Visualizing dynamic competitive reconstruction of trimetallic hybrid catalysts for stable hybrid water electrolysis at large current density

Abstract

Glycerol electrooxidation is an intriguing surrogate reaction for sluggish oxygen evolution in water electrolysis and can simultaneously produce value-added chemicals at the anode, however, the majority of non-precious catalysts suffer from large electrolytic voltage and poor stability for hydrogen production via hybrid water electrolysis at large current density. Here we present a hierarchical multi-level triphasic catalyst comprising bimetallic nitride nanoparticles in situ anchoring on biphasic metal sulfides with multilevel interfaces and multifunctional metal sites (Ni3S2/Co9S8/FeNiN). Benefiting from synergistic multi-metal sites and dynamic iron incorporation into the active species, this catalyst manifests extraordinary activity for both the oxygen evolution and glycerol electrooxidation in term of ultralow potentials of 1.502/1.393 V at 300 mA cm-2 and excellent Faradaic efficiency (95.2 %) toward formate production, along with fabulous durability for over 1100/240 hours, placing it among the best non noble metal-based electrocatalysts. Strikingly, by coupling with NiMoN cathode, this catalyst can readily switch from traditional water electrolysis to hybrid water electrolysis with low cell voltages of 1.713/1.610 V to reach 1000 mA cm-2 durably at an electricity-saving efficiency of 6.0 %, outperforming nearly all the biomass upgrading assisted water electrolyzers reported hitherto. Operando Raman and X-ray photoelectron spectroscopic studies reveal the rapid switch from OH*-involved direct oxidation to oxyhydroxide-involved indirect oxidation for glycerol oxidation, which is in sharp contrast to the rapid generation of high-valence metal oxyhydroxide active species for oxygen evolution. Theoretical calculations further substantiate that the construction of dual heterojunction interfaces facilitates the C-C bond cleavage, dehydrogenation and oxygenation steps with much lower energy barriers, thereby promoting the selective oxidation of glycerol into formic acid.