Electrocatalytic water spitting is a key technology to produce hydrogen to meet the ever-increasing demand for sustainable energy.[1] However, increasing the efficiency and longevity of water electrolyser remains a notorious challenge due to the limitations in activity and stability of anode electrocatalysts at which oxygen evolution reaction (OER) occurs.[2] Perovskite oxides have recently emerged as a new category of efficient electrocatalysts for OER with the advantages of flexible composition and structure, low cost, and excellent catalytic properties.[3] Among them, LaCoO3 (LCO) has been regarded as a promising candidate due to its superior OER activity.[4] However, LCO exhibited poor OER stability.[5] Doping LCO with Ca is an effective way to improve stability and activity, but the effects of Ca on the enhanced electrocatalytic properties of LCO remain elusive. In this context, this study aims to elucidate how Ca doping improves the activity and stability of LCO and why LCO degrades rapidly.

Here, LCO and Ca-doped LaCoO3 nanoparticles (LCO-Ca-0.4) were synthesized by hydrothermal method. The overpotential of LCO-Ca-0.4 is ~372 mV at a current density of 10 mA cm-2, which is lower than that of LCO (416 mV), indicating that LCO-Ca-0.4 has higher OER activity than LCO. The OER activity of LCO decreases remarkably after 1000 cyclic voltammetry (CV) cycles since the overpotential increases to 525 mV. In contrast, there is a negligible change in the OER activity of LCO-Ca-0.4 after 1000 CV cycles. These results demonstrate that Ca doping can effectively improve the OER stability of LCO-Ca-0.4. To further explore the role of Ca in the stability, LCO and LCO-Ca-0.4 were characterized by high-resolution transmission electron microscopy (HRTEM) and atom probe tomography (APT). We observed by HRTEM amorphous layers of 5 - 10 nm on the surface of LCO nanoparticles after 1000 CV cycles, while LCO-Ca-0.4 remains crystalline after OER. Additionally, APT data reveals that the surface of LCO is lean in La, suggesting that the surface amorphization is mainly induced by La leaching. In contrast, the surface concentration of LCO-Ca-0.4 remains unchanged, which implies that Ca doping most likely restrains the La leaching. This work demonstrates that the stability of LCO can be improved by Ca doping since Ca could prevent La leaching and inhibit surface amorphization during OER.

References

[1] P. P. Edwards; V. L. Kuznetsov; W. I. F. David; N. P. Brandon Energy Policy,2008, 36, 4356-4362.

[2] Y. Jiao; Y. Zheng; M. T. Jaroniec; S. Z. Qiao, Chem. Chemical Society Reviews, 2015, 44, 2060-2086.

[3] X. M. Xu; Y. J. Zhong; Z. P. Shao Trends in Chemistry, 2019, 1, 410-424.

[4] C. W. Sun; J. A. Alonso; J. J. Bian Advanced Energy Materials, 2021, 11, 2000459.

[5] R. Xie; Z. Nie; X. Hu; Y. Yu; C. Aruta; N. Yang ACS Applied Energy Materials, 2021, 4, 9057-9065.