Dehydrogenation Kinetics Research Articles

Laser-Regulated Iridium-Diffused Nitrogen-Carbon Sites for Enhanced Hydrazine-Assisted Alkaline Seawater Splitting and Zinc-Hydrazine Batteries.

The current study presents a quick and simple method for synthesizing Ir nanoclusters decorated on an N-doped carbon (NC) matrix via pulsed laser ablation in liquid, followed by pyrolysis. The resulting Ir-NC material acts as a dual-functional electrocatalyst, efficiently facilitating hydrogen generation through the hydrazine oxidation reaction (HzOR) and the hydrogen evolution reaction (HER) in alkaline seawater. The optimized Ir-NC-2 catalyst exhibits a low operating potential of 23mV versus the reversible hydrogen electrode for HzOR and a remarkably low overpotential of 24mV for HER, achieving a current density of 10mAcm-2 in alkaline seawater, surpassing the performance of the Pt/C catalyst. Notably, the Ir-NC-2 catalyst also demonstrates superior dual-functionality in overall hydrazine-assisted seawater splitting, requiring only 0.1V at 10mAcm-2 while maintaining stability. Moreover, density functional theory calculations reveal that the strong electronic interaction between the Ir nanoclusters and the NC matrix enhances mass transfer and electron conductivity, significantly boosting HER activity and accelerating the kinetics of hydrazine dehydrogenation. Consequently, the Ir-NC-2 catalyst performs efficiently in a Zn-hydrazine battery, achieving high energy efficiency of 95.5% and demonstrating excellent stability for 120h (360 cycles), indicating its potential for practical applications.

Vitreous silica supported metal catalysts for direct non-oxidative methane coupling

Direct non-oxidative methane coupling (NMC) transforms methane into valuable chemicals and hydrogen, which is a promising pathway to boost industrial decarbonization. The reaction, however, is challenged by high C-H bond activation temperature, catalyst coking, and low selectivity towards hydrocarbon products. Here we studied the efficacy of five vitreous silica supported 3d transition metal (Mn, Fe, Co, Ni, and Cu) catalysts (denoted as M/SiO2-v) for NMC. These catalysts were prepared by flame fusion of mixtures of quartz and metal silicate precursors. The metal species in the as-synthesized catalysts were fully or partially oxidized, with their stability following the order of Mn > Fe ≈ Co > Ni > Cu in the NMC reaction. The Cu species has low methane reaction rate, due to the high adsorption and dissociation energies of methane. The Mn and Ni species have high methane reaction and coke formation rates, which is supported by easy kinetics of methane deep dehydrogenation to carbon. In contrast, Fe and Co species showed the best hydrocarbon product selectivity. Particularly, the Co species emerged as the optimal catalyst for NMC, showcasing a balanced methane activation, hydrocarbon formation, and low coke yield. The relationship between the evolved metal species under reaction conditions and their NMC performance was discussed. The present study screens and provides effective catalyst formulations for NMC reactions.

Theoretical and modeling studies on the kinetics of diethylamine dehydrogenation and subsequent isomerization and decomposition reactions

Small-molecule nitrogen-containing contaminants can be produced by the pyrolysis of diethylamine (DEA) alone or in conjunction with other molecules. To investigate the theoretical chemistry of the combustion of DEA, the CBS method determines the potential energy surface and the rate constants are calculated based on a combination of RRKM and TST theories. The H-abstraction reactions by H radicals are more kinetically advantageous. Site α has the most difficult H-abstraction procedure, but site γ has the competitive capacity to form subsequent products. The H-abstraction by NO2 radical produces trans-HONO, cis-HONO, and HNO2. For the reaction channels of DEA radicals, decomposition reactions have more kinetic advantages than isomerization. Kinetic parameters were obtained and the model was modified based on the fitted rate constants. The modified model has better predictive ability at low temperatures. This work provides extensive data to improve the modeling of DEA combustion at low and medium temperatures.

