Mesoporous TiO₂ nanospheres loaded with highly dispersed Pd nanoparticles for pH-universal hydrogen evolution reaction

An effective cation exchange strategy is developed to synthesize highly dispersed palladium (Pd) nanoparticle (NP)–embedded mesoporous TiO₂ nanospheres enriched with oxygen vacancies aiming at overcoming the specific service condition and stability limitations of supported metal electrocatalysts. This strategy involves embedding Pd²⁺ cation into the interlayer of sodium titanate sheets through cation exchange with Na⁺, followed by annealing to obtain metallic Pd NP–embedded anatase phase TiO₂ (Pd–TiO₂). The resulting Pd–TiO₂ shows excellent electrocatalytic activity toward hydrogen evolution reaction (HER) (i.e., an overpotential of 108 mV at 10 mA cm⁻²) with good stability in acidic media, along with good activity and excellent stability under basic and neutral conditions. The high HER activity is attributed to the uniform distribution and strong attachment of Pd NPs in the TiO₂ nanospheres, the high porosity of mesoporous TiO₂ nanostructures, and the creation of oxygen vacancies in TiO₂ induced during the cation exchange process. Our findings are supported by the density functional theory calculations, which demonstrate the synergistic effect between Pd and TiO₂ and the contribution of oxygen vacancies to the high HER performance.