1. Chalcogenide based cathode materials for fuel cells K. Atheeque Ahmed K. Atheeque Ahmed 15 th November, 2009

2. Objectives  To search of the new catalyst for the oxygen reduction reaction.  The study is focused on chalcogenide based catalyst (eg., RuTe,RuSe).

3. Comparatively study of the oxygen reduction reaction on RuMSe (M=Cr,Mo,W)   The electro catalysts were synthesized by reacting the corresponding transition metal carbonyl compounds and elemental selenium in 1,6-hexanediol under refluxing conditions for 3 h   The powder electro catalysts were characterized by XRD and SEM   Formation of agglomerates of crystalline particles with nano scale size embedded in an amorphous phase is indicated  The particle size followed the following order : RuxCr y Se z >Ru x W y Se z >Ru x Mo y Se z  Electrochemical studies were done by the RDE  The value of Tafel slope is 120mVdec-1 and exchange current density of around 1×10−5 mAcm−2 and apparent activation energies between 40 and 55 kJ mol−1.  The ORR activity decreased according to the following order : Ru x Mo y Se z >Ru x W y Se z >Ru x Cr y Se z.  The ORR followed the four electron reduction path   RuxWySez electrocatalyst showed poor activity compared toRuxMoySez and RuxCrySez which were considered suitable candidates to be used as cathode Alcantara and Alcantara and Feria, J. Power Sources 192 (2009) 165–169

4.   Kinetics of Ru x Mo y Se z nanoparticles dispersed on carbon powder was studied in 0.5 M H 2 SO 4 electrolyte towards the oxygen reduction reaction (ORR)   Ru x Mo y Se z catalyst was synthesized by decarbonylation of transition-metal carbonyl compounds for 3 h in organic solvent   The powder electro catalysts were characterized by XRD and SEM   Catalyst is composed of uniform agglomerates of nanocrystalline particles with an estimated composition of Ru 6 Mo 1 Se 3, embedded in an amorphous phase  The electrochemical activity was studied by RDE and RRDE) techniques  Tafel slopes for the ORR remained invariant with temperature at −0.116 Vdec−1 with an increase of the charge transfer coefficient in dα/dT = 1.6×10−3  The effect of temperature on the ORR kinetics was analyzed resulting in an apparent activation energy of 45.6±0.5 kJ mol−1 Kinetics and performance of Ru x Mo y Se z nanoparticles as a cathode catalyst

5.  The catalyst generated less than 2.5% hydrogen peroxide during oxygen reduction   The maximum performance achieved for the electro-reduction of oxygen was with a loading of 1.0 mg cm−2 Ru x Mo y Se z 20 wt%/C, arriving to a power density of 240mWcm−2 at 0.3V and 80 ◦C   The catalyst generated less than 2.5% hydrogen peroxide during oxygen reduction Alc´antara and O. Solorza-Feria, Electrochimica Acta 53 (2008) 4981 - 4989

6.   Powder of Ru x Cr y Se z electro catalyst was prepared from decarbonylation of the transition-metal carbonyl compounds in an organic solution containing dissolved selenium   The synthesized catalyst was characterized by XRD, FT-IR, SEM and electroanalytical tools.   The powder catalyst presented high uniformity of cauliflower-like agglomerates of nanocrystalline particles embedded in an amorphous phase   The Tafel slope for the ORR remained constant with temperature at −0.117Vdec−1   The charge transfer coefficient increased in dα/dT = 1.8×10−3   The effect of temperature on the kinetics of ORR was evaluatead and the apparent activation energy of 40.6 kJ mol−1 was determined Ru x Cr y Se z electrocatalyst for oxygen reduction in a polymer electrolyte membrane fuel cell Alc´antara et al., J. Power Sources 157 (2006) 114–120.