Enhancing the dehydrogenation properties of LiAlH4 through the addition of ZrF4 for solid-state hydrogen storage

Hydrogen energy is emerging as an essential alternative to fossil fuels due to its clean energy profile, generating energy without greenhouse gas emissions. Solid-state hydrogen storage, particularly using complex hydrides like LiAlH4, holds promise due to high hydrogen capacities. However, practical applications of LiAlH4 face obstacles due to slow dehydrogenation kinetics and high decomposition temperatures. This study investigates the catalytic effect of ZrF4 on LiAlH4 to improve hydrogen storage properties. Incorporating 10wt.% ZrF4 has significantly lowered the onset desorption temperature from 160 °C to 80 °C. Desoption kinetic result showed that the addition of 10wt.% ZrF4 can enables the release of 5.6wt.% hydrogen in 120min at 100 °C, which is 50 times faster than in undoped samples. X-ray diffraction analysis indicated that ZrF4 facilitated the in-situ formation of Al3Zr and LiF phases during dehydrogenation, thereby enhancing catalytic efficiency. The desorption activation energies for first two reactions decreased significantly by ~ 16kJ/mol and ~24kJ/mol with ZrF4 doping. These findings suggest that ZrF4 effectively improves the hydrogen storage properties of LiAlH4, positioning it as a potential catalyst for solid-state hydrogen storage systems.

2LiBH4-MgH2 System Catalytically Modified with a 2D TiNb2O7 Nanoflake for High-Capacity, Fast-Response, and Long-Life Hydrogen Energy Storage.

To achieve large-scale hydrogen storage for growing high energy density and long-life demands in end application, the 2LiBH4-MgH2 (LMBH) reactive hydride system attracts huge interest owing to its high hydrogen capacity and thermodynamically favorable reversibility. The sluggish dehydrogenation kinetics and unsatisfactory cycle life, however, remain two challenges. Herein, a bimetallic titanium-niobium oxide with a two-dimensional nanoflake structure (2D TiNb2O7) is selected elaborately as an active precursor that in situ transforms into TiB2 and NbB2 with ultrafine size and good dispersion in the LMBH system as highly efficient catalysts, giving rise to excellent kinetic properties with long-term cycling stability. For the LMBH system added with 5 wt% 2D TiNb2O7, 9.8 wt% H2 can be released within 20 min at 400 °C, after which the system can be fully hydrogenated in less than 5 min at 350 °C and 10 MPa H2. Moreover, a dehydrogenation capacity of 9.4 wt% can be maintained after 50 cycles corresponding to a retention of 96%, being the highest reported to date. The positive roles of TiB2 and NbB2 for kinetics and recyclability are from their catalytic nucleation effects for MgB2, a main dehydrogenation phase of LMBH, thus reducing the apparent activation energy, suppressing the formation of thermostable Li2B12H12 byproducts, and inhibiting the hydride coarsening. This work develops an advanced LMBH system, bringing hope for high-capacity, fast-response, and long-life hydrogen energy storage.

Mechanistic Insight of High-Valent First-Row Transition Metal Complexes for Dehydrogenation of Ammonia Borane.

Designing an efficient and cost-effective catalyst for ammonia borane (AB) dehydrogenation remains a persistent challenge in advancing a hydrogen-based economy. Transition metal complexes, known for their C-H bond activation capabilities, have emerged as promising candidates for AB dehydrogenation. In this study, we investigated two recently synthesized C-H activation catalysts, 1 (CoIV-dinitrate complex) and 2 (NiIV-nitrate complex), and demonstrated their efficacy for AB dehydrogenation. Using density functional theory calculations and a detailed analysis, we elucidated the AB dehydrogenation mechanism of these complexes. Our results revealed that both complexes 1 and 2 can efficiently dehydrogenate AB at room temperature, although the abstraction of molecular H2 from these complexes requires slightly elevated temperatures. We utilized H2 binding free energy calculations to identify potentially active sites and observed that complex 2 can release two equivalents of H2 at a temperature slightly higher than room temperature. Furthermore, we investigated AB dehydrogenation kinetics and thermodynamics in iron (Fe)-substituted systems, complexes 3 and 4. Our results showed that the strategic alteration of the central metal atom, replacing Ni in complex 2 with Fe in complex 4, resulted in enhanced kinetics and thermodynamics for AB dehydrogenation in the initial cycle. These results underscore the potential of high-valent first-row transition metal complexes for facilitating AB dehydrogenation at room temperature. Additionally, our study highlights the beneficial impact of incorporating iron into such mononuclear systems, enhancing their catalytic activity.

