Hydrogen production from water electrolysis coupled with ethanol oxidation by membrane electrolyzer combined flow-through and fed-batch operation

To enhance mass transfer in hydrogen production from water electrolysis coupled with ethanol oxidation, a membrane electrolyzer combining flow-through and fed-batch operation was developed. The optimized Co 0.1 Ni 0.9 (OH) 2 /Ni foam electrode was used for ethanol oxidation, with a current density of 200 mA cm −2 at 1.383 V vs. RHE and a Tafel slope of 39.5 mV dec -1 . Employing this electrode as the anode, the mass transfer coefficient ( k m ) in the flow-through electrolyzer was 7.0 × 10 -6 m s −1 under the conditions of electrolyte flow velocity at 0.06 m s −1 , ethanol concentration at 0.2 M and KOH concentration at 6 M, which was 49 % higher than that in the flow-by electrolyzer. This enhancement in k m directly translated to an increase in the mass transfer limiting current density ( i L , from 194 mA cm −2 to 289 mA cm −2 ), significantly higher reaction rate. Both k m and i L would be increased with the increase of electrolyte circulation rates. An analysis of the relationship between intrinsic electrochemical current density and i L showed that the ethanol oxidation process is maintained at or near the i L , which improved current efficiency and product yield. A fed-batch strategy, regulating ethanol concentration around 0.2 M, enabled sustained co-production of acetic acid and hydrogen at current densities of 289 mA cm −2 , with a production rate of 18.54mol h −1 m −2 (electrode) and 43.75 mol h −1 m −2 (electrode) respectively, with an anodic Faradaic efficiency of 92 %. The hydrogen production energy consumption was 3.85 kWh Nm −3 under this condition in flow-through electrolyzer.