NiO electrode for methanol electro-oxidation: Mesoporous vs. nanoparticulate

• Synthesis of α-Ni(OH)2 nanostructure by a novel precipitation strategy in ionic liquid.
• Annealing the flower-like α-Ni(OH)2 produces mesoporous NiO electrode.
• Mesoporous structure of NiO is assembled by ∼5 nm sized grains.
• Mesoporous structure is better than nanoparticulate for methanol electro-oxidation.

Two NiO products with different microstructures have been obtained using a traditional NaOH-induced aqueous-phase precipitation and a homogeneous precipitation in choline chloride/urea mixture-based deep eutectic solvent (DES), respectively. The synthesis processes play a key role in the structure construction of NiO precursors as well as the final NiO products, and possible formation mechanisms are proposed. The DES-based homogeneous precipitation method provides plentiful nucleation sites, moderate crystal growth process and possible template effect, which could conduce to the production of flower-like NiO with continuously self-supporting mesoporous structure assembled by tiny grains. The flower-like NiO electrode exhibits higher current density, faster charge-transfer process, better electrode accessibility, and improved stability for methanol electro-oxidation in an electrolyte of 0.1 M CH3OH + 0.005 M KOH than the disorderly aggregated NiO nanoparticles. We believe that the DES-based homogeneous precipitation method can provide an effective approach to fabricate advanced electrocatalyst materials with homogeneous and well-assembled microstructure.