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

Research on Synergistic Regulation Strategy of Load Range and Electrolysis Efficiency under High Dynamic Condition of 250kW Alkaline Electrolysis System

Abstract: In all hydrogen production water electrolysis technology, alkaline water electrolysis (AWE) hydrogen production technology maturity is the highest, but reduce the minimum load boundary, improve the electrolysis efficiency is the AWE system is an urgent need to optimize the technical challenges. The minimum load is mainly limited by the hydrogen-to-oxygen (HTO) transferred across the membrane and mixed with the lye. HTO exceeding 2.0% is a significant safety risk. Reducing lye flow rate and pressure is effective, while there are few ways to increase HTO by adjusting operating parameters, thereby extending the minimum load boundary, but reducing electrolysis efficiency. Therefore, this study proposes a coordinated adjustment strategy for pressure and lye flow rate: maximum pressure and lye flow rate during high load to ensure high electrolysis efficiency; adjust lye flow rate and pressure during medium load to ensure HTO≤ 2.0% to maximize electrolysis Efficiency; during low load, reduce the lye flow rate and pressure to a low level to expand the minimum load, thereby improving the overall efficiency of the AWE system when the green power load fluctuates. In this paper, the operating path, influencing factors and parameter optimization mechanism of HTO are expounded by establishing system-level steady-state and dynamic gas purity models. The optimal combination curve of pressure and lye flow is obtained, and the control effect of the performance parameters such as minimum load, system energy consumption, energy utilization and electrolytic efficiency is compared and verified under the high dynamic wind photovoltaic (PV) power generation scenario. Finally, on the basis of the optimal operation curve, the optimal wind power photovoltaic power generation ratio is discussed, which provides reference for the large-scale development of the direct coupling hydrogen generation scheme of wind power photovoltaic power generation in the future. The minimum load was increased from 42.0 for the sole lye flow rate control to 21.2 for the sole pressure control and finally to 15.6 for the synergetic control method of lye flow rate and pressure. In the absence of electricity supplement, the energy efficiency of wind energy and photovoltaic energy use reached 98.3 and 95.6, respectively.

21

2023

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12

Experimental Study on Dynamic Performance of 250kW Alkaline Electrolysis System-Hu Song

Focus: • A 250 kW alkaline electrolysis system was established and related experimental studies were carried out. • The dynamic performance of the electrolysis system was observed over multiple time scales. • The system response characteristics during start-stop and variable load processes were studied. • The problems with the kinetics of the electrolysis system are pointed out. Abstract: Alkaline water electrolysis is a mature hydrogen production technology and an important means of large-scale green hydrogen production and energy storage in the future, and improving and optimizing its dynamic characteristics is an urgent problem to achieve this goal. Based on the 250kW industrial alkaline water electrolysis system, the dynamic response characteristics of system current, voltage, temperature, hydrogen to oxygen (HTO) and pressure parameters were studied experimentally at two levels (start, stop and variable load process) and three scales. The experimental study of cold start (25 ℃)→ full load (90 ℃)→ hot stop (75 ℃)→ hot start (70 ℃)→ full load (90 ℃)→ cold stop (30 ℃) shows that the response time of the start-stop process is once per hour, and temperature is the main limiting factor. According to the variable load test, the response time of HTO is minutes: full load (3500 A,1.7MPa)→ minimum load (1400 A,1.7MPa)→ full load (3500 A,1.7MPa)→ minimum load (800 A,0.6 MPa). The response of HTO to parameter changes has serious time lag and inertia links, and the response time of the latter is significantly longer. The response time of the different current steps is in seconds. This experimental study points out the dynamic performance level of the current industrial-scale alkaline water electrolysis system, provides a direction for the optimization of dynamic performance indicators, and provides an important guide for the design of integrated control strategies with renewable energy.

14

2023

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12

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

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

Review on Mathematical Modeling of Alkaline Water Electrolysis-Hu Song

Focus: • The mathematical modeling work of the Alkali Electrolysis System (AWE) is reviewed. • AWE's thermodynamic model is sufficiently accurate and has little value for improvement. • The mechanistic model of AWE electrochemistry is well studied but difficult to calibrate. • Mechanistic models of heat need to be extended from the stack to the system. • Gas purity models have received more and more attention, but the accuracy is poor and lack of research. Abstract: Alkaline water electrolysis (AWE) is a relatively mature water electrolysis technology, which plays an important role in large-scale green hydrogen production and electric energy storage. Modeling is a powerful tool for AWE phenomenon understanding, control analysis and optimization management. AWE has a variety of modeling forms, but there is a lack of an overview of the status quo and problems of modeling development. This article reviews a detailed and comprehensive survey of existing modeling work on thermodynamic, electrochemical, thermal and gas purity models. In the course of studying these models in the published references, we created a concise modeling guide to show the relationship between different sub-models. The paper also summarizes and compares different modeling approaches for the same process or mechanism. On this basis, the effects of characteristic parameters and operating conditions on the performance of AWE are summarized in detail. At the same time, the advantages, disadvantages and shortcomings of this research field are pointed out. Electrochemical modeling studies are comprehensive, but the accuracy of each sub-model requires specialized experimental verification during model calibration. There are few studies on gas purity modeling, and the model prediction accuracy can reach a satisfactory level. The gas purity control strategy and optimization method based on this model need to be developed urgently. There are few studies related to thermal modeling, and the prediction accuracy still needs to be further improved. The application scope and thermal management strategy based on thermal model need to be further discussed. This work can provide guidelines for beginners and future directions for further improvement of AWE modeling.

23

2022

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10

Theoretical Analysis on Energy Saving of Cold Energy Utilization System of Liquid Hydrogen Heavy Truck-Hu Song

Abstract: In this paper, a new type of liquid hydrogen (LH2) heavy-duty fuel cell vehicle-mounted cold energy utilization system model is established, and the energy-saving effect of the original LH2 system without cold energy utilization is compared, and the energy-saving effect of the vehicle-mounted cold energy utilization system is comprehensively evaluated. The cold energy cools the compressor inlet and the coolant of the accessory cooling system through the two-stage evaporator to reduce parasitic power. And considering the environmental temperature, fuel cell stack load and other related factors. In addition, the influence of the cold energy distribution ratio, which is closely related to the design of the two-stage LH2 vaporizer, is also analyzed. Under these influencing factors, the system is divided into three states according to different energy-saving characteristics. The simulation results show that under steady-state conditions, the total parasitic power consumption can be saved by 15%. On this basis, under the China-World Transient Cycle (C-WTVC) conditions, the annual energy saving of heavy-duty fuel cell vehicles using the system in four typical cities in China is simulated. The study found that even in extremely cold areas such as Harbin (126.6 ◦ E,45.8 ◦ N), annual energy saving can be achieved, and the average annual energy saving rate in different cities can reach 9-15%.

22

2022

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10

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