Sn@SnO2 attached on carbon spheres as additive-free electrode for high-performance pseudocapacitor

Utilization of metal oxide/supports interface structures could generate high- performance electrochemical materials for clean energy storage and conversion. However, designing the metal oxide/supports interfaces with highly enhanced conductivity and cycle durability remains a significant challenge. Here, we demonstrate an in-situ growth technique to synthesize a Sn/SnO2@C composite with nano-Sn species attached on surface of carbon spheres (denoted as Sn/SnO2@C) during the carbonization of a sol-gel precursors of tin (IV) tetrachloride pentahydrate (SnCl4·5H2O) and Resorcinol-Formaldehyde (Sn4+-RF) in N2. We investigate the nucleation and crystal growth of Sn/SnO2 from Sn4+-RF precursor to Sn/SnO2@C composite with the variation of the concentration of acid value and heat-treatment temperature. Sn/SnO2@C-(1.0, 800) composite as supercapacitor electrode achieves a maximum specific capacitance of 906.8 F g−1 at a scan rate of 1 mV s−1 in 6 M KOH solution, and an excellent cycle durability of 2000 cycles at 5 A g−1. The electrochemical performances demonstrate that charge storage occurs in Sn/SnO2@C mainly due to redox reactions between the binary oxidation states: Sn↔Sn(OH)62−(IV) in basic electrolyte, hierarchical porosity and Sn/SnO2@C distinct structure, which is formed in situ. The work provides new insights into the rational design of Sn@C composites electrode materials for pseudocapacitor and other electrochemical devices.