Optimized Conductivity and Spin States in N-Doped LaCoO3 for Oxygen Electrocatalysis.

Abstract

The spin state of antibonding orbital (eg) occupancy in LaCoO3 is recognized as a descriptor for its oxygen electrocatalysis. However, the Co(III) cation in typical LaCoO3 (LCO) favors low spin state, which is mediocre for absorbing oxygen-containing groups involved in oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), thus hindering its further development in electrocatalysis. Herein, both experimental and theoretical results reveal the enhancement of bifunctional electrocatalytic activity in LaCoO3 by N doping. More specifically, electron energy loss spectroscopy and superconducting quantum interference devices magnetic analysis demonstrate that the Co(III) cation in N-doped LaCoO3 (LCON) achieves a moderate eg occupancy (≈1) compared with its low spin state in LaCO3. First-principle calculation results reveal that N dopants play a bifunctional role of tuning the spin-state transition of Co(III) cations and increasing the electrical conductivity of LCO. Thus, the optimized LCON exhibits an OER overpotential of 1.69 V at the current density of 50 mA/cm2 (1.94 V for pristine LCO) and yields an ORR limiting current density of 5.78 mA/cm2 (4.01 mA/cm2 for pristine LCO), which offers a new strategy to simultaneously modulate the magnetic and electronic structures of LCO to further enhance its electrocatalytic activity.