Cyanogel-Induced Facile Synthesis of Palladium Hydride for Electrocatalytic Oxygen Reduction

Palladium hydride (PdH_x) is one of the well-known electrocatalytic materials, yet its synthesis is still a challenge through an energy-efficient and straightforward method. Herein, we propose a new and facile cyanogel-assisted synthesis strategy for the preparation of PdH_0.649 at a mild environment with NaBH₄ as the hydrogen source. Unlike traditional inorganic Pd precursors, the unique Pd-CN-Pd bridge in Pd_x[Pd(CN)₄]_y ⋅ aH₂O cyanogel offers more favourable spatial sites for insertion of H atoms. The characteristic three-dimensional backbone of cyanogel also acts as a support scaffold resulting in the interconnected network structure of PdH_0.649. Due to the incorporation of H atoms and interconnected network structure, the PdH_0.649 achieves a high half-wave potential of 0.932 V, a high onset potential of 1.062 V, and a low activation energy, as well as a long-term lifetime for oxygen reduction reaction. Theoretical calculation demonstrates a downshift of the d-band centre of Pd in PdH_0.649 owing to the dominant Pd-H incorporation that weakens the binding energies of the *OH intermediate species. Zn-air batteries (ZAB) based on PdH_0.649 exhibits high power density, competitive open circuit voltage, and good stability, exceeding that of commercial Pt black. This work not only opens up a new avenue for the development of high-efficiency Pt-free catalysts but also provides an original approach and insight into the synthesis of PdH_x.