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In this article, we focus on the understanding of the normalPtxnormalCoy electrocatalysts degradation in polymer electrolyte fuel cell (PEFC) environments. A multiscale atomistic/kinetic model is derived providing mechanistic insights on the impact of the nanostructure and operating conditions on normalPtxnormalCoy nanoparticles durability. On the basis of ab initio (AI) data, we identify favorable pathways of the oxygen reduction reaction (ORR) on normalPtxnormalCoy nanoparticles and of the competitive Pt–Co dissolution in acidic media. The derived AI kinetics is coupled to a description of the atomic reorganization at the nanoparticle level as a function of the cumulated Pt and Co mass losses. This nanoscale model is coupled with a transport microscale model of charges and O2 through a PEFC cathode, and simulation sensitivity studies to operating conditions and initial compositions/morphologies are performed and complimented by microstructural and electrochemical characterizations carried out on aging direct liquid injection metallorganic chemical vapor deposition elaborated model electrodes detailed in our experimental companion paper.

The sustainability through the energy and environmental costs involve the development of new cathode materials, considering the material abundance, the toxicity, and the end of life. Currently, some synthesis methods of new cathode materials and a large majority of recycling processes are based on the use of acidic solutions. This study addresses the mechanistic and limiting aspects on the dissolution of the layered LiNiMnCoO oxide in acidic solution. The results show a dissolution of the active cathode material in two steps, which leads to the formation of a well-defined core-shell structure inducing an enrichment in manganese on the particle surface. The crucial role of lithium extraction is discussed and considered as the source of a "self-regulating" dissolution process. The delithiation involves a cumulative charge compensation by the cationic and anionic redox reactions. The electrons generated from the compensation of charge conduct to the dissolution by the protons. The delithiation and its implications on the side reactions, by the modification of the potential, explain the structural and compositional evolutions observed toward a composite material MnO·Li MO (M = Ni, Mn, and Co). The study shows a clear way to produce new cathode materials and recover transition metals from Li-ion batteries by hydrometallurgical processes.