| Summary: | Only a few strategies have been reported to overcome the limitations of tungsten trioxide (n-WO3) photoanode fabricated via anodic oxidation of metallic tungsten foil for efficient photoelectrochemical (PEC) water splitting. This work presents a method for synthesizing pure iron tungstate (p-FeWO4) nanoparticles (∼37 nm size) via a hydrothermal process, followed by their application as co-catalyst through spin coating onto porous anodic WO3 (∼351 nm total thickness). A thin FeWO4 layer was essential to ensure sufficient light exposure of the underlaying WO3 during front illumination. Due to the high crystallinity of FeWO4 and the favorable band alignment between these two semiconductors, the modified WO3 exhibited suppressed charge carrier recombination and enhanced charge separation and transfer. As a result, the modified photoanode achieved a stable photocurrent density up to 1.5 times higher than that of pristine WO3 under simulated solar illumination with practically unchanged onset potential. Notably, performance under visible light also improved, although no significant red shift of absorption edge (band gap of ∼2.9 eV) was noted. The results demonstrated high reproducibility, and we emphasize the significance of this approach for WO3 photoanodes on opaque substrates, as it should be easily adaptable to WO3 electrodes fabricated by any technique.
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