Electrochemical water splitting, an effective approach of generating high purity hydrogen in a clean way, is composed of two half reactions: hydrogen evolution reaction (HER) and oxygen evolution reaction (OER).^[1] OER is the main rate-limiting half reaction for water splitting due to its sluggish four-electron transfer process.^[2],[3] An efficient electrocatalyst is indispensable to minimize the activation barrier for the reaction and achieve a high efficiency.

Recently, two-dimensional (2D) layered double hydroxides (LDHs) have shown promises as one of the most effective electrocatalysts towards OER. However, the confined nanostructure with poor electronic conductivity inhibits their further enhanced catalytic performance towards OER. Herein, a 3D core-shell LDH structure is synthesized through a facile one-step reaction strategy, in which the terephthalic acid and urea is employed as the organic ligand for the metal organic framework (MOF) precursor and surface coordination buffer between LDH and MOF. Benefiting from the hierarchical 3D microstructure with uniformly nanosheets grown on the surface, the as prepared electrocatalyst exhibits rich edge active sites and enormous electrochemical surface area. The representative sample (namely, CoNi-LDH@BDC) achieves an excellent OER activity with a low overpotential of 280 mV at 100 mA cm^-2 and robust cyclic stability. In addition, quasi-operando studies using X-ray absorption and X-ray photoelectron spectroscopy further elucidate that the Co-Ni dual metal sites act as the main active site while Ni of high valence state is a favorable site to oxygen for the O-O bond formation. The prominent OER performance is also attributed to the synergistic effect between different transition metal atoms.

References

[1] L. Yu, H. Zhou, J. Sun, F. Qin, F. Yu, J. Bao, Y. Yu, S. Chen, Z. Ren, Energy Environ. Sci. 2017, 10, 1820.

[2] Y. Wang, C. Xie, Z. Zhang, D. Liu, R. Chen, S. Wang, Adv. Funct. Mater. 2018, 28, 1703363.

[3] L. Zhuang, L. Ge, Y. Yang, M. Li, Y. Jia, X. Yao, Z. Zhu, Adv. Mater. 2017, 29, 1606793.

[4] R. Frydendal, E. A. Paoli, B. P. Knudsen, B. Wickman, P. Malacrida, I. E. L. Stephens, I. Chorkendorff, ChemElectroChem 2014, 1, 2075.

[5] Y. Lee, J. Suntivich, K. J. May, E. E. Perry, Y. Shao-Horn, Synthesis and activities of rutile IrO 2 and RuO 2 nanoparticles for oxygen evolution in acid and alkaline solutions, Vol. 3, American Chemical Society, 2012, pp. 399–404.

[6] M. Gao, W. Sheng, Z. Zhuang, Q. Fang, S. Gu, J. Jiang, Y. Yan, J. Am. Chem. Soc. 2014, 136, 7077.