It is a challenge to harvest ocean wave energy by electrokinetic principle. We present here film-type generators made of carbon for wave energy harvest. The electrical signals arise from charge transportation along percolating channels driven by moving electric double-layer boundary at generator/seawater interfaces. Both voltage and current outputs are maximized by optimizing carbon dosage, wave frequency, hoisting angle and seawater temperature, producing a voltage of > 20 mV and a current of > 10 microamp from a 15 cm2-sized generator. We illustrate the electricity can be scaled up through series and parallel connections of multiple generators. Upon persistently rushing by waves, these film-type generators are stable over several hours. This approach to ocean wave energy harvest provides new opportunities for unprecedented low-investment, scalable power outputs and high stability.