Insights into an Amorphous NiCoB Nanoparticle-Catalyzed MgH2 System for Hydrogen Storage.

In the paper, we synthesized amorphous NiCoB nanoparticles by a simple chemical reduction method and employed them as high-activity catalysts to considerably improve the hydrogen storage properties of MgH2. The MgH2-NiCoB composite quickly absorbed 3.6 wt % H2 at a low temperature of 85 °C and released 5.5 wt % H2 below 270 °C within 600 s. It is worth noting that the hydrogenation activation energy was reduced to 33.0 kJ·mol-1. Detailed microstructure analysis reveals that MgB2, Mg2Ni/Mg2NiH4, and Mg2Co/Mg2CoH5 were in situ generated during the first de/absorption cycle and dispersed at the surface of NiCoB. These active ingredients created lots of boundary interfaces to facilitate the hydrogen diffusion and destabilize the Mg-H bonds, thus decreasing the kinetic barriers. This work provides support for a promising catalytic effect of amorphous NiCoB on de/absorption reactions of MgH2, showing new ways for designing Mg-based hydrogen storage systems toward practical application.

Transition metal (Co, Ni) nanoparticles wrapped with carbon and their superior catalytic activities for the reversible hydrogen storage of magnesium hydride.

Magnesium hydride (MgH2) exhibits long-term stability and has recently been developed as a safe alternative to store hydrogen in the solid state, due to its high capacity of 7.6 wt% H2 and low cost compared to other metal hydrides. However, the high activation energy and poor kinetics of MgH2 lead to inadequate hydrogen storage properties, resulting in low energy efficiency. Nano-catalysis is deemed to be the most effective strategy in improving the kinetics performance of hydrogen storage materials. In this work, robust and efficient architectures of carbon-wrapped transition metal (Co/C, Ni/C) nanoparticles (8-16 nm) were prepared and used as catalysts in the MgH2 system via ball milling to improve its de/rehydrogenation kinetics. Between the two kinds of nano-catalysts, the Ni/C nanoparticles exhibit a better catalytic efficiency. MgH2 doped with 6% Ni/C (MgH2-6%Ni/C) exhibits a peak dehydrogenation temperature of 275.7 °C, which is 142.7, 54.2 and 32.5 °C lower than that of commercial MgH2, milled MgH2 and MgH2 doped with 6% Co/C (MgH2-6%Co/C), respectively. MgH2 doped with 6% Ni/C can release about 6.1 wt% H2 at 250 °C. More importantly, the dehydrogenated MgH2-6%Ni/C is even able to uptake 5.0 wt% H2 at 100 °C within 20 s. Moreover, a cycling test of MgH2 doped with 8% Ni/C demonstrates its excellent hydrogen absorption/desorption stability with respect to both capacity (up to 6.5 wt%) and kinetics (within 8 min at 275 °C for dehydrogenation and within 10 s at 200 °C for rehydrogenation). Mechanistic research reveals that the in situ formed Mg2Ni and Mg2NiH4 nanoparticles can be regarded as advanced catalytically active species in the MgH2-Ni/C system. Meanwhile, the carbon attached around the surface of transition metal nanoparticles can successfully inhibit the aggregation of the catalysts and achieve the steadily, prompting de/rehydrogenation during the subsequent cycling process. The intrinsic catalytic effects and the uniform distributions of Mg2Ni and Mg2NiH4 result in a favorable catalytic efficiency and cycling stability. Nano-catalysts with this kind of morphology can also be applied to other metal hydrides to improve their kinetics performance and cycling stability.

How can low-carbon help high-quality urban development?-Empirical evidence from low-carbon city pilot policies.

High-quality development is the paramount task for comprehensively building a socialist modernized country. The low-carbon city pilot policy, with cities as the unit of action, provides new opportunities for high-quality economic transformation. Based on panel data from 261 cities between 2005 and 2018, this study calculates the level of high-quality economic development in Chinese cities, constructs a multi-period difference-in-differences model, analyzes the impact of the low-carbon city pilot policy on high-quality economic development, and explores the policy's heterogeneous effects on high-quality development in different types of cities and its transmission mechanism. The research findings show that the low-carbon city pilot policy can significantly promote high-quality economic development in cities and has heterogeneous effects in terms of regional differences, city types, and city scale. The effects are relatively greater in the eastern region, non-resource-based cities, and mega-cities. The low-carbon city pilot policy promotes high-quality economic development through mechanisms such as technological progress effects, resource agglomeration effects, and government action improvement effects. Combining theoretical analysis with empirical results, this study proposes policy recommendations to enhance the effectiveness of the low-carbon city pilot policy in promoting high-quality development.

