The adsorption of a water molecule occurs directly on a Zn atom of the ZnO trimer already adsorbed on graphene or on the ZnO trimer bonded to a functional group in GO. This is of interest as it is the catalytic site at which hydrolysis begins before water splitting. The negative oxygen atom of a water molecule is adsorbed onto a positively charged Zn atom of the ZnO trimer followed by hydrolytic dissociation and proton transfer of a hydrogen atom to an oxygen atom adjacent to zinc. Figure shows the adsorption of a water molecule on the (ZnO) 3 catalyst in the singlet state.