Van Marum Colloquium: Understanding Electrochemical Interfaces on the Atomic Scale
- Thursday 8 December 2022
Niels Bohrweg 2
2333 CA Leiden
- De Sitterzaal
Platinum-based nanoparticulate electrocatalysts are used for a wide range of processes, such as the oxygen reduction reaction in low-temperature fuel cells. However, given the socio-economic implications of precious metal mining, it is necessary to either replace these materials or to optimize their performance as much as possible. To this end, extending the lifetime of Pt electrocatalysts by minimizing material degradation and Pt loading as well as increasing their activity towards the chemical bottleneck processes are paramount objectives. However, these objectives can only be addressed after the dynamic structure and composition of the catalyst as well as its electronic behavior under reaction conditions is fully understood. Only based on this fundamental knowledge, science-driven improvements or alternatives can be developed.
From a theoretical point of view, the electrochemical system is too complex to be handled holistically by any individual theoretical method at the atomistic scale. Therefore, several theoretical approaches at different levels of approximation have been developed to address specific questions in the simulation of electrochemical systems. In contrast to popular DFT-based schemes, for this endeavor a reactive-molecular-dynamics-based multiscale approach has been developed and applied to investigate the morphological changes of a platinum model catalyst at different oxidative conditions, i.e. under ultra-high vacuum, near-ambient pressures and typical fuel cell operating conditions [1,2,3]. This stepwise increase in system complexity enabled direct comparison to experimental results and to confidently make predictions. A crucial outcome of this thorough theoretical investigation was the prediction of stable platinum surface oxides in a wide electrode potential regime―a fact that had been neglected thus far―which might lead to the development of new strategies to overcome current ORR performance limitations, for example.
Furthermore, the multiscale approach enabled reactive molecular dynamics simulations of the ORR at platinum model catalysts at an extended time- and length-scale. These simulations revealed elementary reaction steps, significantly extending the commonly discussed associative and dissociative reaction mechanisms . In addition, these simulations provided interesting new insights in possible degradation mechanisms of platinum electrocatalysts [4,5].
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