Enhancing the Catalytic Activity of Tri-Iodide Reduction by Tuning the Surface Electronic Structure of PtPd Alloy Nanocrystals

PtPd nanocrystals (NCs) with various alloying compositions are strategically prepared through the chemical method and exploited as counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). The photovoltaic results unveil the composition-dependent trend with a volcano-shaped plot of Pt5Pd5 NCs > Pt7Pd3 NCs > Pt3Pd7 NCs > Pt1Pd9 NCs. Among these NCs, the Pt5Pd5 NCs used as CEs in the DSSC exhibit the highest power conversion efficiency (PCE) of 9.8%, which was superior to the PCE of 7.6% obtained from the reference DSSC with the Pt CE in this study. Also, the electrochemical results reveal the composition-dependent activity along with a volcano-shaped trend in the I-/I-3(-) redox reaction. Further theoretical works support that the catalytic activities of I-3(-) reduction follow a sequence of Pt5Pd5(111) surface > Pt7Pd3(111) surface > Pt3Pd7(111) surface > Pt1Pd9(111) surface. The combination of electrochemical and theoretical results thus firmly indicate that the composition of PtPd alloying NCs plays an important role in determining their activities toward the I-3(-) reduction reactions and hence the performance of DSSCs.