China, People’s Republic

The liquid chemical hydrogen storage technology has great potentials for high-density hydrogen storage and transportation at ambient temperature and pressure. However its commercial applications highly rely on the high-performance heterogeneous dehydrogenation catalysts owing to the dehydrogenation difficulty of chemical hydrogen storage materials. In recent years the chemists and materials scientists found that the supported metal nanoparticles (MNPs) can exhibit high catalytic activity selectivity and stability for the dehydrogenation of chemical hydrogen storage materials which will clear the way for the commercial application of liquid chemical hydrogen storage technology. This review has summarized the recent important research progress in the MNP-catalyzed liquid chemical hydrogen storage technology including formic acid dehydrogenation hydrazine hydrate dehydrogenation and ammonia borane dehydrogenation discussed the urgent challenges in the key field and pointed out the future research trends.

The remaining useful life (RUL) prediction for hydrogen fuel cells is an important part of its prognostics and health management (PHM). Artificial neural networks (ANNs) are proven to be very effective in RUL prediction as they do not need to understand the failure mechanisms behind hydrogen fuel cells. A novel RUL prediction method for hydrogen fuel cells based on the gated recurrent unit ANN is proposed in this paper. Firstly the data were preprocessed to remove outliers and noises. Secondly the performance of different neural networks is compared including the back propagation neural network (BPNN) the long short-term memory (LSTM) network and the gated recurrent unit (GRU) network. According to our proposed method based on GRU the root mean square error was 0.0026 the mean absolute percentage error was 0.0038 and the coefficient of determination was 0.9891 for the data from the challenge datasets provided by FCLAB Research Federation when the prediction starting point was 650 h. Compared with the other RUL prediction methods based on the BPNN and the LSTM our prediction method is better in both prediction accuracy and convergence rate.

Hydrogen refueling stations are one of the key infrastructure components for the hydrogen-fueled economy. Skid-mounted hydrogen refueling stations (SHRSs) can be more easily commercialized due to their smaller footprints and lower costs compared to stationary hydrogen refueling stations. The present work modeled hydrogen explosions in a skid-mounted hydrogen refueling station to predict the overpressures for hydrogen-air mixtures and investigate the protective effects for different explosion vent layouts and protective wall distances. The results show that the explosive vents with the same vent area have similar overpressure reduction effects. The layout of the explosion vent affects the flame shape. Explosion venting can effectively reduce the inside maximum overpressure by 61.8%. The protective walls can reduce the overpressures but the protective walls should not be too close to the SHRS because high overpressures are generated inside the walls due to the confined shock waves. The protective wall with a distance of 6 m can effectively protect the surrounding people and avoid the secondary overpressure damage to the container.

It is significant to assess the hydrogen safety of fuel cell vehicles (FCVs) in parking garages with a rapidly increased number of FCVs. In the present work a Flame Acceleration Simulator (FLACS) a computational fluid dynamics (CFD) module using finite element calculation was utilized to predict the dispersion process of flammable hydrogen clouds which was performed by hydrogen leakage from a fuel cell vehicle in an outdoor parking garage. The effect of leakage diameter (2 mm 3 mm and 4 mm) and parking configurations (vertical and parallel parking) on the formation of flammable clouds with a range of 4–75% by volume was considered. The emission was assumed to be directed downwards from a Thermally Activated Pressure Relief Device (TPRD) of a 70 MPa storage tank. The results show that the 0.7 m parking space stipulated by the current regulations is less than the safety space of fuel cell vehicles. Compared with a vertical parking configuration it is safer to park FCVs in parallel. It was also shown that release through a large TPRD orifice should be avoided as the proportion of the larger hydrogen concentration in the whole flammable domain is prone to more accidental severe consequences such as overpressure.

A proton exchange membrane fuel cell (PEMFC) is known as one of the most promising energy sources for electric vehicles. A hydrogen system is required to provide hydrogen to the stack in time to meet the flow and pressure requirements according to the power requirements. In this study a 1-D model of a hydrogen system including the fuel cell stack was established. Two modes one with and one without a proportion integration differentiation (PID) control strategy were applied to analyze the pressure characteristics and performance of the PEMFC. The results showed that the established model could be well verified with experimental data. The anode pressure fluctuation with a PID control strategy was more stable which reduced the damage to the fuel cell stack caused by sudden changes of anode pressure. In addition the performance of the stack with the PID control mode was slightly improved. There was an inflection point for hydrogen utilization; the hydrogen utilization rate was higher under the mode without PID control when the current density was greater than 0.4 A/cm2 . What is more a hierarchical control strategy was proposed which made the pressure difference between the anode and cathode meet the stack working requirements and more importantly maintained the high hydrogen utilization of the hydrogen system.

Supercritical water gasification is a promising technology for wet biomass utilization. In this paper Ni and other metal catalysts were synthesized by wet impregnation. The stability and catalytic activities of Ni catalysts were evaluated. Firstly catalytic activities of Ni Fe Cu catalysts supported on MgO were tested using wheat straw as raw material in a batch reactor at 723 K and water density of 0.07 cm³/g. Experimental results showed that the order of metal catalyst activity for hydrogen generation was Ni/MgO > Fe/MgO > Cu/MgO. Secondly the influence of different supports on Ni catalysts performance was investigated. The results showed that the order of the Ni catalysts’ activity with different supports was Ni/MgO > Ni/ZnO > Ni/Al2O3 > Ni/ZrO2. Finally the effects of Ni loading and the amount of Ni catalyst addition on hydrogen production and the stability of Ni/MgO catalyst were studied. It was found that serious deactivation of Ni catalyst in the process of supercritical water gasification took place. Even if carbon deposited on the catalyst surface was removed by high temperature calcination and the catalyst was reduced with hydrogen the activity of used catalyst was only partially restored.

