Preparation and characterization of CoeRu/TiO2/MWCNTs electrocatalysts in PEM hydrogen electrolyzer

The subject of this study is preparation and characterization of hypoehyper d-electrocatalysts with reduced amount of precious metals aimed for water electrolysis. The studied electrocatalysts contain 10% mixed metallic phase (Co:Ru ¼ 1:1 wt., Co:Ru ¼ 4:1 wt. and Co:Ru:Pt ¼ 4:0.5:0.5 wt.), 18% TiO2 as a crystalline anatase deposited on multiwalled carbon nanotubes (MWCNTs). Previously, MWCNTs were activated in 28% nitric acid. As a reference electrocatalyst for hydrogen evolution reaction, corresponding electrocatalysts with pure Pt metallic phase and mixed CoPt (Co:Pt ¼ 1:1 wt.) metallic phase were prepared. Also, as a reference electrocatalyst for oxygen evolution reaction, electrocatalyst with pure Ru metallic phase was prepared. The prepared electrocatalysts were structurally characterized by means of XPS, XRD,TEM, SEM and FTIR analysis. Electrochemical characterization was performed by means of cyclic voltammetry and potentiodynamic method in the PEM hydrogen electrolyzer. The range of the catalytic activity for hydrogen evolution of studied electrocatalysts was the following: CoRuPt (4:0.5:0.5) > CoPt (1:1) > Pt > CoRu (1:1) > CoRu (4:1). The order of the catalytic activity for oxygen evolution was the following: CoRu (1:1) > Ru > CoRu (4:1) > Pt > CoRuPt (4:0.5:0.5) > CoPt (1:1)

Токсични елементи во ориз, пченично брашно и производи од брашно од македонскиот пазар

The safety of the cereal products is of high nutritional and toxicological interest, since the cereal industry and its products have a big economic and social importance worldwide. In this pilot research the presence and the content of toxic trace elements arsenic, cadmium and lead in three samples of rice: 11,67+5,69mg/kg, 25,67+6,43mg/kg, 47,67+18,01mg/kg for As, Cd and Pb respectively, wheat flour: 7+5mg/kg, 9+1,73mg/kg, 69,92+16,92mg/kg and flour products (bread: 9,33+2,08mg/kg, 6,67+0,58mg/kg, 36+3,6mg/kg, pasta: 1,61+1,15mg/kg, 2,67+2,08mg/kg, 30+7mg/kg and tea biscuits: 4,67+4,04mg/kg, 1,33+0,58mg/kg, 53+9,64mg/kg for As, Cd and Pb respectively) produced by three different manufacturers from Macedonia was determined by applying the hydride generation and electrothermal atomic absorption spectrometry with wet digestion. In this research the contribution to the average daily intake for toxic elements through daily intake of cereal and cereal products (20% of the all-day meal) has been determined. The contribution of As (9,86%), Cd (10,02%) and Pb (11,39%) compared to the average daily intake and the PTDI was low, which indicates that these products are safe for consumption concerning the examined toxic elements. The levels of the toxic elements in the samples of Macedonian rice, wheat flour, bread, pasta and tea biscuits are comparable to those obtained from various parts of the world and their consumption does not pose any health risks.Безбедноста на житата и житните производи е од големо нутритивно и токсиколошко значење, бидејќи житната индустрија и нејзините производи имаат голема економска и социјална важност на светско ниво. Во ова пилот истражување е испитана концентрацијата на токсичните елементи во траги арсен, кадмиум и олово, во три мостри од различни производители на ориз: 11,67+5,69mg/kg, 25,67+6,43mg/kg, 47,67+18,01mg/kg, пченично брашно: 7+5mg/kg, 9+1,73mg/kg, 69,92+16,92mg/kg за As, Cd и Pb, соодветно, и производи од брашно (леб: 9,33+2,08mg/kg, 6,67+0,58mg/kg, 36+3,6mg/kg, тестенини: 1,61+1,15mg/kg, 2,67+2,08mg/kg, 30+7mg/kg и чајни колачи: 4,67+4,04mg/kg, 1,33+0,58mg/kg, 53+9,64mg/kg за As, Cd и Pb, соодветно) од македонскиот пазар, со употреба на хидридно генерирачка и електротермичка атомска апсорпциона спектрометрија со мокра дигестија. Извршена е пресметка на учеството во просечниот дневен внес за токсични елементи внесени преку дневна консумација на жито и производи од жито (20% од целодневниот оброк). Придонесот на As (9,86%), Cd (10,02%) и Pb (11,39 %) спореден со просечниот дневен внес и прифатливиот толериран дневен внес, PTDI, беше низок, што покажува дека овие производи се безбедни за употреба во однос на испитаните токсични елементи. Нивоата на токсичните елементи во мострите на македонскиот ориз, пченично брашно и производи од брашно се споредливи со резултатите добиени од различни делови од светот и нивниот внес не претставува здравствен ризик за потрошувачите

Electrocatalysts in the last 30 years – from precious metals to cheaper but sophisticated complex systems

The paper is concerned with the advance and diversification of materials used as electrodes for evolution of chlorine, hydrogen and oxygen. In the first part a survey is given of our research in the field of electrocatalysis 30 years ago, when Ru and other precious metals were the exclusive electrocatalyst materials. A brief scope of the achievements of electrocatalysis in that period is given as well. The second part deals with our recent research on formulation and characterization of a new class of electrocatalysts, based on a combination of non-precious metals, but still exhibiting an ability to promote hydrogen evolution reaction as successful as platinum and other precious metals are. Among the produced (non-platinum) catalysts the best performance for the hydrogen evolution reaction was measured at the electrocatalyst containing Co or CoNi as hyper d phase and TiO2 as hypo d phase. A typical formulation of the electrodes is, e.g.: 18% (TiO2) alloyed with 10% Co and applied on a substrat of carbon powder (Vulcan XC-72). At this electrocatalyst hydrogen evolution overpotential at 10 mA·cm–2 was 40 mV higher than that on a corresponding electrode containing platinum as hyper d phase. For both electrocatalyst systems of interest analysis is made and aimed to recognize the sources that cause the electrocatalytic activity. This is the proper way how to use the acquired knowledge for further improvement of the existing materials or/and to discover new ones. Key words: electrocatalysis; hydrogen evolution; hypo-hyper d-electrocatalyst

