A Zr/Sm co-doped Fe₂O₃:NiCo-MOF heterojunction photoanode for augmented photoelectrochemical water splitting

It is of utmost importance to enhance the photoelectrochemical water splitting effectiveness of Fe₂O₃ photoanodes by addressing photoanode/electrolyte interface defects, as well as bulk and surface charge carrier recombination. Herein, Zr/Sm co-doped Fe₂O₃ in conjunction with a bimetallic NiCo-metal-organic framework (MOF) cocatalyst to construct an n-p heterojunction is reported. The bulk conductivity was significantly improved by Zr/Sm co-doping, which was accomplished by increasing donor density. The NiCo-MOF cocatalyst passivated surface-trapping states/recombination surface states via alleviating the Fermi level pinning effect, hastened hole transfer to the electrolyte by suppressing surface charge recombination and recombination within the space-charge layer and extended hole lifetime at the intermediate surface states. In addition, the formed p-n heterojunction between NiCo-MOF and Zr/Sm-Fe₂O₃ facilitated bulk conductivity by utilizing an internal built-in electric field at the interface of the heterostructure. As a result, at 1.23 V_RHE, the Zr/Sm-Fe₂O₃:NiCo-MOF exhibited a photocurrent density of 2.36 mA cm⁻² with surface charge separation and surface charge transfer efficiencies of 95.3 and 91.6%, respectively. This present investigation offers valuable insights into the rational design of co-doped semiconductors with MOF-based heterojunctions for the intent of photoelectrochemical water splitting.