The explosion venting is an effective way to reduce hydrogen-air explosion hazards but the explosion venting has been hardly touched in an obstructed container. Current experiments focused on the effects of different blockage ratios on the explosion venting in a small obstructed rectangular container. Experimental results show that three overpressure peaks are formed in the case with the obstacle while only two can be observed in the case of no obstacle. The obstacle blockage ratio has a significant influence on the peak overpressure induced by the obstacle-acoustic interactions but it has an ignorable effect on the peak overpressure caused by the rupture of the vent film. The obstacle-induced overpressure peak first increases and then decreases with the increase of the blockage ratio. In addition all overpressure peaks inside the container decreases with the increase of the vent area and its appearance time is relatively earlier for larger vent area.

One strategy for arresting propagating detonation waves in pipes is by imposing a sudden area enlargement which provides a rapid lateral divergence of the gases in the reaction zone and attenuates the leading shock. For sufficiently small tube diameter the detonation decays to a deflagration and the shock decays to negligible strengths. This is known as the critical tube diameter problem. In the present study we provide a closed form model to predict the detonation quenching for 2D channels. This problem also applies to the transmission of a detonation wave from a confined layer to a weakly-confined layer. Whitham’s geometric shock dynamics coupled with a shock evolution law based on shocks sustained by a constant source obtained by the shock change equations of Radulescu is shown to capture the lateral shock dynamics response to the failure wave originating at the expansion corner. A criterion for successful detonation transmission to open space is that the lateral strain rate provided by the failure wave not exceed the critical strain rate of steady curved detonations. Using the critical lateral strain rate obtained by He and Clavin a closed form solution is obtained for the critical channel opening permitting detonation transmission. The predicted critical channel width is found in excellent agreement with our recent experiments and simulations of diffracting H2/O2/Ar detonations. Model comparison with available data for H2/air detonation diffraction into open space at ambient conditions or for transmission into a weakly confined layer by air is also found in good agreement within a factor never exceeding 2 for the critical opening or layer dimension.

The increasing penetration of variable renewable energies poses new challenges for grid management. The  economic feasibility of grid-balancing plants may be limited by low annual operating hours if they work either only for power generation or only for power storage. This issue might be addressed by a dual-function power plant with power-to-x capability which can produce electricity or store excess renewable electricity into chemicals at different periods. Such a plant can be uniquely enabled by a solid-oxide cell stack which can switch between fuel cell and electrolysis with the same stack. This paper investigates the optimal conceptual design of this type of plant represented by power-to-x-to-power process chains with x being hydrogen syngas methane methanol and ammonia concerning the efficiency (on a lower heating value) and power densities. The results show that an increase in current density leads to an increased oxygen flow rate and a decreased reactant utilization at the stack level for its thermal management and an increased power density and a decreased efficiency at the system level. The power-generation efficiency is ranked as methane (65.9%) methanol (60.2%) ammonia (58.2%) hydrogen (58.3%) syngas (53.3%) at 0.4 A/cm2 due to the benefit of heat-to-chemical-energy conversion by chemical reformulating and the deterioration of electrochemical performance by the dilution of hydrogen. The power-storage efficiency is ranked as syngas (80%) hydrogen (74%) methane (72%) methanol (68%) ammonia (66%) at 0.7 A/cm2 mainly due to the benefit of co-electrolysis and the chemical energy loss occurring in the chemical synthesis reactions. The lost chemical energy improves plant-wise heat integration and compensates for its adverse effect on power-storage efficiency. Combining these efficiency numbers of the two modes results in a rank of round-trip efficiency: methane (47.5%)>syngas (43.3%) ≈ hydrogen (42.6%)>methanol (40.7%)>ammonia (38.6%). The pool of plant designs obtained lays the basis for the optimal deployment of this balancing technology for specific applications.

Hydrogen as a strategy clean fuel is receiving more and more attention recently in China in addition to the policy emphasis on H2. In this work we conceive of a hydrogen production process based on a chemical regenerative coal gasification. Instead of using a lumped coal gasification as is traditional in the H2 production process herein we used a two-step gasification process that included coking and char-steam gasification. The sensible heat of syngas accounted for 15–20% of the total energy of coal and was recovered and converted into chemical energy of syngas through thermochemical reactions. Moreover the air separation unit was eliminated due to the adoption of steam as oxidant. As a result the efficiency of coal to H2 was enhanced from 58.9% in traditional plant to 71.6% in the novel process. Further the energy consumption decreased from 183.8 MJ/kg in the traditional plant to 151.2 MJ/kg in the novel process. The components of syngas H2 and efficiency of gasification are herein investigated through experiments in fixed bed reactors. Thermodynamic performance is presented for both traditional and novel coal to hydrogen plants.