Herein, we synthesize a Cu-cuprous/cupric oxide-based family of catalysts via simple hydrothermal technique, and investigate the effect of copper oxide phases on the application of interest. These catalysts are applied towards dual application namely 4-nitrophenol (4-NP) conversion and electrochemical hydrogen evolution reaction (HER). Due to the difference in mechanism of these both applications, we pick up two best catalysts for either application. We explore these differences through intensive characterizations such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction of hydrogen (H₂-TPR) analysis. XRD reveals the presence of varying copper oxide phases across all the synthesized catalysts. XPS discovers the disparities between catalysts annealed at various temperatures. Reducibility of catalysts is studied via H₂-TPR since they can disclose phase conversions taking place in the material thereby directly affecting the application. Cu-Cu₂O (150℃) could convert 98.6 % of 50 ppm 4-NP into 4-aminophenol (4-AP) with recycle tests up to 10 cycles yielding conversion values between 96.3 and 98.9% which are high enough for any catalyst to reach its maximum potential. CuO-Cu₂O (300℃) exhibits best HER activity with the least onset potential of −0.28 V vs. RHE at 1 mA cm⁻² possessing a maximum current density of 366 mA cm⁻².