Studies On The MEA Of SPE Water Electrolyzer And Regenerative Fuel Cell

Solid polymer electrolyte (SPE) water electrolyzers possess the following advantages: absence of alkaline solution,safety, higher energy efficiency, long lifetime,highly pure hydrogen production and widespread use. As a new energy storage system, regenerative fuel cell (RFC) has advantages in long-term energy storage, specific energy density, and specific power density, ect. The most important technical problem of SPE water electrolyzers and RFC are the development of oxygen electrode electrocatalysts and membrane electrode assemblies (MEA) with high efficiency. The dissertation deals with the R&D of electrocatalysts and MEA technology for SPE water electrolyzers and RFC to reduce the catalysts loading, enlarge the interface between polymer membrane and catalyst layers and thus improve the performance of SPE water electrolyzers and RFC.IrO₂ (2～3nm) and IrO₂-SnO₂ (2～3nm) eletrocatalysts were conveniently and quickly prepared by using modified Adams methods and these electrocatalysts were characterized by XRD, TEM and XPS technique ect. The resulsts reveal that IrO₂-SnO₂ composite materials are homogenous solid solution and the surface enrichment of IrO₂ does not take place in IrO₂-SnO₂ composite eletrocatalysts. The synthesized IrO₂ is a stable and good electrocatalyst for oxygen evolution.A novel manufacturing process for catalyst coated membrane (CCM), which does not reduce the mechanical strength of MEA, was utilized to fabricate MEA for SPE water electrolyzers. The properties and performance of the modified CCM were analyzed and evaluated by SEM, electrochemistry impedance spectroscopy (EIS) and V-I curves. The results show that the modified CCM process are very effective for reducing the contact resistance and increasing the reaction interface between SPE and the electrode catalyst layer and therefore improving the performance of SPE water electrolyzers. At 1mg/cm² of Pt loading and 2mg/cm² of IrO₂ loading and under the electrolysis conditions of 80℃, atmosphere pressure and 1A cm-2, the electrolysis voltages of SPE water electrolyzers produced by using modified CCM technology, CCM technology, transfer- printing, mechanically hot pressing and chemical plating are 1.6V, 1.66V, 1.67V, 1.7V and 1.81V, respectively. At 80℃and atmosphere pressure and 2A cm-2, the modified MEA (1.72V) can lower 0.09V of water electrolysis voltage and is also 0.09V lower than electrolysis voltage of MEA reported in a newly published paper.The dissertation investigates the optimal fabrication conditions of modified CCM for SPE water electrolyzers. The results show that Na+ ionization and glass transition can improve the stability performance of SPE water electrolyzers. The best loading of Nafion in catalyst layers of oxygen electrode is about 30%. The addition of the pore-forming substance-(NH4) 2C2O4 has no influence on the performance of SPE water electrolyzer and does not need in the fabrication of MEA.The effects of impure ions such as Ni²⁺, Cu²⁺,Mg²⁺ and Ca²⁺ on SPE water electrolyzers were studied in detail. After Ni²⁺ and Cu²⁺ transferred from anodic chamber to cathode, the two ions were electrodeposited at the cathode and the formed Ni and Cu covered cathode catalysts, decreased reaction active sites and weaken the performance of SPE water electrolyzers. Mg²⁺ and Ca²⁺ have much higher affinity than H+ to the ion exchange sites of Nafion in catalyst layers,which resulted in the loss of proton conductivity and coverage of reaction active sites and thus reduced the performance of SPE water electrolyzers.The dissertation did some research on the preparation of a bifunctional RuO₂-IrO₂/Pt electrocatalyst and fabrication technology of MEA of regenerative fuel cells. A bifunctional RuO₂-IrO₂/Pt electrocatalyst was prepared by colloid deposition. The result reveals that RuO₂-IrO₂ was well dispersed and deposited on the surface of Pt black. With deposited RuO₂-IrO₂/Pt as oxygen electrode catalyst, RFC has better performance and cycle stability under the fuel cell mode and water electrolysis mode.