Self-Bound Catalytic Layer of Porous Hollow Ru for Transport-Boosted Alkaline Water Electrolysis

Ru-based catalysts exhibit substantial potential for high-current-density alkaline water electrolysis. However, the ionomer incorporated into the final Ru catalytic layer (CL) used to disperse and bind catalyst particles during electrode fabrication introduces additional charge and mass transport resistances. This study demonstrates a self-bound Ru (Ru-SB) CL constructed from a superhydrophilic Ru precursor coordinated with polar N-vinylpyrrolidone (NVP). This design reduces the ionomer content required for stable ink dispersion to merely one-tenth of that in conventional systems; notably, the residual ionomer can be efficiently removed via a simple heat treatment. This process simultaneously yields a robust Ru-SB CL without compromising mechanical stability. When tested in an alkaline water electrolyzer (15% KOH, 60 °C), the Ru-SB CL delivers operating voltages of only 1.728 V and 1.916 V at current densities of 1.0 A cm⁻² and 2.0 A cm⁻², respectively — representing significant reductions of 81 mV and 107 mV relative to the conventional ionomer-bound Ru (Ru-IB) CLs. Furthermore, this study establishes a general and scalable aerosol-microdroplet method for screening more efficient superhydrophilic Ru-based precursors, enabling a further reduced operating voltage of 1.892 V at 2.0 A cm⁻². This work paves a way to build more efficient alkaline water electrolyzer for hydrogen production.