Disentangling heterogeneous thermocatalytic formic acid dehydrogenation from an electrochemical perspective

Heterogeneous thermocatalysis of formic acid dehydrogenation by metals in solution is of great importance for chemical storage and production of hydrogen. Insightful understanding of the complicated formic acid dehydrogenation kinetics at the metal-solution interface is challenging and yet essential for the design of efficient heterogeneous formic acid dehydrogenation systems. In this work, formic acid dehydrogenation kinetics is initially studied from a perspective of electrochemistry by decoupling this reaction on Pd catalyst into two short-circuit half reactions, formic acid oxidation reaction and hydrogen evolution reaction and manipulating the electrical double layer impact from the solution side. The pH-dependences of formic acid dehydrogenation kinetics and the associated cation effect are attributed to the induced change of electric double layer structure and potential by means of electrochemical measurements involving kinetic isotope effect, in situ infrared spectroscopy as well as grand canonical quantum mechanics calculations. This work showcases how kinetic puzzles on some important heterogeneous catalytic reactions can be tackled by electrochemical theories and methodologies.

Enhanced De/hydrogenation Kinetics and Cycle Stability of Mg/MgH2 by the MnOx-Coated Ti2CTx Catalyst with Optimized Ti-H Bond Stability.

MXene based catalysts can significantly enhance hydrogenation and dehydrogenation (de/hydrogenation) kinetics of Mg/MgH2, but they suffer from uncontrollable catalysts-hydrogen bond strength and structural instability. Here, we propose Tx density control of MXene-based catalysts and MnOx coating as a promising solution. The MnOx@Ti2CTx-catalyzed Mg/MgH2 can release 5.97 wt % H2 at 300 °C in 3 min and 5.60 wt % H2 at 240 °C in 15 min with an activation energy of 75.57 kJ·mol-1. In addition, the samples showed excellent de/hydrogenation-cycle stability, and the degradation of hydrogen storage capacity is negligible even after 100 cycles. DFT calculations combined with XPS analysis showed that the Tx defect on the surface of the MnOx@Ti2CTx catalyst could optimize the strength of the Ti-H bond, accelerating both hydrogen dissociation and diffusion processes. The catalyst's surface properties were protected by the MnOx coating, achieving high chemical and catalytic stability. These findings offer a strategy for surface structure optimization and protection of MXene-based catalysts, realizing controllable catalyst-hydrogen bond strength.

Mxene-supported NbVH nanoparticles as efficient catalysts for reversible hydrogen storage in magnesium borohydride

Bimetallic niobium vanadium hydride nanoparticles (NbVH NPs) anchored on Ti3C2 were synthesized using a facile ball milling method as an effective catalyst for the dehydrogenation kinetics and reversibility of Mg(BH4)2. It was found that the onset dehydrogenation temperature of the Mg(BH4)2 + 30NbVH NPs@Ti3C2 composite was 105.7 °C and released 9.07 wt% of hydrogen at 330 °C, while undoped Mg(BH4)2 only released 4.2 wt% of H2 from 248 °C to 330 °C. Additionally, the Mg(BH4)2 + 30NbVH NPs@Ti3C2 composite achieved remarkable hydrogen release of over 9.44 wt% at a temperature as low as 230 °C, indicating unexpected dehydrogenation kinetics. In the reversible hydrogen desorption tests, Mg(BH4)2 + 30NbVH NPs@Ti3C2 released 5.98 wt% of H2 in the 2nd cycle at 250 °C and maintained a reversible capacity of 4.35 wt% after 10 cycles, demonstrating a remarkable enhancement in reversibility. The enhancement in the dehydrogenation kinetics of Mg(BH4)2 could be attributed to the greatly reduced activation energies from 343 kJ·mol−1 and 138.3 kJ·mol−1 to 103.7 kJ·mol−1 and 124 kJ·mol−1. Investigations on the evaluation of catalyst and Mg(BH4)2 during reversible hydrogen storage have revealed that NbVH NPs actually acted as a “bidirectional hydrogen pump”, facilitating both the hydrogen release and uptake from Mg(BH4)2. This strategy of multi-component hydrides may show a new way to design effective catalysts for solid-state hydrogen storage materials.

