Foteini Sapountzi - Academia.edu (original) (raw)

Papers by Foteini Sapountzi

This study investigates the production of hydrogen from the electrochemical reforming of short-ch... more This study investigates the production of hydrogen from the electrochemical reforming of short-chain alcohols (methanol, ethanol, iso-propanol) and their mixtures. High surface gas diffusion Pt/C electrodes were interfaced to a Nafion polymeric membrane. The assembly separated the two chambers of an electrochemical reactor, which were filled with anolyte (alcohol + H2O or alcohol + H2SO4) and catholyte (H2SO4) aqueous solutions. The half-reactions, which take place upon polarization, are the alcohol electrooxidation and the hydrogen evolution reaction at the anode and cathode, respectively. A standard Ag/AgCl reference electrode was introduced for monitoring the individual anodic and cathodic overpotentials. Our results show that roughly 75% of the total potential losses are due to sluggish kinetics of the alcohol electrooxidation reaction. Anodic overpotential becomes larger as the number of C-atoms in the alcohol increases, while a slight dependence on the pH was observed upon changing the acidity of the anolyte solution. In the case of alcohol mixtures, it is the largest alcohol that dictates the overall cell performance.

Water electrolysis is the most promising method for efficient production of high purity hydrogen ... more Water electrolysis is the most promising method for efficient production of high purity hydrogen (and oxygen), while the required power input for the electrolysis process can be provided by renewable sources (e.g. solar or wind). The thus produced hydrogen can be used either directly as a fuel or as a reducing agent in chemical processes, such as in Fischer–Tropsch synthesis. Water splitting can be realized both at low temperatures (typically below 100 °C) and at high temperatures (steam water electrolysis at 500– 1000 °C), while different ionic agents can be electrochemically transferred during the electrolysis process (OH − , H + , O 2−). Singular requirements apply in each of the electrolysis technologies (alkaline, polymer elec-trolyte membrane and solid oxide electrolysis) for ensuring high electrocatalytic activity and long-term stability. The aim of the present article is to provide a brief overview on the effect of the nature and structure of the catalyst–electrode materials on the electrolyzer's performance. Past findings and recent progress in the development of efficient anode and cathode materials appropriate for large-scale water electrolysis are presented. The current trends, limitations and perspectives for future developments are summarized for the diverse electrolysis technologies of water splitting, while the case of CO2/H2O co-electrolysis (for synthesis gas production) is also discussed.

Catal. Sci. Technol., 2015

Topics in Catalysis, 2014

Nanoparticles of platinum were dispersed on an oxygen ionically conducting support, Yttria-Stabil... more Nanoparticles of platinum were dispersed on an oxygen ionically conducting support, Yttria-Stabilized Zirconia (YSZ), on non-doped zirconia and on silica. The role of the support oxygen lattice in the mechanism of propane deep oxidation was investigated by using 18 O 2 Temperature-Programmed Desorption, catalytic activity measurements using isotopic oxygen, and isotopic exchange experiments. The results emphasize that the propane combustion mechanism on Pt/YSZ presents a different pathway compared with that involved on Pt/SiO 2 and Pt/ZrO 2 because, propane is preferentially oxidized by lattice YSZ oxygen species on Pt/YSZ. Strong Pt nanoparticles/YSZ interactions generate a promoted state similar to that observed on polarizations during electrochemical promotion of catalysis.

