Electrochemical aspects of the Hybrid Sulfur Cycle for large scale hydrogen production

• The Hybrid Sulfur Cycle is a viable and renewable option for large scale hydrogen production.
• Anodic electrolysis is an important limiting aspect of the process.
• Here we report of features of the system that influence the kinetics of sulfur dioxide oxidation.
• The oxidation reaction is also significant because it is one of the few examples of an oscillating electrochemical reaction.

The Hybrid Sulfur Cycle is a thermo-electrochemical process designed for the large scale production of hydrogen. The two-step process is essentially based on water splitting using various sulfur species as intermediates. The limiting step in the overall process is the electrochemical oxidation of sulfur dioxide to form sulphuric acid, which suffers from a substantial (∼0.4 V) anodic overpotential. Here we report on various aspects of sulfur dioxide oxidation in an acidic media including the effects of electrode preconditioning, the electrode substrate and electrolyte effects, the combination of which has allowed development of a sulfur dioxide oxidation mechanism which is described and discussed. Additionally, the electrochemical oxidation of sulfur dioxide has been shown to be an oscillating reaction, which is also a novel finding.