The construction of efficient photocatalysts for water splitting is still challenging, mainly due to the unexpected recombination of photogenerated carriers. Ferroelectric polarization-induced charge separation of photo catalysts has been demonstrated as an effective method for improving photocatalytic performance. However, ferroelectric domains in existing works are random before polarization-switching, which results in lower polarization electric field intensity and limits the charge separation efficiency. Here, we report that the spontaneous ferroelectric polarization in a single domain for efficient charge separation over a representative semiconductor CdS, in the form of CdS/Au/Ti/Pb(Mg1/3Nb2/3)(0.7)Ti0.3O3 (CdS/Au/Ti/PMN-PT), for water splitting in absence of any cocatalyst or external voltage. The photocurrent value of the positive polarized CdS/Au/Ti/PMN-PT yields 1.70 mA.cm(-2), which is about 20 times higher than the value of the non-polarized sample. In addition, a biphotoelectrode cell composed of a positively and a negatively polarized CdS/Au/Ti/PMN-PT was constructed. A considerable solar-to-hydrogen conversion efficiency of 0.19% was achieved. It was found that the interfacial resistance and the surface reaction kinetics may be the main factors governing the photocatalytic performance. This work not only provides a strategy to promote charge separation but also develops a new biphotoelectrode cell capable of obtaining efficient solar water splitting.