Efficient hydrogen absorption and dehydrogenation of synergistically catalyzed Mg10Fe by MoS2 and Y2O3 via one-step synthesis and multistage regulation

To effectively deal with the long preparation period and low hydrogen absorption capacity issue of Mg-based hydrogen storage materials. One-step multistage control strategy and high-pressure hydrogenation have been employed to prepare Mg10Fe-M (M = MoS2 or Y2O3 or both) composites. The phase composition, microstructure, morphology, non-isothermal dehydrogenation thermodynamics and isothermal dehydrogenation kinetics at different milling time (2, 4, 8 h) were explored, and the catalytic hydrogen absorption and discharge mechanism of Mg10Fe–MoS2–Y2O3 was proposed. The addition of MoS2 nanoflowers and Y2O3 powder can synergistically regulate and improve the hydrogenation capacity and dehydrogenation temperature of Mg10Fe. The hydrogen absorption and dehydrogenation of Mg10Fe–MoS2–Y2O3 in short time milling for 2 h are 3.64 wt% and 3.27 wt% respectively. After extending the milling time to 8 h, the thermodynamic and kinetic behavior of Mg10Fe-M (M = MoS2 or Y2O3 or both) is greatly improved. Kinetically, the hydrogenation or dehydrogenation capacity increases significantly, Mg10Fe–MoS2 doesn't need activation, and the hydrogenation capacity reaches 5.42 wt% at 623 K, with a yield of about 85.9 % in 60 min. Thermodynamically, the initial dehydrogenation peak temperature drops to about 310 °C, and the apparent activation energy also decreases significantly, among which Mg10Fe–MoS2–Y2O3 was 91.87 kJ/mol. These are attributed to the fact that MoS2 nanoflowers provide many active sites for H2 adsorption and H atom dissociation. Synchro-efficient synthesis and regulation of Mg-rich composite hydrogen storage materials are expected to shorten the synthesis cycle, improve the hydrogen storage performance, and lay a material foundation for the design and development of solid hydrogen storage devices.

Effectively enhanced catalytic effect of sulfur doped Ti3C2 on the kinetics and cyclic stability of hydrogen storage in MgH2

Designing catalysts with high catalytic activity and stability is the key to achieve the commercial application of MgH2. Herein, the sulfur doped Ti3C2 (S-Ti3C2) was successfully prepared by heat treatment of Ti3C2 MXene under Ar/H2S atmosphere to facilitate the hydrogen release and uptake from MgH2. The S-Ti3C2 exhibited pleasant catalytic effect on the hydriding/dehydriding kinetics and cyclic stability of MgH2. The addition of 5 wt% S-Ti3C2 into MgH2 resulted in a reduction of 114 °C in the starting dehydriding temperature compared to pure MgH2. MgH2 + 5 wt% S-Ti3C2 sample could quickly release 6.6 wt% hydrogen in 17 min at 220 °C, and 6.8 wt% H2 was absorbed in 25 min at 200 °C. Cyclic testing revealed that MgH2 + 5 wt% S-Ti3C2 system achieved a reversible hydrogen capacity of 6.5 wt%. Characterization analysis demonstrated that Ti-species (Ti0, Ti2+, Ti–S, and Ti3+) as active species significantly lowered the dehydrogenation temperature and promoted the re-/dehydrogenation kinetics of MgH2, and sulfur doping can effectively improve the stability of Ti0 and Ti3+, contributing to the improvement of cyclic stability of MgH2. This study provides strategy for the construction of catalysts for hydrogen storage materials.

Dehydrogenation of n-butane to 1,3-butadiene on chromia-alumina catalyst: 1. Kinetics of dehydrogenation and coke formation

The kinetics of dehydrogenation of n-butane to butadiene was studied on K-CrOx /γ-Al2O3 catalyst particles of 56–94 μm size by varying the temperature T = 550÷625 °C, the time of catalytic step TOS = 5÷30 min, and the space velocity GHSV = 4400÷35200 h–1. The catalyst was similar to the commercial one. Prior to the studies, the catalyst granules were stabilized during the reduction-dehydrogenation-regeneration cycle at 593 °C, then the catalyst particles milled to a size of 56–94 μm were stabilized during the dehydrogenation-regeneration cycle at 650 °C. The highest butadiene selectivity of ~25 mol.% was obtained at n-butane conversion of 26–30 % (GHSV = 35200 h–1) at T = 600 °C and TOS = 5 min, and the highest butadiene yield of ~10 mol.% was obtained when the conversion was increased to ~50 % (GHSV = 8800 h–1) under the same conditions. Increasing T to 625 °C, TOS to 30 min and decreasing GHSV to ~4400 h–1 resulted in an increase in by-product selectivity to ~50 mol.%. It was found that the observed activation energy of product formation rates decreases in the series: by-products > butylene > butadiene. A kinetic model is proposed that takes into account the formation of butadiene via butylene, the formation of by-products such as ethane/ethylene and methane/propylene in the butylene hydrocracking reactions, and the secondary conversion reactions of by-products. Inhibition of dehydrogenation reactions by components of the reaction mixture, coke formation and its effect on catalyst activity are also considered in the model. The adequacy of the kinetic model is confirmed by good agreement of the calculated results with the experimental data.

