Experimental investigation and comprehensive analysis of performance and membrane electrode assembly parameters for proton exchange membrane fuel cell at high operating temperature

Abstract:The future trend in proton exchange membrane fuel cells (PEMFCs) is developing towards higher operating temperatures, although the current lack of comprehensive investigation into the PEMFC characteristics at elevated temperatures. This work provides a comprehensive summary of commonly used test methods and data processing methods for PEMFCs, encompassing polarization decomposition, electrochemical impedance spectroscopy (EIS) processing methods, electrochemical surface area (ECSA) and hydrogen crossover current density (iH) calculation methods. Experiments on PEMFC performance and membrane electrode assembly (MEA) parameters at 80 to 95 ℃ under various humidities are conducted. The experimental results indicate that elevated temperatures contribute to increased ohmic loss and reduced mass transfer and activation losses. Increased temperature can substantially accelerate the reaction rate and compensate for the decrease in ECSA. The ECSA decreases at elevated temperatures, and higher temperatures will result in a faster drop. The iH demonstrates an increase with both temperatures and humidities, with higher humidities leading to faster growth. Based on the comprehensive test and analysis methods for PEMFC, this study could enhance understanding and provide valuable guidance for PEMFC performance variation laws at high operating temperatures.

30

2024

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07

Heterojunction catalysts of ultra-thin carbon layer activated Platinum nanoparticles for bifunctional pH-universal hydrogen evolution reaction and oxygen reduction reaction

Abstract:Platinum catalysts are widely used in electrocatalytic water splitting for the hydrogen evolution reaction and in hydrogen fuel cells for the oxygen reduction. Nonetheless, the practical use of the noble metal platinum in commercial applications faces significant challenges due to its exorbitant cost and the intricate nature of its synthetic methods. In this work, nitrogen-doped carbon layers covering platinum particles (Pt@NCL) are uniformly distributed on carbon nanofiber (CNF) substrates to synthesize heterojunction catalysts (Pt@NCL-CNF). Multiple characterization methods reveal that the nanoscale ultra-thin carbon layer successfully activates platinum nanoparticles and creates a tremendous accumulation of valence electrons at the interface of the heterojunction catalysts. Furthermore, the greater the number of defects produced in the ultra-thin carbon layer of Pt@NCL-CNF during the reaction, the more active sites are exposed. Therefore, Pt@NCL-CNF exhibits much better hydrogen evolution reaction and oxygen reduction reaction performance in pH-universal electrolytes than the commercial carbon-supported platinum (Pt/C) catalyst. This study elucidates the reaction mechanism, highlighting the crucial role of the ultra-thin carbon layer within the catalyst, and also confirms the catalyst performance in device applications. The proposed method can provide a simple and feasible mass-produced approach for the preparation and application of high performance low platinum catalyst.

30

2024

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07

Experimental and Modeling Study on Energy Flow of 250kW Alkaline Electrolysis System under Steady State Condition and Cold Start Process

Abstract: Improving the energy efficiency of alkaline water electrolysis system (AWE) is one of the problems to be solved. In this study, by establishing a multi-physical field coupling AWE system model of heat transfer, mass transfer and electrochemistry, the heat flow and energy distribution under steady state and cold start process are discussed, and on this basis, a method to improve energy efficiency is proposed. The full load power consumption of the system is 272.7 kW, and the electrolytic cell accounts for 88.4%. The useless heat generation and parasitic current are the main factors causing the energy loss of the electrolytic cell, accounting for 21.2% and 3.1% of the total power consumption respectively. The useless heat production of the electrolyzer is also an important factor in the energy consumption of the chiller, accounting for 5% of the system power consumption. Improving the performance of the electrolyser and minimizing its heat generation are critical to optimizing the efficiency of the system. During the AWE cold start process, the constant pressure control has a shorter cold start time than the constant current control, but their power consumption difference in heat and hydrogen production is small. Compared with the optimized power load type, reducing the system heat capacity is very effective in accelerating the cold start process, which can shorten the cold start time to less than 1h.

02

2023

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06

The nonlinear method of fuel cell life evaluation and online prediction-Chen Dongfang.

Focus: · A non-linear formula for evaluating and predicting the service life of fuel cells is proposed. • Non-linear degradation is mainly due to changes in hydrogen crossover. Determine the line segment points between the linear and nonlinear formulas. · The calculation formula is verified by experimental and actual vehicle operation results. · Proposed methods for laboratory life assessment and on-line vehicle prediction. Abstract: Life evaluation and prediction is a key issue for proton exchange membrane (PEM) fuel cells, which helps to extend the durability of fuel cells and accelerate the commercialization of fuel cells. In this paper, a linear formula for evaluating the maximum service life of fuel cells for automobiles and several nonlinear formulas for predicting the service life of fuel cells are given. The terminal voltage of the fuel cell under the rated condition means that the average voltage of the cell is reduced by about 10% from the initial rated voltage under the rated condition. A nonlinear formula is derived based on the change of hydrogen crossing point, which shows that the change of hydrogen crossing point is the main factor of nonlinear life degradation of fuel cell. A nonlinear formula for the whole process based on the time response of the first-order control system (FOCS) is proposed, and the segment point between linear and nonlinear degradation is defined by this formula. On this basis, based on the time response of the local process, a more accurate linear life formula and nonlinear life formula are derived. Finally, through the experimental results of single cell and fuel cell stack and the actual operation results of fuel cell vehicles, the validity of the segmented formula is verified. In addition, the methods of laboratory life evaluation and vehicle online prediction are also proposed.

20

2019

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08

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