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The chain-like carbon nanotubes (CNTs) decorated with CoFeB (CoFeB/CNTs) prepared by oxidation-reduction method is introduced into MgH2 to facilitate its hydrogen storage performance. The addition of CoFeB/CNTs enables MgH2 to start desorbing hydrogen at only 177 °C. Whereas pure MgH2 starts hydrogen desorption at 310 °C. The dehydrogenation apparent activation energy of MgH2 in CoFeB/CNTs doped-MgH2 composite is only 83.2 kJ/mol, and this is about 59.5 kJ/mol lower than that of pure MgH2. In addition, the completely dehydrogenated MgH2−10 wt% CoFeB/CNTs sample can start to absorb hydrogen at only 30 °C. At 150 °C and 5 MPa H2, the MgH2 in CoFeB/CNTs doped-MgH2 composite can absorb 6.2 wt% H2 in 10 min. The cycling kinetics can remain rather stable up to 20 cycles, and the hydrogen storage capacity retention rate is 98.5%. The in situ formation of Co3MgC, Fe, CoFe and B caused by the introduction of CoFeB/CNTs can provide active and nucleation sites for the dehydrogenation/rehydrogenation reactions of MgH2. Moreover, CNTs can provide hydrogen diffusion pathways while also enhancing the thermal conductivity of the sample. All of these can facilitate the dehydrogenation/rehydrogenation performance and cyclic stability of MgH2.

Waste sorting is being gradually implemented as a key measure for circular and sustainable development in China, food waste will be separately collected and separated from municipal solid waste (MSW), thus the plastic content in food waste also will be reduced. In this study, supercritical water gasification (SCWG) of food waste with different contents of plastic (0–3.5 wt%) was experimentally investigated to simulate the influence of waste sorting on the food waste treatment. The results showed that lower plastic content in food waste favored higher gas yield and gasification efficiencies. The highest H2 yield and total gas yield were 3.11 mol/kg and 8.41 mol/kg in the plastic-free case, respectively. When the plastic content decreased from 3.5 wt% to 0 wt%, the cold gas efficiency (CGE), carbon conversion efficiency (CE) and hydrogen gasification efficiency (HE) increased by 125.97%, 173.48% and 94.09%, respectively. However, lower plastic content negatively affected the quality of produced syngas through decreasing H2 mole fraction and LHV. The solid residues from SCWG of food waste with lower plastic content had higher ratio of fixed carbon to volatile matter (FC/VM). Based on the analysis of pyrolysis properties and combustion behavior, decreasing the plastic content in food waste helped to improve the thermal stability of solid residues. Moreover, lower plastic content resulted in a decrease of total organic carbon (TOC) concentration in liquid effluent, which is favorable for further treatment of liquid effluent.

In order to improve the hydrogen storage performance of MgH2, graphene and CeF3 co-catalyzed MgH2 (hereafter denoted as MgH2+CeF3@Gn) were prepared by wet method ball milling and hydriding, which is a simple and time-saving method. The effect of CeF3@Gn on the hydrogen storage behavior of MgH2 was investigated. The experimental results showed that co-addition of CeF3@Gn greatly decreased the hydrogen desorption/absorption temperature of MgH2, and remarkably improved the dehydriding/hydriding kinetics of MgH2. The onset hydrogen desorption temperature of Mg + CeF3@Gn is 232 °C，which is 86 °C lower than that of as-milled undoped MgH2, and its hydrogen desorption capacity reaches 6.77 wt%, which is 99% of its theoretical capacity (6.84 wt%). At 300 °C and 200 °C the maximum hydrogen desorption rates are 79.5 and 118 times faster than that of the as-milled undoped MgH2. Even at low temperature of 150 °C, the dedydrided sample (Mg + CeF3@Gn) also showed excellent hydrogen absorption kinetics, it can absorb 5.71 wt% hydrogen within 50 s, and its maximum hydrogen absorption rate reached 15.0 wt% H2/min, which is 1765 times faster than that of the undoped Mg. Moreover, no eminent degradation of hydrogen storage capacity occurred after 15 hydrogen desorption/absorption cycles. Mg + CeF3@Gn showed excellent hydrogen de/absorption kinetics because of the MgF2 and CeH2-3 that are formed in situ, and the synergic catalytic effect of these by-products and unique structure of Gn.

