Electrocapillary coupling coefficients for hydrogen electrosorption on palladium

The surface stress f, a capillary force at solid surfaces, has important implications for the behavior of nanomaterials. Surface stress is known to vary considerably when atoms adsorb on the surface, yet the underlying mechanisms are poorly understood. Our in situ dilatometry study of H adsorption on porous nanocrystalline Pd provides quantitative data for the response of f to changes in the adsorbate coverage. The porous body is immersed in aqueous electrolyte and H adsorption is controlled and measured electrochemically. The surface stress response is quantified by means of the electrocapillary coupling parameter, ς, defined as the derivative of f with respect to the superficial charge density. The results support previous, more indirect, findings for ς. We show that ς is precisely predicted by a model based on the continuum mechanics of superficial layers containing misfitting solute.