Effect of Fe state on electrocatalytic activity of Pd–Fe/C catalyst for oxygen reduction

The carbon-supported Pd–Fe catalyst (Pd–Fe/C) is prepared in the H2O/tetrahydrofuran (THF) mixture solvent under the low temperature. The homemade Pd–Fe/C catalyst contains two forms of iron species, alloying and non-alloying Fe. The alloying Fe species is hardly dissolved in 0.5 M H2SO4 solution, while the non-alloying Fe species is easily dissolved in 0.5 M H2SO4 solution. The electrochemical measurements show the electrocatalytic activity of the Pd–Fe/C catalyst with the acid treatment for the oxygen reduction is higher than that of the Pd–Fe/C catalyst without the acid treatment, illustrating that the non-alloying Fe species suppresses the electrocatalytic activity of the Pd–Fe/C catalyst. In contrast, the alloying Fe species promotes the electrocatalytic activity of the Pd–Fe/C catalyst for the oxygen reduction, which is likely attributed to the change of the electron structure of Pd atom and/or bond length of Pd–Pd in the Pd–Fe/C catalyst.