Enhanced hydrogen storage kinetics of MgH2 by the synergistic effect of Mn3O4/ZrO2 nanoparticles.

As an ideal material for solid-state hydrogen storage, magnesium hydride (MgH2) has attracted enormous attention due to its cost-effectiveness, abundant resources, and outstanding reversibility. However, the high thermodynamics and poor kinetics of MgH2 still hinder its practical application. In this work, a simple stirring-hydrothermal method was used to successfully prepare bimetallic Mn3O4/ZrO2 nanoparticles, which were subsequently doped into MgH2 by mechanical ball milling to improve its hydrogen sorption performance. The MgH2 + 10 wt% Mn3O4/ZrO2 composite began discharging hydrogen at 219 °C, which was 111 °C lower compared to the as-synthesized MgH2. At 250 °C, the MgH2 + 10 wt% Mn3O4/ZrO2 composite released 6.4 wt% hydrogen within 10 min, whereas the as-synthesized MgH2 reluctantly released 1.4 wt% hydrogen even at 335 °C. Moreover, the dehydrogenated MgH2 + 10 wt% Mn3O4/ZrO2 sample started to charge hydrogen at room temperature. 6.0 wt% hydrogen was absorbed when heated to 250 °C under 3 MPa H2 pressure, and 4.1 wt% hydrogen was taken up within 30 min at 100 °C at the same hydrogen pressure. In addition, compared with the as-synthesized MgH2, the de/rehydrogenation activation energy values of the MgH2 + 10 wt% Mn3O4/ZrO2 composite were decreased to 64.52 ± 13.14 kJ mol-1 and 16.79 ± 4.57 kJ mol-1, respectively, which incredibly contributed to the enhanced hydrogen de/absorption properties of MgH2.

Cervical lymph node metastasis prediction of postoperative papillary thyroid carcinoma before 131I therapy based on clinical and ultrasound characteristics.

Background: The status of lymph nodes is crucial to determine the dose of radioiodine-131(131I) for postoperative papillary thyroid carcinoma (PTC). We aimed to develop a nomogram for predicting residual and recurrent cervical lymph node metastasis (CLNM) in postoperative PTC before 131I therapy. Method: Data from 612 postoperative PTC patients who underwent 131I therapy from May 2019 to December 2020 were retrospectively analyzed. Clinical and ultrasound features were collected. Univariate and multivariate logistic regression analyses were performed to determine the risk factors of CLNM. Receiver operating characteristic (ROC) analysis was used to weigh the discrimination of prediction models. To generate nomograms, models with high area under the curves (AUC) were selected. Bootstrap internal validation, calibration curves and decision curves were used to assess the prediction model's discrimination, calibration, and clinical usefulness. Results: A total of 18.79% (115/612) of postoperative PTC patients had CLNM. Univariate logistic regression analysis found serum thyroglobulin (Tg), serum thyroglobulin antibodies (TgAb), overall ultrasound diagnosis and seven ultrasound features (aspect transverse ratio, cystic change, microcalcification, mass hyperecho, echogenicity, lymphatic hilum structure and vascularity) were significantly associated with CLNM. Multivariate analysis revealed higher Tg, higher TgAb, positive overall ultrasound and ultrasound features such as aspect transverse ratio ≥ 2, microcalcification, heterogeneous echogenicity, absence of lymphatic hilum structure and abundant vascularity were independent risk factors for CLNM. ROC analysis showed the use of Tg and TgAb combined with ultrasound (AUC = 0.903 for "Tg+TgAb+Overall ultrasound" model, AUC = 0.921 for "Tg+TgAb+Seven ultrasound features" model) was superior to any single variant. Nomograms constructed for the above two models were validated internally and the C-index were 0.899 and 0.914, respectively. Calibration curves showed satisfied discrimination and calibration of the two nomograms. DCA also proved that the two nomograms were clinically useful. Conclusion: Through the two accurate and easy-to-use nomograms, the possibility of CLNM can be objectively quantified before 131I therapy. Clinicians can use the nomograms to evaluate the status of lymph nodes in postoperative PTC patients and consider a higher dose of 131I for those with high scores.

Constructing Mg2Co-Mg2CoH5 nano hydrogen pumps from LiCoO2 nanosheets for boosting the hydrogen storage property of MgH2.

