Covalently anchored nickel phthalocyanine networks on carbon nanotubes for efficient Ni(II)/Ni(III)-mediated methanol oxidation

Efficient and durable non-noble metal electrocatalysts for alkaline methanol oxidation remain a key challenge for the development of direct methanol fuel cells. Herein, we report a hybrid nanostructured catalyst consisting of molecularly dispersed nickel phthalocyanine sites covalently anchored within an imidazolium-based polymeric network on multi-walled carbon nanotubes (Ni-PC@MWCNTs). The covalent wiring of the phthalocyanine units provides a well-defined coordination environment for Ni centres, ensuring their molecular dispersion, accessibility, and efficient electronic communication with the conductive carbon support. Electrochemical studies indicate that methanol oxidation proceeds predominantly through an indirect Ni(II)/ Ni(III) redox pathway involving electrochemically generated Ni(III)-oxyhydroxide-like intermediates. As a result, the Ni-PC@MWCNTs catalyst delivers a high current density of 23.98 mA cm(-2) and an exceptional mass activity of 5.4 A mg(-1) Ni Ni at 0.7 V vs. Ag/AgCl in 1 M NaOH containing 1 M methanol, together with excellent durability, over 17 h of continuous operation. Electrochemical impedance spectroscopy and Tafel analysis confirm fast charge-transfer kinetics and efficient utilization of active sites enabled by the covalently integrated architecture. In addition, visible-light irradiation further enhances methanol oxidation, leading to a current-density increase of approximately 8 mA cm(-2) under the investigated conditions. Spectroscopic analysis combined with density functional theory calculations indicates that photoexcitation of the phthalocyanine units modifies the electronic distribution within the NiPc moiety and may facilitate the Ni(II)/Ni(III)-mediated catalytic cycle. These results demonstrate that covalently wired molecular nickel sites on carbon nanotubes represent an effective strategy for designing highly active and stable non-noble metal electrocatalysts for alkaline alcohol oxidation.