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The more sluggish kinetics of hydrogen evolution catalysts in base as compare to that in acid to some degree restricts hydrogen production performance of hydroxide exchange membrane electrolyzers, especially when using earth‐abundant catalysts. Here a ternary nickel–copper–molybdenum hydrogen evolution catalyst is reported that exhibits ≈5 times higher turnover frequency than without copper doping. The X‐ray absorption near‐edge structure and valence band spectrum demonstrate that the light doping of copper into nickel–molybdenum alloy modulates the electronic structure and downshifts the d‐band center, resulting in accelerated hydrogen desorption, as consolidated by H2 temperature programmed desorption and theoretical calculation. An electrolyzer employing this cathode catalyst and a nickel–iron anode, gives a current density of 1.7 A cm−2 at 2.0 V with a pure‐water feed through the anode, which outperforms the 2025 target proposed by the United States Department of Energy, and even is operated continuously for over 1000 h with a decay rate of as low as 0.5 mV h−1. Post‐mortem analysis discloses that hydroxide exchange ionomer migration is one of the key factors affecting long‐term durability. This work demonstrates the feasibility of a low‐cost, water‐fed hydroxide exchange membrane electrolyzer achieving industrial‐level performance and lifetime. [ABSTRACT FROM AUTHOR]

The hydrogen circulation pump (HCP) is an important power component of the hydrogen fuel system, used to recover the unconsumed hydrogen from the anode and transport it back to the inlet of the battery stack to improve the hydrogen utilization efficiency. In this paper, to determine the optimal parameter configuration of the HCP, a multifactor and multi-objective optimization design method is proposed, and the influences of various design parameters on the performance of the HCP are analyzed based on the verified overset grid simulation method. The research results show that the proposed coupling design method can effectively achieve the optimal parameter configuration of the HCP, with diameter-to-pitch ratio κ = 1.47, rotor blade number Z = 3, and helix angle φ = 60°, which is validated using another model with significant performance advantages. In the process of studying the influence of design parameters, it is found that the average flow rate of the HCP is directly proportional to the diameter-to-pitch ratio and the blade number, gradually decreases in the range of helix angle from 0° to 22.5°, and increases in the range of helix angle from 22.5° to 60°. The flow pulsation value and pressure pulsation value of the HCP are less affected by the diameter-to-pitch ratio, decrease with the increase of the blade number, and show a trend of first increasing and then decreasing with the increase of the helix angle. [ABSTRACT FROM AUTHOR]

Summary: The lumped parameter model of the hydrogen system based on exhaust hydrogen recirculation and the CFD model of PEMFC stack were established in this paper. The system simulation results were used as the input of the stack model. The purge characteristics of the stack were studied and the purge strategy was formulated considering the hydrogen utilization and performance characteristics. The results show that during anode purging, the anode pressure fluctuated significantly and the nitrogen concentration decreased rapidly. The output voltage of the stack fluctuates greatly, and the fluctuation of voltage intensifies with the extension of emission duration. In addition, the voltage fluctuation range of unit cell decreases gradually from inlet to outlet. After the system stabilizes, the component distribution of anode was improved and the stack performance was recovered to the initial state. During the purge interval, the performance of the stack degrades due to the increase of anode nitrogen concentration. The hydrogen utilization rate of the hydrogen system was directly related to the purge strategy, and the purge strategy of short period‐short duration was beneficial to reduce the fluctuation of the stack performance in the purging process, and reduce the differences of performance and component distribution of different single cell. [ABSTRACT FROM AUTHOR]

