see also D. K. Spaulding et al., Nat. Commun. 5, 5739 (2014)] above 10 GPa. However, we found that these NxH (0.5 < x < 1.5) compounds transform abruptly to new oligomeric materials through barochemistry above 47 GPa and photochemistry at pressures as low as 10 GPa. These oligomeric compounds can be recovered to ambient pressure at T < 130 K, whereas at room temperature, they can be metastable on pressure release down to 3.5 GPa. Extensive theoretical calculations show that such oligomeric materials become thermodynamically more stable in comparison to mixtures of N2, H2, and NH3 above approximately 40 GPa. Our results suggest new pathways for synthesis of environmentally benign high energy-density materials. These materials could also exist as alternative planetary ices.