Spatially Separated Ru, Ni Sites on Extrusion 3D Printed Carbonaceous Electrodes for Enhanced Alkaline Water Splitting

Efficient electrochemical water splitting is crucial for advancing hydrogen technologies, yet reverse reactions from the close proximity of hydrogen and oxygen evolution sites often hinder performance. We present a site-isolation strategy using extrusion-based 3D printing that spatially separates Ru and Ni catalysts within chitosan-derived carbon electrodes. By formulating chitosan inks with Ru-ZIF and Ni-Zn BTC precursors, we achieve precise filament-level segregation, resulting in pyrolyzed electrodes with Ru clusters and Ni nanoparticles anchored on distinct layers. This design delivers outstanding bifunctional activity, reaching 87 mV for HER and 172 mV for OER at 10 mA cm^-2, along with remarkable stability for over 700 h at 0.5 A cm^-2 during HER and 1.54 V at 10 mA cm^-2 for overall water splitting, surpassing conventional and non-isolated electrodes. In anion exchange membrane electrolyzers, the site-isolated electrodes maintain robust operation for 300 h at 0.5 A cm^-2. Theoretical calculations and XAFS analysis reveal that spatially separated Ru and Ni sites exhibit localized electronic structures, which effectively lower the d-band center, enhancing hydrogen and oxygen desorption, and suppressing reverse reactions. This scalable 3D printing approach enables advanced electrocatalytic performance through device-level spatial control.