An in situ dual modification strategy for enhancing the electrocatalytic oxygen evolution performance of ZIF-67

Abstract

Enhancing the electrocatalytic performance of metal–organic frameworks (MOFs) remains a key challenge in energy materials research. In this study, the cobalt-based zeolitic imidazolate framework ZIF-67 (Z67) was modified using an all-inorganic coordination polymer, {(H₂O)₂K-μ-(H₂O)₃Ni(H₂O)₃}_2n[V₁₀O₂₈]_n (NiV₁₀), which introduces both nickel (Ni) centers and decavanadate (V₁₀) polyoxometalate (POM) clusters into the framework. An in situ synthetic approach was employed to generate a series of nanocomposites (25NZ67, 50NZ67, and 75NZ67) by varying the amount of NiV₁₀ added during Z67 synthesis. The integration of Ni²⁺ and V₁₀ clusters led to a significant structural reorganization in the Z67 framework, leading to the formation of a more open architecture, unlocking coordinatively unsaturated metal active sites (CUMAS), and enriching the material with abundant electroactive centres. Electrochemical evaluation revealed significantly improved oxygen evolution reaction (OER) performance for all composites compared to pristine Z67. The onset potential for all three composites was in the range of 1.44–1.46 V. The composite 75NZ67 exhibited an overpotential of 350 mV at j = 10 mA cm⁻², which was ∼200 mV and ∼130 mV lower than Z67 and NiV₁₀, respectively, at the same current density. Further, 75NZ67 exhibited the highest OER activity, with a 3-fold increase in current density compared to pristine Z67. It also displayed an improved Tafel slope of 120 mV dec⁻¹, outperforming most of the control compounds studied and Z67 (144 mV dec⁻¹). The encapsulation of POM within the ZIF cavity reduces the charge transfer resistance, leading to improved electrochemical performance during OER, as evidenced by the linear sweep voltammetry (LSV) curves. Notably, 25NZ67 demonstrated the best long-term stability, maintaining its performance over extended operation, and also the highest intrinsic activity when normalized by electrochemical surface area (ECSA). Control experiments confirmed that the enhanced activity arises from the synergistic effect of Ni doping and V₁₀ encapsulation, achievable only via the in situ synthetic route. This work highlights a room-temperature in situ design strategy for Z67-based electrocatalysts by leveraging transition metal–polyoxometalate hybridization for improved OER performance.