Local Proton‐Mediated Synthesis of a High‐Entropy Borate Library

High-entropy compounds (HECs) provide extensive possibilities for exploring distinctive properties and potential applications. However, most HECs reported so far are synthesized by an arduous high-temperature treatment and special equipment, which is clearly not scalable for practical application. Here a scalable room-temperature solution synthetic strategy is reported for a library of high-entropy borates with arbitrary metal component numbers from 5 to 12 up to 3302 kinds in total and more than a hundred grams per operation within one minute. In conjunction with theoretical and in situ investigations, it is uncovered that the highly local concentration of protons at ethanol/aqueous interface is favorable to the creation of a stable thermodynamic microenvironment and a desirable kinetic miscibility reservoir, thus enabling a formation of single-phase borates. With the FeCoNiMoCu high-entropy borate, it is further shows that it functions as a highly active catalyst for catalytic oxygen evolution reaction. The work opens up opportunities for the scalable synthesis of HECs for energy storage and conversion applications.