However, the surface complexation acts as a diffusion barrier and, depending on its magnitude, can affect the hopping of an ion from one site to the next. Therefore, the surface diffusion is perturbed by the presence of acetate (or a residue) bound to the positively charged surface sites, forming a diffusion barrier. This finding accounts for the smaller grain sizes observed in experiments (Figure 2 C) when residual acetate species are present in the GBs.