Electrochemical water splitting coupled with organic compound oxidation: The role of active chlorine species

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 ₂SO ₄. The observed substrate (S) degradation kinetics (k ^s _obs) 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 ₂SO 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 ^s _obs'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 AEEs. (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.