Three CuO nanocrystal morphologies (willow-leaf, spiny, and flower-shaped) with different exposed crystal facets are prepared through a two-step liquid-phase procedure. The CuO crystals have high hydrazine oxidation reaction (HOR) activity and good stability. Flower-shaped CuO has the highest HOR activity and stability of the three forms, with a positive onset-potential of -0.14 V and a high oxidation peak current density of 5.23 mA cm(-2). HOR activity of the CuO crystals correlates to the type of exposed crystalline facet. (C) 2015 Elsevier B.V. All rights reserved.