Aiming at the off-grid application of distributed renewable energy, this study proposes a combined hydrogen, heating and power system based on solar energy, which mainly includes alkaline water electrolysis, metal-hydride hydrogen storage and proton exchange membrane fuel cells. To achieve the best combination of electricity, heat, and hydrogen, four energy management strategies based on mass, energy, and information flow are proposed. Taking an ecological community in Ningbo as the application scenario, the system performance under four control strategies in typical summer and winter days is studied, and the best control strategies in summer and winter are given, respectively. Electricity-led and high-led strategies are recommended for summer and winter, and both strategies can achieve a real-time supply of electric power, heating power, and hydrogen. After a day of operation, the two strategies have surpluses of 0 and 221.5 kW h of electricity, 5706 and 102.16 MJ of heat, and 57 and 17.82 kg of hydrogen, respectively. • A coordinated control system based on three-flow theory is proposed. • Four energy management strategies are proposed to achieve load matching. • Fluctuation characteristics of multi-source heat flow are studied. • The optimal control strategies in winter and summer are obtained. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) have been recognized as one of the most compelling physical adsorption hydrogen storage materials owing to their ultrahigh surface area and excellent hydrogen adsorption performance. In order to further improve their hydrogen adsorption performance, lithium doping is an effective approach to increase the number of hydrogen adsorption sites as well as enhance the interaction strength towards hydrogen molecules according to grand canonical Monte Carlo(GCMC) simulations. However, in previous simulation studies, lithium ions were commonly assumed to be randomly distributed in MOF frameworks. In fact, the lithium-doped MOFs were prepared by immersing MOFs in a lithium salt solution and then drying them under high temperatures, in which the distribution of Li+ in MOF frameworks is elusive. In this work, the lithium-doped MIL-101 models (i.e., Immersion model) with varying lithium contents were constructed according to experimental operation and their hydrogen adsorption performance from GCMC simulations was also investigated in comparison with the equivalent models with randomly distributed lithium ions (i.e., Random model). It is found that in contrast to the uniform distribution of lithium ions in Random model, the accumulation of lithium ions was inspected in Immersion models especially at high loadings, leading to the reduced pore size. On the contrary, the hydrogen adsorption capacities of Immersion models are significantly improved owing to the enhanced interaction strength with hydrogen molecules resulting from the reduced pore size and the strengthened charged-induced dipole interaction. • Random and Immersion models of Li@MIL-101 are simulated by molecular simulation. • The aggregation of lithium ions of Immersion models was observed. • The smaller pore size and pore volume of Immersion model in contrast to Random model. • The hydrogen uptake of Immersion model is higher than Random model. • Lithium ion aggregation results in reduced pore size and enhanced interaction with hydrogen. [ABSTRACT FROM AUTHOR]

SUMMARY Hydrogen permeation across the membrane is unavoidable in proton exchange membrane fuel cells, especially for super-thin membranes, which lowers the open-circuit voltage and could even be a safety concern. In this paper, hydrogen permeation across two membranes (25-um-thick Nafion® 211 and 18-um-thick reinforced composite membrane) are evaluated at various temperatures, relative humidity (RH), and gas pressure differences between the anode and cathode. The results indicate that the hydrogen permeation rate in both membranes increases almost exponentially with temperature and linearly with pressure differences. Compared with RH, the effects of temperature and pressure differences are more crucial to hydrogen permeability. However, the effect of RH on the hydrogen permeation is quite complicated. The permeability exhibits a minimum value at intermediate RH (approximately 40% RH) for both applied membranes. The permeability of Nafion® 211 appears more sensitive to RH than that of reinforced composite membrane at elevated temperature. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This study proposes a combined hydrogen, heating and power system based on solar energy for the off-grid application of distributed renewable energy. With hydrogen as the energy carrier, the stable consumption of renewable energy can be achieved by integrating alkaline water electrolysis (AWE), metal hydride (MH) hydrogen storage, and proton exchange membrane fuel cells (PEMFCs). An energy management strategy is proposed based on the coordinated control of mass, energy, and information flow. Fluctuations in multi-source heat flow during solar photovoltaic (PV) power generation, hydrogen production, hydrogen-storage, and PEMFC power generation were studied based on electric and heating loads of typical winter and summer days in an eco-neighborhood in Ningbo, China. Owing to differences in solar radiation between summer and winter, the total electric energy generated by PV panels was 6179 kWh and 3667 kWh for summer and winter, respectively. The start-up times for AWE and MHs were 0.92 h and 0.32 h in summer and 1.70 h and 0.55 h in winter, respectively. After one day of operation, the hydrogen and heat surpluses were 57.17 kg and 5735.83 MJ in summer, while in winter the hydrogen surplus and heat deficit were 30.87 kg and 226.41 MJ, respectively. • An off-grid combined hydrogen, heating and power system based on solar energy is proposed. • With hydrogen as carrier, renewable energy is consumed stably using AWE, MH and PEMFC. • Investigating fluctuation and coupling of multi-source heat flux during power generation. • Proposing an energy management strategy based on mass, energy, and information flow. • The performance of the system is studied based on the typical load in winter and summer. [ABSTRACT FROM AUTHOR]

