Hydrogen production from wastewater: using the photo-electrochemical (PEC) approach to recover high-value products

The present work focuses on developing a versatile photo-electrochemical (PEC) system designed to operate in both gas and liquid phases for the photo-upgrading of ethanol. This device, made of Plexiglas, was developed adopting a modular approach. It consists of two gas-tight half-cells separated by a reinforced proton-exchange membrane and connected to two small tanks for electrolytes, which also serve as gas storage. The photo-electrode used is a membrane of TiO2 nanotubes supported onto a Ti mesh. This novel 2D-3D electrode, located in direct contact with the exchange membrane, enables gas-phase (zero-gap) operation and shows superior performance in terms of photocurrent generation and reduced ohmic resistance. The photo-reforming tests were conducted using a 20% ethanol solution in water as the anolyte and a 0.050 M Na2SO4 aqueous solution as the catholyte. Hydrogen (H2) production rates of 11.2 µmol h-1 and 6.5 µmol h-1 were obtained in the gas-phase (GP) and liquid-phase (LP) configurations, respectively. Note that in the GP configuration, an inert gas stream transported the ethanol vapour to the anode operating in gas phase. Interestingly, the LP configuration yielded higher production rates of value-added chemicals, including 13.3 µmol h-1 of acetaldehyde and 0.4 µmol h-1 of acetic acid, compared to the GP configuration, which produced 4.2 µmol h-1 of acetaldehyde and no detectable acetic acid.