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Proton exchange membrane fuel cell (PEMFC) usually need an activation process to obtain its best electrochemical performance.Compared with the traditional activation methods, electrochemical hydrogen pump has the advantages of saving time and hydrogen cost. The electrochemical hydrogen pump is a method in which hydrogen is oxidized into protons at the anode, and the protons migrate to the cathode with an applied electric field, and then are reduced to hydrogen again. The performance, internal impedance and electrochemical specific area(ECSA) changes of PEMFC after electrochemical hydrogen pump activation were studied with the help of polarization curves, electrochemical impedance spectroscopy(EIS) and cyclic voltammetry(CV) tests. Then the mechanism of the hydrogen pump activation was analyzed. Moreover, the influence of different current densities, inlet humidities and activation temperatures were investigated. The results show that after the hydrogen pump activation, the fuel cell performance is improved obviously, the slope of Tafel curve is decreased, the charge transfer resistance and mass transfer resistance get lower values, while the ohmic resistance is basically unchanged, and the ECSA is increased. Therefore, the mechanism of the hydrogen pump activation is related to the quantity of active species and microstructure of catalyst layer. The performance of hydrogen pump activation under 200 mA·cm-2 is better than that of under 100 mA·cm-2. The performance of hydrogen pump activation under the inlet humidity of 150%RH is better than that of 100%RH and 200%RH. In addition, the activation temperature has little impact on the PEMFC performance after hydrogen pump activation, and the fuel cell can be fully activated by hydrogen pump activation for 30 min at room temperature.

As renewable energy with no pollution but wide sources and high calorific value， hydrogen becomes increasingly important in the context of energy shortage and dual carbon goals. The safety of liquid hydrogen is an important factor impeding its application. In this regard， the research results of worldwide liquid hydrogen safety in recent years are summarized. The hazards of liquid hydrogen are discussed in view of its low temperature， leakage， and combustion. The research results of the liquid hydrogen leakage and dispersion law from experimental and numerical simulations are introduced. The latest research progress of liquid hydrogen safety protection measures is outlined. Overall， the hazards of liquid hydrogen have now been fully understood， but liquid hydrogen leakage and dispersion laws must be further studied. There are few experimental data on liquid hydrogen leakage and dispersion， and the related numerical simulations still face many difficulties. No comprehensive standards， laws， and regulations are yet formulated for the safety requirements of liquid hydrogen storage， transportation and application.

The hydrogen-electric coupling system is an important and indispensable part of a new-type power system， and its safety is a prerequisite for large-scale application. The hydrogen-electric coupling system is studied， and the accidents in key hydrogen-related equipment are summarized and investigated.Furthermore， fault tree analysis （FTA） is used for safety risk evaluation on the combustion and explosion of the hydrogen-electric coupling system caused by hydrogen leakage. The study shows that hydrogen storage and compression equipment is prone to safety accidents， and design defects， sealing， and operation errors are major causes of hydrogen accidents. The fault tree analysis shows that there are five ways to effectively prevent the hydrogen-electric coupling system from fire or explosion due to hydrogen leakage. The importance of the hazard sources and basic events of the system obtained from the study lays the foundation for developing safety protection measures.