A hierarchical 3D-nanoflower LDH heterojunction: a bifunctional electrocatalyst for total water splitting

Abstract

Hydrogen is a clean energy alternative to conventional hydrocarbons in various applications. Water electrolysis is the fastest and most efficient approach for generating pure hydrogen with zero carbon emissions. Layered double hydroxides (LDHs) are the most prominent materials for developing efficient and cost-effective electrocatalysts for water splitting. A highly efficient approach for designing an electrocatalyst with improved performance is to develop a hierarchical LDH heterojunction with a modulated electronic structure. In this work, we designed a hierarchical NiFe-LDH/NiCo-LDH heterostructure over Ni foam via a hydrothermal process, which exhibits enhanced OER and HER performance under alkaline conditions. Additionally, the heterostructure shows a high faradaic efficiency value of 93.4% at 1.65 V potential, demonstrating excellent selectivity toward the electrocatalytic reaction. Furthermore, the prolonged stability over 60 h at 1.55 V highlights its sturdiness. The prepared catalyst exhibits a TOF value (0.155 s⁻¹) that is 13 and 24 times greater than that of NiFe-LDH (0.0125 s⁻¹) and NiCo-LDH (0.0063 s⁻¹), respectively, towards the OER. The pH-dependent study reveals that the NiFe-LDH/NiCo-LDH heterostructure follows the adsorbate enhancement mechanism (AEM) rather than the lattice oxygen mechanism (LOM). DFT studies further confirm the synergistic interaction in the NiFe-LDH/NiCo-LDH interface which facilitates the enhanced activity in the OER, whereas in the HER, the reduction in the ΔG_H* value increases the adsorption and desorption process of the H atom over the catalyst. This work offers a new route for improving electrocatalytic performance by developing a hierarchical LDH heterojunction.