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In order to study the effects of temperature and humidity on the performance of proton exchange membrane fuel cell (PEMFC), a temperature and relative humidity-current (TRH-C) model was proposed. The model took the water flow and membrane water content of anode and cathode flow channels into consideration, and revealed the law of current density distribution and membrane water content distribution under the condition of current step change. According to the real flow channel configuration of the experimental single cell, a simplified PEMFC geometric model was established and the calculation grid was divided, and the TRH-C model was coupled to the multi-physical field calculation software COMSOL. A PEMFC test platform was established to test PEMFC under different temperature and humidity conditions. The operating temperatures of PEMFC were 65 °C and 70 °C, and the inlet humidities were 50% and 75%. The polarization curve, the membrane current density, and the membrane water content under different working conditions were analyzed and discussed. The results show that the TRH-C model can accurately predict the output performance of PEMFC. When the operating temperature is 70 °C, the inlet humidity is 50%, and the current density is 0. 018 A/cm², the relative errors of the TRH-C model of voltage and power density both reach the maximum value, which are 7.306% and 8.837%, respectively. The performance of PEMFC can be improved by increasing operating temperature and inlet air humidity. As the operating temperature increases, the distribution uniformity of membrane current density fluctuates and the mem-brane water content decreases. With the increase of inlet air humidity, the film current density distribution becomes more uniform and the film water content increases. This work provides a new theoretical method for optimizing inlet air strategy control and improving the output performance. [ABSTRACT FROM AUTHOR]

Newly fabricated proton exchange membrane fuel cells (PEMFCs) need an activation process to improve the initial performance. The long activation time leads to a high cost and a low production efficiency, thus it is significant to develop rapid and non-destructive activation methods. This review summaries possible activation mechanisms, compares and analyzes various activation methods, and afterwards, proposes the design principles for activation. Some criteria for evaluating activation completion are also provided as references. Finally, the influence of several activation methods on cell durability is overviewed from present available researches. In this review, hydrogen pumping, short circuit, and cathode starvation are considered as more effective methods versus traditional approaches. The performance improvement after activation is ascribed to the change in membrane morphology, the reduction of contamination, and the optimization of catalyst layers. More importantly, five factors including high temperature, sufficient water, change in current or voltage, reductive atmosphere, and valid combination of different methods are highlighted in designing rapid activation procedures. • Several common activation mechanisms are summarized. • Various activation procedures are further compared and analyzed. • Internal relationship among multiple activation methods is discussed. • Five principles of activation procedure design are proposed. • Influence of several activation methods on cell durability is reviewed. [ABSTRACT FROM AUTHOR]

• Propose a combined activation procedure reducing time and gas consumption. • Validate effectiveness of the procedure at single-cell and stack level. • Reveal change of electrochemical factors and microstructure in activation. • Activation performance is related to hydration status and oxide reduction. Activation is a crucial procedure to improve the performance of newly fabricated fuel cell stacks to meet the power requirements in actual application scenarios. However, traditional activation procedures generally last for several hours or even days, which greatly increases the cost and limits the production efficiency. In response to this problem, this paper proposes a rapid activation procedure composed of hydrogen pumping (HP) and limiting-current activation with limited air (LCA). The influence of current density for HP and air supply for LCA on activation effect is studied and the best operating conditions are determined. The importance of water supply to the cathode is highlighted during HP. The influence of air supply for LCA on activation effect is limited, which contributes to gas saving. According to the experiments conducted on a single cell and a 10-cell stack, only 40 min are needed with this combined procedure, which is much shorter than that of the traditional step-current activation. Furthermore, nearly 75% of hydrogen is saved due to the short activation time and the control of gas supply, thus significantly reducing the cost during activation. Furthermore, to reveal the underlying mechanisms, membrane electrode assembly parameters before and after activation are obtained by micro-current excitation. A decrease in ohmic resistance and an increase in roughness factor of catalyst are observed, which contribute to performance improvement. According to the characterizations in the microstructure of membrane electrode assembly and platinum catalyst valence state, the electrolyte hydration and oxide reduction are determined as key factors and principles during activation. [ABSTRACT FROM AUTHOR]

