Activity and durability of intermetallic PdZn electrocatalyst for ethanol oxidation reaction

Intermetallic or substitutional solid-solution PdZn alloy nanoparticle (NP)-loaded carbon black (i-PdZn/C, s-PdZn/C) was prepared by reducing equimolar palladium acetate and zinc acetate in ethanol dispersion of carbon black with sodium tetrahydroborate with and without the following heat-treatment in an autoclave. The Pd 3d and Zn 2p core-level spectra exhibited that the binding energy of Pd and Zn for i-PdZn/C shifted positively and negatively compared to that for metallic Pd and Zn sheets, respectively, suggesting a strong electronic interaction between Pd and Zn. In contrast, for s-PdZn/C, the binding energy for Pd shifted positively, but only a peak for ZnO was observed. In 1 M KOH aqueous solution at 20 ºC, the Zn content of s-PdZn/C was almost zero in 30 min, while i-PdZn/C held the Zn component of 75% at 20 ºC and 70% at 60 ºC after 30 min, indicating that i-PdZn/C was much more tolerant to alkaline medium than s-PdZn/C. Consequently, s-PdZn NPs were changed to porous Pd NPs, whereas i-PdZn NPs were changed to core–shell NPs whose surface was porous Pd. In the (1 M KOH + 1 M ethanol) aqueous solution at 20 ºC, i-PdZn/C and s-PdZn/C significantly enhanced the activity for ethanol oxidation reaction (EOR) compared to Pd NP-loaded carbon black (Pd/C). In the potentiostatic electrolysis at 0.7 V for 10,000 s, the deterioration of i-PdZn/C was effectively delayed compared to Pd/C and s-PdZn/C due to the electronic effect of the intermetallic PdZn core.