All Iron‐Group and Platinum‐Group Elements Metal High‐Entropy Alloy Nanoparticles

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High‐entropy alloys (HEA) are promising catalyst materials for important energy transformations. So far, the focus has been on platinum‐group metals, which possess excellent catalytic performance and similar properties, thus being easy to synthesize. However, incorporating more abundant and cheaper elements is preferable for large‐scale applications and is fundamentally more interesting, as elements with different properties are expected to greatly affect the structural and electronic characteristics of the resulting alloy. Unfortunately, significant differences in elemental properties greatly complicate the synthesis and require extreme reaction conditions. In this work, we demonstrate the first synthesis of high‐entropy alloy nanoparticles containing the nine neighboring elements used most often in heterogeneous catalysis: all the iron‐group metals (Fe, Co, and Ni) and all the platinum‐group metals (Ru, Rh, Pd, Os, Ir, and Pt) through a simple low‐temperature solution process. Remarkably, alloying the iron‐group base metals with the platinum‐group metals results in 30% increase in the catalytic activity for the hydrogen evolution reaction (HER) under acidic conditions (TOF@25 mV = 1.58 s −1 ) compared to the equivalent alloy containing only platinum‐group metals conditions (TOF@25 mV = 1.2 s −1 ). This activity is three times that of a commercial Pt/C catalyst (TOF@25 mV = 0.58 s −1 ), demonstrating simultaneous reduction in precious metal content and performance enhancement of electrocatalysts.