7.   A new procedure has been introduced to enhance catalytic activity of ruthenium– selenium electro-catalysts for oxygen reduction, in which materials are treated under hydrogen atmosphere at elevated temperatures   Characterisation using SEM and EDS indicated that the treatment at 400 ◦C made catalysts denser with out effecting their porous nature. This has led to a good degree of crystallinity and an optimum Se:Ru ratio.   The catalyst treated at 400 ◦C gave the highest reduction current (55.9mAcm−2 at −0.4 V) and a low methanol oxidation effect coefficient (3.8%).   The direct methanol fuel cell with the RuSe 400 ◦C cathode catalyst (2 mg RuSe cm−2) generated a power density of 33.8mWcm−2 using 2Mmethanol and 2 bar oxygen at 90 ◦C.   The best sample was compared to the Pt and to the reported Ru–Se catalyst   The influence of a new fabrication procedure on the catalytic activity of Ru–Se catalysts Cheng, Electrochemical Acta 52 (2006) 466–473

8.   Ru-Se-Fe and Ru-Mo-Fe alloy nanoparticles were synthesized from high purity powders (Ru, Se and Mo) by means of the high-energy mechanical alloying   Fe was integrated to the alloys because of the erosion of the mill balls.   The ORR electro catalytic performance of the alloys (lixiviated   or not) was evaluated in a RDE at room temperature   XRD, SEM and TEMwere used for the structural characterization of the materials   Small-particle clusters with granular morphology and nano scale sizes were obtained in all the cases.   Tafel parameters indicated the presence of a first order ORR in both electrocatalytic systems through a 4e- global multi electron transference to form water: O 2 +4 H+ +e−→H 2 O   The electro catalytic activity showed that the mechanical alloying enabled to obtain nanoparticle electro catalysts with good ORR performance   Lixiviation of the mechanical alloying powders has not improved the catalytical responses Effect of the leaching of Ru-Se-Fe and Ru-Mo-Fe obtained by mechanical alloying on electrocatalytical behavior for the oxygen reduction reaction Ezeta et al., J. Alloys and Compounds 483 (2009) 429–431

9.   The effect of CoSe 2 /C nanoparticle loading rate on ORR activity was investigated   H 2 O 2 production using the RDE and the RRDE techniques was carried out   Carbon-supported CoSe 2 nanoparticles with different nominal loading rates were prepared and evaluated by means of XRD   All the catalysts had an OCP value of 0.81V vs. RHE.   H 2 O 2 production during the ORR process decreased with an increase in catalytic layer thickness   This decrease was related to the CoSe 2 loading on the disk electrode.   H 2 O 2 production also decreased with increasing catalytic site density, a phenomenon related to the CoSe 2 loading rate on the carbon substrate.   The cathodic current density significantly increased with increasing catalytic layer thickness, but decreased with increasing catalytic site density.   In the case of 20 wt% CoSe 2 /C nanoparticles at 22gcm−2 it was found that the transfer process involves about 3.5 electrons Oxygen reduction reaction on carbon-supported CoSe 2 nanoparticles in an acidic medium Feng et al., Electrochimica Acta 54 (2009) 5252–5256

10. Fuel cell performance of templated Ru/Se/C-based catalysts Garsuch et al., J. Power Sources 189 (2009) 1008–1011 The catalytic activity of highly porous Ru/Se/C-based catalysts was investigated. Fuel cell measurements were carried out in a 5cm2 cell using pure hydrogen and oxygen at a temperature of 75 ◦C and ambient pressure. Maximum power densities of 100, 144 and 150mWcm−2 were observed for MEA containing of 0.04, 0.12 and 0.22 mgcm−2 Ruthenium, respectively The catalysts were further characterized by XRD, HRTEM and XPS