Dopant induced hollow Ni2P nanocrystals regulate dehydrogenation kinetics for highly efficient solar-driven hydrazine assisted H2 production

Replacing kinetically sluggish oxygen evolution reaction (OER) with a thermodynamically favorable hydrazine oxidation reaction (HzOR) to produce hydrogen has emerged as a more energy-efficient alternative than water splitting. However, the lack of promising bifunctional electrocatalysts hinders its scalable applications. Here, we report a colloidal synthesis of Mn-dopant induced hollow Ni2P nanocrystals (NCs) using a heat-up approach, which act as superior bifunctional electrocatalysts for both HzOR (55 mV at 10 mA/cm2) and hydrogen evolution reaction (HER, 192 mV at 50 mA/cm2). The two-electrode electrolyzer requires a low cell voltage of 59 mV to achieve 10 mA/cm2 and a current density of ∼ 50.4 mA/cm2 to reach 0.5 V. Theoretical studies unraveled that Mn-doping regulates the electronic structure of Ni2P and optimizes the H* adsorption/desorption and dehydrogenation kinetics. When integrated with a Si photovoltaic device, the bifunctional hollow Mn-doped Ni2P NCs enabled solar-driven hydrazine assisted H2 production with a ∼ 14.6 % efficiency.

Intercalated and Surface-Adsorbed Phosphate Anions in NiFe Layered Double-Hydroxide Catalysts Synergistically Enhancing Oxygen Evolution Reaction Activity.

The oxygen evolution reaction (OER), a crucial semireaction in water electrolysis and rechargeable metal-air batteries, is vital for carbon neutrality. Hindered by a slow proton-coupled electron transfer, an efficient catalyst activating the formation of an O-H bond is essential. Here, we proposed a straightforward one-step hydrothermal procedure for fabricating PO43--modified NiFe layered double-hydroxide (NiFe LDH) catalysts and investigated the role of PO43- anions in enhancing OER. Phosphate amounts can efficiently regulate LDH morphology, crystallinity, composition, and electronic configuration. The optimized sample showed a low overpotential of 267 mV at 10 mA cm-2. Density functional theory calculations revealed that intercalated and surface-adsorbed PO43- anions in NiFe LDH reduced the Gibbs free energy in the rate-determining step of *OOH formation, balancing oxygen-containing intermediate adsorption/dissociation and promoting the OER. Intercalated phosphate ions accelerated precatalyst dehydrogenation kinetics, leading to a rapid reconstruction into active NiFe oxyhydroxide species. Surface-adsorbed PO43- interacted favorably with adsorbed *OOH on the active Ni sites, stabilizing *OOH. Overall, the synergistic effects of intercalated and surface-adsorbed PO43- anions significantly contributed to enhanced OER activity. Achieving optimal catalytic activity requires a delicate equilibrium between thermodynamic and kinetic factors by meticulously regulating the quantity of introduced PO43- ions. This endeavor will facilitate a deeper comprehension of the influence of anions in electrocatalysis for OER.

