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

摘要

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-TiO2/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 Na2SO4, The observed substrate (S) degradation kinetics (k_(obs)~S) are found to correlate well with the cell current (I_(cell)) and the H2 production energy efficiency (EE) in the presence of NaCl as the background electrolyte. In the case of Na2SO4, 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 Cl2~(·-) 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 H2 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 H2 production.