Aluminum-Doped Lithium-Vacant Layered Li1-xCr1-xAlxO2: A Potentially Active Electrocatalyst for the Oxygen Evolution Reaction

Abstract

Electrochemical water splitting is considered the most promising and highly efficient method for the production of highly pure hydrogen (a green fuel) on a large scale with zero emissions. Here, we have explored the anisotropic behavior of a layered lattice coupled with the tuning of ionicity of M-O bonding in layered oxides to develop cost-effective superior oxygen evolution reaction (OER) catalysts. In the layered LiCrO2 lattice, the strategy of Al3+ ion substitution at both the Cr site and Li interstitial site leads to an increase in the ionicity of counterpart Cr-O and Li-O bonds. The higher ionicity results in high Li+-ion mobility and superior mixing of the Cr(3d) and O(2p) levels. The doping of Al significantly causes partial oxidation of Cr3+ to Cr6+, which then occupies the Li interstitial site, creating a dumbbell defect in the hexagonal lattice of Li1-xCr1-xAlxO2 and thereby stabilizing the layered structure of the system with partial Li deficiency and cation mixing (Cr/Al in the Li layer). The high polarizing power of the Al3+ ion results in the formation of more covalent Al-O bonds in Li1-xCr1-xAlxO2, causing higher ionicity or polarization of the counterpart Cr-O and Li-O bonds due to the inductive effect. This, in turn, lowers the redox energy of filled antibonding states and shifts the redox potential to a more positive side, resulting in superior electrocatalytic OER activity of the Al-doped catalyst. The activity of Li0.75Cr0.75Al0.25O2 (327 mV at 10 mA cm-2) remarkably approaches the performance of the benchmark oxide catalyst RuO2 (336 mV at 10 mA cm-2) and is superior or comparable to that of the best known OER catalysts such as α-MnO2, Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF), and LaNiO3 © 2024 American Chemical Society