Yuan-Yuan Feng

Electrochemical Anodic Dissolution Kinetics of Titanium in Fluoride-Containing Perchloric Acid Solutions at Open-Circuit Potentials

The influence of fluoride on the anodic dissolution kinetics of titanium was studied by several electrochemical techniques at steady-state open-circuit potentials in 1.0 M HClO 4 containing fluoride with various concentrations ranging from 0 to 0.1 M. The promoting effect of fluoride (especially when [F - ] > 1 × 10 -3 M) on the anodic dissolution behavior of titanium was characterized and discussed by taking into account the changes in the estimated electrochemical and kinetic parameters. The faradaic impedance for the anodic dissolution of titanium was analyzed both by fitting based on an equivalent electrical circuit model and by theoretical derivation based on a two-step mechanism involving one adsorbed intermediate species. By correlating the faradaic impedance expression derived from the dissolution mechanism with that deduced from the equivalent electrical circuit model, some important kinetic parameters (such as the apparent rate constants K 1 and K 2 and the surface coverage θ ss ) could be estimated from the equivalent circuit elemental parameters (such as R c1 , R a , and C a ). The charge-transfer reaction was the rate-determining step at lower fluoride concentrations of [F - ] ≤ 1 × 10 -3 M, leading to a high surface coverage of θ ss = 1, while the chemical dissolution reaction is the rate-determining step at higher fluoride concentrations of [F-] > 1 × 10 -3 M, leading to a decreased surface coverage of θ ss < 0.5.

Promoting effects of Fe 2 O 3 to Pt electrocatalysts toward methanol oxidation reaction in alkaline electrolyte

Abstract Fe2O3 nanorods and hexagonal nanoplates were synthesized and used as the promoters for Pt electrocatalysts toward the methanol oxidation reaction (MOR) in an alkaline electrolyte. The catalysts were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, cyclic voltammetry and chronoamperometry. The results show that the presence of Fe2O3 in the electrocatalysts can promote the kinetic processes of MOR on Pt, and this promoting effect is related to the morphology of the Fe2O3 promoter. The catalyst with Fe2O3 nanorods as the promoter (Pt-Fe2O3/C-R) exhibits much higher catalytic activity and stability than that with Fe2O3 nanoplates as the promoter (Pt-Fe2O3/C-P). The mass activity and specific activity of Pt in a Pt-Fe2O3/C-R catalyst are 5.32 A/mgPt and 162.7 A/m2Pt, respectively, which are approximately 1.67 and 2.04 times those of the Pt-Fe2O3/C-P catalyst, and 4.19 and 6.16 times those of a commercial PtRu/C catalyst, respectively. Synergistic effects between Fe2O3 and Pt and the high content of Pt oxides in the catalysts are responsible for the improvement. These findings contribute not only to our understanding of the MOR mechanism but also to the development of advanced electrocatalysts with high catalytic properties for direct methanol fuel cells.

Promoting effect of polyaniline on Pd catalysts for the formic acid electrooxidation reaction

Abstract Pd-based nanomaterials have been considered as an effective catalyst for formic acid electrooxidation reaction (FAOR). Herein, we reported two types of polyaniline (PANI)-promoted Pd catalysts. One was an n PANI/Pd electrocatalyst prepared by the electropolymerization of aniline and the electrodeposition of Pd. The other was a Pd/C/ n PANI catalyst prepared by the direct electropolymerization of aniline on a commercial Pd/C catalyst. The results show that PANI alone has no catalytic activity for FAOR; however, PANI can exhibit a significant promoting effect to Pd. The current densities of FAOR on the Pd catalysts with a PANI coating show a significant increase compared with that of the Pd reference catalyst without PANI as a promoter. The promoting effects of PANI are strongly dependent on the electropolymerization potential cycles ( n ). The highest catalytic activities for FAOR of all the n PANI/Pd and Pd/C/ n PANI catalysts were those of 15PANI/Pd and Pd/C/20PANI. The mass-specific activity (MSA) of Pd in 15PANI/Pd was 7.5 times that of the Pd catalyst, and the MSA and intrinsic activity of Pd/C/20PANI were 2.3 and 3.3 times that of the Pd/C catalyst, respectively. The enhanced performance of Pd catalysts is proposed as an electronic effect between Pd nanoparticles and PANI.

Dealloyed PdAg core Pt monolayer shell electrocatalyst for oxygen reduction reaction

A core–shell nanostructure (Pt–PdAg/C–D) with dealloyed PdAg nanoparticles (PdAg/C–D) as the core and a Pt monolayer as the shell is prepared and employed as an electrocatalyst toward oxygen reduction reaction (ORR). Compared with its counterpart alloyed PdAg core-Pt monolayer shell catalyst (Pt–PdAg/C), the Pt–PdAg/C–D catalyst shows significantly higher catalytic activities for ORR. The half wave potential (E1/2) on Pt–PdAg/C–D is located at −0.17 V, which is comparable to that on the commercial Pt/C catalyst and ca. 30 mV more positive than that on Pt–PdAg/C. The MSA of Pt in Pt–PdAg/C–D is 171.8 A gPd+Pt−1, which is 3.2 and 2.4 times higher than those of Pt–PdAg/C and commercial Pt/C catalysts, respectively. The Pt monolayer shell on the surface of the nanoparticles would induce much higher utilization of Pt atoms, and the dealloying process would result in a nanostructured PdAg core with a rough surface and a Pt shell with a numbers of low-coordinated atoms. It is concluded that the change in the electronic and geometric structure of Pt in the Pt–PdAg/C–D catalyst may contribute to the increase in catalytic performance for ORR.