Phase transformation of a ZIF-on-ZIF heterostructure for uniform NiCo incorporation with enhanced oxygen evolution performance

Abstract

Transition-metal nanoparticles loaded on N-doped carbon (M@NC) derived from zeolitic imidazolate frameworks (ZIFs) are promising catalysts for various electrochemical transformations. However, conventional ZIF precursors are usually restricted to afford Co- or Zn-based nanoparticles, leaving highly active Ni-containing systems largely inaccessible. Here, we report a ZIF-on-ZIF phase transformation strategy to achieve uniform NiCo incorporation and hollow-structure formation. A ZIF-8@ZIF-67 precursor is transformed into a hollow MOF-74 (Zn, Co, Ni), then carbonized to produce CoNi alloy nanoparticles uniformly embedded in a hollow N-doped carbon matrix (H-CoNi@CN). The H-CoNi@CN electrocatalyst exhibits exceptional activity in oxygen evolution reaction (OER), achieving a low overpotential of 223 mV at a current density of 10 mA cm−2 and demonstrating excellent long-term stability. Material characterization and density functional theory simulations reveal that the hollow structure can maximize the exposure of active sites, while the strong electronic coupling between Ni and Co within the alloy structure can effectively enhance charge transfer and decrease the energy barrier for OER. This ZIF-on-ZIF transformation approach provides an avenue to design multifunctional catalysts with tunable compositions and architectures for diverse energy applications.