Ni/Al2O3 catalyst is the one of promising catalysts for enhancing H2 production from supercritical water gasification (SCWG) of biomass. However, due to carbon deposition, the deactivation of Ni/Al2O3 catalyst is still a serious issue. In this work, the effects of lanthanum (La) as promoter on the properties and catalytic performance of Ni/Al2O3 in SCWG of food waste were investigated. La promoted Ni/Al2O3 catalysts with different La loading content (3–15 wt%) were prepared via impregnation method. The catalysts were characterized using XRD, SEM, BET techniques. The SCWG experiments were carried out in a Hastelloy batch reactor in the operating temperature range of 420–480 °C, and evaluated based on H2 production. The stability of the catalysts was assessed by the amount of carbon deposition on catalyst surface and their catalytic activity after reuse cycles. The results showed that 9 wt% La promoter is the optimal loading as Ni/9La–Al2O3 catalyst performed best performance with the highest H2 yield of 8.03 mol/kg, and H2 mole fraction of 42.46% at 480 °C. La promoted Ni/Al2O3 catalysts have better anti-carbon deposition properties than bare Ni/Al2O3 catalyst, resulting in better gasification efficiency after reuse cycles. Ni/9La–Al2O3 catalyst showed high catalytic activity in SCWG of food waste and had good stability as it was still active for enhancing H2 production when used in SCWG for the third time, which indicated that La promoted Ni/Al2O3 catalysts are potential additive to improve the SCWG of food waste.

An integrated system of supercritical water gasification (SCWG) and combined cycle has been developed for H2 production and power generation. Sewage sludge and lignite coal were selected as raw material in this simulation. The effects of feed concentration (10–30 wt%) and lignite coal addition (0–50 wt%) on syngas yield and H2 yield were also investigated in the temperature range of 500 °C–700 °C. Several heat exchangers were considered in the proposed integrated system to minimize energy loss. High pressure syngas was expanded by using turbo-expander to produce electricity, resulting in the improvement of the total efficiency. The results showed that the minimum feed concentrations of 14.25 wt%, 18.75 wt%, and 25.50 wt% were required to achieve self-sufficient energy at 500 °C, 600 °C, and 700 °C, respectively. However, the lower feed concentration and higher temperature were preferable for syngas production. The highest syngas and H2 yield were obtained at 700 °C and 10 wt% feed concentration. The SCWG could produce 178.08 kg syngas from 100 kg feed and 9.06 kg H2 were obtained after H2 separation. The total power generation from turbo-expander and combined cycle module was 48.37 kW. By combining SCWG and combined cycle, the total efficiency could reach 63.48%. It worth mentioning that the addition of lignite coal could help reduce the minimum feed concentration to achieve autothermal condition, but did not have significant improvement on H2 production.

Food waste is a kind of wet bio-waste which has been a challenge for the ecological environment and disposal. In this paper, hydrogen production from subcritical water gasification (SbWG) of food waste with and without catalyst loading was systematically investigated. The effects of reaction temperature (300–360 °C), residence time (30–90 min), food waste concentration (10–30 wt%) and catalysts (Ni/γ-Al2O3, Ni/ZrO2, NaOH, KOH, and FeCl3) were studied within a pressure range of 10.5–20 MPa. The optimal process condition for SbWG of food waste without catalysts loading was determined to be 360 °C and 90 min with 10 wt% food waste. The liquid products and hydrochar were characterized by TOC, TGA/DTG, and SEM. The TOC concentration of liquid products decreased vastly with increasing reaction temperature. The highest H2 yield (1.88 mol/kg), H2 mole fraction (35.01%), and H2 selectivity (53.86%) were achieved at 360 °C for 90 min with 5 wt% loading of KOH. It can be concluded that the performance of the catalysts for improving hydrogen production in SbWG of food waste was in the following order: KOH > NaOH > Ni/γ-Al2O3 > Ni/ZrO2 > FeCl3. The catalytic SbWG can be a potential alternative for energy conversion of food waste and hydrogen production.

This paper presents the results from experimental study of syngas production by catalytic cracking of tar in wastewater under supercritical condition. Ni/Al2O3 catalysts were prepared via the ultrasonic assisted incipient wetness impregnation on activated alumina, and calcined at 600 °C for 4 h. All catalysts showed mesoporous structure with specific surface area in a range of 146.6–215.3 m2/g. The effect of Ni loading (5–30 wt%), reaction temperature (400–500 °C), and tar concentration (0.5–7 wt%) were systematically investigated. The overall reaction efficiency and the gas yields, especially for H2, were significantly enhanced with an addition of Ni/Al2O3 catalysts. With 20%Ni/Al2O3, the H2 yield increased by 146% compared to the non-catalytic experiment. It is noteworthy that the reaction at 450 °C with the addition of 20%Ni/Al2O3 had a comparable efficiency to the reaction without catalyst at 500 °C. The maximum H2 yield of 46.8 mol/kgtar was achieved with 20%Ni/Al2O3 at 500 °C and 0.5 wt% tar concentration. The catalytic performance of the catalysts gradually decreased as the reuse cycle increased, and could be recovered to 88% of the fresh catalyst after regeneration. 20%Ni/Al2O3 has a potential to improve H2 production, as well as a good reusability. Thus, it is considered a promising catalyst for energy conversion of tar in wastewater.

