Direct measurement of the hydrogen adsorption entropy on shape-controlled Pt nanoparticles using electrochemical microcalorimetry

Platinum nanoparticles are indispensable in electrochemical applications, e.g., for the generation and usage of green hydrogen. Therefore, understanding the properties of these materials before and during operation is of crucial research interest. However, their investigation is complicated by the variety of adjustable parameters under operating conditions. Researchers thus often revert to studying model systems, like single crystal Pt surfaces, yet it is not always clear how gained insights translate to actual applications. Conducting comprehensive physico-chemical studies on nanoparticles with preferential shapes could help bridge this gap. In this contribution, we use electrochemical microcalorimetry to investigate hydrogen adsorption on different shape-controlled platinum nanoparticles (quasi-spheres, cubes and octahedrons). From this method, we obtain the entropy of the adsorbed hydrogen on the different particles, which we aim to relate to its binding condition with the surface. This quantity often serves as a descriptor for the catalytic performance in the hydrogen evolution reaction. We show that the entropy of adsorption on the particles with different geometries is in good agreement with the adsorption on the single crystal sites related to the respective faces of the particles, by a comparison with entropy values obtained on platinum single crystals using the electrocapillary equation. The consistency between both methods opens possibilities for further research on analogous surfaces. The study is completed by investigating the effect of roughening of the particle surface by continuously cycling the potential into the platinum oxidation region. This enables the investigation of adsorbed hydrogen under more realistic conditions.