Electrochemical study of Pt and Fe and electrodeposition of PtFe alloys from air- and water-stable room temperature ionic liquids

The voltammetric behavior of Pt(II), Fe(II), and mixtures of Pt(II) and Fe(II) was studied in N-butyl-N-methylpyrrolidinium dicyanamide ionic liquid (BMP-DCA IL), N-butyl-N-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide ionic liquid (BMP-TFSI IL), and a mixture of BMP-DCA and BMP-TFSI, respectively. Electrodeposition of PtFe coatings was achieved by controlled-potential electrolysis on tungsten from the aforementioned ILs containing Pt(II) and Fe(II). The Pt(II) species required to prepare these PtFe coatings was introduced into the ILs by addition of PtCl2. In BMP-TFSI, an additional two equivalents of N-butyl-N-methylpyrrolidinium chloride (BMP-Cl) were essential to assist one equivalent of PtCl2 to dissolve. The Fe(II) species was introduced into the ILs by addition of FeCl2 or by anodizing an iron spiral electrode. In BMP-TFSI, additional BMP-Cl had to be added to assist FeCl2 dissolution (FeCl2:BMP-Cl = 1:2 (mol:mol)). The PtFe coatings with various atomic ratios of Pt/Fe were studied for their voltammetric behavior towards the oxygen reduction reaction (ORR) in acidic solutions. This study shows that the PtFe alloy coatings with atomic ratios of ∼0.5/0.5 had the highest reductive current density for ORR, better than regular Pt or Pt-electrodeposited electrodes.