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Catalytic decomposition of hydrazine monohydrate (N2H4·H2O) represents a promising hydrogen storage/production technology. Nowadays, the development of N2H4 decomposition catalysts is sluggish due primarily to a lack of universal screening rules. Herein, with the aid of first-principles calculations, we identify a reliable descriptor, N2H4 adsorption energy, to properly address N2H4 decomposition kinetics on TM catalysts. Particularly, we extract linear scaling relations between the adsorption energetics of key intermediates, H (and N2H3) vs. NH2 that exert a fundamental limitation on the H2 selectivity of N2H4 decomposition over elementary transition metal catalysts. We propose that catalysts with optimum H2 selectivity may be achieved by independently stabilizing and destabilizing adsorption of H (or N2H3, or both) and NH2, respectively. The disclosed dissociation behaviors of N2H4 and their physical origins are expected to advance the rational design of advanced catalysts for selectively promoting H2 production from N2H4.

Rechargeable zinc-ion batteries (ZIBs) appear to be a promising candidate for large-scale energy storage system because of the abundance and inherent safety of the zinc negative electrode. Despite these benefits, huge polarization caused by the intercalation of multivalent charge carrier Zn2+ into the cathodic hosts remains a long-standing challenge impeding the development of high-performance ZIBs. Herein, we demonstrate the viability of the V2O5 nanorods constructed 3D porous architectures (3D-NRAs-V2O5) as cathode for ZIBs. Notably, the 3D-NRAs-V2O5 can be scaled up to kilo-gram production based on a simple sol-gel reaction followed by an annealing process. The synergic contributions from the 3D porous framework and layered structures of the 3D-NRAs-V2O5 lead a more facile Zn2+ ions (de)intercalation storage process. Consequently, it offers high reversible capacity of 336 mAh g−1 at a high current density of 50 mA g−1 and exhibits excellent long-term cyclic stability with a capacity retention of 85% over 5000 cycles at a high current density of 10 A g−1. Furthermore, the use of various ex-situ characterization techniques and first-principles calculations has successfully unravelled the Zn2+ ions storage mechanism of the 3D-NRAs-V2O5. Besides the excellent electrochemical performance of the 3D-NRAs-V2O5, it can also be easily scaled up based on the simple synthetic protocol, which shows great potential to be practically used for the next-generation large-scale energy storage applications.

The rhenium-based transition metal dichalcogenides (TMDs), as new members in the TMDs family, have raised great interests recently. Due to the anisotropic structure and unique photoelectric properties, they have potential applications for electrochemical energy conversion and storage. In this work, we performed density functional theory (DFT) calculations on pristine 1T′-ReSe2 toward hydrogen evolution reaction (HER). The results indicated that the Gibbs free energy of the 1T′-ReSe2 edge site for HER could be as small as 0.01 eV, superior to other reported TMDs. Experimentally, we developed a strategy to fabricate sub-5 nm sized 1T′-ReSe2 nanoflakes on carbon nanotubes. Such a small size for the nanoflakes brought abundant edge exposure, which boosted the catalytic activity in the HER. Specifically, the 1T′-ReSe2 nanoflakes needed only 23 and 60 mV overpotentials to achieve −1 and −10 mA cm−2 current densities, along with a low Tafel slope of 37 mV dec−1 and a high exchange current density of 0.3 mA cm−2. The edge-rich and layered 1T′-ReSe2 was also explored as an anode for sodium ion battery. The in operando X-ray absorption near edge structure (XANES) technique was applied to investigate the TMD behavior in real-time during the sodiation/desodiation process. The in situ results revealed that the nanosized 1T′-ReSe2 is electrchemically reversible during discharge/charge cycles. The electrochemical test results demonstrated that 1T′-ReSe2 could be a promising anode material for alkaline batteries.

In this paper, van der Waals heterostructures consisting of MX2 (M = Zr, Hf and X = S, Se) monolayers are modeled. The favorable stacking and stability of the modeled monolayer heterostructures are confirmed through binding energy and phonon dispersion calculations. After confirming stability, the electronic and thermoelectric properties of these compounds are explored using the first-principles calculations combined with semiclassical Boltzmann transport theory. It is found that type-II band alignment in ZrS2 HfSe2 facilitates charge separation for optoelectronics and solar energy conversion. All studied heterostructures show remarkably higher electrical conductivity than corresponding monolayers, responsible for large power factor values, especially at 1200 K. These findings indicate that the creation of van der Waals heterostructures from MX2 may be promising for efficient optoelectronic and thermoelectric devices.

Synthesis of high-performance and cost-effective electrocatalysts towards hydrazine electrooxidation is vital to develop the direct hydrazine fuel cell (DHFC) as a viable energy conversion technology. Herein, we report a combined experimental and theoretical study of nickel phosphides (NixP) as promising catalysts for hydrazine electrooxidation. NixP nanowire array supported on a Ni foam (NF) was synthesized by a one-step phosphorization method using hypophosphite as a P-source. Ni12P5 and Ni2P phases are observed as the products of the direct phosphorization of commercial NF under the applied conditions with Ni2P nanoparticles exclusively distributing on the surface of Ni12P5. The NixP/NF catalyst exhibits a synergetic capabilities of exceptionally high activity, excellent durability and nearly 100% selectivity towards the complete electrooxidation of hydrazine in alkaline condition, which is among the best performance reported on hydrazine electrooxidation catalysts. First-principles calculations have been conducted to gain insight into the catalytic mechanism of Ni phosphides towards hydrazine electrooxidation.

