Controlled Synthesis of Highly Active Nonstoichiometric Tin Phosphide/Carbon Composites for Electrocatalysis and Electrochemical Energy Storage Applications

Three types of new-structured phosphorized tin microspheres (Sn–P), phosphorized tin microsphere-carbon (Sn–P–C), and phosphorized tin nanoparticles embedded in interconnected porous carbon microspheres (Sn–P@PCMs) were prepared through a carbothermal reduction-assisted phosphorization strategy. The characterization of the formation mechanism and microstructure of Sn–P, Sn–P–C, and Sn–P@PCMs composites demonstrated that the controllable evaporation of coordinated phosphorus in the thermally unstable tin phosphide intermediate by accurate thermal treatment contributed to the formation of a ca. 3 wt % P-doped metallic tin structure featuring a nonstoichiometric SnxPy (y/x = 0.2) core, a Sn-rich phosphorized metallic (y/x = 0.05) shell, and an increased phosphorus concentration from the outer surface to the inner core. The as-prepared phosphorized tin-based composites were applied as counter electrode materials for dye-sensitized solar cells (DSSCs), in which the Sn–P–C counter electrode exhibited the lowest charge transfer resistance of 3.47 Ω and the assembled DSSCs delivered an optimum power conversion efficiency of 8.59%, superior to those of Pt-based cells (6.78 Ω and 7.46%, respectively). The unique bifunctional structure of the SnxPy conductive core coupled with the phosphorized metallic Snδ+ (0 < σ < 0.6) electrocatalytic shell accounts for its excellent electrocatalytic activity and electrical conductivity. In addition, the phosphorized tin-based composites were utilized as potential anodic material for lithium-ion batteries, in which the Sn–P@PCMs electrode showed a specific capacity of 743 mAh g–1 at 0.1C after 400 cycles and 435 mAh g–1 at 5C after 30 cycles. The superior Li-ion storage, cyclability, and rate performance of Sn–P@PCMs could be attributed to the incorporation of Sn–P nanoparticles into interconnected porous carbon microspheres that effectively buffered the large volumetric change and enhanced the electronic–ionic conductivity during the lithiation and delithiation process.