Improving Electrocatalytic Oxygen Evolution through Local Field Distortion in Mg/Fe Dual‐site Catalysts

• Published in: Angewandte Chemie International Edition 2023-12, Vol.62 (52), p.e202314303-n/a
• Main Authors: Zhang, Jing, Zhao, Yufeng, Zhao, Wanting, Wang, Jing, Hu, Yongfeng, Huang, Chengyu, Zou, Xingli, Liu, Yang, Zhang, Dengsong, Lu, Xionggang, Fan, Hongjin, Hou, Yanglong
• Format: Article
• Language: English
• Subjects: Catalysts; Configurations; Deformation; Distortion; Dual-site; Electrocatalysts; Electrolysis; Electron spin; Evolution; Iron; Local field distortion; Magnesium; Metals; Nitrogen; Overall water splitting; Oxygen; Oxygen evolution reaction; Oxygen evolution reactions; Spin regulation; Spin transition; Spin transitions; Transition metals; Water splitting
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202314303

Transition metal single atom electrocatalysts (SACs) with metal‐nitrogen‐carbon (M−N−C) configuration show great potential in oxygen evolution reaction (OER), whereby the spin‐dependent electrons must be allowed to transfer along reactants (OH−/H2O, singlet spin state) and products (O2, triplet spin state). Therefore, it is imperative to modulate the spin configuration in M−N−C to enhance the spin‐sensitive OER energetics, which however remains a significant challenge. Herein, we report a local field distortion induced intermediate to low spin transition by introducing a main‐group element (Mg) into the Fe−N−C architecture, and decode the underlying origin of the enhanced OER activity. We unveil that, the large ionic radii mismatch between Mg2+ and Fe2+ can cause a FeN4 in‐plane square local field deformation, which triggers a favorable spin transition of Fe2+ from intermediate (dxy2dxz2dyz1dz21, 2.96 μB) to low spin (dxy2dxz2dyz2, 0.95 μB), and consequently regulate the thermodyna‐mics of the elementary step with desired Gibbs free energies. The as‐obtained Mg/Fe dual‐site catalyst demonstrates a superior OER activity with an overpotential of 224 mV at 10 mA cm−2 and an electrolysis voltage of only 1.542 V at 10 mA cm−2 in the overall water splitting, which outperforms those of the state‐of‐the‐art transition metal SACs. A regulation of the Fe spin state in a Mg−Fe dual‐site catalyst is realized by taking advantage of the local crystal field distortion induced by the large ionic radii difference between Fe/Mg. The as‐synthesized catalyst demonstrates a low overpotential of 224 mV at 10 mA cm−2 for oxygen evolution reaction and an electrolysis voltage of only 1.542 V at 10 mA cm−2 for the overall water splitting.