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

The Mott–Schottky study highlights the semiconductor properties of the LDH catalysts. While both the OER and HER catalysts are P-type semiconductors, they exhibit distinct redox properties. At cathodic bias, the charges are depleted in Al40 CoFe30 and lift the fermi-level near 0V (HER). At anodic bias, the charges are accumulated within Al60 CoFe20 and push the fermi-level near 1.23 V (OER).

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.