Herein, an active positive electrode material, LiCoO2 nanosheets, was synthesized via a two-step method, which demonstrated a remarkable catalytic effect for the hydrogen storage property of MgH2. Incorporated with LiCoO2 nanosheets, MgH2 started to release hydrogen at 180 °C and a desorption content as high as 5.5 wt% H2 was attained within 60 min at 250 °C. The dehydrogenation activation energy was significantly decreased to 48.5 ± 0.4 kJ mol-1, achieving a 68.9% reduction compared to MgH2. It was verified by microstructural studies that Li+ served as an "anchor" to facilitate a uniform distribution of LiCoO2 "boat" among the MgH2 "ocean", benefitting the self-assembly of numerous Mg2Co-Mg2CoH5 couples on the surface of MgH2 during the cycling process. Meanwhile, the in situ formed Mg2Co-Mg2CoH5 couples were not restricted to offering multiple channels for fast hydrogen diffusion but also worked as "nano hydrogen pumps" to accelerate Mg/MgH2 hydrogen charging and discharging. This study provides an interesting example of effective cooperation between Li+ and Co3+ on improving the catalytic action toward MgH2. It shall shed light on efficient designing of high-efficient catalysts in hydrogen storage areas or other energy-related fields.

The remarkably improved hydrogen storage performance of MgH2 by the synergetic effect of an FeNi/rGO nanocomposite.

Magnesium hydride (MgH2) has been considered as a promising hydrogen storage material for buildings that are powered by hydrogen energy, but its practical application is hampered by poor kinetics and unstable thermodynamics. Herein, we describe a feasible method for preparing FeNi nanoparticles dispersed on reduced graphene oxide nanosheets (FeNi/rGO), and we confirmed that excellent catalytic effects increased the hydrogen storage performance of MgH2. 5 wt% FeNi/rGO-modified MgH2 began to release hydrogen at 230 °C and liberated 6.5 wt% H2 within 10 min at 300 °C. As for the hydrogenation process, the dehydrogenated sample absorbed 5.4 wt% H2 within 20 min at 125 °C under a hydrogen pressure of 32 bar. More importantly, a hydrogen capacity of 6.9 wt% was maintained after 50 cycles without compromising the kinetics during each cycle. A unique catalytic mechanism promoted synergetic effects between the in situ-formed Mg2Ni/Mg2NiH4, Fe, and rGO that efficiently promoted hydrogen dissociation and diffusion along the Mg/MgH2 interface, anchored the catalyst, and prevented MgH2 from aggregation and growth.

Realizing Hydrogen De/Absorption Under Low Temperature for MgH2 by Doping Mn-Based Catalysts.

Magnesium hydride (MgH2) has been considered as a potential material for storing hydrogen, but its practical application is still hindered by the kinetic and thermodynamic obstacles. Herein, Mn-based catalysts (MnCl2 and Mn) are adopted and doped into MgH2 to improve its hydrogen storage performance. The onset dehydrogenation temperatures of MnCl2 and submicron-Mn-doped MgH2 are reduced to 225 °C and 183 °C, while the un-doped MgH2 starts to release hydrogen at 315 °C. Further study reveals that 10 wt% of Mn is the better doping amount and the MgH2 + 10 wt% submicron-Mn composite can quickly release 6.6 wt% hydrogen in 8 min at 300 °C. For hydrogenation, the completely dehydrogenated composite starts to absorb hydrogen even at room temperature and almost 3.0 wt% H2 can be rehydrogenated in 30 min under 3 MPa hydrogen at 100 °C. Additionally, the activation energy of hydrogenation reaction for the modified MgH2 composite significantly decreases to 17.3 ± 0.4 kJ/mol, which is much lower than that of the primitive MgH2. Furthermore, the submicron-Mn-doped sample presents favorable cycling stability in 20 cycles, providing a good reference for designing and constructing efficient solid-state hydrogen storage systems for future application.

Excellent catalysis of Mn3O4 nanoparticles on the hydrogen storage properties of MgH2: an experimental and theoretical study.

