Palladium-rhodium binary oxide composite nanofibers with various composition ratios for highly efficient electrochemical sensing of carbon monoxide in neutral aqueous media

Binary palladium (Pd) and rhodium (Rh) oxide composite nanofibers with diverse atomic ratios (PdxRh1_xOy NFs, x = 0.34, 0.55 and 0.75) were synthesized by electrospinning and post-calcination. The component phases of PdxRh1_xOy NFs varied with the Pd/Rh atomic ratio: PdRhO2 and amorphous RhOy in Pd0.34Rh0.66Oy; mainly PdRhO2 with a slight PdO in Pd0.55Rh0.45Oy; and PdO along with a rather small amount of PdRhO2 in Pd0.75Rh0.25Oy. The electrocatalytic activities of the synthesized materials were characterized for CO oxidation in neutral aqueous solution at room temperature. The anodic current of PdxRh1_xOy NFs increased in a linear proportion to CO concentration change, demonstrating the CO oxidation catalytic activity. For amperometric CO sensing, all the PdxRh1_xOy NFs exhibited considerably enhanced activity and sensitivity compared to the materials containing single metal only (i.e., Rh2O3 NFs and PdO NFs). Pd0.55Rh0.45Oy NFs exhibited the greatest CO sensitivity among the group of PdxRh1_xOy NFs. This high activity of Pd0.55Rh0.45Oy NFs was attributed mainly to the following factors: The similar contents of Pd and Rh in the material can (1) maximize the synergetic effect between Pd and Rh, producing the largest number of Pd atoms adjacent to Rh atoms; and (2) form the greatest amount of highly conductive PdRhO2 delafossite phase. In addition to the high sensitivity of Pd0.55Rh0.45Oy NFs in amperometric CO sensing, the excellent reproducibility, resistance for CO poisoning and selectivity over NO were also verified. This study demonstrates a feasibility of Pd0.55Rh0.45Oy NFs as a promising electrode material for electrochemical CO sensing.