The surge of alternative clean energy with minimal environmental impact in a cost-effective way requires the exploration of new materials and/or structures as efficient electrodes for industry-level photoelectrochemical (PEC) water splitting into usable H₂ fuel. Considerable efforts have been made on anodic/cathodic photoelectrolysis of water with metal oxides, which have been featured by their abundance, environmental friendliness, and chemical stability. As a type of fascinating functional materials, delafossites with an ABO₂-type general composition, where ‘A’ is monovalent (1+ metals of Cu, Ag, etc.) and ‘B’ is trivalent (3+ metals of Al, Ga, In, Fe etc.) have been highly oriented for applications as optoelectronics. Recently some aspects have been uncovered in the delafossite material field, e.g. they can be used as electrocatalysts and photocatalysts which are invaluable to rational design and optimization for various catalytic applications. Therefore, it is emergent to improve their optical and electrochemical activity for their electrochemical and photoelectrochemical (PEC) catalytic applications. One widely used strategy is to increase the surface area of functional materials. Here delafossite CuGaO₂ nanoflakes have been synthesized by a hydrothermal method in the presence of sodium dodecyl sulfate (SDS) as surfactant at 190^oC for 60 h and compared with CuGaO₂ microplates synthesized under the same conditions without SDS. The synthesized samples were thoroughly characterized by powder X-ray diffraction, SEM, EDX, XPS, FT-IR, UV-Vis and BET surface area measurements. Moreover, their electrocatalytic and photoelectrocatalytic performance for OER in 0.5 M KOH electrolyte versus Ag/AgCl along with their stability were studied for cost-effective and active electrode material. It was demonstrated that the delafossite CuGaO₂ nanoflakes synthesized in the presence of SDS showed better (photo)electrocatalytic performance and stability for OER than those synthesized without surfactant SDS. Thus, this hydrothermal method in combination of surfactant was an efficient approach towards the synthesis of delafossite CuGaO₂ with reduced size as cost-effective and high performance (photo)electrocatalysts.