Successful and rapid startup of proton exchange membrane fuel cells (PEMFCs) at subfreezing temperatures (also called cold start) is of great importance for their commercialization in automotive and portable devices. In order to maintain good proton conductivity, the water content in the membrane must be kept at a certain level to ensure that the membrane remains fully hydrated. However, the water in the pores of the catalyst layer (CL), gas diffusion layer (GDL) and the membrane may freeze once the cell temperature decreases below the freezing point (T_f). Thus, methods which could enable the fuel cell startup without or with slight performance degradation at subfreezing temperature need to be studied. This paper presents an extensive review on cold start of PEMFCs, including the state and phase changes of water in PEMFCs, impacts of water freezing on PEMFCs, numerical and experimental studies on PEMFCs, and cold start strategies. The impacts on each component of the fuel cell are discussed in detail. Related numerical and experimental work is also discussed. It should be mentioned that the cold start strategies, especially the enumerated patents, are of great reference value on the practical cold start process.

Silicon (Si) has been considered to be one of the most promising anode materials for high energy density lithium−ion batteries (LIBs) due to its high theoretical capacity, low discharge platform, abundant raw materials and environmental friendliness. However, the large volume changes, unstable solid electrolyte interphase (SEI) formation during cycling and intrinsic low conductivity of Si hinder its practical applications. Various modification strategies have been widely developed to enhance the lithium storage properties of Si−based anodes, including cycling stability and rate capabilities. In this review, recent modification methods to suppress structural collapse and electric conductivity are summarized in terms of structural design, oxide complexing and Si alloys, etc. Moreover, other performance enhancement factors, such as pre−lithiation, surface engineering and binders are briefly discussed. The mechanisms behind the performance enhancement of various Si−based composites characterized by in/ex situ techniques are also reviewed. Finally, we briefly highlight the existing challenges and future development prospects of Si−based anode materials.

The addition of hydrogen to natural gas is an effective approach to broaden the range of applications for hydrogen and address the issue of global warming. However, the inclusion of hydrogen alters the combustion properties of natural gas. The paper established a simplified mechanism consisting of 19 components and a 67-step reaction for hydrogen-doped natural gas combustion. With this simplified mechanism, the effects of hydrogen doping and the utilization of porous media combustion techniques on the combustion characteristics of natural gas were investigated numerically. The results suggested that the utilization of porous media combustion technology is beneficial for achieving the complete combustion of hydrogen-doped natural gas and reducing pollutant emissions. Additionally, the total gas cost and environmental impact of domestic gas water heaters with hydrogen-doping natural gas were estimated. The findings show that the use of 20% hydrogen-doped natural gas contributes to a decrement in fuel costs and reduced emissions of CO by 25.4%, NO_X by 53.9%, and CO₂ by 6.78%.

In order to solve the problem of power supply and heating in remote rural household of north China, taking rural houses in Yinchuan as the research object, a solar-proton exchange membrane fuel cell (PEMFC) combined heat and power (CHP) system that is suitable for supplying power and heating to household in remote rural areas in north China is proposed in this paper. The simulation model is developed by using the MATLAB/Simulink platform and the effects of key operating parameters (i.e. current density and active area) on the performances of the PEMFC are studied. And the control effects of PID and fuzzy PID on the outlet temperature of the PEMFC stack are analyzed. The changes in temperature of water tank and indoor heating temperature under different electric loads and solar radiation are compared and studied. Meanwhile, the change in temperature of water tank is analyzed with or without solar energy, and the electrical efficiency, thermal efficiency, and CHP efficiency of PEMFC CHP are studied. The results show that the current density and active area have a significant impact on PEMFC stack. The temperature of water tank can be increased by 20°C combining solar energy and PEMFC. In winter, under different electric loads and solar radiation, the solar-PEMFC CHP system can make the temperature of the water tank reach above 55°C, and make the indoor heating temperature reach 20°C~27°C.In addition, the maximum efficiency of PEMFC CHP system is about 83%.