Performance and durability enhancement for hydrocarbon-based polymer electrolyte membrane water electrolysis

Abstract

As the demand for renewable energy continues to increase, grid-scale electricity storage technology is becoming more important to overcome the intermittent and fluctuating nature of the renewable energy sources such as wind, wave and solar. The water electrolysis is considered as a clean and efficient process because it produces hydrogen without carbon emission. In addition, the produced hydrogen is of high purity and can be used to regenerate electricity in a short time and serve as clean transportation fuel for many energy storage devices.Among the various types of water electrolysis, proton-exchange membrane water electrolysis (PEMWE) has attracted interest due to its high efficiency of hydrogen production with high purity. Nafion membrane is widely used as the proton-exchange membrane for PEMWE system. Hydrocarbon-based membranes are attractive candidates to replace the Nafion membrane due to its low gas permeability and high proton conductivity under PEMWE operating conditions. Various hydrocarbon based membranes have been applied to PEMWE, including sulfonated poly(ether ether ketone) (sPEEK), sulfonated poly(arylene ether sulfone) (sPAES), and sulfonated poly(phenylene sulfide) (sPPS). They showed higher performance and lower hydrogen contamination than Nafion membranes due to their superior material properties. However, few studies have been conducted on the durability of hydrocarbon-based PEMWE, and the latest study confirmed that cell failure occurred during long-term operation of more than 60 h. As the duration of operation for PEMWE is required to the range of 50,000 to 100,000 h, the durability of hydrocarbon membrane based PEMWE need to be further developed.In chapter 2, a poly(p-phenylene)-based multiblock polymer with an oligomeric chain extender (CE-sPP-PPES) is presented for improved mechanical stability and extended operating current range. With the introduction of the chain extender, the mechanical and chemical stability are notably enhanced. The effects of ion exchange capacity on mechanical properties, proton conductivity, and hydrogen crossover are investigated compared to a Nafion membrane. The CE-sPP-PPES-based PEMWE has a 2.1 times wider operating current range than a Nafion-based PEMWE due to its smaller overvoltage and lower gas crossover at an optimal ion exchange capacity (IEC), demonstrating the possibility of a new hydrocarbon-based membrane for PEMWE.In chapter 3, a radical-scavenger-embedded interlocking interfacial layer (IIL) is presented to prevent the interfacial delamination. The ball-socket joint structure of the IIL imparts mechanical interlocking and the CeO$_2$ radical scavenger included in the IIL prevents the hydrothermal chemical degradation of IIL. The CeO$_2$-containing IIL-based PEMWE achieves more than 500 h operation at a voltage increase rate of 65 μV h$^{-1}$ which is much lower than that of state-of-the-art hydrocarbon-based PEMWE and even comparable to that of Nafion-based PEMWE (63 μV h$^{-1}$).