To improve upon our previously reported slow hydrogen evolution rate RH at the energy-efficient lower voltages in CAWE (carbon-assisted water electrolysis) at room temperature, new results using different carbons and catalysts to improve RH are reported here. Compared to earlier results with carbon GX203, about a ten-fold increase in RH is reported using high surface area carbon BP2000 at the operating voltage E degrees = 1.12 V. With added FeSO(4) catalyst, E degrees is lowered to 0.72 V without lowering RH, representing about 30% decrease in the energy barrier of the process. For comparison, in water electrolysis without carbon, measurable RH is observed only for E degrees >= 2 V. This large improvement in RH at the energy efficient E degrees = 0.72 V is suggested to result from nanoscale particle size of carbon BP2000 as well as from electrons provided by the catalyst through the reaction Fe(2+) (sic) Fe(3+) + e(-) . By measuring the amounts of H(2) evolved at the cathode and CO(2) evolved at the anode using gas chromatography, the mechanism for CAWE is established to be the reaction: C (s) + 2H(2)O (l) -> CO(2) (g) + 2H(2) (g). The reaction slows down with time as carbon is depleted by oxidation. (C) 2009 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.