Abstract: Piezocatalysis has attracted unprecedented research interest as a newly emerging catalysis technology. However, the inherent insulating property of ferroelectric materials ultimately leads to the poor vibration–electricity conversion ability. Herein, this work reports the (K_0.52Na_0.48)NbO₃ ferroelectric ceramics (KNNFCx), for which the FeCo modification strategy is proposed. The substitution of the moderate amount of FeCo (x = 0.015) at Nb site not only optimizes ferroelectricity but also produces beneficial defects, notably increasing Rhodamine B water purification efficiency to 95%. The pinning effect of monovalent oxygen vacancies on ferroelectric domains is responsible for the excellent ferroelectric polarization of KNNFC0.015 through the generation of an internal field to promote charge carriers separation and reduce nonradiative recombination. Importantly, the accompanying electron carriers can easily move to the material surface and participate in redox reactions because they have low activation energy. Therefore, ferroelectric polarization and defects play synergetic roles in enhancing piezocatalytic performance.