A Versatile Screening Strategy for the Rapid Optimization of High-Entropy Oxide Compositions via Gradient Electrodeposition.

High-entropy materials offer vast opportunities for electrocatalysis due to their tunable compositions and synergistic effects among multiple elements. However, the compositional complexity of high-entropy materials poses a significant challenge to the rapid identification of optimal elemental ratios, as conventional synthesis and evaluation strategies typically rely on discrete, trial-and-error approaches with limited throughput. Here, we report a gradient electrodeposition strategy that enables the construction of compositionally diverse high-entropy material libraries on a single carbon paper substrate. Five metals are deposited along distinct directions to form individual gradients. Subsequent thermal annealing treatment yields high-entropy oxide (HEO) catalysts with continuously varied local compositions, enabling direct correlation between elemental composition and ORR performance via sample-specific electrochemical measurements. This approach provides an efficient and scalable platform for high-throughput screening and rational optimization of high-entropy material electrocatalysts.