At low volume fractions, drying occurs in the bulk of the solution. This regime is also referred to as "wet drying". Evaporation of the solvent occurs from the solvent-air interface and is purely a function of the solvent composition. The rate of drying affects the stratification of colloidal particles (especially given the different diffusivities of Pt/C and ionomer) . This is usually predicted by means of a dimensionless quantity, the Péclet number. The Péclet number is the ratio of the rate of a particle's diffusion to the rate evaporation of the solvent . Hence, the Péclet number is used to quantify the diffusive/advective nature of a solution. By imposing a slow drying rate, we assume a low Péclet number drying regime (diffusion dominant), which leads to the uniform aggregation of particles. Beyond a certain volume fraction, the particles reach the jamming limit. At this point, the colloidal particles are highly compact, and drying is driven by capillary evaporation . This regime is referred to as "moist drying". In this stage, we assume that the microstructure is frozen in place and diffusion of particles are severely limited, hence terminating the "drying" process.