Electrochemical Water Splitting by Pseudo‐spinel, Disordered and Layered Lithium Nickel Oxides: Correlation between Structural Motifs and Catalytic Properties

Abstract

In this work, three different structures of lithium nickel oxide (LNO) synthesized by simple methods as inexpensive and efficient electrocatalyst for OER were presented. The catalytic activities of LNO catalysts for OER were pseudo‐spinel (PS‐LiNiO2) > disordered (DO‐LiNiO2) > layered (L‐LiNiO2) lithium nickel oxide. Particularly, PS‐LiNiO2 demonstrated much lower tafel slope of 62 mV dec−1 with the highest durability whereas the layered LNO catalysts exhibited the higher tafel slope of 88 mV dec −1, respectively. To elucidate the origin of high activities of LNO catalysts, three structures of LNO were studied by EXAFS measurements and DFT theoretical calculation. Compared to L‐LiNiO2, PS‐LiNiO2, including Ni4O4 cubane structural motifs, exhibited higher valent states and lower Ni d‐band center to drive the catalytic reaction. Thus, our results demonstrated that the activities of LNO can be optimized by controlling the value states, chemical and local electronic structure of Ni via novel design approaches.

Unusual double ligand holes as catalytic active sites in LiNiO2

“…4f, the lower potential limit decreased stepwise from 1.41 V (used in Figs. 4a) to 1.11 V, close to the values generally used in previous studies [44][45][46][47][48][49] . When the lower potential limit was set to 1.41 V, the OER current is optimal and remains stable over multiple CV cycles.…”

“…When undergoing the Ni 2+ /Ni III redox, the surface structure of LiNiO 2 transforms and degrades into NiOOH, which has a poor OER activity in the absence of Fe. In contrast, the pristine and structurally unaltered LiNiO 2 , whose real active species has been covered and neglected in previous LiNiO 2 OER studies 44,45,[47][48][49] , exhibits better intrinsic OER activity.…”