Topotactic Transformations in an Icosahedral Nanocrystal to Form Efficient Water‐Splitting Catalysts

Designing high‐performance, precious‐metal‐based, and economic electrocatalysts remains an important challenge in proton exchange membrane (PEM) electrolyzers. Here, a highly active and durable bifunctional electrocatalyst for PEM electrolyzers based on a rattle‐like catalyst comprising a Ni/Ru‐doped Pt core and a Pt/Ni‐doped RuO2 frame shell, which is topotactically transformed from an icosahedral Pt/Ni/Ru nanocrystal, is reported. The RuO2‐based frame shell with its highly reactive surfaces leads to a very high activity for the oxygen evolution reaction (OER) in acidic media, reaching a current density of 10 mA cm−2 at an overpotential of 239 mV, which surpasses those of previously reported catalysts. The Pt dopant in the RuO2 shell enables a sustained OER activity even after a 2000 cycles of an accelerated durability test. The Pt‐based core catalyzes the hydrogen evolution reaction with an excellent mass activity. A two‐electrode cell employing Pt/RuO2 as the electrode catalyst demonstrates very high activity and durability, outperforming the previously reported cell performances. A high‐performance bifunctional electrocatalyst for water electrolysis by topotactic transformations of Pt/Ni/Ru nanocrystals is designed. A rattle‐like open nanostructure with a Ni/Ru‐doped Pt core and a Pt/Ni‐doped RuO2 frame shell not only promotes oxygen evolution with very high activity and durability but also enables a high activity for hydrogen evolution. In the two‐electrode system, the catalyst exhibits excellent performance than previously reported cells.