Binary Ni-Fe-Layer Double Hydroxide and Zeolite Composites Materials for High-Efficiency Water Splitting

Abstract

The noble metal catalysts represented by Ru- and Ir- based catalysts and their oxides have excellent OER properties, but their limited earth reserves and high prices have severely limited the large-scale commercial application of noble metal catalysts. Nickel-iron hydroxide (Ni/Fe-LDHs) is considered to be a promising non-precious metal OER electrocatalyst due to its special layered structure and adjustable composition. Nevertheless, the edge sites serve as the primary active centers of Ni/Fe-LDHs, and the formation of the highly oxidized catalytic phase is impeded by the closely packed substrate. Therefore, activation of these substrates is particularly important for further enhancing the catalytic activity of Ni/Fe-LDHs. An effective strategy for addressing this issue is to replace two-dimensional sheets with three-dimensional materials. In this study, a simple, inexpensive, and self-assembly strategy was developed for the large-scale preparation of Ni/Fe-LDHs under hydrothermal conditions. The fabrication mechanism involves a stepwise and orderly process where LDH nanosheets gradually grow into nanopetals before assembling into flower-like microspheres, based on a systematic investigation of the zeolite 4A (ZA) feeding ratio. The specific surface area of the Ni/Fe-LDHs/0.3 mg ZA composite material (336.0 m2/g) is increased by more than three times compared that with pure Ni/Fe-LDHs (96.53 m2/g). Owing to their large specific surface area, ultrathin structure, and the synergistic effects of the Ni/Fe-LDHs/ZA composite, these Ni/Fe-LDHs/ZA microspheres exhibit excellent electrochemical performance. The Cdl value, overpotential, and OER activity of Ni/Fe-LDHs/ZA composites were also enhanced compared with pure Ni/Fe-LDHs.

Keywords: OER electrocatalysts, Ni/Fe-LDHs, zeolite, specific surface area, 3D