Sulfite permeability and sulfur accumulation in a sulfite depolarized electrolyser

•A sulfite depolarized electrolyser adopting sulfite wastewater is developed.•Sulfite permeability and sulfur accumulation are investigated.•The electrochemical behaviors of SO32− reduction on the cathode are revealed.•It exhibits excellent potentials of hydrogen production and trash-to-treasure. Sulfur dioxide or sulfite depolarized electrolyser is considered a promising technology for green hydrogen production. A sulfite depolarized electrolyser adopting sulfite wastewater is developed for both hydrogen production and wastewater treatment in our project, e.g. flue gas desulfurization wastewater and lead plate pre-desulfurization solution. Sulfite permeability and sulfur accumulation are primary challenges of the sulfite depolarized electrolyser for long-term stability. The electrochemical behaviors of SO32− reduction are investigated particularly here, which exhibits a 3.06-electron route on the homemade Pt-Pd/C catalyst. The reduction of SO32− to S0 is observed using an electrochemical quartz crystal microbalance. The sulfite diffusion coefficients of three proton exchange membranes are also determined. A frequent polarity inverted electrolysis is developed to remove the sulfur deposits and keep cell stability. Adopting a lead plate pre-desulfurization solution as the anolyte, both the fresh and repaired sulfite depolarized electrolyser can achieve a remarkable current density of > 500 mA/cm2 at 2.0 V. 200 h long-term test indicates excellent anodic depolarization and long-term stability for hydrogen production. The strategy may shed light on the further development of industrial applications.