Solvation Effect-Determined Mechanisms of Cation Exchange Reactions for Efficient Multicomponent Nanocatalysts

Abstract

Cation exchange (CE) reaction is a classical synthesis method for creating complex structures. A lock of study on intrinsic mechanism limits its understanding and practical application. Using X-ray absorption spectroscopy, we observed that the evolution from Ru−Cl to Ru−O/OH occurs during the CE between K₂RuCl₆ and CoSn(OH)₆ in aqueous solution, while CE between K₂PtCl₆ and CoSn(OH)₆ is inhibited due to the failure of structural evolution from Pt−Cl to Pt−O/OH. Theoretical simulations imply that the interaction between Ru−O and CoSn(OH)₆ with Co vacancy (CoV_CoSn(OH)₆) endows the electron transfer, as a result of strengthened adsorption on CoV_CoSn(OH)₆. Moreover, this mechanism is validated for CE between K₂RuCl₆ and ASn(OH)₆ (A=Mg, Ca, Mn, Co, Cu, Zn), and CE between K₂PdCl₆/Na₃RhCl₆/K₂IrCl₆ and CoSn(OH)₆. Impressively, the Pt-free CoRuSn(OH)_x produced via CE displays a mass activity and a power density of 15.0 A mg_Ru⁻¹ and 11.6 W mg_Ru⁻¹, respectively, for anion exchange membrane fuel cell (AEMFC) exceeding the values of commercial PtRu/C (11.8 A mg_Ru+Pt⁻¹ and 9.0 W mg_Ru+Pt⁻¹). This work, for the first time, reveals the intrinsic mechanism of CE as structural evolution of target ion breaking through the traditional classic etch-adsorption mechanism and will promote fundamental research and practical application in various fields.