Precise Cooling Time Control in Joule Heating for Efficient Oxygen Evolution Reaction of High-Entropy Oxides

Uncontrolled high temperatures cause catalyst morphology collapse and phase transformation, hindering active site exposure. To address this issue, we extend Newton's law of cooling to achieve precise cooling time control within seconds using a Joule heating device. This approach enables the synthesis of CoFeNiMnCr high-entropy oxide (HEO) with a large surface area and abundant defect states. The resulting HEO catalyst demonstrates excellent performance, requiring only 219 mV of overpotential at 10 mA cm-2 and maintaining stability for 320 h at 100 mA cm-2, ranking among the most effective OER catalysts to date. Notably, our findings indicate that cooling time has a more significant influence on the OER activity of HEO than heating time. In situ Raman spectroscopy confirms the transformation of spinel-type HEO to metal (oxy)hydroxide active sites and highlights the synergistic effects of the multimetallic composition. This work provides valuable insights into optimizing cooling time for the synthesis of high-performance materials.