Apparent inverse Gibbs-Thomson effect in dealloyed nanoporous nanoparticles.

The Gibbs-Thomson effect (the reduction of local chemical potential due to nanoscale curvature) predicts that nanoparticles of radius r dissolve at lower electrochemical potentials than bulk materials, decreasing as 1/r. However, we show here that if the particle is an alloy--susceptible to selective dissolution (dealloying) and nanoporosity evolution--then complete selective electrochemical dissolution and porosity evolution require a higher electrochemical potential than the comparable bulk planar material, increasing empirically as 1/r. This is a kinetic effect, which we demonstrate via kinetic Monte Carlo simulation. Our model shows that in the initial stages of dissolution, the less noble particle component is easily stripped from the nanoparticle surface, but owing to an increased mobility of the more noble atoms, the surface of the particle quickly passivates. At a fixed electrochemical potential, porosity and complete dealloying can only evolve if fluctuations in the surface passivation layer are sufficiently long-lived to allow dissolution from percolating networks of the less-noble component that penetrate through the bulk of the particle.