Study On The Self-regulating Function Of The Open-cathode PEMFC

Proton exchange membrane fuel cells(PEMFCs)have long been recognized as promising clean power generating devices to overcome issues related to environmental pollution and fossil fuels depletion.It offers advantages of zero emission,quick start-up,low noise and simple construction,and plays an important role in fields of stationary power generation,portable and transportation.Open-cathode PEMFCs use forced airconvection generated by a fan or fans to deliver oxidant to the cathode and also to remove heat generated by the electrochemical reactions.This configuration could reduce the balance of plant(BOP)of the fuel cell system and thus improve the system efficiency,and it has attracted increasing interest in unmanned aerial vehicles.However,complex and difficult water management and heat management are considered as the most important barriers to the further commercialization of open-cathode PEMFCs.Currently,in order to realize the water and heat balances in open-cathode PEMFCs,most researches adopt additional control strategies to control the fan speed and thus to realize the water and heat balances in fuel cells.However,low-power fuel cell stacks need simpler cooling system to simplify the design and improve the system efficiency.In this study,self-regulating function of fuel cells was used in designing the open-cathode PEMFC systems to avoid the complicate cooling system design and increase the net power output of fuel cell systems.Such a function enables the fuel cell to achieve water and heat balances in the fuel cell and thus to achieve stable and efficient fuel cell operation without external controlling circuits.In this study,experimental researches were conducted based on a 100 W metallic open-cathode PEMFC purchased from Horizon Fuel Cells to investigate the self-regulating function of the PEMFC,the main work and the obtained results are as follows:Firstly,in order to provide theoretical support for the performance differential of the stack under different operating conditions,the air flow and the air velocity distribution at different fan operating modes and voltages were measured.The results indicate that at the same fan operating voltage,the air flow in fan blow mode is higher than that in fan suction mode.However,the air velocity distribution in fan blow mode is highly non-uniform,with a large drop in velocity at the middle of the fan.Secondly,comparative experiments of the galvanostatic test and electrochemical impedance spectra(EIS)test were conducted on the stack under different fan operating modes and voltages.The results show that when the cooling fan was operated at suction mode with 7.5 V and blow mode with 8.5 V,the stack could output stable voltages under0.5 A-7 A current loads,and the stack voltage in fan blow mode is higher than that in fan suction mode.This may be attributed to the water and heat balances of the fuel cell,which could regulate the heat removal and water discharge quickly when the load changes,avoiding the occurrence of membrane dehydration and water flooding.According to the EIS results,the voltage differential between fan blow and suction modes is caused by the polarization resistance and ohmic resistance.Therefore,the most suitable fan operating mode and voltage were determined: operating in blow mode and 7.5 V.Finally,according to the proposed selection method of the cooling fan working conditions,6 V in blow mode was selected for the cooling fan of another PEMFC(60 W)with metallic bipolar plates.The temperature distribution and the cell voltage distribution of the stack are simultaneously measured under different current loads.The results demonstrate that the temperature and the cell voltages of the stack are evenly distributed,which indicates the correctness of the fan selection method proposed in this paper,and verify that the self-management characteristics of the open cathode PEMFC has a positive influence on the fuel cell consistent.