The Effect of Cation Mixing in LiNiO₂ toward the Oxygen Evolution Reaction

Abstract

Nickel‐based oxide catalysts are widely used for the oxygen evolution reaction (OER) in alkaline water electrolysis because of their low cost and high activity. In particular, the LiNiO2 catalyst shows high activity. Therefore, to elucidate the fundamental relationship between the local structure, catalyst activity, and stability of LiNiO2, we investigated the cation mixing effect by mixing sites of lithium and nickel ions in the LiNiO2‐based catalysts. Lower degrees of cation mixing lead to higher intrinsic OER activity but lower long‐term stability. The X‐ray absorption spectra (XAS) displayed a strong hybridization state of the Ni 3d and O 2p orbitals, which is the origin of the different catalytic activity behaviors. Meanwhile, operando XAS studies combined with potentiostatic stability tests and inductively coupled plasma optical emission spectrometry (ICP‐OES) demonstrated the Li ion loss during the OER process. Thus, the instability of LiNiO2 originates from de‐intercalation of Li ions and this irreversible structure change deteriorates the performance. Hindering the lithium diffusion path by cation mixing is a useful strategy for maintaining performance. This strategy could provide a novel design principle for compatible high activity and long‐lasting catalysts by reasonable structure mediation.

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.…”

The Influence of Alkali Cations on the Performance of Pt Electrodes in Kolbe Electrolysis of Acetic Acid

“…[37] For the OER, a significant effect was also reported for low concentrations of bivalent and trivalent cations, such as Ba 2 + , Mg 2 + , Zn 2 + , Al 3 + , Cr 2 + and Ca 2 + , for a variety of electrodes. [40][41][42][43][44][45] Bivalent cations strongly impact the OER reaction and DFT calculations [46] have shown that strong binding of cations with the (OER) reaction intermediates negatively impacts the activity. Similarly, multivalent cations negatively impact the Kolbe reaction.…”