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

Abstract 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.