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

摘要

To improve upon our previously reported slow hydrogen evolution rate R_H at the energy-efficient lower voltages in CAWE (carbon-assisted water electrolysis) at room temperature, new results using different carbons and catalysts to improve R_H are reported here. Compared to earlier results with carbon GX203, about a ten-fold increase in R_H is reported using high surface area carbon BP2000 at the operating voltage E° = 1.12 V. With added FeSO_4 catalyst, E° is lowered to 0.72 V without lowering R_H, representing about 30% decrease in the energy barrier of the process. For comparison, in water electrolysis without carbon, measurable R_H is observed only for E° ≥ 2 V. This large improvement in R_H at the energy efficient E° = 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+) ← → 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_2O (e) → CO_2 (g) + 2H_2 (g). The reaction slows down with time as carbon is depleted by oxidation.