Topics in Catalysis, 2007

The electrochemical promotion of catalysis (or NEMCA effect) was studied for the CO oxidation and... more The electrochemical promotion of catalysis (or NEMCA effect) was studied for the CO oxidation and water gas shift reaction on a Pt anode in a polymer electrolyte membrane (PEM) fuel cell. It was found that this phenomenon plays a significant role in a normal fuel cell operation (fuel mixture – air) but not in a hydrogen pumping operation (fuel mixture – H2). This implies that the role of oxygen crossover in the electropromotion (EP) of CO oxidation is vital. During fuel cell operation, the increase in the rate of CO consumption is 2.5 times larger than the electrochemical rate, I/2F of CO oxidation, while for oxygen bleeding conditions (fuel mixture + O2−air) the increase is five times larger than I/2F. This shows that the catalytic properties of the Pt anode are significantly modified by varying the catalyst potential. In order to confirm the role of oxygen crossover, Nafion membranes (117, 1135) with different thickness, were studied. The results show that upon decreasing the membrane thickness the crossover is increased and thus the electrochemical promotion effect becomes more pronounced.

Solid State Ionics, 2012

ABSTRACT Electrochemical investigations have been carried out on Pd/YSZ catalyst-electrodes for d... more ABSTRACT Electrochemical investigations have been carried out on Pd/YSZ catalyst-electrodes for deep oxidation of methane in excess of oxygen. A wet impregnation technique has been used to achieve highly active Pd catalyst films. It was found that co-feeding of ethylene in oxidizing gas mixtures enhances the rate of methane conversion and allows for electrochemical promotion of methane oxidation at temperatures as low as 320 °C. The electrochemical promotion behavior has been studied with long term potentiostatic transients together with AC impedance measurements during polarization.

Journal of Electroanalytical Chemistry, 2011

The optimal amount of Nafion ionomer applied on IrO2 sputter-deposited electrodes on Ti covered c... more The optimal amount of Nafion ionomer applied on IrO2 sputter-deposited electrodes on Ti covered carbon paper was investigated during low temperature PEM water splitting. Different Nafion ionomer loadings were applied on IrO2 electrodes and their performance towards the oxygen evolution reaction was evaluated. An optimum Nafion loading of 1.5mgcm−2 was found which gives a current density of 0.18Acm−2 at 1.75V

Catalysis Today, 2007

The treatment of methanol reformate, containing up to 2500 ppm CO, by the anode of a PEM fuel cel... more The treatment of methanol reformate, containing up to 2500 ppm CO, by the anode of a PEM fuel cell, operating as a preferential oxidation (PROX) reactor, was investigated in order to examine the possibility of electrochemically promoting the water-gas-shift (WGS) reaction and thus making the gas mixture suitable for anodic oxidation. It was found that the electrochemical promotion effect plays a significant role in a normal fuel cell operation (air at the cathode) but not in a hydrogen pumping operation (H 2 at the cathode). This implies that the role of oxygen crossover in the electropromotion (EP) of the WGS reaction and in the CO oxidation is vital. During fuel cell operation, the increase in the rate of CO consumption over a Pt/C anode is 2.5 times larger than the electrochemical rate, I/2F of CO consumption, while for oxygen bleeding conditions (fuel mixture + 1% O 2 at the anode) the increase is up to five times larger than I/2F, i.e. the Faradaic efficiency is up to 5. This shows that the catalytic properties of the Pt anode are significantly modified by varying catalyst potential and by the extent of O 2 crossover.

Electrochimica Acta, 2011

The effect of triode operation on the performance of CO poisoned PEM fuel cells was investigated.... more The effect of triode operation on the performance of CO poisoned PEM fuel cells was investigated. In this mode of operation a third, auxiliary, electrode is introduced in addition to the anode and the cathode. Application of electrolytic current in the auxiliary circuit, comprising the cathode and the auxiliary electrode was found to significantly enhance the time-averaged power output of

Solid State Ionics, 2006

The triode fuel concept is discussed together with some of its first applications in the areas of... more The triode fuel concept is discussed together with some of its first applications in the areas of SOFCs and PEMFCs. It is shown that, when the electrodes are polarizable, both the power output and the thermodynamic efficiency can be improved quite significantly via application of electrolytic currents between the anode or cathode and an auxiliary electrode.

