In situ growth of Ni-encapsulated and N-doped carbon nanotubes on N-doped ordered mesoporous carbon for high-efficiency triiodide reduction in dye-sensitized solar cells

Abstract

A new micro-nanostructured composite (NOMC-Ni@NCNTs) of Ni-encapsulated and N-doped carbon nanotubes (Ni@NCNTs) pinned on N-doped ordered mesoporous carbon (NOMC) is constructed by a two-step synthesis strategy. The strategy involves the self-assembly preparation of water-soluble phenolic resin/F127 colloid by a hydrothermal route and the subsequent catalytic pyrolysis of as-prepared phenolic resin/F127 copolymer and melamine with nickel acetate as Ni source and self-generated catalyst, leading to the in situ growth of dispersive Ni@NCNTs pinned on NOMC through the Ni junction. In the resultant NOMC-Ni@NCNTs, the NOMC shows reduced particle size and shortened mesopore channel length of 15–30 μm compared to 850 μm-2 mm of pristine NOMC. The pinned Ni@NCNTs constructs a 3D conductive scaffold in the composite and the conductivity is correspondingly raised from 20.4 S cm−1 of pristine NOMC to 254.1 S cm−1 of NOMC-Ni@NCNTs. The particle size, mesoporosity and surface area of NOMC-Ni@NCNTs composite are also flexibly regulated by tailoring the relative content of Ni@NCNTs and NOMC. The new-structured NOMC-Ni@NCNTs composites are developed as counter electrode (CE) materials for DSSCs, which demonstrates an excellent catalytic activity towards I3- reduction. The optimum NOMC-Ni@NCNTs CE delivers a low charge-transfer resistance of 2.21 Ω and the assembled DSSC achieves a high power conversion efficiency of 8.39%. Moreover, the NOMC-Ni@NCNTs CE based DSSC also manifests a preeminent electrochemical stability in corrosiveI-/I3- electrolyte with a remnant efficiency of 7.82% after 72 h of illumination. The outstanding electrocatalytic performance is mainly correlated with their unique architecture, in which the pinned Ni@NCNTs conductive substrate accelerates the electron transportation among NOMC micron-particles, and the amorphous NOMC with short-range mesopores accelerates the electrolyte diffusion and supplies abundant ions-accessible defects for I3- reduction.