An attractive approach to obtain effective and stable electrode for water electrolysis is to directly deposit the electrocatalyst on current collector surface. Herein, we show the influence of electrochemical activation of carbon cloth substrate on the morphology and electrocatalytic properties of bifunctional electrodes for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). A simple one-step electrodeposition technique was applied to directly grow mixed Co-based films on electrochemically activated carbon cloth (EACC) surface. The produced films are composed of metallic Co, and largely amorphous CoO/Co(OH)2 phases. Variation of Co2+ concentration in the solution for electrodeposition enabled tuning the composition of mixed films in order to achieve the optimal HER and OER electrocatalytic performance in 0.1 M KOH. The synthesized electrodes require the overpotentials of 195 mV for HER and 340 mV for OER to deliver the current density of 10 mA/cm2. The results indicate that the facile oxidation of carbon cloth prior to the electrodeposition decreases the overpotential at 10 mA/cm2 by 150 and 60 mV for HER and OER respectively, thus opening the perspective of improving the activity of carbon-based self-supported composite electrocatalytic electrodes for advanced energy conversion processes.