(1) where pK a1 and pK a2 are the corresponding acidity constants of BiVO 4 (010) surface. With adding reactions 1 and 2, leads to the PZC, while with subtracting reaction 1 from reaction 2, gives the dissociation free energy of adsorbed water. The relations among pK a1 , pK a2 , PZC, and ∆A diss are as follows: