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Here, we report the effect of substrate for tuning the active reaction center of precious and non-precious electrocalysts for efficient oxygen reduction reaction (ORR) activity. We have selected surface modified carbon morphologies to study the substrate effect on Pt and CoSe2 catalytic center. Pt supported on surface modified carbon nanotube (CNT) substrates shows, defective sites is important for effective dispersion of Pt on it. CO stripping process probes the effect of Pt interaction with defective and graphitic domains of carbon support. Improved mass activity and specific activity is observed for Pt supported on pyridine functionalized CNT compared to Pt on other CNT substrate. Similarly, CoSe2 supported on nitrogen doped carbon nanohorn (NCNH) shows improved ORR activity in alkaline and acid conditions compared to other carbon based substrates. Enhanced mass activity and specific activity of CoSe2/NCNH is observed in both alkaline and acidic media compared to CoSe2 supported on other modified substrates.

Here, we report the tuning of active reaction center of the CoSe2 nanoparticles by nitrogen doped carbon nanohorns (NCNH). CoSe2 nanoparticles supported on NCNH (CoSe2/NCNH) shows improved oxygen reduction reaction (ORR) activity compared to the same supported on carbon nanohorns and Vulcan carbon. An improved positive shift in onset potential (50 mV) and half-wave potential (150 mV) of CoSe2/NCNH compared to other catalysts indicates the intrinsic activity as well as active reaction center of CoSe2 modulated by the presence of NCNH. CoSe2/NCNH reduces molecular oxygen to hydroxide through a four-electron transfer pathway with improved electrochemical stability in alkaline condition. Air breathing direct methanol micro laminar flow fuel cells (DM-µLFFC) performance of CoSe2/NCNH as cathode catalyst shows a maximum power density and current density respectively of 10.05 mW cm-2 and 124.20 mA cm-2 with 5M methanol as fuel.

One of the major issues for the development of long-term stable electrodes for fuel cells deals with the improvement of the stability of the catalyst support. Substrates with different nature can be used as support for metallic nanoparticle catalysts. Among them, carbon based materials, e.g., Vulcan XC-72, carbon nanotubes (CNTs) have been mostly considered as a choice. Highly dispersed carbon as the classical support for electrocatalytic metal nanoparticles, e.g. Pt, leads to its oxidation to CO2 occurring at E > 0.97 V vs. RHE [1-2]. This well known corrosion phenomenon leads to the reduction of the platinum active surface area [3] either by aggregation or dissolution of the metallic active centers and consequently to a decrease of the fuel cell performances. Chemical modification of carbon based materials and elaboration of carbon-oxide composites are two suitable strategies leading to an improvement of the stability of the catalytic system. Moreover, the technique for depositing platinum on the support seems also to be responsible to mastering the nature of the interaction between the catalyst and the support. In particular, the photo-deposition technique [4] is very adapted to realize strong metal substrate interaction (SMSI) figure 1 [5]. The electrocatalytic activity of a material depends on both its chemical nature and its morphology. Therefore it is evident that an interaction allows not only an increased stability of the catalyst center but also modifies the catalytic properties and therefore the fuel cell performance based on platinum electrodes.

Synthesized carbon-supported Pt nanoparticles (10 wt% Pt/C) and their commercial counterpart (40 wt% Pt-Etek/C) have been used to study the electrochemical reduction of NOx- ions at different concentrations in alkaline and acid pH. A comparative study between nanostructured and massif platinum was evaluated. Cycling Voltammetry (CV), Rotating Disc Electrode (RDE) and Differential Mass Spectrometry (DEMS) were used for this purpose. Stationary current-potential curves indicate that the adsorption-desorption phenomena take place in two different regions of potential: the electrochemical reduction of NOx- ions for potentials ranging from -0.60 to -0.95 V/SCE, and the hydrogen evolution reaction (HER) at potential lower than -0.95 V/SCE. These results confirmed that the reduction of NOx- ions follows the order Pt/C > Pt-Etek/C > Pt-massif. DEMS demonstrated the formation of nitrogen species such as N2, NO, N2O and NO2.

