B-Site-Metal Exsolution on Perovskite Oxides Activates Alkaline Water Oxidation via the Lattice Oxygen Mechanism

Effective electrocatalysts are crucial for facilitating the oxygen evolution reaction (OER), the anodic reaction of water electrolysis for renewable green hydrogen production. Perovskite oxides are a group of potential catalysts featuring the lattice oxygen mechanism (LOM) for OER, where O2 formation commences via a lattice oxygen redox process. The LOM pathway breaks the thermodynamic limitation of the adsorbate evolution mechanism (AEM) and achieves a high intrinsic activity. However, perovskite oxides often suffer high OER overpotentials due to the insufficient activation of the LOM pathway. Typically, the overpotential exceeds 300 mV at 10 mA cm-2. This greatly impedes the practical applications of perovskite oxide based OER catalysts. Here, it is demonstrated that the B-site-metal exsolution of a La0.6Sr0.4Fe0.8Ni0.2O3-delta perovskite increases the activity of LOM by a factor of 3.8 at 400 mV overpotential. The activated LOM pathway leads to a 36-mV reduction in the overpotential at 10 mA cm-2 (from 310 mV to 274 mV) and a 2x increase in the turnover frequency (TOF) at 450 mV overpotential. A membrane electrode assembly (MEA) water electrolyzer equipped with this LSFN-based catalyst offers 1 A cm-2 current density at 2.46 V and 24-h operation stability. B-site-metal exsolution of perovskite oxides by H2 treatment at high temperatures increases the O vacancy concentration and enhances oxygen evolution activity via the lattice oxygen mechanism (LOM) pathway. As an example, La0.6Sr0.4Fe0.8Ni0.2O3-delta (LSFN) with B-site-metal exsolution offers a 3.8x increase in LOM activity compared to the pristine LSFN and 1 A cm-2 current density at 2.46 V during 24-h electrolysis.image