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Iron-doped catalyst Fe x Cu–N–C were prepared from an N-rich Fe-Cu-BTT precursor. The introduction of Fe significantly increases the selectivity of CO 2 -to−CO due to the increase of the BET surface, the total pore volume, the Fe–N x sites, as well as the decrease of Cu NPs density in the carbon matrix. • Iron-doped catalyst Fe x Cu–N–C were prepared from an N-rich Fe-Cu-BTT precursor. • The introduction of Fe significantly increases the BET surface and the total pore volume. • Fe x Cu–N–C shows abundant Fe–N x active sites. • Fe x Cu–N–C increases the selectivity of CO 2 -to−CO. • Fe 0.07 Cu–N–C 800 exhibits the highest CO faradaic efficiency. Fe–N–macrocycles have been viewing as the most promising catalyst for CO 2 ER. It is of great importance to explore the performance of composite CuFe–N–C in CO 2 ER. Fe-Cu–BTT precursor was prepared by introducing the ferrous ion to a microporous N-rich MOF. It exhibits a lower plateau temperature of 800 ℃ than the prototype. The pyrolysis product of Fe x Cu–N–C increases the selectivity of CO 2 -to−CO due to the increase of the BET surface area, the total pore volume, and the Fe–N x sites, as well as a lower density of Cu NPs in the carbon matrix. The Fe 0.07 Cu–N–C 800 exhibits the highest FE CO of 48.5 %. [ABSTRACT FROM AUTHOR]

Reactions between alkali metal hydrides MH (M = Li, Na, or K) and carbon dioxide (CO 2 ) at room temperature were systematically investigated for the first time. It was found that the raw alkali metal hydrides did not react with CO 2 under static-pressure conditions at room temperature, but the mechanically activated alkali metal hydrides reacted with CO 2 and released large amounts of hydrogen (H 2 ). Under the same ball-milling conditions, the order of reactivity of the alkali metal hydrides with CO 2 was KH > NaH > LiH. The particle size of the activated alkali metal hydrides had a large influence on the reactivity of the alkali metal hydrides with CO 2 . During the reactions, CO 2 was reduced by alkali metal hydrides, generating elemental carbon, alkali metal oxides and H 2 , and it was consumed by alkali metal oxides, forming carbonates. [ABSTRACT FROM AUTHOR]

In this study, we first examined the hydrogen release, uptake, and reversibility properties of the KLi 3 (NH 2 ) 4 -4LiH system and elucidated the influence of potassium cations' substitution into LiNH 2 on the hydrogen storage properties of the LiNH 2 -LiH composite. Our results show that mixing of the potassium cations into LiNH 2 can destabilize LiNH 2 , therefore decreasing the hydrogen desorption temperature and enhancing hydrogen desorption rate of the LiNH 2 -LiH system. Notably, the KLi 3 (NH 2 ) 4 -4LiH composite exhibits a superior cycling stability compared with the LiNH 2 -LiH composite prepared under the same condition. [ABSTRACT FROM AUTHOR]

In this study, the hydrogen desorption properties for the reactions between lithium hydride with different particle sizes and NH 3 (0.5 MPa, NH 3 /MH = 1 mol/mol) at 50–200 °C were systematically investigated to design the LiH–NH 3 hydrogen storage system with better kinetic properties. Moreover, various kinds of potassium compounds were also examined as potential catalysts to improve the kinetic properties of the hydrogen desorption reaction in the system. It is found that the kinetic properties of the hydrogen desorption in the LiH–NH 3 system are improved with the particle size of LiH reducing or the reaction temperature increasing. KBr, KCl, KF, and KOH are effective to enhance the kinetic properties, among which, KBr shows the best effect. [ABSTRACT FROM AUTHOR]

