Showing papers by "Edson A. Ticianelli published in 2017"

Effect of temperature on the activities and stabilities of hydrothermally prepared IrOx nanocatalyst layers for the oxygen evolution reaction

Abstract: Iridium oxide nanoparticles are prepared via a hydrothermal method, treated at different calcination temperatures, and their activities and stabilities for the oxygen evolution reaction (OER) evaluated. The catalysts are physicochemically characterized using several techniques including X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Voltammetric profiles obtained for the catalysts calcined up to 300 °C are similar to that of electrochemically prepared hydrous iridium oxide, while the CV profiles are characteristic of thermally prepared iridium oxide after calcination at higher temperatures. Performance as an OER catalyst decreases with increasing IrOx calcination temperature, while the opposite trend in stability is observed for these materials. Catalysts calcined between 400 and 500 °C exhibit better balances between activity and stability. However, despite higher performance losses, the non-calcined IrOx material still exhibits higher mass activity at the end of the aging experiments at electrode potentials up to 1.6 V vs. RHE. The causes of electrode activity degradation are investigated using identical location transmission electron microscopy, which reveal that IrOx electrode instability is due to the degradation of the thin IrOx layer, in addition to iridium oxide dissolution.

Pd-M/C (M = Pd, Cu, Pt) Electrocatalysts for Oxygen Reduction Reaction in Alkaline Medium: Correlating the Electronic Structure with Activity.

Abstract: The increasing global needs for clean and renewable energy have fostered the design of new and highly efficient materials for fuel cells applications. In this work, Pd–M (M = Pd, Cu, Pt) and Pt nanoparticles were prepared by a green synthesis method. The carbon-supported nanoparticles were evaluated as electrocatalysts for the oxygen reduction reaction (ORR) in alkaline medium. A comprehensive electronic and structural characterization of these materials was achieved using X-ray diffraction, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Their electrochemical properties were investigated by cyclic voltammetry, while their activities for the ORR were characterized using steady-state polarization experiments. The results revealed that the bimetallic nanoparticles consist of highly crystalline nanoalloys with size around 5 nm, in which the charge transfer involving Pd and M atoms affects the activity of the electrocatalysts. Additionally...

Effect of transition metals in the hydrogen evolution electrocatalytic activity of molybdenum carbide

Abstract: In this work, the effect of transition metals (TMs), such as Fe, Co, Ni and Cu, on the activity toward the hydrogen evolution reaction (HER) of modified molybdenum carbide (TM-Mo2C) catalysts has been evaluated. Catalysts were prepared by a temperature programmed reduction method in both an inert and a reductive atmosphere, and characterized by different physicochemical techniques. A high activity toward the HER is measured for all TM-Mo2C catalysts, with onset potentials lower than −0.06 V, as detected by on-line differential electrochemical mass spectrometry, and mass activities between 29 and 50 mA mg−1, which suggest them as promising non-precious electrocatalysts for this reaction. However, a decrease in the HER activity upon metal doping is measured, following an activity trend of α-Mo2C > Fe-Mo2C > Co-Mo2C > Ni-Mo2C > Cu-Mo2C. In situ near-edge X-ray adsorption analysis reveals a positive charge of the TM in the materials in the electrochemical environment, at the origin of the deleterious effect of Fe, Co, Ni and Cu, in terms of an electronic effect that modifies the d-electron configuration of α-Mo2C particles. Additionally, results also suggest that TM-Mo2C is more stable (lower catalyst dissolution) in acid media than α-Mo2C. Finally, because there is a catalyst deactivation toward the HER after the α-Mo2C component of the catalysts is oxidized at E > 0.7 V, the oxidation process of α-Mo2C is employed for estimating, as a first approximation, the number of surface active sites for the HER.

CO tolerance and stability of proton exchange membrane fuel cells with nafion and aquivion membranes and Mo‑based anode electrocatalysts

Abstract: This work presents a CO tolerance study of PtMo/C (70:30, Pt:Mo) and Pt/MoO2-C anode catalysts on proton exchange membrane fuel cells (PEMFC) with Nafion® and Aquivion® ionomer membranes. Results denote improved activity for the hydrogen oxidation reaction (HOR) in the presence of CO on both anode catalysts at 85 oC. Experiments of identical location transmission electron microscopy evidenced very good stability of the Pt particles along an accelerate stress test (AST) applied to the Mo-based anode catalysts. However, a crossover of degradation Mo products originated in the anode and going to the cathode takes place along this anode AST, causing a PEMFC performance decay. A very little effect of the nature of the membrane, Nafion® or Aquivion®, is observed over these crossover phenomena. Results also denote that when operating at appropriate high temperatures (105 oC for Nafion® and 125 oC for Aquivion®), there is no need of incorporating unstable oxophilic transition metals on Pt to achieve improved CO tolerance on PEMFCs, when the CO level in the hydrogen fed is of the order of 100 ppm.