Rational Design of LaNiO₃/Carbon Composites as Outstanding Platinum-Free Photocathodes in Dye-Sensitized Solar Cells With Enhanced Catalysis for the Triiodide Reduction Reaction

In many photovoltaics (PVs), including dye-sensitized solar cells (DSSCs), triiodide/iodide (I₃ ⁻/I⁻) redox couple plays an important role, and an active and stable electrocatalyst is required for promoting I₃ ⁻ reduction reaction (IRR) to minimize efficiency losses. Platinum (Pt) is the state-of-the-art electrocatalyst for IRR, which unfortunately suffers from high cost and poor stability. Herein, strongly coupled LaNiO₃ perovskite/carbon composites are developed for the first time as highly efficient, stable and low-cost electrocatalysts for IRR to enable better DSSCs. High-energy ball milling of crystallized LaNiO₃ with carbon material is applied for the facile synthesis of LaNiO₃/carbon composites. This ball-milling process simultaneously leads to partial reduction of LaNiO₃ by carbon with the creation of oxygen vacancies inside the perovskite oxide lattice, a decrease in LaNiO₃ particle size and the creation of strong coupling between LaNiO₃ and carbon. Particularly, DSSC with LaNiO₃/multi-walled carbon nanotubes photocathode delivers a high power conversion efficiency of 9.81% with an attractive enhancement of 21% compared with Pt electrocatalyst, superior to most state-of-the-art highly efficient Pt-free photocathodes in DSSCs. LaNiO₃ or carbon alone demonstrates a much poorer performance. Moreover, LaNiO₃/carbon composites demonstrate excellent operational stability. This study highlights the extended applications of perovskites in other I₃ ⁻/I⁻-mediated PVs, electrochromic devices or batteries.