Abstract The lifetime of automotive fuel cells is one of the key issues that restrict their commercialization. Previous research results have shown that frequent changing load conditions are the main reason leading to its life attenuation. At present, the dynamic response characteristics and mechanism of fuel cells are not yet clear. The control and structural design for the key components of the long-life, high-dynamic response fuel cell systems requires theoretical guidance. To solve this problem, this paper studies the dynamic response characteristics and distribution quality of reactant gas in the process of load change. In this paper, a three-dimension, five serpentine channels, single-phase model of proton exchange membrane fuel cell (PEMFC) single cell is built. A new method is created to describe the variation of fuel cell voltage and distribution of reactant gases under the condition of steady state and dynamic state. The effects of working pressure, stoichiometric ratio and variable loading amplitude on the performance of the fuel cell were analyzed in detail, and the gas distribution on the electrode surface under various operating conditions was quantitatively studied. The final conclusions have important guiding significance for the selection of fuel cell operation parameters and variable loading parameters and optimization of operating conditions. The research methods and conclusions of this paper will provide a reference for optimal control and structural design of high-dynamic-response fuel cells, providing a theoretical basis for long-life research of fuel cells. [ABSTRACT FROM AUTHOR]

Abstract: Mathematical models were applied to predict the results of different strategies to improve automotive fuel cell driving systems. First, a fuel cell system was optimized on the base of a fuel cell stack model. Then calculations about the utilization of recovered energy from air exhaust steam were carried out. Two methods to combine the turbocharger with an electric compressor, namely in series and in parallel, were evaluated for a fuel cell system. Finally, research on the effect of removing the big power DC/DC converter, which is located between the fuel cell system and the driving motor, was conducted for a fuel cell driving system. The main results show that it is highly advantageous to connect the turbocharger with an electric compressor in series than in parallel; and that the fuel cell driving system without DC/DC converter before its motor could reach much higher performance characteristics, and even be so in lower power range while the cell voltage was designated to be lower. [Copyright &y& Elsevier]

This paper is to present a test platform for automotive fuel cell systems and report some test results on this platform. The test platform was developed based on a test bed of internal combustion engine with a dynamometer, the dynamometer acted as both a load and a measurement instrument. A fuel cell engine, a DC/DC converter and an induction traction drive motor with a DC/AC inverter were integrated to a system and were tested in the platform. Test results of one fuel cell system showed that the efficiency was 41% (LHV) while 50 kW of electrical power is produced in the engine; the cell current density was 400 mA/cm2 when 0.65 V of average cell voltage is obtained in the stacks; the maximum mechanical power of the fuel cell system was 41 kW, and the best specific fuel consumption was 102 g/kWh. This test platform is feasible for evaluating all components of fuel cell systems, such as stacks, parasitic powers, engines, DC/DC converters and traction drive motors; and in this platform it is convenient to uncover problems of electromagnetism compatibility in the fuel cell systems before being mounted into vehicles. [Copyright &y& Elsevier]

A guanidinium-functionalized anion exchange membrane (AEM) was prepared and characterized. The AEM stability in an alkaline environment and transition structures during the degradation process were studied with DFT (density functional theory)/B3LYP method, 6-31 + G (d) basis set. Experimental results and theoretical analysis showed that the second step (Step 2′) of degradation reaction was the control procedure; guanidinium cation was unstable under alkaline condition. It had lower energy barriers, which decided it was easier for the degradation reaction to occur in high pH environment. The ionic conductivity of AEM was 2.4 × 10 −2 S cm −1 at 80 °C. However, the AEM soaked in 1 M NaOH solution, fragments were found after 10 days. The FTIR analysis showed that the structure of the membrane had been changed due to the attack of hydroxide ion. A new substance, tetramethylurea, had produced. [ABSTRACT FROM AUTHOR]