11. Chalcogenide (S, Se, and Te)-modified ruthenium catalysts prepared by a wet impregnation method demonstrated the electrocatalytic activities in the order of Ru–Te > Ru–Se > Ru–S for the oxygen reduction reaction (ORR) in acidic media The ORR activity of Ru–Te supported on carbon black (Ru–Te/C) significantly depends on the initial Te/Ru atomic ratio The catalyst obtained at a Te/Ru = 2 produced the maximum value of current density, the reaction was confirmed to form a RuTe2 intermetallic compound based on XRD The TEM image of RuTe2/C showed that the loaded RuTe2 particles consist of well-crystallized plate-like particles with diameters of about 10 nm. RRDE) measurements indicated that RuTe2/C generates about 4% H2O2 during the ORR, preferentially proceeding via the four-electron charge transfer pathway to form H2O. RuTe2/C showed a comparable activity with regard to the cathodic current to that of the conventional Pt/C catalyst at the same metal loading. The only lack is onset electrode potential for oxygen reduction by RuTe2/C was more negative than that catalyzed by the commercial Pt/C by about 0.2 V Electrocatalytic properties of ruthenium modified with Te metal for the oxygen reduction reaction Hara et al., Appl. Catal., A: General 340 (2008) 59–66

12.   Powder of nanosized particles of Ru-based (Ru x, Ru x Se y and Ru x Fe y Se z ) clusters were prepared as catalysts for oxygen reduction in 0.5M H 2 SO 4 and for fuel cells prepared by pyrolysis in organic solvent   These electrocatalysts show a high uniformity of agglomerated nanoscale particles   The reaction kinetics were studied using rotating disk electrodes and an enhanced catalytic activity for the powders containing selenium and iron was observed.   The Ru-based electrocatalysts were used as the cathode in a single prototype PEM fuel cell, which was prepared by spray deposition of the catalyst on the surface of Nafion® 117 membranes   The electrochemical performance of each single fuel cell was compared to that of a platinum/platinum conventional membrane electrode assembly (MEA), using hydrogen and oxygen feed streams   A maximum power density of 140mWcm−2, at 80 ◦C with 460mAcm−2 was obtained for the RuxFeySez catalysts; approximately   55% lower power density than that obtained with platinum Electrocatalysis of oxygen reduction on carbon supported Ru-based catalysts in a polymer electrolyte fuel cell Huerta et al., J. Power Sources 153 (2006) 11–17

13.   Catalyst based on a novel ternary non-noble metal chalcogenide, W–Co–Se was synthesized for the ORR in acidic medium   The non-noble metal chalcogenide catalyst was electrochemically stable in the potential range of 0.05–0.8 V vs NHE in 0.5 M H 2 SO 4 aqueous solution   This catalyst demonstrated significant catalytic activity towards the ORR, showing   The ORR onset potential at 0.755 V versus NHE in 0.5 M H2SO4 at 25 C.   high activity might be attributed to the electronic structure of non-noble metals modified by chalcogen Ternary non-noble metal chalcogenide (W–Co–Se) as electrocatalyst for oxygen reduction reaction Lee et al., Electrochemistry Communications 9 (2007) 1704–1708

14.   The chalcogenide samples – as well as the starting chalcogens-free Ru nanoparticle material – were immobilized on a gold disk for XPS characterization.   The oxygen in most of the samples, predominantly from Ru oxides, we conclude that the oxygen on Ru/Smay be located in subsurface sites: the subsurface oxygen.   that the transformation of the oxidized Ru black to metallic Ru required   intensive electrochemical treatment, including hydrogen evolution. In contrast, five cyclic voltammetric scans in the potential range from 0.00 and0.75V versus RHE were sufficient to remove the oxygen forms from Ru/Se and, to a large extent, from Ru/S.   The voltammetric treatment in the 0.00 and 0.75V range also removed   the SeO2 or SOx forms leaving anionic/elemental Se or S on the surface.   Larger amplitude voltammetric cycling, from 0.00 to 1.20V versus   RHE, both Se and S were dissolved and the dissolution process was coincidental with the oxygen growth in/on the Ru sample Chalcogenide oxygen reduction reaction catalysis: X-ray photoelectron spectroscopy with Ru, Ru/Se and Ru/S samples emersed from aqueous media Lewera et al., Electrochimica Acta 52 (2007) 5759–5765

15. Thank you Thank you