Oxygen vacancy engineering of core-shelled Nickel-Molybdenum dioxide nanoparticles doped by Ruthenium atoms for overall anion exchange membrane water electrolysis.

Adjusting the electronic structure of active sites within one catalyst to achieve the bi-functional activity for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential to developing low-cost overall water electrolysis technology. Herein, highly dispersed atomic Ruthenium-doped core-shelled Nickel and Molybdenum dioxide nanoparticles with Ni nanoparticles as cores covered by MoO nanolayers (Ni@MoO-Ru) on 3-dimensional porous graphene was synthesized via a coupling strategy of hydrothermal and Ru-impregnation process. The introduction of Ru atoms onto Ni@MoO not only promotes the formation of more O defects accompanying the valence increase from Mo to Mo but also enlarges the work function difference to induce a strong built-in electric field, resulting in high HER and OER performance of 36 mV and 290 mV at 10 mA cm in 1.0 M KOH, respectively and much higher Ru mass activity than Ru-based catalysts reported so far. Meanwhile, the anion exchange membrane water electrolysis test demonstrates a lower voltage of 2.1 V at 500 mA cm than that of commercial RuO||Pt/C (2.4 V). Interestingly, the in-situ Fourier transforms infrared spectroscopy measurement further reveals that after Ru atom doping, the OER prefers the oxide pathway mechanism route rather than the adsorption oxygen evolution mechanism for Ni@MoO, while the HER via Volmer-Heyrovsky pathway is improved via an enhanced OH desorption. The theoretical calculations also identify that atomic Ru-doping with more O vacancy can enable the d-band center of the Ni-MoO to approach the Femi level, inducing the formation of O-O* intermediate for OER and lowering the adsorption energy of H* for HER, thereby promoting OER and HER. This work provides a new concept for designing bifunctional electrocatalysts with atomic Ru for overall water electrolysis.