A review on fundamentals for designing oxygen evolution electrocatalysts The oxygen evolution reaction (OER) is a critical step in water splitting, which is essential for storing electrical energy as hydrogen gas. Despite its importance, OER is kinetically sluggish due to its four-electron transfer nature. Developing low-cost and efficient OER catalysts is crucial for improving the efficiency of water splitting. This review summarizes recent progress in understanding OER mechanisms, including the conventional adsorbate evolution mechanism (AEM) and lattice oxygen-mediated mechanism (LOM), and discusses strategies for designing efficient OER catalysts. The AEM involves four proton-electron transfer steps, with the reaction free energies of intermediates playing a key role in determining the overpotential. The scaling relations between intermediates, such as HO* and HOO*, are important for predicting OER activity. However, these scaling relations have limitations, and strategies to overcome them include stabilizing HOO*, introducing proton acceptor functionality, and switching to the LOM. The LOM bypasses the scaling relation by directly coupling lattice oxygen to form O2, thus avoiding the limitations of the AEM. The review also discusses various strategies for designing efficient OER catalysts, including substitution of foreign elements, creation of vacancies, strain engineering, and interface engineering. These strategies aim to optimize the binding energies of intermediates and improve the catalytic activity. Additionally, descriptors such as e_g orbital occupancy and metal-oxygen covalency are highlighted as important factors in determining OER activity. The review concludes with a discussion on the remaining questions and challenges in OER catalyst design, as well as potential future research directions. Overall, the review provides a comprehensive overview of the fundamentals for designing efficient OER catalysts, emphasizing the importance of understanding reaction mechanisms and optimizing catalyst properties.A review on fundamentals for designing oxygen evolution electrocatalysts The oxygen evolution reaction (OER) is a critical step in water splitting, which is essential for storing electrical energy as hydrogen gas. Despite its importance, OER is kinetically sluggish due to its four-electron transfer nature. Developing low-cost and efficient OER catalysts is crucial for improving the efficiency of water splitting. This review summarizes recent progress in understanding OER mechanisms, including the conventional adsorbate evolution mechanism (AEM) and lattice oxygen-mediated mechanism (LOM), and discusses strategies for designing efficient OER catalysts. The AEM involves four proton-electron transfer steps, with the reaction free energies of intermediates playing a key role in determining the overpotential. The scaling relations between intermediates, such as HO* and HOO*, are important for predicting OER activity. However, these scaling relations have limitations, and strategies to overcome them include stabilizing HOO*, introducing proton acceptor functionality, and switching to the LOM. The LOM bypasses the scaling relation by directly coupling lattice oxygen to form O2, thus avoiding the limitations of the AEM. The review also discusses various strategies for designing efficient OER catalysts, including substitution of foreign elements, creation of vacancies, strain engineering, and interface engineering. These strategies aim to optimize the binding energies of intermediates and improve the catalytic activity. Additionally, descriptors such as e_g orbital occupancy and metal-oxygen covalency are highlighted as important factors in determining OER activity. The review concludes with a discussion on the remaining questions and challenges in OER catalyst design, as well as potential future research directions. Overall, the review provides a comprehensive overview of the fundamentals for designing efficient OER catalysts, emphasizing the importance of understanding reaction mechanisms and optimizing catalyst properties.