Water splitting involves a hydrogen evolution reaction (HER) at the cathode and an oxygen evolution reaction (OER) at the anode, and OER has been considered as the major bottleneck for water splitting due to the sluggish reaction kinetics and high OO bond formation energy barrier caused by its four-electron coupling process. [2][3][4][5] Designing the external-and internal structure of electrocatalysts is fundamental to achieve high catalytic activities at low overpotential and equally important to the electrocatalysts themselves, the reaction efficiency also strongly depends on the mass transfer outside the electrode surface and electron transfer inside the electrode structure. [4][5][6] The mass transfer at the interfaces between the catalyst and electrolyte is responsible for the immediate supplying of electrolytes (and reactants) and associated with rapid release of bubbles generated by the reactions (O 2 gas, for the case of OER). [7] The kinetics of mass transfer as the rate-controlling step, therefore, govern the efficiency of the electrochemical reaction, by taking much larger time constant compared with that of the electron transfer. [8,9] For gas-evolving electrochemical system, bubbles may adhere to the catalyst's surface and block the active sites by forming bubble froth layers. This process
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.