Carbon‑paper‑supported Fe‑doped WO3 catalysts engineered as a high‑performance bifunctional electrode for alkaline water splitting

Tungsten trioxide (WO 3 ) is an earth‑abundant and chemically robust semiconductor predominantly explored as a photoanode. A key limitation in earlier WO 3 studies is the reliance on fluorine‑doped tin oxide (FTO) substrates, whose flat 2D geometry, moderate conductivity, and susceptibility to reductive degradation restrict catalytic performance. In contrast, carbon paper (CP) offers a 3D porous fiber network with a substantially larger real surface area, superior electrical conductivity, and excellent electrochemical stability in alkaline media, making it a more suitable platform for high‑current water electrolysis. Here, Fe‑doped WO 3 (Fe: WO 3 ) powders were immobilized onto CP using a simple three‑cycle dip‑coating process with a poly(vinyl alcohol)/carbon‑nanotube binder, producing self‑supported Fe: WO 3 /CP electrodes with a geometric area of 1 cm 2 . XRD, FTIR, and Raman analyses show that both WO 3 and Fe:WO 3 crystallize in mixed hexagonal/monoclinic phases, while Fe incorporation broadens and attenuates W–O–W vibrational modes, indicating increased lattice disorder. Cross‑sectional SEM and EDX mapping reveal a continuous 1–2 µm catalyst overlayer with homogeneous W, O, and Fe distribution across the carbon fibers. Fe doping narrows the optical band gap from 2.57 to 2.42 eV, red‑shifts the absorption edge from 481 to 512 nm, and decreases the Mott–Schottky slope, consistent with an increased donor density. Electrochemical testing in 1 M KOH shows that Fe: WO 3 /CP outperforms undoped WO 3 /CP for both half‑reactions: the overpotential at 10 mA cm −2 decreases from 0.74 to 0.59 V for HER and from 0.71 to 0.46 V for OER, while the Tafel slopes decrease from 514.5 to 406.0 mV·dec −1 and from 573.6 to 357.7 mV·dec −1 , respectively. The double‑layer capacitance increases by a factor of 1.65, and the electrode maintains 24 h of continuous cathodic operation without morphological or compositional degradation. These results demonstrate that combining Fe doping with conductive‑carbon immobilization provides a simple and effective route toward WO 3 ‑based bifunctional electrodes with enhanced activity and durability for alkaline water electrolysis.