Improvement of performances of complex non-platinum electrode materials for hydrogen evolution

Abstract 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% TiO2 +C. All materials were prepared of amorphous or crystalline TiO2, 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 TiO2 into anatase form lowers the HER overpotential for 60mV. Introduction of MWCNTs was even more effective, lowering η for 120mV. Co addition to metallic phase lowers η for utmost 195mV. Combined modification of TiO2 and carbon substrate lowers η for 145mV, while the complete modification of all three catalyst’s components was the most effective with 230mV decrease of overpotential. © 2006 Elsevier Ltd. All rights reserved. Keywords: Hydrogen evolution; Hypo–hyper d-electrocatalysts; Non-platinum metal

Детекција и анализа на стопанските експлозиви по нивното активирање - експлозија

Во трудот се вршени испитувања, односно детекција на стопанските експлозиви после нивната експлозија. За таа цел извршено е активирање на 1 кг стопански експлозив амонекс. Активирањето е извршено со стандардно средство за иницирање. По експлоатацијата, на разни растојанија, е земен брис. Во двете проби со помош на методот на течна хроматографија регистрирано е присуство на амониум нитрат, тринитротолуен и хексоген

Modifications for the improvement of catalyst materials for hydrogen evolution

Abstract: The structural and electrocatalytic characteristics of composite materials based on non-precious metals were studied. Precursors of metallic phase (Ni, Co or CoNi) and oxide phase (TiO2) were grafted on a carbon substrate (Vulcan XC-72) by the sol–gel procedure and thermally treated at 250 ºC. Ni and CoNi crystals of 10–20 nm were produced, in contrast the Co and TiO2 were amorphous. The dissimilar electronic character of the components gives rise to a significant electrocatalytic activity for the hydrogen evolution reaction (HER), even in the basic series of prepared materials. Further improvement of the catalysts was achieved by modification of all three components. Hence, Mo was added into the metallic phase, TiO2 was converted into the crystalline form and multiwall carbon nanotubes (MWCNTs) were used instead of carbon particles. The improvement, expressed in terms of the lowering the hydrogen evolution overpotential at 60 mA cm-2, was the most pronounced in the Ni-based systems grafted on MWCNTs (120 mV lower HER overpotential) compared to 60 mV in case of Ni-based systems grafted on crystalline TiO2 (TiO2 prepared at 450 ºC) and of Ni-based systems containing 25 at.% Mo. Nevertheless, even with the realized enhancement, of all the tested materials, the Co-based systems remained superior HER catalysts. Keywords: composite electrocatalysts, hydrogen evolution, electronic interaction, real surface area

Study of structural and electrochemical characteristics of Co-based hypo–hyper d-electrocatalysts for hydrogen evolution

Abstract 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 TiO2 and Vulcan XC-72, by sol–gel procedure. A number of modifications were applied aimed at improving the materials performances: (i) TiO2 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 TiO2 into anatase form lowers the HER overpotential (η) for 15mV at 60mAcm−2. Introduction of MWCNTs lowered η for 30mV, while addition of Mo to metallic phase for 40mV. The complete modification of all three catalyst’s components (10% MoCo3 + 18% anatase + MWCNTs) was the most effective with 60mV decrease of overpotential. Characterization was made by XRD, SEM, IR and XPS methods. Surface area was measured by means of cyclic voltammetry. © 2007 Elsevier Ltd. All rights reserved. Keywords: Hydrogen evolution; Hypo–hyper d-electrocatalysis; Co-based electrocatalyst

Избор на растворувач за идентификација на бризантните експлозивни материи

Вршени се испитувања, односно идентификација на бризантни експлозивни материи кои се употребуваат за минирање во рударството. За таа цел извршено е активирање на 1 кг. бризантен експлозив, познат под името амонекс. Активирањето е извршено со стандардно средство за иницирање..

Co-Magneli phases electrocatalysts for hydrogen/oxygen evolution

The 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 TiO2 (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

Effect of activation/purification of multiwalled carbon nanotubes (MWCNTs)on the activity of non-platinum based hypo-hyper d-electrocatalysts for hydrogen evolution

Commercial multiwalled carbon nanotubes (MWCNTs) were used as a catalyst support for non-platinum hypo-hyper d-electrocatalysts. In order to improve the performance of these catalysts, activation/ purification of MWCNTs in acid medium (HNO3) was carried out. The physical and surface changes of MWCNTs were investigated by DTA/TGA analysis, Raman spectroscopy, and cyclic voltammetry. Structural changes of the electrocatalysts were observed by infrared spectroscopy and SEM. Their use as a support for electrocatalysts for hydrogen evolution was demonstrated, and shown to be more suitable compared to the traditional carbon support material � carbon black (Vulcan XC-72). The electrocatalysts consisted of 10% Co + 18% TiO2 + MWCNTs. Activation/purification removes the amorphous carbon phase in theMWCNTs. As a result of both shortening and opening of carbon nanotubes, better dispersion of metallic particles (the active catalytic centers) was achieved. Thus, trans-particle and inter-particle porosity of the electrocatalytic material was improved, implying increase of catalytic activity for hydrogen evolution