Ultrafine Transition Metal Phosphide Nanoparticles Semiembedded in Nitrogen-Doped Carbon Nanotubes for Efficient Counter Electrode Materials in Dye-Sensitized Solar Cells

Developing an efficient and economic synthetic approach to massively prepare non-precious-metal counter electrode (CE) electrocatalysts with superior catalytic activity and electrochemical stability is highly desirable for the commercialization of dye-sensitized solar cells (DSSCs). Herein, a unique electrocatalytic architecture of Co2P and Ni2P nanoparticles linked and semiexposed at the end points of nitrogen-doped carbon nanotubes (MxP-NCNTs) were first prepared by a metal-catalyzed graphitization–nitridization driven tip-growth process and the followed phosphonation and carbothermal reduction reaction. The prepared MxP-NCNTs were evaluated as CEs in DSSCs and showed high electrocatalytic activity, electrical conductivity, and electrochemical stability for triiodide reduction. The DSSCs assembled with Co2P-NCNTs and Ni2P-NCNTs CEs reached a high power conversion efficiency of 9.76% and 9.21%, respectively, exceeding the efficiency of conventional Pt-based device (7.84%). The extraordinary DSSCs’ performance was mainly attributed to the structural advantages of MxP-NCNTs CE, in which the open porous nanotube arrays and integrated heterointerfacial connection in one-dimensional nanostructure of MxP-NCNTs accelerated the electron–ion transport, and the highly dispersed and semiexposed MxP nanocrystals improved the catalytic activity for triiodide reduction. This work provides a avenue to exploring highly effective and robust non-precious-metal CE electrocatalysts for DSSCs.