In this study, the model food waste was gasified to hydrogen-rich syngas in a batch reactor under supercritical water condition. The model food consisted of rice, chicken, cabbage, and cooking oil. The effects of the main operating parameters including temperature (420–500 °C), residence time (20–60 min) and feedstock concentration (2–10 wt%) were investigated. Under the optimal condition at 500 °C, 2 wt% feedstock and 60 min residence time, the highest H2 yield of 13.34 mol/kg and total gas yield of 28.27 mol/kg were obtained from non-catalytic experiments. In addition, four commercial catalysts namely FeCl3, K2CO3, activated carbon, and KOH were employed to investigate the catalytic effect of additives at the optimal condition. The results showed that the highest hydrogen yield of 20.37 mol/kg with H2 selectivity of 113.19%, and the total gas yield of 38.36 mol/kg were achieved with 5 wt% KOH addition Moreover, the low heating value of gas products from catalytic experiments with KOH increased by 32.21% compared to the non-catalytic experiment. The catalytic performance of the catalysts can be ranked in descending order as KOH > activated carbon > FeCl3 > K2CO3. The supercritical water gasification (SCWG) with KOH addition can be a potential applied technology for food waste treatment with production of hydrogen-rich gases.

In this paper, a conceptual process design of the integrated supercritical water gasification (SCWG) and reforming process for enhancing H2 production has been developed. The influence of several operating parameters including SCWG temperature, SCWG pressure, reforming temperature, reforming pressure and feed concentration on the syngas composition and process efficiency was investigated. In addition, the thermodynamic equilibrium calculations have been carried out based on Gibbs free energy minimization by using Aspen Plus. The results showed that the higher H2 production could be obtained at higher SCWG temperature, the H2 concentration increased from 5.40% at 400 °C to 38.95% at 600 °C. The lower feed concentration was found to be favorable for achieving hydrogen-rich gas. However, pressure of SCWG had insignificant effect on the syngas composition. The addition of reformer to the SCWG system enhanced H2 yield by converting high methane content in the syngas into H2. The modified SCWG enhanced the productivity of syngas to 151.12 kg/100kgfeed compared to 120.61 kg/100kgfeed of the conventional SCWG system. Furthermore, H2 yield and system efficiency increased significantly from 1.81 kg/100kgfeed and 9.18% to 8.91 kg/100kgfeed, and 45.09%, respectively, after the modification.

Aluminium hydride (AlH3) is a promising hydrogen storage material because it possesses a high theoretical hydrogen capacity of 10.01 wt%. However, the stability and decomposition mechanism of some AlH3 polymorphs (e.g., γ-AlH3) still remain unclear. In this work, the hydrogen desorption behaviours of γ-AlH3 with or without TiF3 addition were investigated by hydrogen desorption measurement and thermal analysis. It was revealed that the decompositions of the outer layer and the inner part of γ-AlH3 particle follow diverse decomposition mechanisms. The outer layer of γ-AlH3 particle tends to decompose directly, while the inner part of γ-AlH3 particle prefers to first transform to more stable α-AlH3 and then decompose. TiF3 addition significantly lowers the temperature for the direct decomposition of outer layer γ-AlH3 by about 30 °C but scarcely impacts the decomposition of inner part γ-AlH3, which further confirms the decomposition mechanism of γ-AlH3. It was suggested that the particle size plays an important role in the thermal stability of γ-AlH3. The results of this work will help understanding the decomposition mechanisms of other AlH3 polymorphs for hydrogen storage.

CeF 3 as a catalyst is first added to activated carbon (AC) by ball milling under low rotation speed. Then the treated AC was used as the scaffold to confine LiBH 4 by melt infiltration process. The combined effects of confinement and CeF 3 doping on the hydrogen storage properties of LiBH 4 are studied. The experimental results show that LiBH 4 and CeF 3 are well dispersed in the AC scaffold and occupy up to 90% of the pores of AC. Compared with pristine LiBH 4 , the onset dehydrogenation temperature for LiBH 4 -AC and LiBH 4 -AC-CeF 3 decreases by 150 and 190 °C, respectively. And the corresponding dehydrogenation capacity increases from 8.2 wt% to 13.1 wt% for LiBH 4 -AC and 12.8 wt% for LiBH 4 -AC-CeF 3 , respectively. The maximum dehydrogenation speed of LiBH 4 -AC and LiBH 4 -AC-CeF 3 is 80 and 288 times higher than that of pristine LiBH 4 at 350 °C. And LiBH 4 -AC andLiBH 4 -AC-CeF 3 show good reversible hydrogen storage properties. On the during 4th dehydrogenation cycle, the hydrogen release capacity of LiBH 4 -AC and LiBH 4 -AC-5 wt% CeF 3 reaches 8.1 and 9.3 wt%, respectively.

