Aligned cobalt metal nanoparticles were prepared from the pyrolysis of cobalt oxalate nanoplate precursors for efficient electrocatalytic water oxidation. The 2D morphology of the precursor guided the 2D alignment of the derived cobalt metal nanoparticles. The as-prepared Co@CoOx electrocatalyst requires an ultra-low overpotential of 289 mV to achieve a current density of 10 mA cm-2 on a simple glassy carbon (GC) electrode in a 1 M KOH aqueous solution. The metallic nature of the bulk of the electrocatalyst and the compact alignment of the nanoparticles can facilitate the inner- and inter-particulate charge transfers.