Journal of Applied Electrochemistry, 2010

The electrochemical promotion of Pt/YSZ and Pt/TiO 2 /YSZ catalyst-electrodes has been investigat... more The electrochemical promotion of Pt/YSZ and Pt/TiO 2 /YSZ catalyst-electrodes has been investigated for the model reaction of C 2 H 4 oxidation in an atmospheric pressure single chamber reactor, under oxygen excess between 280 and 375°C. It has been found that the presence of a dispersed TiO 2 thin layer between the catalyst electrode and the solid electrolyte (YSZ), results in a significant increase of the magnitude of the electrochemical promotion of catalysis (EPOC) effect. The rate enhancement ratio upon current application and the faradaic efficiency values, were found to be a factor of 2.5 and 4 respectively, higher than those in absence of TiO 2 . This significantly enhanced EPOC effect via the addition of TiO 2 suggests that the presence of the porous TiO 2 layer enhances the transport of promoting O 2species onto the Pt catalyst surface. This enhancement may be partly due to morphological factors, such as increased Pt dispersion and three-phase-boundary length in presence of the TiO 2 porous layer, but appears to be mainly caused by the mixed ionic-electronic conductivity of the TiO 2 layer which results to enhanced O 2transport to the Pt surface via a self-driven electrochemical promotion O 2transport mechanism.

Applied Catalysis B: Environmental, 2012

The effect of electrochemical promotion of catalysis (NEMCA effect or EPOC) has been studied for ... more The effect of electrochemical promotion of catalysis (NEMCA effect or EPOC) has been studied for the methane oxidation reaction over Rh catalytic films interfaced with YSZ, an oxygen ion conductor, at temperatures from 350 to 550 • C, under reducing, stoichiometric and oxidizing conditions. CO 2 is the main reaction product; however, CO is produced in small amounts at high temperatures. The effect of electrochemical promotion of catalysis on the reaction catalytic rate has been found to decrease by increasing partial pressure of oxygen and temperature. Under reducing conditions, at 430 • C, positive current application can cause a 3-fold increase of the catalytic rate, while the apparent Faradaic efficiency is 170. After positive current interruption the catalytic rate reversibly returns to the initial open-circuit state value. Negative current application results in a 57% decrease of the catalytic rate with an apparent Faradaic efficiency equal to 40. After negative current interruption the catalytic rate slowly increases but remains lower than the initial value. This permanent poisoning effect has been interpreted by formation of a surface oxide layer by the strongly adsorbed oxygen from the gas phase upon negative polarization. A poisoning index, ␤, has been defined to quantify the magnitude of the effect. Moreover, under stoichiometric conditions, a periodical oscillation of the rate is observed both under open-circuit and polarization conditions in a narrow temperature window between 480 and 520 • C, which is attributed to catalyst phase transition phenomena.

ABSTRACT International @ AIR+ABO:LRE:PVE:MTS

Journal of Applied Electrochemistry, 2012

The performance of La 0.75 Sr 0.25 Cr 0.9 M 0.1 O 3 (M = Mn, Fe, Co, and Ni) perovskitic material... more The performance of La 0.75 Sr 0.25 Cr 0.9 M 0.1 O 3 (M = Mn, Fe, Co, and Ni) perovskitic materials as anodes was studied for a CO-fueled solid oxide fuel cell. The electrocatalytic performance and the tolerance to carbon deposition were investigated, while electrochemical characterization was carried out via AC impedance spectroscopy and cyclic voltammetry. The La 0.75 Sr 0.25 Cr 0.9 Fe 0.1 O 3 perovskite showed the best anode performance at temperatures above 900°C; while at temperatures below 900°C, the best performance was achieved with the La 0.75 Sr 0.25 Cr 0.9 Co 0.1 O 3 material. AC impedance spectroscopy was used for a semi-quantitative analysis of the LSC-M 0.1 anodes performance in view of total cell and charge transfer resistance. All anode materials exhibit high electronic conductivity and presumably do not substantially contribute to the overall cell resistance and concomitant ohmic losses.

Chemical Physics Letters, 2012