Synthesis of high-performance and cost-effective catalysts towards the hydrogen evolution reaction (HER) is critical in developing electrochemical water-splitting as a viable energy conversion technique. For non-precious metal Co- and Ni-based catalysts, hydroxides were found to form on the surface of the catalysts under alkaline environments and benefit the catalytic performance, whereas there is limited systematic study on the explicit influence of hydroxides on the electrocatalytic mechanism and performance of these catalysts. Herein, we report a close correlation observed between the amount of the surface hydroxides formed and the resulting electrocatalytic performance of a Co-Mo-O nanocatalyst through careful comprehensive structural and property characterizations. We found that an appropriate amount of hydroxide can be moderated by simply coating the catalyst surface with carbon shells to optimize the catalytic properties. As a result, a carbon-coated Co-Mo-O nanocatalyst was successfully developed and is among the best reported non-precious HER catalysts with a superior electrocatalytic activity and outstanding durability for the HER under alkaline environment. First-principles calculations were further conducted to probe the nature of the active sites and the role of hydroxides in the Co-Mo-O@C/NF catalyst towards the HER.

Understanding on the photogenerated charge separation from a microscopic level remains a challenge and is highly desirable as it provides a cornerstone for designing high-performance photocatalysts. Herein, facet engineering is chosen as a tool to reveal the relationship between the charge separation/transfer and crystal structure. A series of BiOBr nanosheets with dominantly exposed facets of (001) or (010) as well as different lateral facet exposure ratios are constructed via adjusting pH value during the hydrothermal process. It is found that exposure of anisotropic crystal facets allows the separative transfer of photogenerated electrons and holes onto the lateral facet and dominantly exposed facets, respectively, which is attributed to the junction formed between distinct facets (i.e., facet junction). In the case of BiOBr-5 with (010)/(102) facet junction, the electron transfer rate (kET) and efficiency (ηET) are 3.658 × 106 s-1 and 54.09%, which are superior than the counterpart of BiOBr-1 with (001)/(110) facet junction. The fast electron transfer rate and high transfer efficiency of BiOBr-5 result in the high CO evolution rate from CO2 photoreduction under artificial sunlight. Our work may bring some new insights into the mechanism understanding of facet junction and rational design of photocatalysts with high performance for solar energy storage in future.

Quantitatively simultaneous detection of hydroquinone (HQ) and catechol (CC) with low limit of detection (LOD) and wide detection range is of critical significance in water quality control but faces great challenges due to their isomer similarity and a large range of contamination concentrations. Herein, high density of boron atoms is introduced into nitrogen-doped nanocarbon (BNC) to realize simultaneous detection of HQ and CC with a large separation of peak potential (ΔEp) of 111 mV between oxidations of HQ and CC by differential pulse voltammetry. Besides, extremely low LODs of 33.3 and 16.3 nM for HQ and CC were achieved through amperometric I-t curve with wide linear ranges of 0.099 ∼ 43340 µM and 0.049 ∼ 5110 µM, respectively. The systematical investigation of the enhancement mechanism by spectroscopy and DFT calculations clearly reveal that the boron-nitrogen co-doping creates rich electroactive sites for high sensing performance toward HQ and CC, thereby shedding lights on the great effect of a unique nanostructure on electrocatalysis in sensing applications.

The rational design of efficient electrocatalysts based on comprehensive mechanistic insights is crucial to widespread penetration of future sustainable and eco-friendly energy technologies. Herein, via systematic first-principles calculations, we propose a general two-step strategy for developing highly active single-atom catalyst (SACs) supported on a prototypical substrate (g-C3N4) for bifunctional oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Our results show that the intrinsic activity can be properly evaluated by a robust screening rule, and, particularly, the descriptor can be readily calculated by a few handy and basic properties. According to the knowledge, we propose an effective approach (i.e., creating an N vacancy in the cavity of g-C3N4) that enables further activity improvement. Specifically, the predicted ORR/OER activity on Ag and Rh based SACs are comparable or even outperforms that of respective benchmark catalysts. This study not only provides several promising candidates for bifunctional ORR/OER, but also directs a new avenue for rational design of high-performance catalysts.

In this work, the MoSe 2 nanosheets were firstly prepared by hydrothermal method. We found the magnetism of MoSe 2 nanosheets obviously enhance with the decrease of temperature. Further, we fabricated a memristor using as-prepared MoSe 2 nanosheets, and observed temperature can regulate the memristor memory behavior of the device. In a word, this work reveals the potential multifunctional applications of MoSe 2 nanosheets with magnetism and memristive memory effects in future device technology.