20 wt. % Co3S4/C nanoparticles as novel non-precious metal electrocatalysts were synthesized by two routes based on the in situ decomposition of cobalt carbonyl (Co2(CO)8) in p-xylene solvent: with the surfactants of oleic acid and trioctylphosphane oxide, and without surfactant directly using the supporting carbon (Vulcan XC-72) as the dispersing agent. The corresponding structure, thermal stability, electrochemical properties were investigated by means of powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and rotating disk electrode (RDE) techniques. The particles synthesized without surfactant show the higher electrocatalytic activities toward oxygen reduction reaction (ORR) with the onset potential ca. 0.7 V vs. RHE in 0.5 M H2SO4 relative to those synthesized with the surfactants with the onset potential ca. 0.3 V vs. RHE, possible resulting from the surfactants blocking the active sites on the surface of the electrocatalysts. The synthesized 20 wt. % Co3S4/C nanoparticles demonstrate the thermal stability below 360 oC under air atmosphere and the electrochemical stability in the acid medium below 0.8 V vs. RHE.

Partial replacement of Ru in chalcogenide nanoparticles (RuxSey) by a less noble metal, such as Fe, was studied by electrochemical and materials-characterization techniques. The synthesis of the nanoparticles consisting of Ru, Fe, and Se was performed using two different chemical routes, which led either to a combination of RuxSey with oxidized iron or a true alloying of iron with the RuxSey bulk. The physical-chemical properties of the different types of three-component system were subsequently examined. The electrochemical performance in oxygen reduction reaction (ORR) in acidic medium (0.5 M H2SO4) was evaluated relative to the iron-free catalyst. The results demonstrate that the reaction mechanism (four-electron charge transfer) is not perturbed at the modified metal center, even when Ru is replaced by 50 at.% of Fe.

We report on the synthesis of composites Polypyrrole/Carbon (PPy/C) to be used as matrix-support of platinum nanoparticles prepared by carbonyl chemical route. The composite materials with different PPy loading were characterized by physical chemical methods, such as elemental analysis, infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The catalysts: 20 wt. % Pt/composites were used as substrates for the oxygen reduction reaction in acid medium. For the same catalyst loading (50 µg cm-2), it was observed that the nature of the composite strongly influences the electrochemical activity of nanoparticulated platinum.

The electrical performances of a membrane-less glucose/O2 biofuel cell was measured, using a biocathode composed of laccase co-immobilized with 2,2'-azinobis (3-ethylbenzothiazoline-6-sulfonate) diammonium salt (ABTS2-) on the external face of a carbon porous tube, and Au-Pt alloy nanoparticles as anode. A 40 wt. % Au-Pt/C anode catalyst was dispersed in an ultrasonically homogenized ink to be immobilized on the inner face of a carbon tube by painting. Inserting the biocathode into the anode, which has a large internal diameter, assembled the cell. O2 diffuses by porosity through the inner carbon tube to react with laccase, while the top and the bottom of the cell are sealed with two Teflon gaskets. The electrolyte (phosphate buffer 0.2 M pH 7.4) containing 10 mM glucose was analyzed by ionic chromatography with a ternary gradient of elution necessary to separate the remaining glucose from gluconic, glucuronic and glucaric acids, which were the detected reaction products.

We have recently developed a method for obtaining chalcogenide catalysts, which is based on surface modification of ruthenium black particles rather than the synthesis of a bulk metal-chalcogen compound [1]. Electrochemical, non- electrochemical and fuel cell testing have revealed high ORR activity and very good methanol tolerance of such surface chalcogenide catalysts [2,3]. Uniquely for Pt-free cathode catalysts, such surface chalcogenides also exhibit very good performance durability under fuel cell operating conditions at 70{degree sign}C. In this paper, we focus on hydrogen-air and direct methanol fuel cell performance of chalcogen-modified Ru blacks as well as on the mechanism of oxygen reduction on such catalysts, as determined in rotating ring disk-electrode (RRDE) studies.