Earth-abundant and non-toxic metal oxides are attractive catalysts for energy conversion and storage applications. While extensive searches for efficient and selective catalysts have been enthusiastically carried out mostly for n-type semiconductors, p-type photocathode materials have been the subject of a much fewer studies with very few noticeable exceptions. One example is the fascinating delafossites with an AMO2-type general composition, where ‘A’ is monovalent metals of Cu, Ag, etc. and ‘M’ is trivalent metals of Al, Ga, In, Fe, etc. Some recent studies on delafossites have demonstrated that they could be used as electrocatalysts and photocatalysts and are invaluable to rational design and optimization for various catalytic applications. Therefore, it is emergent to improve their optical and electrochemical activity and explore their potential electrochemical (EC) and photoelectrochemical (PEC) catalytic applications. Based on a widely used strategy to increase the surface area of functional materials, here using CuGaO2 as an example, we synthesized delafossite nanoflakes by a hydrothermal method. Their EC and PEC performance for oxygen evolution reaction (OER) in 0.5 M KOH electrolyte versus Ag/AgCl along with their stability were studied for cost-effective and active electrode material and compared with CuGaO2 microplates synthesized under the same conditions without SDS. It was demonstrated that the delafossite CuGaO2 nanoflakes synthesized in the presence of SDS showed better EC and PEC performance and stability for OER than those synthesized without surfactant SDS. Furthermore, PEC performance was better than the EC performance for the same samples under identical measurement conditions. Thus, this hydrothermal method in combination of surfactant was an efficient approach towards the synthesis of delafossite CuGaO2 nanostructures with reduced size as cost-effective and high performance (photo)electrocatalysts.