Nanocarbon boosts energy-efficient hydrogen production in carbon-assisted water electrolysis

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 Eo = 1.12 V. With added FeSO4 catalyst, Eo 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 Eo ≥ 2 V. This large improvement in RH at the energy efficient Eo = 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 Fe2+ ⇌ Fe3+ + e−. By measuring the amounts of H2 evolved at the cathode and CO2 evolved at the anode using gas chromatography, the mechanism for CAWE is established to be the reaction: C (s) + 2H2O (ℓ) → CO2 (g) + 2H2 (g). The reaction slows down with time as carbon is depleted by oxidation.