Artificially steering electrocatalytic oxygen evolution reaction mechanism by regulating oxygen defect contents in perovskites

Abstract

The regulation of mechanism on the electrocatalysis process with multiple reaction pathways is more efficient and essential than conventional material engineering for the enhancement of catalyst performance. Here, by using oxygen evolution reaction (OER) as a model, which has an adsorbate evolution mechanism (AEM) and a lattice oxygen oxidation mechanism (LOM), we demonstrate a general strategy for steering the two mechanisms on various La x Sr 1− x CoO 3−δ . By delicately controlling the oxygen defect contents, the dominant OER mechanism on La x Sr 1− x CoO 3−δ can be arbitrarily transformed between AEM-LOM-AEM accompanied by a volcano-type activity variation trend. Experimental and computational evidence explicitly reveal that the phenomenon is due to the fact that the increased oxygen defects alter the lattice oxygen activity with a volcano-type trend and preserve the Co 0 state for preferably OER. Therefore, we achieve the co-optimization between the activity and stability of catalysts by altering the mechanism rather than a specific design of catalysts.

Lattice Oxygen Activation for Enhanced Electrochemical Oxygen Evolution

“…For the chosen candidates, the oxygen deficiency (i.e., δ value) controlled the Co valence state to alter the lattice oxygen reactivity. 47 As shown in Figure 6c, the LOM pathway proceeded at the moderate level of oxygen deficiency, accompanied by a volcano-type activity variation trend.…”

“…The difference from the AEM pathway is that the deprotonated *O directly couples with the activated lattice oxygen to form *OO species rather than waiting for nucleophilic attack of H 2 O/OH – from the electrolyte. The representative case is the La 1– x Sr x CoO 3−δ perovskite oxides with a high Sr 2+ component, together with the related derivatives. ,,− DFT calculations underlined that the direct O–O coupling of *O with lattice oxygen was thermodynamically spontaneous (i.e., Δ G < 0) in SrCoO 3−δ (Figure a) . Similarly, in a proposed Zn x Co 1– x OOH oxyhydroxide with the Zn 2+ -induced O NB state, integrating *OH deprotonation with hole-doped lattice oxygen in one step (Step 1 in the SMSM pathway; see Figure b) became energetically favorable as compared to conventional *OH-to-*O in the AEM pathway alongside the Zn 2+ increment as well as the ligand hole level in the O NB state .…”

“…More recently, the transformation of the OER mechanism was subtly tuned by Xi and co-workers over La x Sr 1– x CoO 3−δ (LSCO- x ) perovskite oxides. For the chosen candidates, the oxygen deficiency (i.e., δ value) controlled the Co valence state to alter the lattice oxygen reactivity . As shown in Figure c, the LOM pathway proceeded at the moderate level of oxygen deficiency, accompanied by a volcano-type activity variation trend.…”

Toward Superb Perovskite Oxide Electrocatalysts: Engineering of Coupled Nanocomposites

“…[ 23,149,174–188 ] Currently, significant progress has been witnessed in improving the single‐phase perovskite oxide electrocatalysts for OER, including but not limited to alien cation doping, phase tailoring, defect engineering, and morphology control. [ 23,189–193 ] On the other hand, compared with optimizing single‐phase perovskite oxide catalysts, both theoretical and experimental investigations have shown the superior performances of a heterostructure of perovskite oxides because of the improved electron/mass transfer, tailored lattice strains, and synergistic effect between different components. [ 3,149,194–199 ] Furthermore, introducing the concept of nanocomposite engineering that produces the uniquely intimate and robust interconnected phases for low‐temperature OER applications would break new ground in discovering excellent perovskite oxide‐based electrocatalysts with high catalytic activity and stability.…”

“…[23,149,[174][175][176][177][178][179][180][181][182][183][184][185][186][187][188] Currently, significant progress has been witnessed in improving the single-phase perovskite oxide electrocatalysts for OER, including but not limited to alien cation doping, phase tailoring, defect engineering, and morphology control. [23,[189][190][191][192][193] On the other hand, compared with optimizing single-phase perovskite oxide catalysts, both theoretical and experimental investigations have shown the superior performances of a heterostructure of perovskite oxides because of the improved electron/mass transfer, tailored lattice strains, and synergistic effect between different components. [3,149,[194][195][196][197][198][199] and 40% GDC-PBCC in SOFC and SOEC modes.…”