Non-faradaic catalytic decomposition of hydrazine (N2H4) is a vital but underappreciated problem for direct hydrazine fuel cell (DHFC). Herein, a careful study of a nickel molybdenum oxide derived catalyst for N2H4 electrooxidation is reported, with special focus on the method for effectively suppressing non-faradaic decomposition of hydrazine as well as the underlying mechanism. A hierarchically nanostructured catalyst consisting of tiny Ni10Mo alloy nanoparticles dispersed on porous Ni Mo O nanosheets is synthesized using a simple hydrothermal method followed by reductive annealing treatment. Thus-prepared catalyst shows high activity towards N2H4 electrooxidation, but is entangled with the problematic selectivity towards non-faradaic decomposition of N2H4. Our study find that this problem can be circumvented by a controlled phosphorization method. The resultant catalyst (Ni2P@Ni10Mo/Ni-Mo-O/NF) exhibits exceptionally high activity, excellent durability and nearly 100 % selectivity towards N2H4 electrooxidation. A detailed structural characterization and density functional theory calculations are conducted to understand the phosphorization-induced modification of catalytic property.

Based on the models built with our “cyclic replacement” method we introduced local strain into the (111) facet of the Si 〈112〉 nanowires. With ab initio approach, it is found that the electronic band structures of the nanowires are modulated efficiently by the surface strains: the indirect band gap declines by strong surface compression, while it always decreases and impressively changes to a direct band gap with surface tension. Moreover, the local deformations result in spatial separation of the valence band minimum to the compressed surface and the conduction band minimum to the tensed surface.

Effects of Ni vacancy, Ni antisite in Al sublattice, Cr in Al sublattice, Pt in Ni sublattice on the second-order elastic constants (SOECs) and third-order elastic constants (TOECs) of the B2 NiAl have been investigated using the first-principles methods. Lattice constant and the SOECs of NiAl are in good agreement with the previous results. The brittle/ductile transition map based on Pugh ratio G/B and Cauchy pressure Pc shows that Ni antisite, Cr, Pt and pressure can improve the ductility of NiAl, respectively. Ni vacancy and lower pressure can enhance the Vickers hardness Hv of NiAl. The density of states (DOS) and the charge density difference are also used to analysis the effects of vacancy, Ni antisite, Cr and Pt on the mechanical properties of NiAl, and the results are in consistent with the transition map.

Based on the quasiharmonic approach from first-principles phonon calculations, the volume versus temperature relations for Al, Ni and Cu are obtained. Using the equilibrium volumes at temperature T, the temperature dependences of generalized planar fault energies have also been calculated by first-principles calculations. It is found that the generalized planar fault energies reduce slightly with increasing temperature. Based on the calculated generalized planar fault energies, the twinnabilities of Al, Ni and Cu are discussed with the three typical criteria for crack tip twinning, grain boundary twinning and inherent twinning at different temperatures. The twinnabilities of Al, Ni and Cu also decrease slightly with increasing temperature. Ni and Cu have the inherent twinnabilities. But, Al does not exhibit inherent twinnability. These results are in agreement with the previous theoretical studies at 0 K and experimental observations at ambient temperature.

The interactions of a hydrogen atom with clean, vacancied, and transition metal-doped (TM = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Au, Pt) Mg(0001) surfaces are investigated using first-principles calculations. The H adsorption on Mg(0001) with TMs doped within the second layer is generally more stable than that on clean Mg but clearly weaker than that on Mg surfaces with TM in the first layer. We find, however, that all these TM atoms prefer to substitute for the Mg atoms in the second layer rather than for those in the outermost layer of the Mg surface. To enhance the catalytic effect of the TM dopants, we investigated various co-doping conditions of TMs, and we found that i) Ti is a good “assistant” that stabilizes co-doped Co, Ni, Pd, Ag, Pt, and Au within the first layers and that ii) Ni and Co are more easily incorporated into the first layer of a Mg surface when co-doped with Ti, V, and Nb. These observations may lead to a possible approach to stabilize the TM dopants within the first layer and thus promote the hydrogenation of Mg accordingly.

Density functional theory (DFT) calculations are performed to investigate CO and O 2 adsorption as well as CO oxidation on the Au m Pd n ( m + n = 2–6) bimetallic clusters. It is found that the adsorption energies of both CO and O 2 on Au m Pd n ( m + n = 2–6) are greater than those on the pure gold clusters of corresponding sizes, and unexpectedly greater than those on Pd clusters in some cases. At the same time, the calculated reaction barrier of CO oxidation on Au 2 Pd is lower than those on Au 3 and Pd 3 , indicating that Au/Pd bimetallic cluster could potentially have a better catalytic activity for CO oxidation potentially.

The co-adsorption of CO and C, O on Na pre-covered Pd(1 1 1) surface are studied by density functional theory (DFT). CO adsorption is affected by the short-range Na–CO electrostatic interactions, especially the Na–O attraction, and the Na-induced long-range surface polarizability as well as the indirect interactions through substrates. Na stabilizes C and O adsorptions, particularly O adsorption, though both C–Pd and O–Pd bonds are elongated. Na reduces CO dissociation barrier by ∼25%. The promotional effects are primarily ascribed to the short-range Na–O electrostatic interaction which stabilizes the transitional state. The Na-induced long-range effects are not significant and hardly promote CO dissociation.