Here we introduce an ecological facile method to grow heterogeneous copper oxide (CuxO) nanocomposites on a Cu mesh using spinach leaf extract. After annealing at different temperatures, morphological and structural characterizations revealed that samples annealed at 300 °C comprise the highest Cu+/Cu2+ ratio and reveal the most porous structure. Such samples exhibited dual catalytic functions as both photocatalysts for dye degradation, and electrocatalysts for hydrogen evolution. Their photocatalytic activity for degradation of methylene blue (MB) was investigated under sunlight irradiation of 7 mW/cm2. A complete degradation, with an average kinetic rate of 63.2 m min−1, was achieved after 60 min. Moreover, the samples revealed a good electrochemical catalytic property for hydrogen evolution reaction (HER) in acidic medium. They exhibited HER onset at 357 mV with a small charge transfer resistance of 8.2 Ω. Such promising outcomes could open a new path for mass-production applications in water-energy fields.