HYDROGEN SORPTION IMPROVEMENT OF NaAlH4 CATALYSED BY K2 SiF6 FOR SOLID STATE HYDROGEN STORAGE

Sodium alanate (NaAlH4) has been recognised as a complex metal hydride that is frequently used as a hydrogen storage material. However, dealing with its poor kinetic characteristics and high decomposition temperatures becomes challenging. This research added potassium hexafluorosilicate (K2SiF6) as a catalyst to reduce the dehydrogenation temperature and improve sorption kinetics compared to the undoped NaAlH4. The dehydrogenation temperature of the NaAlH4 composite with 10 wt.% K2SiF6 addition was determined to be 145°C, a decrease of about 31% compared to 210°C for the undoped NaAlH4. The 10 wt.% K2SiF6-added NaAlH4 samples released roughly 1.77 wt.% hydrogen at 200°C after 60 minutes of dehydrogenation, representing faster dehydrogenation kinetics, but the milled NaAlH4 only produced around 1.39 wt.% of hydrogen. According to Kissinger’s analysis, the apparent activation energy, Ea for the decomposition of NaAlH4 was 87.74 kJ/mol in 1st stage and for NaAlH4 10 wt.% K2SiF6 composite, lowered by 30.45 kJ/mol or 25.8% than as-milled NaAlH4 (118.19 kJ/mol). The enhancement of the dehydrogenation performance of the NaAlH4-K2SiF6 composite can be attributed to the formation of the new phases of KAlF4. These findings might alter the reaction pathway of the composite system and improve its thermodynamic properties. The improvement of dehydrogenation performance and the discovery of the role played by KAlF4 in the dehydrogenation process of the NaAlH4-K2SiF6 composite give us valuable insights for developing and optimising future hydrogen storage materials.

Synthesis of Co0·52Cu0·48/Cu@S–C arrays for the enhanced performance of hydrazine-assisted hydrogen production

The development of efficient bifunctional catalysts is the key technology to replace oxygen evolution reaction (OER) with hydrazine oxidation reaction (HzOR) with lower theoretical potential to achieve high efficiency and energy-saving hydrogen production. In this work, the Co0·52Cu0·48/Cu@S–C (−1.3 V) composite with flower-like array was prepared by two-step electrodeposition coupled pyrolysis method. The electrochemical measurements showed that the driving voltages of the optimal composite for HzOR and hydrogen evolution reaction (HER) are respectively −118 mV and 47 mV at a current density (j) of 10 mA cm−2. The excellent performance of Co0·52Cu0·48/Cu@S–C (−1.3 V) composite is attributed to the fact that the flower-like structure exposes more active areas and facilitates the diffusion of electrolyte, the strong electron interaction between Co0·52Cu0·48/Cu and S–C substrate, which can be verified by X-ray photoelectron spectroscopy (XPS), enhances the electrical conductivity, the Co0·52Cu0·48/Cu heterogeneous interface reduces the water dissociation barrier and facilitates the dehydrogenation kinetics of N2H4 determined by density functional theory (DFT) calculations. Due to the excellent performance of Co0·52Cu0·48/Cu@S–C (−1.3 V), the overall hydrazine splitting (OHzS) electrolytic cell was constructed with Co0·52Cu0·48/Cu@S–C (−1.3 V) as electrodes. The results showed the voltages required by the cell are 36, 210 and 282 mV at the current density values of 10, 100 and 200 mA cm−2 respectively, showing that Co0·52Cu0·48/Cu@S–C (−1.3 V) can be used for energy-saving hydrogen production by hydrazine assisted water electrolysis.

Amorphous mixed transition metal oxides: A novel catalyst for boosting dehydrogenation of MgH2

Magnesium hydride (MgH2) has been recognized as a promising hydrogen storage material. However, the sluggish hydrogen desorption kinetics is one of the main factors hindering its practical applications. To enhance the dehydrogenation kinetics of MgH2, an amorphous mixed TiO2-ZrO2-V2O5 catalyst is synthesized in this work. After adding the as-synthesized catalyst into MgH2 by ball milling, the dehydrogenation activation energy can be decreased to 65.7 kJ mol−1. Meanwhile, the catalyzed MgH2 shows excellent cycling stability after fifty hydrogen absorption-desorption cycles. The significant improvement of hydrogen desorption kinetics is attributed to the synergistic effect of abundant oxygen vacancies and in situ formed multivalent species in the catalyst. This highlights the importance of designing and synthesizing efficient catalysts for dehydrogenation of MgH2.