• A novel pressure-based purging PEMFC system in DEAC mode is developed. • The hydrogen and oxygen utilization rates both reach 100%. • The water generated has been collected in this system. Proton exchange membrane fuel cells (PEMFCs) have been wildly used for marine and aerospace applications as energy devices, where pure hydrogen and oxygen are fed into the two sides of the membrane electrode assembly (MEA). The release of unreacted hydrogen and oxygen not only reduces the efficiency of the system but also causes the serious problem of hydrogen starvation. For this reason, fuel flow driving devices and methods such as pumps, ejectors, and solenoid valves are designed to recycle this unused gas. However, even with these devices, the release of gas into the environment is still inevitable. Therefore, this paper introduces a novel method that solves these problems and mitigates gas emissions using a dead-ended anode and cathode (DEAC) system. Pressure difference is formed between the inlet and outlet of PEMFC by controlling the purge valve to remove water and recycle hydrogen during purging. The dynamic response characteristics of this system under different current densities, pressure differences, and purging intervals are experimentally investigated in detail. The results show that both the hydrogen and oxygen utilizations can reach 100% and the collection of generated water during gas purging can be achieved in the DEAC mode. [ABSTRACT FROM AUTHOR]

Reliable thermal management ensures stable and efficient operation of proton exchange membrane (PEM) fuel cells. An air-cooled fuel cell stack with metal bipolar plates was developed, and 32 micro-thermocouples were arranged for in situ measurement of the temperature distribution. The resistance characteristic of the stack was tested in a wind tunnel, and then the effects of hydrogen pressure and airflow rate were analyzed. The results show that the highest and average temperatures in the stack exhibit a "parabolic" distribution as well as the maximum temperature difference of each single cell on the inlet side of the cathode. However, the temperature difference on the outlet side shows an "anti-parabolic" distribution. With a decrease in the airflow rate, the temperature uniformity in the stack deteriorates gradually. When the maximum pulse width modulation (PWM) duty cycle of the fans was 70% and the current density was 500 mA/cm2, the temperature difference between different single cells and inside a single cell can reach 19.7 °C and 8.4 °C, respectively. The temperature uniformity in the stack at high current densities could be effectively improved by increasing the airflow rate. In addition, the hydrogen pressure and airflow rate have a certain effect on the voltage consistency. • An open-cathode air-cooled fuel cell stack with metal bipolar plates was developed. • The flow resistance characteristic of the fuel cell stack was tested in a wind tunnel. • In situ measurement of temperature distribution in the fuel cell stack was conducted. • The effects of anode pressure and airflow rates were analyzed in detail. • The temperature distributions inside a single cell and the stack were obtained respectively. [ABSTRACT FROM AUTHOR]

During the proton exchange membrane fuel cell (PEMFC) operation, liquid water accumulates in the PEMFC, causing water flooding and performance degradation, especially at high current densities. Moisture dehumidification has been used to remove excess water in PEMFCs by forming a high water vapor concentration gradient between the inside and outlet of PEMFCs. In this study, the cathode outlet gas was condensed by adding thermoelectric refrigeration equipment to the cathode outlet of a single cell, and the influence of gas condensation on PEMFC performance under different working conditions was studied. The results showed that the effect of moisture dehumidification on PEMFC performance depended on the water content in the PEMFC, and the positive effect was more evident under high current density, high relative humidity, and high pressure. Moreover, moisture dehumidification is beneficial to alleviate the degradation of the catalyst layer. When there was no exhaust gas condensation, large-area fractures and loss occurred in the catalyst layer after 100 h of operation, and the electrochemically active area (ECSA) was reduced by 22.28%. There was only a slight reduction in the thickness of the catalyst layer with moisture dehumidification, and the ECSA was only reduced by 1.82%. Therefore, the degree of moisture dehumidification should be adjusted according to the water content inside the PEMFC in actual operation. • The effects of moisture dehumidification on the PEMFC performance is studied. • The effect of moisture dehumidification depended on the water content. • Moisture dehumidification can effectively alleviate water flooding. • The more water content in the PEMFC, the more obvious the positive effect. • The degree of moisture dehumidification should be adjusted according to the water content. [ABSTRACT FROM AUTHOR]

Abstract: Temperature mapping is measured by micro-thermocouples embedded into the cathode plate of the model cell. The effects of different operation conditions on temperature distribution are investigated in detail. The results show that the temperature of the stack turns on “Parabola” distribution, and the temperature increases along the flow field from the inlet to the outlet under various conditions. Temperature difference of the single cell in the stack increases with the increased operation current density, and decreases with the increased air flow rate. The effect of the inlet air temperature on the temperature difference can be neglected in the stack, and the temperature uniformity can be improved by increasing the mass flow rate of the coolant water. [Copyright &y& Elsevier]