Stabilization of NiFe Layered Double Hydroxides on n-Si by an Activated TiO₂ Interlayer for Efficient Solar Water Oxidation

NiFe layered double hydroxides (LDH) on n-Si can be an expectable photoanode because of its advantages of earth-abundant materials, high photoelectrochemical properties, and wide solar spectrum. However, the open-channeled structure of LDH cannot effectively passivate silicon from corrosion and weak van der Waals force between the catalyst and substrate could lead to delamination. Herein, we demonstrated a cyclic voltammetry (CV)-activated amorphous TiO2 (a-TiO2) interlayer for the stabilization of NiFe LDH on n-Si. Stability of the photoanode could be enhanced through the insertion of the activated a-TiO2 layer, leading ∼140 h stability in the K-borate electrolyte, which is the longest stability reported so far using the NiFe- or TiO2-based Si photoanode. Additionally, CV activation led a-TiO2 into the conductive state through Ti3+ and oxygen vacancies, resulting in the facilitation of hole transfer. Synergetic heterolayers on the n-Si photoanode exhibited 0.92 ± 0.1 V versus reversible hydrogen electrode (RHE) onset potential, ∼36 mA/cm2 photocurrent density at 1.23 V versus RHE, and ∼100% charge injection efficiency at 1.3 V versus RHE. A high external quantum efficiency of ∼90% was achieved at 800 nm, and the optimized photoanode generated a photovoltage as high as 610 mV. Such a photovoltage could be attributed to the photoanode without the buried junction (adaptive junction) which consists of amorphous and thin NiFe LDH and a-TiO2 layers on n-Si. These results state that our strategy of introducing the CV-activated a-TiO2 layer for the stabilization and boosting the effect of NiFe LDH catalysts on n-Si and forming adaptive junction for yielding high photovoltage can be a prominent solution for effective solar water oxidation.