Photoelectrochemical Hydrogen Production from Surfactant-Rich Wastewaters: Proof-of-Concept and Mechanisms Investigation

Abstract

Solar hydrogen production currently employs pure water to prevent side reactions and damage to materials. Nevertheless, pure water is an increasingly valuable resource, and alternative substrates are required. In this work, we investigated a strategy for photoelectrochemical (PEC) solar hydrogen production from surfactant-rich wastewater. Sodium dodecyl sulfate (SDS) was used as a test-surfactant because of (1) its large use in industrial and domestic applications and consequently relevant concentration in wastewaters and (2) its potential suitability as a hole scavenger to enhance H₂ production. The working electrode of the PEC cell was a Ti-doped hematite photoanode, fully characterized to obtain information about crystallinity, morphology, and optical properties. Ongoing mineralization of SDS at the photoanode was characterized by the Gas Chromatographic (GC) detection of CO₂, with a radical-mediated oxidation mechanism revealed by fluorescence-based methods and Electrochemical Impedance Spectroscopy (EIS). H₂ production with simultaneous SDS oxidation and oxygen evolution, at 2.15 V RHE applied voltage, was quantified by GC. With a 1 cm² electrode, the production rate was 4.6 ± 0.3 μmol/h with a power saving efficiency (η, with respect to dark conditions) of 0.3%. A scale-up to 16.8 cm² area resulted in 22 ± 2 μmol/h with a η of 0.13%. These results provide a proof-of-concept for the valorization of surfactant-rich wastewaters as solar H₂ substrates.