(166ah) Layered Double Hydroxide As Co-Catalyst to Improve the Oer Kinetics of Hematite Photoelectrode

Semiconductor based photoelectrodes to produce hydrogen from water in the presence of sunlight is considered as one of the most promising solution to overcome the energy crisis and global warming the world is facing today. The basic requirements for a semiconductor to be used in photoelectrochemical (PEC) water splitting are efficient absorption of visible light, high stability, low overpotential and good charge transport. Over the years, hematite (α-Fe₂O₃) based photoelectrodes have received a lot of attention because of its non-toxicity, availability, low cost, high photochemical stability in basic media and narrow bandgap (1.9 to 2.2 eV). From the perspective of scalability, hematite (α-Fe₂O₃) holds immense potential because of its high theoretical solar to hydrogen efficiency (~ 15 %). However, its application in PEC water splitting suffers from several limitations such as comparatively low absorptivity, very short excited-state lifetime (10^-12 s) and short hole diffusion length (2 to 4 nm). The resulting high recombination of photogenerated electron-hole pairs and slow oxygen evolution reaction (OER) kinetics need to be improved. Herein, we report the synthesis of Sn doped hematite and its integration with NiFe layered double hydroxide (LDH) as co-catalyst to overcome the aforementioned drawbacks. SnCl₂ at varying concentrations is used as the Sn source to prepare Sn doped hematite nanostructures. Furthermore, NiFe LDH is coupled to Sn doped hematite using Ni and Fe precursors. The nanostructured photoelectrodes were investigated by XRD, SEM with EDX, UV-VIS and the Sn elemental doping was confirmed by XPS analysis. The cocatalyst loaded sample exhibited a much higher photocurrent density ca. 2.2 mAcm^-2 at 1.75 V vs. RHE compared to 0.2 mAcm^-2 for Sn doped hematite at the same potential. Electrochemical Impedance Spectroscopy analysis further confirms that addition of cocatalyst overlayer helps in enhancing the surface reaction kinetics and reducing the OER barrier.