NHC-Ni Nanoclusters covalently ligated on Carbon Nanotubes: Highly Active Electrocatalysts for the Oxygen Evolution Reaction

Abstract

Developing robust and efficient oxygen evolution reaction (OER) electrocatalysts is essential for advancing renewable energy technologies like water electrolysis. Here, we present an electrocatalyst comprising N-heterocyclic carbene (NHC)-ligated nickel nanoclusters (NiNCs) covalently anchored on multi-walled carbon nanotubes (MWCNTs), with only 3.9 % Ni/C atomic content. The unique nanoarchitecture, featuring a conductive NHC-Ni(0) core and an electroactive NiOx shell, was prepared via a dual metal-reduction and transmetalation strategy, offering exceptional electrocatalytic stability and efficiency, whereas MWCNTs offer mechanical robustness and a conductive nanocarrier support contributing in the enhanced OER kinetics. The electrocatalyst demonstrates low overpotentials of 320 mV and 500 mV at 10 mA/cm2 and 200 mA/cm2, respectively, in 1 M KOH, with very high specific (jESCA = 133 mA/cm2) and intrinsic (jnNi = 2.8×109 mA/mol.cm2) activities, as well as exceptional turnover frequencies (TOF), reaching up to 7.4 s-1 under industrially relevant conditions (200 mA/cm2). Electrochemical impedance spectroscopy reveals rapid charge transfer kinetics (Rct: 66 Ω to 9.7 Ω) and efficient interfacial processes, driven by high dispersion and ultrafine NiNC size (<1.6 nm). The synergistic interplay between the NHC-Ni(0) core, which stabilizes the electroactive shell structure, and the MWCNTs, which enhance electron transport and provide mechanical robustness, ensures durability under prolonged cycling, with minimal losses (<1.3% overpotential gain and <0.5% apparent loss of Ni active sites). These results establish MWCNTs-NHC-ligated NiNCs as a scalable and high-performing electrocatalyst, surpassing RuO2 and competitive NiFe-based materials, highlighting how precise nanoengineering through innovative covalent architectures can enable efficient and durable OER technologies in clean energy systems.