Modeling plated nickel nuclei population growth on carbon substrates

Since the NICKEFFECT projects aims at replacing platinum catalyst based PEM Fuel Cell (FC) cathodes by porous graphite electrodes that are covered with nickel alloy (nano-)particles, the plating process for creating these nickel nuclei populations  must be properly understood and controlled.   Same as for Water Electrolysis (WE) cells, the use of porous electrodes allows creating a high surface to volume ratio.  The throwing power of a full coverage nickel alloy plating process into a porous structure as for example a carbon fiber cloth is limited (WE cathodes), and the same holds for a nucleation plating process into a porous carbon structure (FC cathodes).  But whereas the main specifications in case of a full coverage nickel alloy plating process for WE cathodes involve primarily the local plating layer thickness and alloy content, for FC cathodes practically all local characteristics of the nuclei population are of importance, involving nuclei density, nuclei size distribution and nuclei alloy content.

 

Modeling challenges

 

Modeling this nickel alloy nucleation plating process with Multi-Ion Transport and Reaction (MITRe) models, as was done for the full coverage nickel alloy plating process for WE cathodes, brings the additional challenge that local polarization conditions will not only depend on the local electrolyte potential and metal ion concentrations, but also on the actual nuclei population that has already been formed at a certain point in time, since the polarization of these nickel alloy nuclei and the still exposed carbon substrate are widely different.

 

Elsyca’s innovative modeling strategy

 

Elsyca has developed a hybrid heuristic / physically based nucleation model that involves nuclei birth, transition of meta-stable nuclei to stable nuclei, and nuclei growth.  Thereby the entire nuclei population (nuclei density and size distribution) is tracked over time.  The kinetic parameters of this model are retrofitted by VUB for the nickel alloy plating process that was retained for the NICKEFFECT project, based on a series of plating experiments as conducted on non-porous carbon substates by UAB.  The achieved nuclei population for each experiment is quantified by means of SEM pictures that are subsequently analyzed by an AI enhanced pit quantification algorithm.

 

Full coupling of this nucleation model with the Multi-Ion Transport and Reaction (MITRe) software tools of VUB and Elsyca is still ongoing.

 

Expected outcome

 

A retrofitted nucleation model, when coupled to a MITRe model and applied to a porous structure, will allow predicting how the nuclei population characteristics will evolve from the outside to the inner sections of the porous structure, for a given set of process conditions.  This is crucial information for the finally to be expected performance of the FC cathodes.