Active Platinum Nanoparticles as a Bifunctional Promoter for Lithium-Sulfur Batteries

As a widely used electrocatalyst in fuel cells, metallic platinum has achieved great success in terms of kinetic promotion. Still plagued by a familiar problem, owing to the sluggish kinetics of irreversible Li2S2/Li2S species deposition, lithium-sulfur batteries with high theoretical energy are far from being realized. Inspired by the similarity between oxygen and sulfur, being in the same group, commercially available Pt/C was investigated here to explore the possible effect on the sulfur cathode. The electrochemical tests show that the electrode with 2wt% Pt added delivers a 61% enhancement in the discharging specific capacity compared to the control electrode after 200 cycles at 0.5C, along with an average coulombic efficiency of 98.3%. It is proven that these beneficial results can be attributed to the favorable capability of polysulfide immobilization and effective inhibition of self-discharging behavior. The ex situ XPS analysis and the increased exchange current density further reveal that the involved platinum nanoparticles could not only function as a static chemical absorber for polysulfide species, but, more importantly, to promote the redox kinetic effectively as an electrochemical catalyst. The positive effect of utilizing commercial Pt/C materials directly on sulfur cathodes is of great significance in developing sulfur cathodes for Li/S batteries.