Constructing an anatase/rutile TiO2 homojunction-supported Pd electrocatalyst via band alignment and oxygen vacancy engineering for direct methanol fuel cells

Abstract

Maximizing the reaction kinetics of Pd catalysts for oxygen reduction reaction (ORR) while minimizing CO poisoning during the methanol oxidation reaction (MOR) remains a key challenge for advancing direct methanol fuel cells (DMFCs). Herein, we synthesize an anatase/rutile TiO₂ homojunction (A/R-TiO₂) through energy band alignment and oxygen vacancy engineering, providing support for Pd nanoparticles to decipher the strong correlation between this unique structure and the electrocatalytic properties of Pd/A/R-TiO₂ catalysts. Combined experimental results and theoretical calculations demonstrate that the near perfect energy band alignment and abundant oxygen vacancies in A/R-TiO₂ not only accelerate electron transfer to the Pd surface, thereby maximizing the reaction kinetics and catalytic efficiency, but also optimize the electronic structure of Pd active sites to reduce the adsorption energy of key intermediates (*OH, *CH₂OH, *CO) during the ORR and MOR. Consequently, the Pd/A/R-TiO₂ catalyst delivers a remarkably positive E_1/2 of 0.929 V and an enhanced mass activity of 4.27 A mg_Pd⁻¹ at 0.85 V for ORR, respectively, nearly 13 and 27 times greater than those of Pt/C and Pd/C catalysts commercially available at present. The Pd/A/R-TiO₂ catalyst displays high selectivity for an effective four-electron transfer pathway, a lower H₂O₂ yield (1.66%), and excellent methanol crossover tolerance. Importantly, the catalyst demonstrates exceptional stability, exhibiting minimal activity decay and negligible structural degradation after 10 000 cycles. Furthermore, the as-synthesized catalyst achieves superior MOR activity (4.10 A mg_Pd⁻¹ and 8.85 A cm⁻²) and enhanced CO tolerance, surpassing commercial Pt/C and Pd/C catalysts. These bifunctional catalysts thus hold great potential for large-scale and industry-orientated use of DMFCs.