5f Covalency Synergistically Boosting Oxygen Evolution of UCoO4 Catalyst.

Xiao Lin,Chih-Wen Pao,Jian Sun,Jian-Qiang Wang,Yu-Chung Chang,Qingyun Zhao,Chien-Te Chen,Zhiwei Hu,Yu-Cheng Huang,Haoliang Huang,Chung-Li Dong,Jing Zhou,Linjuan Zhang,Lili Li,Hong-Ji Lin

doi:10.1021/jacs.1c10311

Abstract

Electronic structure modulation among multiple metal sites is key to the design of efficient catalysts. Most studies have focused on regulating 3d transition-metal active ions through other d-block metals, while few have utilized f-block metals. Herein, we report a new class of catalyst, namely, UCoO4 with alternative CoO6 and 5f-related UO6 octahedra, as a unique example of a 5f-covalent compound that exhibits enhanced electrocatalytic oxygen evolution reaction (OER) activity because of the presence of the U 5f–O 2p–Co 3d network. UCoO4 exhibits a low overpotential of 250 mV at 10 mA cm–2, surpassing other unitary cobalt-based catalysts ever reported. X-ray absorption spectroscopy revealed that the Co2+ ion in pristine UCoO4 was converted to high-valence Co3+/4+, while U6+ remained unchanged during the OER, indicating that only Co was the active site. Density functional theory calculations demonstrated that the OER activity of Co3+/4+ was synergistically enhanced by the covalent bonding of U6+-5f in the U 5f–O 2p–Co 3d network. This study opens new avenues for the realization of electronic structure manipulation via unique 5f involvement.

Highlights

Increasing energy demands and environmental issues have prompted intense research on electrochemical water splitting for energy storage and conversion technologies
The crystal structures and morphologies of the synthesized UCoO4 samples were investigated through X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) (Figure 1 and Figure S1a)
The formation process of UCoO4 was evaluated by conducting differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) of the precursor and XRD patterns of the sol−gel precursor calcined at different temperatures (Figure S3)

Summary

■ INTRODUCTION

Increasing energy demands and environmental issues have prompted intense research on electrochemical water splitting for energy storage and conversion technologies. Article electrons of rare earth metals because of the more localized properties of the 4f orbitals, which do not involve bonding except those of Ce4+ ions.[15,16] Compared to the 4f orbitals, the extended U 5f electrons can directly participate in chemical bonding in actinide compounds.[17] Recent research shows that uranium and iron oxide heterojunction catalysts exhibit high activity toward water oxidation because of the adjustment of band alignment induced by the “multivalence” of U and Fe ions according to density functional theory (DFT) analysis.[18] Generally, in uranium oxides, U6+-5f and O 2p hybridization is stronger than the hybridization between U4+-5f and O 2p,19 which implies that U6+ modulates the band alignment more because of a stronger U6+−O covalent bond.[20] it is unclear whether the U 5f−O 2p−Co 3d network can enhance the catalytic activity toward the OER Based on these considerations, the structurally ordered catalysts formed by combining 3d TM ions and 5f ions are ideal structural models to explore the possible synergistic enhancement of OER activity due to 3d−5f states. DFT calculations demonstrated that the U 5f−O 2p−Co 3d network facilitated synergistically accelerated OER performance

■ RESULTS AND DISCUSSION

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES