The effect of Pt loading amount on SO2 oxidation reaction in an SO2-depolarized electrolyzer used in the hybrid sulfur (HyS) process

The effect of Pt loading amount on SO2 oxidation reaction in an SO2-depolarized electrolyzer used in the hybrid sulfur (HyS) process for hydrogen generation was investigated by using transmission electron microscopy (TEM), cyclic voltammetry (CV), and linear sweep voltammetry (LSV). From the analysis of the CVs, it was found that the electrochemical active surface area increased as the Pt loading amount increased, while Pt utilization decreased. The CVs obtained in the SO2-free and SO2-saturated 50 wt.% H2SO4 solutions indicated that the chemical transformation of the adsorbed species to PtO at a higher potential creates passivation layers which partially cover the electrode surface and inhibit SO2 oxidation reaction. The LSVs revealed that the increase in Pt loading amount resulted in a considerable improvement of SO2 oxidation kinetics in a low potential region as compared with that in a high potential region. However, the area-specific activity for SO2 oxidation reaction decreased due to the reduction of Pt utilization.