Lattice Oxygen Mechanism (LOM) in Oxygen Evolution Reaction (OER) on Perovskite Oxides

In 2016, Mefford et al. discovered a correlation between the concentration of oxygen vacancies and oxygen diffusion coefficient in La1-xSrxCoO3-δ and the corresponding catalytic activity, supporting their hypothesis on the role of lattice oxygen in LaNiO3. The study found that an increase in oxygen vacancy or oxygen diffusion coefficient led to a linear increase in OER activity. Through DFT calculations, they identified a key intermediate with adsorbed –OO and lattice O vacancy that determines the LOM over AEM by its relative stability to conventional adsorbed –O intermediate. They also linked the stability of the catalyst to the reaction mechanism, suggesting that catalysts with low stability tend to follow the LOM reaction mechanism. Binninger et al. speculated that the ABO3 perovskite oxide would dissolve A and B cations into the electrolyte under OER via LOM in which B cation would redeposit with OH- forming a hydrous amorphous layer. Kolpak et al. found that for strongly bound lanthanide perovskite oxides, the OER process following the LOM mechanism is thermodynamically limited by OH* → VO + OO*, whereas for moderately bound perovskite oxides, limited by VO + OO* → VO + O2(g) + OH*, while for weakly bound perovskite oxides, limited by HO-site* + OH* → OH*. The theoretical minimum overpotential is estimated to be 0.17−0.41 eV for LOM. Shao Horn and Koper's research group confirmed that the O2 generated on some perovskite contains lattice oxygen from oxides by isotope labeling and in-situ mass spectrometry. The study proposed that lattice oxygen reacts with absorbed oxygen to form an Oads-Olatt bond which acts as an active site, and then dioxygen is released through non-concerted proton-electron transfer as evidenced from the pH-dependent OER activity on the RHE scale.