Lowering oxygen evolution overpotential via morphology control of NiOx nanocatalysts

Abstract NiO x nanocatalysts with two distinct morphologies, nano-spindles and nano-plates, were synthesized and evaluated for oxygen evolution reaction (OER) performance. Spindle-like NiO x was prepared via a hydrothermal reaction of nickel nitrate and urea with cetyltrimethylammonium bromide as a surfactant at 120 °C for 24 h, forming Ni(OH) 2 -based intermediates that were subsequently calcined at 300 °C for 3 h. In contrast, platelet-like Ni(OH) 2 nanocrystals were obtained using nickel(II) acetate and KOH at 180 °C for 24 h, followed by calcination at 400 °C or 500 °C for 4 h to yield NiO x nano-plates. The NiO x nano-spindles exhibited an OER overpotential of 395 mV at 10 mA/cm 2 , whereas the NiO x nano-plates annealed at 400 °C and 500 °C showed overpotentials of 565 mV and 474 mV at 10 mA/cm 2 , respectively. Structural characterization and X-ray photoemission spectroscopy indicate these differences arise from morphology-dependent surface structures that govern catalytic activity. Graphical abstract