Influence of catalyst coated membranes on electrochemical bunsen reaction in the sulfur-iodine cycle

Abstract

Bunsen reaction is the initial step of the sulfur-iodine (SI) cycle for hydrogen production, and it has a significant effect on the subsequent reactions. Compared with traditional methods, electrochemical Bunsen reaction is more advantageous for SI cycle as it requires less amounts of iodine for the reaction. In this method, the two acid phases are generated separately in two chambers of the electrolytic cell. In a typical electrochemical Bunsen method, sulfur dioxide is oxidized at the anode to form sulfuric acid while iodine is reduced at the cathode to generate hydrogen iodide. However, the high cell voltage can lead to high energy consumption. In this work, two Catalyst Coated Membranes (CCMs) were synthesized to study the effects of Pt/C catalysts on the electrolytic reaction with a two-chamber membrane electrolyzer. The properties of the membranes were characterized by constant current electrolysis curves, polarization curves, cyclic voltammetry method and electrochemical impedance spectroscopy (EIS). All the electrochemical measurements were carried out at 298 K. At the current density of 50 mA/cm2, the average cell voltage with commercial Nafion 115 membrane was 1.37 V, while the cell voltage with the home-made CCMs was as low as 0.5 V. With the help of Pt/C catalyst coated on the membrane, a significant reduction in charge transfer resistance (Rct) was observed according to the Nyquist plots. The titration results indicated that the permeation decreased with the increase in catalyst loadings. Furthermore, the current efficiency increased by 54.23% (from 63.16% to 97.41%) and the energy required to produce 1 mol hydrogen reduced by 75.68% (from 1084.546 kJ to 263.785 kJ).