Significant hydrogen productivity (0.33 mol% in products) from H2O splitting by atmospheric dielectric barrier discharges has been achieved with tubular plasma reactors at room temperature. The water splitting activity varies with different metal-coated inner electrodes and different peak voltages across the reactor. An optimal emission spectroscopic study was performed in order to explain the metal effect. O*/Ar* emission intensity ratio as well as excitation temperatures were used for rationalizing the metal effect.