Unveiling the Aluminum Doping Effects of In-Situ Transmogrified Dual-LDH Heterostructure and Its Fermi-Level Alignment to Water Splitting Potentials

Abstract

The layered double hydroxide (LDH) captivates the starlight of electrochemical water-splitting applications due to its stacked layers and larger surface area. A novel approach is reported to integrate CoFe-LDH/NiAl-LDH heterostructure through a single-step in situ transmogrification, harnessing the benefits of LDH. The in situ Raman spectroscopy reveals that aluminum (Al) doping promotes the formation of high-valent Co^III/IV-O active species concentration in LDH, whereas without Al dopants, the catalyst predominantly exhibit Ni^II/III-O species and underperform the catalytic activity. The projected density of states is very close to the Fermi level positions in Al-doped samples which significantly enhance the electron transfer processes. The Mott–Schottky studies confirm that both Al40 CoFe30 and Al60 CoFe20 catalysts are p-type semiconductors, exhibiting a distinct redox behaviors under applied bias. At positive bias, Al60 CoFe20 undergoes downward band bending (accumulation), and align the Fermi-level near the water oxidation potential, which promotes the oxygen evolution reaction (OER). The negative bias causes upward band bending (deep depletion) in the Al40 CoFe30, and shifts the Fermi-level near the water reduction potential, and hence facilitates hydrogen evolution reaction (HER). Overall, this study highlights the importance of manipulating Fermi-level alignment in LDH catalysts through strategic metal doping to achieve targeted water-splitting reactions.