SnO2/PbOx (x = 1, 2) Core–Shell Nanowires and Their Growth on C-Fiber Networks for Energy Storage

Abstract

SnO2 nanowires were grown on Si, fused SiO2, and C fibers by the vapor–liquid–solid mechanism at 800 °C and 10–1 mbar, and SnO2/PbO core–shell nanowires were obtained by the deposition of 50 nm Pb over the SnO2 nanowires followed by annealing between 100 and 200 °C. The SnO2/PbO nanowires have diameters of 100–300 nm and lengths up to 100 μm and consist mainly of tetragonal rutile SnO2 and PbO. Higher temperatures between 300 and 500 °C resulted in the formation of Pb2O3 and Pb3O4 with monoclinic and orthorhombic crystal structures, but the SnO2/PbO and SnO2/Pb2O3 nanowires had low conductivities of 10–1 S/cm. In contrast, highly conductive SnO2/PbO2 nanowires were obtained by electrodeposition of PbO2 in 0.3 M HNO3 and 1 M Pb(NO3)2 (aq). PbO2 forms a straddling-type heterojunction with SnO2, and the one-dimensional (1D) electron gas distribution is confined in the PbO2 shell for sufficiently thick shells, as shown by the self-consistent solution of the Poisson–Schrödinger equations in the effective mass approximation. The SnO2/PbO2 nanowires exhibit an open-circuit potential of 1.8 V versus C-fiber networks in 5 M H2SO4 (aq) and show symmetric cyclic voltammetry curves, suggesting a suppression of the redox reactions related to SnO2 and a high specific capacity of 206 mAh/g. We discuss the potential of both SnO2 and SnO2/PbO2 nanowires on C fibers for the attainment of even higher specific capacity in a Li-ion battery.