Although the light density decreased exponentially with the length from the electrochemical cell surface due to the light absorption and scattering by cyanobacterial cells, the photon density within the electrolytic solution was maintained more than 50 mmol s–1 m–2.The anodic and cathodic half-cell compartments were bubbled continuously with argon and dioxygen gas, respectively, at a flow rate of 0.4 L min–1