Simultaneous Sulfite Electrolysis and Hydrogen Production Using Ni Foam-Based Three-Dimensional Electrodes

The electrochemical oxidation of sulfite ions offers encouraging advantages for large-scale hydrogen production, while sulfur dioxide emissions can be effectively used to obtain value-added byproducts. Herein, the performance and stability during sulfite electrolysis under alkaline conditions are evaluated. Nickel foam (NF) substrates were functionalized as the anode and cathode through electrochemical deposition of palladium and chemical oxidation to carry out the sulfite electro-oxidation and hydrogen evolution reactions, respectively. A combined analytical approach in which a robust electrochemical flow cell was coupled to different in situ and ex situ measurements was successfully implemented to monitor the activity and stability during electrolysis. Overall, satisfactory sulfite conversion and hydrogen production efficiencies (>90%) at 10 mA·cm^-2 were mainly attributed to the use of NF in three-dimensional electrodes with a large surface area and enhanced mass transfer. Furthermore, stabilization processes associated with electrochemical dissolution and sulfur crossover through the membrane induced specific changes in the chemical and physical properties of the electrodes after electrolysis. This study demonstrates that NF-based electrocatalysts can be incorporated in an efficient electrochemical flow cell system for sulfite electrolysis and hydrogen production, with potential applications at a large scale.