Fe(III)-Mediated Formation of Cu Nanoinclusions and Local Heterojunctions in CuWO4 Photoanodes

Enhancing the photoelectrochemical (PEC) performance of CuWO₄ photoanodes has typically relied on doping or co-catalyst strategies to improve charge carrier dynamics. In this work, an alternative approach is presented in which Fe(III) acts as a self-assembly mediator during hydrothermal synthesis, enabling the formation of a core–shell heterostructure composed of a crystalline CuWO₄ core, a partially amorphous CuO/WO₃ shell, and embedded metallic Cu nanoinclusions. Rather than functioning as a dopant or co-catalyst, Fe(III) is completely removed during post-synthetic treatment, mediating a redox-guided phase reorganization without being incorporated into the final material. This architecture establishes local heterojunctions that facilitate charge separation, suppress recombination, and enhance oxygen evolution reaction (OER) activity. A relative increase of ≈30-fold in photocurrent is observed compared to pristine CuWO₄, as confirmed by structural, spectroscopic, and electrochemical analyses. While absolute photocurrents remain modest, this enhancement reflects intrinsic modifications in charge transport and recombination behavior driven by Fe(III)-mediated structural reorganization. Complementary photocatalytic dye degradation experiments reveal that Fe-activated particles act as highly efficient ROS-generating catalysts in suspension, demonstrating functionality beyond thin-film devices. These findings offer a new paradigm for oxide photoanode design, leveraging Fe(III)-induced self-assembly to engineer multifunctional heterostructures without relying on conventional doping.