Ammonia is a vital intermediate in the hydrogen desorption process of Metal-N-H system. KH has strong reactivity with NH 3 to form KNH 2. We speculate that KNH 2 is also an intermediate formed during hydrogen desorption of the potassium-doped M-N-H systems. In this research, the dehydrogenation performance of the KNH 2 -doped LiNH 2 and LiH composition was first studied. Compared with the broad dehydrogenation curve of the composite material of LiNH 2 and LiH without the catalyst, the dehydrogenation curve of 0.05 mol KNH 2 -doped composite material was significantly narrowed. The initial and peak dehydrogenation temperature of the composite to which 0.05 mol of KNH 2 was added was lowered remarkably. Besides, the cyclic dehydrogenation properties of the LiNH 2 and LiH system was also significantly enhanced by the introduction of KNH 2. The cyclic conversion of KNH 2 to KH is the main reason for the enhancement of the hydrogen evolution performance of the LiNH 2 –LiH system doped with KNH 2. We found the KNH 2 -doped Li–N–H system exhibits similar dehydrogenation property with that of the KH-doped Li–N–H system. This work proves that KNH 2 plays a key role in improving the hydrogen desorption performances of the potassium-doped M-N-H systems. Image 1 • Hydrogen desorption properties of the KNH 2 -doped Li–N–H system was examined. • Hydrogen desorption kinetics are significantly enhanced by introducing KNH 2. • The dehydrogenation temperature is lowered drastically. • The improved properties induce from the cyclic conversion from KNH 2 to KH. • KNH 2 may be formed during dehydrogenation of the potassium-doped M-N-H system. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mechanochemical hydrogenation of shell wastes was studied at room temperature. • Alkaline metals can selectively assist the hydrogenation of shell wastes to CH 4. • The calcium metal has a better effect and the methane yield can reach 45.04%. • By doping Ru the methane yield of shell wastes can be improved to 54.76%. • This study provides a method to eliminate shell wastes and produce CH 4 fuel. Producing clean fuel using shell wastes (eggshell and clamshell) can eliminate food waste and alleviate the energy shortage. Mechanochemical hydrogenation of eggshell/clamshell was investigated at room temperature. The results show that the alkaline earth metals can effectively assist the hydrogenation of shell wastes to CH 4. The calcium metal has a better effect, and the methane yield for the calcium-assisted hydrogenation of clamshell and eggshell reaches 45.04% and 33.30% with 100% CH 4 selectivity. At the same time, the calcium-assisted methanation of shell wastes in the presence of transition metals (Fe, Co, Ni, Ru) was investigated. By doping Ru, the methane yield of clamshell and eggshell was improved to 52.62% and 54.76%, respectively. The milling time, rotating speed, hydrogen pressure, and the species of the doped transition metals influence the calcium-assisted methanation of shell wastes. This study provides an alternative method to eliminate shell wastes and produce clean CH 4 fuel at room temperature. [ABSTRACT FROM AUTHOR]

In this work, we report a novel, simple and convenient method for CO 2 methanation and synthesis of hydrogen and methane fuel mixtures at room temperature. CO x -free hydrogen and methane fuel mixtures have been successfully generated for the first time in one pot at room temperature through the solid/gas mechanochemical reactions of selected light metal hydrides with CO 2 . It is noted that methane is the sole hydrocarbon product in the mechanochemical reactions of selected light metal hydrides with CO 2 , which suggests that the mechanochemical reduction of CO 2 by light metal hydrides is highly selective. The yield and mole fraction of methane in the gas product depend mainly on the species of light metal hydride, rate and duration of ball milling, and CO 2 pressure. [ABSTRACT FROM AUTHOR]

In this paper, the hydrogen storage properties of the LiNH 2 LiH system doped with K 2 TiF 6 were investigated and discussed. Interestingly, the hydrogen storage properties are significantly enhanced by introducing K 2 TiF 6 into the LiNH 2 LiH system. By doping 5 mol% K 2 TiF 6 in the LiNH 2 LiH system, we obtain the hydrogen desorption peak temperature (233 °C) at a heating rate of 10 °C min −1 , which is approximately 66 °C lower than that of the pristine LiNH 2 LiH system. Moreover, the system begins to desorb H 2 at 75 °C, which is approximately 124 °C lower than in the pristine LiNH 2 LiH system. The isothermal desorption kinetics at 250 °C and 300 °C clearly reflects the dramatically improved kinetic properties. Additionally, the reversibility of the LiNH 2 LiH system can be drastically enhanced by adding K 2 TiF 6 . We propose that the dehydrogenation property of the K 2 TiF 6 -doped LiNH 2 LiH sample is improved by the synergetic effects of K, Ti and F. [ABSTRACT FROM AUTHOR]

In this paper, the influence of multi-walled carbon nanotube (MWCNT)-doping on the hydrogen storage properties of the Li 3 N system was systematically investigated. Compared with the pure Li 3 N sample, the MWCNT-doped Li 3 N sample shows faster hydrogen absorption and desorption kinetics and a drastically improved cycling stability. Along with increasing MWCNT content, the hydrogen storage improvement becomes more apparent. When the MWCNT doping level reaches 10 mol%, the enhancement effect is significant. The improved hydrogen storage properties of the Li 3 N system by MWCNT-doping can be reduced to the physical effect of ball milling, the increased specific surface area and large pores as well as the good thermal conductivity of MWCNTs. [ABSTRACT FROM AUTHOR]