Feeling the strain: Enhancing the thermodynamics characteristics of magnesium nickel hydride Mg2NiH4 for hydrogen storage applications through strain engineering

This work is based on density functional theory (DFT) and studies the structural, electronic, thermodynamic properties and dehydrogenation kinetics of the hydride Mg2NiH4 under different uniaxial and biaxial strain applied to Mg2Ni or Mg2NiH4. structural properties are first studied based on generalized gradient (GGA) and local density (LDA). Thermodynamic and electronic properties and dehydrogenation kinetics are then studied using the GGA method based on the Perdew-Burke-Ernzerhor (PPE) approximation. The results obtained show that uniaxial/biaxial tensile and compressive strains are capable of inducing structural deformation by increasing the value of the strain step on both Mg2Ni and Mg2NiH4, and that these strains applied to Mg2NiH4 are capable of reducing the stability of the system more than strains applied to Mg2Ni, due to the contribution of strain energy. More specifically, it lowers the enthalpy of formation to −40 kJ/mol.H2 under compressive strain ε = −7.5% or biaxial tensile strain ε = +7.8%, which corresponds exactly to the ideal value suggested by the US Department of Energy (DOE) for materials suitable for hydrogen storage. And the decomposition temperature fell within the fuel cell operating range (PEM) of 289–393 K. On the other hand, under uniaxial and biaxial strains, the activation energy of hydrogen atom diffusion in Mg2NiH4 varied between 0.40 eV and 0.22 eV, resulting in a remarkable improvement in dehydrogenation properties. Analysis of the total (TDOS) and partial (PDOS) density curves shows that the Mg2NiH4 system has a metallic characteristic, and that this characteristic is maintained by increasing the strain pitch, with a variation in the energy width of the valence band.

Optimizing the Dehydrogenation Kinetics of Metal Nitrides for Energy‐Efficient Seawater Hydrogen Production at 2 A cm−2

AbstractSeawater hydrogen production, vital for sustainable energy solutions and freshwater preservation, faces challenges due to seawater complexity and high energy consumption. A strategy to modulate dehydrogenation kinetics of dual‐phase metal nitrides using low‐loaded Pt quantum dots (QDs), achieving stable and energy‐efficient hydrogen generation is introduced. The Pt QDs@Ni3N‐MoN/Ti catalyst displays outstanding bifunctional seawater catalytic performance, enabling efficient hydrogen production and hydrazine degradation in a flow anion exchange membrane water electrolysis (AEMWE) device. Operating at a low voltage of 1.41 V, it achieves 2 A cm−2 for 300 h, circumventing chlorine corrosion and yielding record‐breaking energy equivalent input (2.68 kWh m−3 H2 at 1 A cm−2), a 47.1% reduction compared to traditional methods. Integration with solar and biomass energy facilitates self‐powered hybrid seawater hydrogen production, highlighting its potential applications. This work facilitates energy‐efficient marine resource conversion to green hydrogen and offers viable insights into industrial hazardous pollutant degradation using metal‐nitride electrocatalysts.

Polyoxometalate-derived bi-functional crystalline/amorphous interfaces with optimized d-electron configuration for efficient self-powered hydrazine-seawater splitting

Hydrazine-assisted water electrolysis is a promising energy-efficient strategy for hydrogen production. Nonetheless, developing high-performance bi-functional electrocatalysts towards both hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR) remains great challenges, especially for hydrazine-seawater splitting. Herein, we report a polyoxometalate-assisted in-situ synthesis protocol for constructing bi-functional crystalline/amorphous Pt/MoO3-x interfaces toward both efficient HER and HzOR. The polyoxometalate-derived crystalline/amorphous Pt/MoO3-x interfaces deliver working potentials of only –23 and −41 mV at 10 mA cm−2 for HER and HzOR in seawater electrolyte, respectively. Meanwhile, ultrahigh mass activities of 38.39 AmgPt-1 for HER at −100 mV potential and 23.84 AmgPt-1 for HzOR at 50 mV potential are also achieved, over 30.2 and 52.9 times higher than those of commercial Pt/C. As bi-functional electrocatalysts for overall hydrazine-seawater splitting, the electrolyzer requires a cell voltage of only 55/238 mV at 10/100 mA cm−2, 1.584/1.543 V lower than that of the seawater splitting system. Moreover, a proof-of-concept self-powered hydrazine-seawater electrolysis system driven by direct hydrazine fuel cell is further demonstrated, which achieves a hydrogen production rate of 0.29 mL cm−2min−1. DFT calculations verify that, the crystalline/amorphous interfaces endow Pt/MoO3-x an optimized d-electron configuration with favorable H* adsorption and promoted dehydrogenation kinetics of *N2H4 to *N2H3 in the potential-determining step. This work provides a novel strategy and inspiration toward the design of efficient bi-functional electrocatalysts for hydrazine-assisted hydrogen production from seawater.