An increasing energy demand and the need to reduce greenhouse gas emissions promotes a need for sustainable energy systems. Polymer-electrolyte-membrane fuel cells, comprising a carbon-platinum catalyst layer (CL), have reached (pre-)commercial viability. However, performance, durability, and cost targets are not entirely met yet. In a larger perspective, this thesis aims to contribute to the development of novel catalyst quality monitoring methods, gradual catalyst loading strategies, and the link between water management and catalyst degradation. The objectives of this thesis are to design tools and develop methods of investigation for catalyst degradation, characterize different accelerated stress test (AST) protocols, indicate stressors of the occurring degradation, deconvolute the performance decay, and to analyze the locally occurring degradation. Carbon corrosion and platinum dissolution are the major degradation mechanisms during the operation. Start-up and shutdown (SU/SD) events where air purges through the hydrogen containing anode, accelerates the progression of these mechanisms, and amplified performance decay results.

This study develops an ex-situ tool and a method to link the water content within the CL to the degradation behavior. Higher water content may accelerate CL failure. The comparison of different SU/SD ASTs revealed the degradation behavior and the influence of various mitigation strategies to reduce the occurring voltage decay. The application of an external resistance resulting in the consumption of electrons reduces the degradation. If the voltage is suppressed by applying an external load, the degradation in high current densities is marginal. The deconvolution of the voltage decay at high current densities reveals the ratio of carbon to non-carbon related losses. The non-carbon related losses remain dominant throughout the initial stages of the AST;​ later the carbon corrosion related losses become significant. The novel multi-channel-characterization-system revealed larger losses towards the cell’s exit during SU/SD and platinum dissolution ASTs. Chemical platinum degradation caused by higher water content towards the exit dominates. Longer residence times of oxygen within the anode promote degradation towards the exit.

In conclusion, this study developed novel diagnostics, assessed the ratio of performance decay related to its mechanisms, estimated a dominance of the non-carbon related losses throughout the initial phase, while localizing the degradation.