Experimental Study Of Flow Field Pattern And Dynamic Characteristics Of Proton Exchange Membrane Electrolysis Cell

Hydrogen production by proton exchange membrane(PEM)water electrolysis is a promising renewable energy storage technology with outstanding advantages such as non-pollution,high hydrogen production efficiency and fast dynamic response,but the conventional flow field with high fabrication cost has become the primary problem limiting the commercialization of electrolytic cells.In recent years,novel flow distribution methods such as flow field without channels and metal foams have gradually become attractive solutions,and experimental studies of porous transport layer(PTL)design parameters and operating conditions are crucial to optimize electrolyzer performance.In this thesis,PEM electrolytic cell performance tests were carried out using two flow field types,namely,flow field without channels and metal foam,and compared with conventional parallel flow fields.The effects of structural dimensions(material,thickness and porosity)and operating parameters(temperature,clamping pressure and water flow rate)of PTL on the electrolytic cell performance were investigated by building an experimental test platform based on characterization means such as polarization curves and electrochemical impedance spectra,and the effects of different dynamic operating capability of the electrolytic cell with different flow field types were also investigated.The results showed that the electrolytic cell exhibited greater ohmic loss using0.4 mm thin titanium felts and lower ohmic and activation impedance using high porosity(65%)titanium felts.For the flow field type without channels,the inlet and outlet pressure drops of the electrolytic cell is more than five times that of the other two flow fields,thin(0.4 mm)or low porosity(55%)PTLs severely affect the transport of liquid water and gas within the cell,thus significantly reducing the performance of the cell.The electrolytic cell is more susceptible to mass transport in the range of medium to high current densities when the flow field without channels is used in the cathode side,which requires a higher in-plane permeability of the cathode PTL to optimize hydrogen production,while the metal foam flow field is more sensitive to the cathode PTL material type,the use of a more rigid titanium felt improves performance by 10.7%over carbon paper.As for the operating parameters,the variation of water flow rate with high stoichiometry does not have a significant effect on the electrolytic cell performance,while the increase of temperature and clamping pressure has a positive effect on the electrolytic cell performance.The increase of temperature leads to better reaction kinetics and the increase of clamping pressure makes the contact pressure on the membrane more uniform and reduces the ohmic resistance of the electrolytic cell.However,too high clamping pressure is not conducive to the performance improvement of the electrolytic cell.For the metal foam flow field type,the carbon paper is susceptible to the porous structure of the foam,which causes more severe morphological damage and performance degradation under pressure.Overall,the two simple flow field types provide competitive performance under optimal operating conditions,with less than 30 m V difference in performance from the conventional parallel flow field electrolytic cell at an operating current of 1A/cm~2.Finally,the differences of dynamic characteristics between different flow field types were evaluated in combination with the dynamic parameter changes.It is found that the sudden change of flow rate mainly affected the temperature magnitude in the electrolytic cell;the flow field without channels had the fastest stabilization time and the smallest voltage change during the sudden change of current,and the metal foam had the worst dynamic response ability during the high step of current.In the short-term low-load cycling tests,the electrolytic cells all exhibited rapid performance degradation at the beginning of the cycle,after which the decline slows down,with the metal foam flow field achieving a high performance degradation value of 0.14V per 100 cycles at 2A/cm~2.