Interestingly, an obvious enhancement of the hydrogen storage property is achieved by introducing KF into the LiNH 2 –LiH system, while KCl, KBr or KI does not show obvious effect on improving the hydrogen storage properties of the LiNH 2 –LiH system. In comparison with that of the LiNH 2 –LiH composite, the hydrogen desorption curve of the LiNH 2 –LiH–0.05 KF composite becomes sharp and the dehydrogenation onset and peak temperatures are decreased by about 36 °C and 38 °C, respectively. The cyclic capacity and desorption kinetic of the LiNH 2 –LiH–0.05 KF composite in the tenth cycle are still much better than that of the LiNH 2 –LiH composite in the second cycle. Cyclic performance can be improved at least 4 times by addition of 5 mol% KF. Detailed structural investigations reveal that during the heat-treatment, the doped potassium fluoride can react with LiH and convert to potassium hydride, which induces the improvement in hydrogen storage properties of the LiNH 2 –LiH system. [ABSTRACT FROM AUTHOR]

Liquid ammonia electrolysis is conducted out at ambient temperature using different ammonium salt electrolytes with and without the reference electrode. It is determined that electrolytes containing NH 4 + increase the current density and reduce the solution resistance. Moreover, ammonium salts of NH 4 Br, NH 4 NO 3 and NH 4 Cl preserve >80% current efficiency and a 0.6–0.8 mL min −1 average rate of H 2 generation during chronopotentiometry tests at 120 mA cm −2 for 3 h. A minimum electrolysis voltage ( E min ) of ca . 1.2 V is required for the NH 4 Cl electrolyte when using Pt-foil as the anode and cathode. To decrease the overpotential of the anode reaction, five types of electrocatalysts were prepared and characterized: Pt-black, Rh, Pt–Ir, Rh–Pt and Ph–Pt–Ir alloys. Trimetallic Rh–Pt–Ir and bimetallic Pt–Ir, Rh–Pt (1:1) alloy electrodes exhibit a combined benefit of better activity and minimized deactivation. The ternary Rh–Pt–Ir alloy anode shows the best electrocatalytic activity with the lowest E min of ca . 0.47 V and highest current density of 46.9 mA cm −2 at 2.0 V. In comparison with the Pt-foil anode, the E min is reduced by two-thirds, and the current density is increased two-fold. [ABSTRACT FROM AUTHOR]

CO x -free H 2 -mixed CH 4 fuel was successfully prepared by thermochemical reduction of solid CO 2 (inorganic carbonates) with solid hydrogen (activated metal hydrides). [Display omitted] • Thermochemical reaction of carbonate with hydride was first investigated. • CO x -free H 2 -mixed CH 4 fuel was successfully prepared at moderate condition. • The CH 4 yield and content depend on reaction condition and reactant nature. • For carbonate-hydride system, CH 4 yield can reach 84.5% with 100% selectivity. • This work opens new way to in-situ synthesize H 2 -mixed CH 4 fuel utilizing CO 2. Converting CO 2 into methane is realistic and conducive to addressing environmental and energy issues. The mixture of hydrogen and methane shows superior combustion efficiency, while the investigation on the storage and in-situ preparation of hydrogen-mixed methane was neglected. In this work, thermochemical reduction of solid CO 2 (inorganic carbonates) with solid hydrogen (activated metal hydrides) was first investigated, and we successfully prepared CO x -free H 2 -mixed CH 4 fuel with high yields and selectivity. As respects to the inorganic carbonate-metal hydride systems, the volume energy density can reach as high as 12055.4 kJ/mol, CH 4 yield can reach 84.5% with approximate 100% selectivity, and the CH 4 content ranging from 8.6% to 88.1% is able to be tuned. It was confirmed that the nature of inorganic carbonates/hydrides, heating time and temperature, and the composition of the reaction mixture has a significant influence on methane yield and content. These results demonstrate that heat treatment of nanosized inorganic carbonates and activated metal hydrides is a promising process for in-situ preparation of H 2 -mixed CH 4 fuel and CO 2 utilization. [ABSTRACT FROM AUTHOR]

In this paper, we studied the mechanochemical reactions between a series of metal carbonates and metal hydrides in the absence of a catalyst and found that the alkaline earth metal carbonate-hydride systems show better methanation performances because these systems possess favorable thermodynamic properties. Among them, the CaCO 3 -MgH 2 system shows the best methanation performances. By tuning the reaction mixture composition and enhancing the rate and duration of ball milling, the CH 4 yield and content of the CaCO 3 -MgH 2 system can reach 89% and 90%, respectively, which are increased by 16% and 40%, compared to the best results in the previous reports. Image 1 • The mechanical reactions of metal carbonates with metal hydrides was investigated. • The alkaline metal carbonate can be effectively reduced to methane by the alkaline metal hydride. • The CaCO 3 -MgH 2 system shows the best methanation performances. • The CH 4 yield and content of the CaCO 3 -MgH 2 system can reach 89% and 90%. • The work provides a simple and efficient method for synthesizing H 2 -CH 4 fuel mixtures. [ABSTRACT FROM AUTHOR]