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

Abstract

The spin state of antibonding orbital (e g ) occupancy in LaCoO 3 is recognized as a descriptor for its oxygen electrocatalysis. However, the Co(III) cation in typical LaCoO 3 (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 LaCoO 3 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 LaCoO 3 (LCON) achieves a moderate e g occupancy (≈1) compared with its low spin state in LaCO 3 . 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/cm 2 (1.94 V for pristine LCO) and yields an ORR limiting current density of 5.78 mA/cm 2 (4.01 mA/cm 2 for pristine LCO), which offers a new strategy to simultaneously modulate the magnetic and electronic structures of LCO to further enhance its electrocatalytic activity.

Surface-Electronic-Structure Reconstruction of Perovskite via Double-Cation Gradient Etching for Superior Water Oxidation

“…The nonrenewability of traditional fossil fuels and the growing demands for energy resources have encouraged us to develop new sustainable energy technologies. , Water electrolysis, involving oxygen evolution reaction (OER) at the anode and hydrogen evolution reaction (HER) at the cathode, has been regarded as one of the promising energy conversion systems. − OER with sluggish kinetics is the linchpin step to limit the overall efficiency of water splitting, leading to the exploration of efficient oxygen electrocatalysts. , Although a few precious metal catalysts (such as IrO 2 and RuO 2 ) exhibit excellent electrocatalytic performance for OER, it is difficult to undertake large-scale applications because of their scarce reserves and unsatisfactory stability. , Developing highly efficient and durable non-noble metal-based catalysts is imperative but challenging. Perovskite oxides have attracted substantial attention as OER electrocatalysts since 1980s, and different perovskite materials were fabricated as alternative OER catalysts to date. − Among these catalysts, the LaCoO 3 (LCO) perovskite was identified with high intrinsic activity and wonderful thermal stability. , The current exploration results discover that the catalytic activity in LCO mainly contributes to the Co sites at octahedral environments. , However, the natural surfaces of LCO are preferentially occupied by inert La sites, which seriously limits the actual activity. − Additionally, it has a wide energy bandgap, resulting in seriously poor conductivity. , Therefore, it is crucial to optimize the structure of LCO for active sites construction and fast electron transfer.…”

Significant Change of Metal Cations in Geometric Sites by Magnetic‐Field Annealing FeCo2O4 for Enhanced Oxygen Catalytic Activity

“…[6,7] Ideally, remarkable ORR/OER bifunctional electrocatalysts should have excellent catalytic activity, stability, and economic feasibility. [8][9][10][11] In recent years, increasing attention has been paid to spinel oxides (AB 2 O 4 ), which are excellent oxygen electrocatalysts with distinct d-band electronic configurations. [12][13][14][15][16][17][18][19][20] In the spinel lattice, A 2+ and B 3+ ions occupy the tetrahedron and octahedron, and they are surrounded by four and six oxygen anions, respectively.…”

“…[26] However, the effective magnetic moment increases significantly with the intermediate-spin state (t e 2g 5 g 1 ) of Co 3+ in the octahedral site, which can be magnetically polarized. [10] Recently, the application of an external magnetic field during catalytic process for magnetic catalyst has received much attention, as it can change the spin polarization by accelerating the electron transitions from low-spin states to high-spin states, [29] enhancing the spin selection, [30] and thereby having a positive effect on the ORR/ OER progress of the catalysts. [29][30][31] Coincidentally, magnetic moments related to the extrinsic spin polarization of magnetic…”

Precursor accumulation on nanocarbons for the synthesis of LaCoO3 nanoparticles as electrocatalysts for oxygen evolution reaction

“…For example, LaCoO 3 is known to promote OER in alkaline media. [7][8][9][10][11][12][13] Furthermore, Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-d and La 0.8 Sr 0.2 Co 0.5 Fe 0.5 O 3d have been reported as active OER catalysts with activities comparable to those of the state-of-the-art noble metal catalysts. [14][15][16][17][18][19][20][21] Solid-state synthesis (i.e., heat treatment of solid reactants) is a conventional method for preparing perovskites.…”