Recently, transition metal oxides have been evidenced to be superior catalysts for improving the hydrogen desorption/absorption performance of MgH2. In this paper, Mn3O4 nanoparticles with a uniform size of around 10 nm were synthesized by a facile chemical method and then introduced to modify the hydrogen storage properties of MgH2. With the addition of 10 wt% Mn3O4 nanoparticles, the MgH2-Mn3O4 composite started to release hydrogen at 200 °C and approximately 6.8 wt% H2 could be released within 8 min at 300 °C. For absorption, the completely dehydrogenated sample took up 5.0 wt% H2 within 10 min under 3 MPa hydrogen even at 100 °C. Compared with pristine MgH2, the activation energy value of absorption for the MgH2 + 10 wt% Mn3O4 composite decreased from 72.5 ± 2.7 to 34.4 ± 0.9 kJ mol-1. The catalytic mechanism of Mn3O4 was also explored and discussed with solid evidence from X-ray diffraction (XRD), Transmission Electron Microscope (TEM) and Energy Dispersive X-ray Spectroscopy (EDS) studies. Density functional theory calculations revealed that the Mg-H bonds were elongated and weakened with the doping of Mn3O4. In addition, a cycling test showed that the hydrogen storage capacity and reaction kinetics of MgH2-Mn3O4 could be favourably preserved in 20 cycles, indicative of promising applications as a solid-state hydrogen storage material in a future hydrogen society.

Enhancing Hydrogen Storage Properties of MgH2 by Transition Metals and Carbon Materials: A Brief Review.

Magnesium hydride (MgH2) has attracted intense attention worldwide as solid state hydrogen storage materials due to its advantages of high hydrogen capacity, good reversibility, and low cost. However, high thermodynamic stability and slow kinetics of MgH2 has limited its practical application. We reviewed the recent development in improving the sorption kinetics of MgH2 and discovered that transition metals and their alloys have been extensively researched to enhance the de/hydrogenation performance of MgH2. In addition, to maintain the cycling property during the de/hydrogenation process, carbon materials (graphene, carbon nanotubes, and other materials) have been proved to possess excellent effect. In this work, we introduce various categories of transition metals and their alloys to MgH2, focusing on their catalytic effect on improving the hydrogen de/absorption performance of MgH2. Besides, carbon materials together with transition metals and their alloys are also summarized in this study, which show better hydrogen storage performance. Finally, the existing problems and challenges of MgH2 as practical hydrogen storage materials are analyzed and possible solutions are also proposed.

Catalytic Effect of Facile Synthesized TiH1.971 Nanoparticles on the Hydrogen Storage Properties of MgH2.

Abstract: Catalytic doping plays an important role in enhancing the hydrogen storage performance of MgH2, while finding an efficient and reversible catalyst remains to be a great challenge in enhancing the de/rehydrogenation properties of MgH2. Herein, a bidirectional nano-TiH1.971 catalyst was prepared by a wet chemical ball milling method and its effect on hydrogen storage properties of MgH2 was studied. The results showed that all the TiH1.971 nanoparticles were effective in improving the de/rehydrogenation kinetics of MgH2. The MgH2 composites doped with TiH1.971 could desorb 6.5 wt % H2 in 8 min at 300 °C, while the pure MgH2 only released 0.3 wt % H2 in 8 min and 1.5 wt % H2 even in 50 min. It was found that the smaller the size of the TiH1.971 particles, the better was the catalytic effect in promoting the performance of MgH2. Besides, the catalyst concentration also played an important role and the 5 wt %-c-TiH1.971 modified system was found to have the best hydrogen storage performance. Interestingly, a significant hydrogen absorption amount of 4.60 wt % H2 was evidenced for the 5 wt %-c-TiH1.971 doped MgH2 within 10 min at 125 °C, while MgH2 absorbed only 4.11 wt% hydrogen within the same time at 250 °C. The XRD results demonstrated that the TiH1.971 remained stable in cycling and could serve as an active site for hydrogen transportation, which contributed to the significant improvement of the hydrogen storage properties of MgH2.

Superior catalytic effects of FeCo nanosheets on MgH2 for hydrogen storage.

Magnesium hydride (MgH2) is considered as a promising hydrogen storage material for "hydrogen economy" due to its high capacity; however, its stable thermodynamics and slow kinetics hinder its practical applications. Transition metal catalysts attract intense interest in modifying MgH2 systems. Herein, FeCo nanosheets with a thickness of 50 nm were successfully prepared and confirmed to have superior catalytic effects on MgH2. The nano-FeCo-catalyzed MgH2 started to release hydrogen at 200 °C which ended at 320 °C, while the hydrogen desorption process of pure MgH2 occurred at 350-420 °C. Besides, the dehydrogenated FeCo-containing sample could rapidly take up 6.7 wt% H2 within 1 min at 300 °C. Furthermore, after doping with nano-FeCo, the activation energy of hydrogen desorption and absorption was dramatically reduced to 65.3 ± 4.7 kJ mol-1 and 53.4 ± 1.0 kJ mol-1, respectively. In a word, our findings may provide references for designing and producing nano-level intermetallic catalysts for the research area of hydrogen storage or other energy-related research.