Structural and electrochemical characteristics of hypo-hyper d-electrocatalytic materials aimed for preparation of electrodes for hydrogen evolution were studied and modified in order to improve their performances. All studied materials were of general composition 10% Ni + 18% TiO 2 + C.All materials were prepared of amorphous or crystalline TiO 2 , crystalline Ni or NiCo (10-20 nm) and Vulcan XC-72, by sol-gel procedure. Both, material's intrinsic catalytic activity and surface area were affected by applied modifications. As a result, the electrocatalytic activity was improved, e.g. transformation of TiO 2 into anatase form lowers the HER overpotential for 60 mV. Introduction of MWCNTs was even more effective, lowering η for 120 mV. Co addition to metallic phase lowers η for utmost 195 mV.Combined modification of TiO 2 and carbon substrate lowers η for 145 mV, while the complete modification of all three catalyst's components was the most effective with 230 mV decrease of overpotential.
Structural and electrochemical characteristics of hypo-hyper d-electrocatalytic materials aimed for preparation of electrodes for hydrogen evolution were studied. The basic catalytic material was prepared of 10% amorphous Co (grain size <2 nm), 18% amorphous TiO 2 and Vulcan XC-72, by sol-gel procedure. A number of modifications were applied aimed at improving the materials performances: (i) TiO 2 was transformed into anatase by heating at 480 • C for 1 h, (ii) multiwalled carbon nanotubes (MWCNT) were used as a catalyst support instead of Vulcan XC-72 and (iii) Mo was added to Co phase in a quantity of 25 at.% (Mo:Co = 1:3).Both, material's intrinsic catalytic activity and surface area were affected by these modifications. As a result, the electrocatalytic activity for hydrogen evolution was improved, e.g. transformation of TiO 2 into anatase form lowers the HER overpotential (η) for 15 mV at 60 mA cm −2 . Introduction of MWCNTs lowered η for 30 mV, while addition of Mo to metallic phase for 40 mV.The complete modification of all three catalyst's components (10% MoCo 3 + 18% anatase + MWCNTs) was the most effective with 60 mV decrease of overpotential.Characterization was made by XRD, SEM, IR and XPS methods. Surface area was measured by means of cyclic voltammetry.
were studied by means of XRD, TEM, SEM and FTIR. The electrocatalytic activity was assessed in aqueous alkaline and polymer acidic electrolytes by means of steady-state galvanostatic method. It was found that Co strongly affects the platinum particle size. The addition of Co reduces platinum particle's size from 11 nm (in pure Pt metallic system) to 4 nm (in both systems 4:1 and 1:1), i.e. almost by 3 times. The corresponding increase of the surface area and the number of the active catalytic centres improves the efficiency, despite the fact that the amount of used platinum was decreased up to 5 times. The catalyst based on CoPt (1:1) performed the best, while the activity of the pure platinum and CoPt (4:1) systems were very close. Generally, the studied electrocatalysts have shown good and stable performances for hydrogen evolution in PEM electrochemical cell. The influence of the hydrogen electrodes under investigation on the water electrolysis efficiency at current density of 0.3 A cm À2 was assessed, using previous data oxygen evolution on IrO x electrode.Related to the performances of commercial Pt (ELAT) electrode, when hydrogen electrodes with the prepared mixed electrocatalysts were used, the water electrolysis efficiency was only 5% lower for CoPt (1:1), nearly 10% lower for CoPt (4:1) and 13% lower in the case of pure Co-based electrocatalyst.
Ebonex CoHydrogen evolution Oxygen evolution a b s t r a c tThe subject of this work is the use of non-stoichiometric titanium oxides e Magneli phases as support material of Co-based electrocatalysts aimed for hydrogen/oxygen evolution reaction. Commercial micro-scaled Ebonex (Altraverda, UK) was mechanically treated for 4, 8, 12, 16 and 20 h and further Co metallic phase was grafted by sol-gel method.Morphology of Co/Ebonex electrocatalysts was observed by means of TEM and SEM microscopy, while electrochemical behavior by means of cyclic voltammetry and steadystate galvanostatic method.As the duration of mechanical treatment increases, the size of Magneli phases decreases, and consequently catalytic activity of the corresponding electrocatalysts increases.Structural characteristics of the electrocatalysts deposited on Ebonex treated for 16 and 20 h are very similar. Also, these electrocatalysts show similar electrocatalytic activity for both hydrogen and oxygen evolution reaction. So, optimal duration of mechanical treatment of Magneli phases is in the range of 16e20 h.Catalytic activity for hydrogen evolution of the studied electrocatalysts is inferior related to the corresponding catalysts deposited on carbonaceous support materials such as activated multiwalled carbon nanotubes or Vulcan XC-72 þ TiO 2 (anatase). This inferiority is due to lower real surface area of the Magneli phases.Catalytic behavior for oxygen evolution achieves its maximal value even at the catalyst deposited on Ebonex treated for 12 h and it is very promising related to the similar electrocatalytic system such as CoPt/Ebonex. ª 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. IntroductionRecent intensive development of hydrogen economy as an alternative energy system in the future imposes invention and research on new effective electrode materials. The modern electrode materials are composed of nanostructured catalytic phase dispersed over the support material that has to possess several very important characteristics, such as: i) highly developed surface area to provide better dispersion of the nano-scaled catalytic particles; ii) high electric conductivity to allow efficient electron transfer to ions involved in the electrochemical reactions, iii) mechanical and chemical stability and iv) to improve intrinsic catalytic activity of the active catalytic phase through the strong metalesupport interaction (SMSI) [1,2]. Carbon nanostructured materials such as carbon blacks are commercially the most used support material [3,4], * Corresponding author. Tel./fax: þ389 2 3064 392. E-mail address: pericap@tmf.ukim.edu.mk (P. Paunovi c).A v a i l a b l e a t w w w . s c i e n c e d i r e c t . c o m j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / h e i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y 3 5 ( 2 0 1 0 ) 1 0 0 7 3 e1 0 0 8 0
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