LiBH4 can be destabilized by AlH3 addition. In this work, the hydrogen desorption kinetics of the destabilized LiBH4 AlH3 composites were investigated. Isothermal hydrogen desorption studies show that the LiBH4 + 0.5AlH3 composite releases about 11.0 wt% of hydrogen at 450 °C for 6 h and behaves better kinetic properties than either the pure LiBH4 or the LiBH4 + 0.5Al composite. The apparent activation energy for the LiBH4 decomposition in the LiBH4 + 0.5AlH3 composite estimated by Kissinger's method is remarkably lowered to 122.0 kJ mol−1 compared with the pure LiBH4 (169.8 kJ mol−1). Besides, AlH3 also improves the reversibility of LiBH4 in the LiBH4 + 0.5AlH3 composite. For the LiBH4 + xAlH3 (x = 0.5, 1.0, 2.0) composites, the decomposition kinetics of LiBH4 are enhanced as the AlH3 content increases. The sample LiBH4 + 2.0AlH3 can release 82% of the hydrogen capacity of LiBH4 in 29 min at 450 °C, while only 67% is obtained for the LiBH4 + 0.5AlH3 composite in 110 min. Johnson−Mehl−Avrami (JMA) kinetic studies indicate that the reaction LiBH4 + Al → ‘Li Al B’ + AlB2 + H2 is controlled by the precipitation and subsequently growth of AlB2 and Li Al B compounds with an increasing nucleation rate.

Lithium borohydride (LiBH4) possesses a very high hydrogen capacity (18.5 wt%) but suffers from high thermal stability. In this work, the as-prepared aluminium hydride (AlH3) was ball milled with LiBH4 forming 2LiBH4 + AlH3 composite to improve the hydrogen desorption properties of LiBH4. Hydrogen desorption measurements showed that a hydrogen capacity of 11.2 wt% is obtained from the 2LiBH4 + AlH3 composite and the desorption temperature of LiBH4 with AlH3 addition is reduced by more than 30 °C. AlH3 is better as an Al source than the as-received Al in that the hydrogen desorption extent of AlH3-doped LiBH4 reaches 70%, while it is 54% and 61% for the pure LiBH4 and the Al-doped LiBH4. This is due to the brittle and oxide-free nature of AlH3. Microstructure investigations showed that during heating process, the 2LiBH4 + AlH3 composite undergoes AlH3 decomposition forming Al* and releasing hydrogen, followed by the decomposition of LiBH4. LiBH4 will react with Al* forming AlB2 and Li Al B compounds during its decomposition, which contributes to the improved hydrogen desorption properties of LiBH4.

The ternary imide Li 2 Mg(NH) 2 is considered to be one of the most promising on-board hydrogen storage materials due to its high reversible hydrogen capacity of 5.86 wt%, favorable thermodynamic properties and good cycling stability. In this work, Li 2 Mg(NH) 2 was synthesized by dynamically dehydrogenating a mixture of Mg(NH 2 ) 2 –2LiH up to 280 °C under different gas (Ar and H 2 ) and pressures (0–9.0 bar). The crystal structure of Li 2 Mg(NH) 2 was found to depend on the gas back pressure in the dehydrogenation process. The crystal structure of Li 2 Mg(NH) 2 and the dehydrogenation/rehydrogenation properties of the Mg(NH 2 ) 2 –2LiH system strongly depend on the gas back pressure in the dehydrogenation process due to the effect of the pressure on the dehydrogenation kinetics. This study provides a new approach for improving the hydrogen storage properties of the amide–hydride systems.

AlH3 is a promising hydrogen storage material due to its high hydrogen capacity (10 wt%) and relatively low dehydriding temperature. In this work, γ-AlH3 was prepared by organometallic synthesis method and the effects of ball milling on dehydriding properties of γ-AlH3 were investigated systematically. Experimental results shows that as-prepared γ-AlH3 releases about 8.3 wt% of hydrogen in the temperature range of 130–160 °C at a heating rate of 2 °C/min. Ball milling significantly improves the dehydriding behavior of γ-AlH3. DSC-MS analysis reveals that the dehydriding temperature of γ-AlH3 ball-milled for 10 h decreases by around 30 °C. In addition, the dehydriding activation energy of γ-AlH3 ball-milled for 2 h decreased from 87 to 68 kJ/mol. Isothermal dehydriding measurements demonstrate that duration needed to release 90% hydrogen for as-prepared γ-AlH3 is 280 min, but it takes only 82 min after ball milled for 10 h to release the same amount of hydrogen. Moreover, the dehydriding path of γ-AlH3 is changed by ball milling. As-prepared γ-AlH3 transforms to α-AlH3 before dehydriding, while ball-milled γ-AlH3 prefers to dehydride directly without firstly transforming to α-AlH3.