CeO2-δ as Electron Donor in Co0.07Ce0.93O2-δ Solid Solution Boosts Alkaline Water Splitting

Abstract

Optimizing the electronic structure with increasing intrinsic stability is a usual method to enhance the catalysts' performance. Herein, a series of cerium dioxide (CeO_2-δ) based solid solution materials is synthesized via substituting Ce atoms with transition metal (Co, Cu, Ni, etc.), in which Co_0.07Ce_0.93O_2-δ shows optimized band structure because of electron transition in the reaction, namely Co³⁺ (3d⁶4s⁰) + Ce³⁺ (4f¹5d ⁰6s⁰) → Co²⁺ (3d⁷4s⁰) + Ce⁴⁺ (4f⁰5d⁰6s⁰), with more stable electronic configuration. The in situ Raman spectra show a stable F2g peak at ≈452 cm^-1 of Co_0.07Ce_0.93O_2-δ, while the F2g peak in CeO_2-δ almost disappeared during HER progress, demonstrating the charge distribution of *H adsorbed on Co_0.07Ce_0.93O_2-δ is more stable than *H adsorbed on CeO_2-δ. Density functional theory calculations reveal that Co_0.07Ce_0.93O_2-δ solid solution increases protonation capacity and favors for formation of *H in alkaline media. General guidelines are formulated for optimizing adsorption capacity and the volcano plot demonstrates the excellent catalytic performance of Co_0.07Ce_0.93O_2-δ solid solution. The alkaline anion exchange membrane water electrolysis based on Co_0.07Ce_0.93O_2-δ/NiFe LDH realizes a current density of 1000 mA cm^-2 at ≈1.86 V in alkaline seawater at 80 °C and exhibits long-term stability for 450 h.

Keywords: CeO2−δ; HER; alkaline water splitting; electronic structures; solid solutions.