Enhanced hydrogen evolution reaction on highly stable titania-supported PdO and Eu₂O₃ nanocomposites in a strong alkaline solution

In this work, PdO/TiO₂ and Eu₂O₃/TiO₂ nanocomposites (NCs) were synthesized using a new facile, template-free, and one-step solvothermal approach and characterized by several instrumentation techniques. X-ray photoelectron spectroscopy studies revealed the presence of oxidized form of the Pd and Eu nanoparticles within the NC materials (PdO and Eu₂O₃). The two catalysts exhibited remarkable activity for the hydrogen evaluation reaction (HER) in a strong alkaline solution (4.0 M NaOH) with PdO/TiO₂ catalyst being the best, which recorded an exchange current density (j_o) of 0.26 mA cm⁻² and a Tafel slope (β_c) of 125 mV dec⁻¹. Such parameters are not far from those recorded for a commercial Pt/C catalyst (0.71 mA cm⁻² and 120 mV dec⁻¹) performed here under the same operating conditions. Eu₂O₃/TiO₂ catalyst recorded j_o and β_c values of 0.05 mA cm⁻² and 135 mV dec⁻¹. The Tafel slopes 125 and 135 mV dec⁻¹ calculated on the PdO/TiO₂ and Eu₂O₃/TiO₂ catalysts suggest a HER kinetics controlled by the Volmer step. PdO/TiO₂ catalyzed the HER with a high turnover frequency of 2.3 H₂/s at 0.2 V versus the reversible hydrogen electrode, while Eu₂O₃/TiO₂ catalyst only measured a turnover frequency value of 1.25 H₂/s at the same overpotential. The two catalysts exhibited excellent stability and durability after 10 000 cycles and 72 hours of controlled potential electrolysis at a high cathodic overpotential, reflecting their practical applicability. Scanning electron microscope and X-ray photoelectron spectroscopy examinations revealed that the morphology and chemistry of both catalysts were not altered as a result of the performed long-term stability and durability tests.