Electrochemical Water Splitting Coupled with Organic Compound Oxidation: The Role of Active Chlorine Species

Abstract

The need for alternative energy sources with minimal to no carbon footprint is growing. A solar-powered electrochemical system that produces hydrogen via water splitting using organic pollutants as sacrificial electron donors is a possible solution. The hybridization of a BiO x −TiO 2 /Ti anode with a stainless steel cathode powered by a photovoltaic (PV) array has been shown to achieve this process. The electrochemical degradation kinetics of a variety of organic substrates is investigated as a function of a background electrolyte, NaCl versus Na 2 SO 4 . The observed substrate (S) degradation kinetics ( k obs S ) are found to correlate well with the cell current ( I cell ) and the H 2 production energy efficiency (EE) in the presence of NaCl as the background electrolyte. In the case of Na 2 SO 4, no correlation is observed and the degradation rates are greatly reduced in comparison to NaCl. This suggests that the primary chemical oxidant is electrolyte-dependent. The k obs S ’s are found to be proportional to the bimolecular rate constants of Cl 2 •− with the substrate ( k Cl 2 •− +S ) and to substrate-induced ΔEEs (EE with substrate − EE without substrate) in the presence of NaCl. The ΔEE correlation arises from the active chlorine species acting as an electron shuttle, which compete with H 2 production for cathodic electrons. In the presence of the organic substrates, the active chlorine species are quenched, increasing the fraction of electrons utilized for the H 2 production.