Defect-Engineered Charge Transfer in a PtCu/PrxCe1–xO2 Carbon-Free Catalyst for Promoting the Methanol Oxidation and Oxygen Reduction Reactions

Platinum (Pt) and Pt-based alloys have been extensively studied as efficient catalysts for both the anode and cathode of direct methanol fuel cells (DMFC). Defect engineering has been revealed to be practicable in tuning the charge transfer between Pt and transition metals/supports, which leads to the charge density rearrangement and facilitates the electrocatalytic performance. Herein, Pr-doped CeO₂ nanocubes were used as the noncarbon support of a PtCu catalyst. The concentration and structure of oxygen vacancy (V_o) defects were engineered by Pr doping. Besides the V_o monomer, the oxygen vacancy with a linear structure is also observed, leading to the one-dimensional PtCu. The V_o concentration shows the volcanic scenario as Pr increased. Accordingly, the activities of PtCu/Pr_xCe_1-xO₂ toward methanol oxidation and oxygen reduction reactions exhibit the volcanic scenario. PtCu/Pr_0.15Ce_0.85O₂ exhibits the optimal catalytic performance with the specific activity 3.57 times higher than that of Pt/C toward MOR and 1.34 times higher toward ORR. The MOR and ORR mass activities of PtCu/Pr_0.15Ce_0.85O₂ reached 1.05 and 0.12 A·mg^-1, which are 3.09 and 0.92 times the values of Pt/C, respectively. The abundant V_o afforded surplus electrons, which tailored the electron transfer between PtCu and Pr_xCe_1-xO₂, leading to enhanced catalytic performance of PtCu/Pr_xCe_1-xO₂. DFT calculations on PtCu/Pr_0.15Ce_0.85O₂ revealed that Pr doping reduced the band gap of CeO₂ and lowered the overpotential.