Electrochemical studies of Pd-based anode catalysts in alkaline medium for direct glycerol fuel cells

his study investigates the most effective electrocatalyst for glycerol oxidation reaction (GOR) in alkaline medium for five synthesized electrocatalysts, Pd, PdNi, PdNiO, PdMn3O4 and PdMn3O4NiO, supported on multi-walled carbon nanotubes (MWCNTs) prepared using the polyol method. The particle size and crystalline size of the electrocatalysts were determined using HR-TEM and XRD techniques, respectively, while EDS was used to determine the elemental composition. XRD showed crystalline sizes ranging from 3.4 to 10.1 nm, while HR-TEM revealed particle sizes within the range of 3.4 and 7.2 nm

Multilayered nanoclusters of platinum and gold : insights on electrodeposition pathways, electrocatalysis, surface and bulk compositional properties

Electrochemical, surface and bulk compositional properties of multilayered nanoclusters of Pt and Au, electrochemically deposited on glassy carbon under conditions involving sequential surface–limited redox–replacement reactions (performed at open–circuit) and voltammetric dealloying of templating adlayers of electrodeposited Cu, have been studied in the direction of electrocatalytic applications. Variations in open–circuit potentials during redox–replacement steps indicated thermodynamically–favored formation of Pt(s) and Au(s). Unique bimetallic interfacial active sites, Pt|Au or Au|Pt, were effectively generated as evidenced by their distinct surface electrochemistry and multicomponent X–ray photoelectron spectral features. The bulk and surface–to–near surface distribution of Pt and Au appeared to be influenced by the stoichiometry of the surface redox–replacement reactions and sequential dealloying processes through which the nanoclusters were synthesized. Interactions between metal centers, carbon and oxygen containing surface functional groups on the glassy carbon appeared to have played a significant role in the overall stabilization and catalytic activity of the nanoclusters. Profound effects were also found on interfacial charge–transfer and adsorptive properties involving carbon monoxide and its subsequent electrooxidation to CO2, as well as on the electrocatalytic activity involving formic acid oxidation reaction, where the Pt–rich (Pt|Au) exhibited the highest activity.University of Pretoria and CSIR.http://jes.ecsdl.org/hb2016Chemistr

Electrocatalytic oxidation of ethylene glycol at palladium-bimetallic nanocatalysts (PdSn and PdNi) supported on sulfonate-functionalised multi-walled carbon nanotubes

Electrocatalytic oxidation of ethylene glycol (EG) in alkaline medium using nano-scaled palladium-based bimetallic catalysts (PdM, where M = Ni and Sn) supported on sulfonated multi-walled carbon nanotubes (SF-MWCNTs) is compared. The bimetallic mixture (i.e., SF-MWCNT–PdSnmix and SF-MWCNT–PdNimix) showed better electrocatalysis towards EG oxidation than the SF-MWCNT–Pd. At the SF-MWCNT– PdSnmix platform, oxidation of EG occurred at lower onset and peak potentials, higher current density, and faster kinetics (lower impedance) than at the SF-MWCNT–PdNimix platform. EG oxidation at the SF-MWCNT–PdNimix is more stable than at the SF-MWCNT–PdSnmix. Indeed, Sn is a more favoured cocatalyst with Pd in EG electro-oxidation.CSIR and NRFhttp://www.elsevier.com/locate/jelechemhb201

Fast microwave-assisted solvothermal synthesis of metal nanoparticles (Pd, Ni, Sn) supported on sulfonated MWCNTs : Pd-based bimetallic catalysts for ethanol oxidation in alkaline medium

The preparation of metal nanoparticles (Pd, Ni, Sn) supported on sulfonated multi-walled carbon nanotubes (SF-MWCNTs) using a very rapid microwave-assisted solvothermal strategy has been described. Electrocatalytic behaviour of the SF-MWCNT-Pd and its ‘mixed’ bimetallic electrocatalysts (i.e., SF-MWCNT-PdSnmix and SF-MWCNT-PdNimix) towards ethanol oxidation in alkaline medium was investigated. The result shows that the mixed Pd-based catalysts (obtained by simple ultrasonic-mixing of the individual MWCNT-metal nanocomposites) gave better electrocatalytic activity than their alloy nanoparticles (obtained by co-reduction of metal salts) or Pd alone. The SF-MWCNT platform gave better electrocatalytic performance compared to the unsulfonated and commercial Vulcan carbons. Detailed electrochemical studies (involving cyclic voltammetry, chronoamperometry, chronopotentiometry, and impedance spectroscopy) prove that the electrocatalytic oxidation of ethanol at the SF-MWCNT-PdNimix platform is more stable, occurs at lower potential, gives lower Tafel slopes, with faster charge-transfer kinetics compared to its SF-MWCNT-PdSnmix counterpart. Also, result revealed that SF-MWCNT-PdNimix is more tolerant to CO poisoning than the SF-MWCNT-PdSnmix. The results provide some important insights into the electrochemical response of microwave-synthesised Pd-based bimetallic catalysts for potential application in direct ethanol alkaline fuel cell technology.The CSIR and NRF.http://www.elsevier.com/locate/electact

Effect of inclusion of MOF-polymer composite onto a carbon foam material for hydrogen storage application

Despite the extensive studies done on the remarkable characteristics of metal–organic frameworks (MOFs) for gas storage applications, several issues still preclude their widespread commercial lightweight applications. In most cases, MOF materials are produced in powdery form and often require shaping to attain application-specific properties. Fabrication of MOF-polymer composites is considered an attractive approach for shaping MOF powders. In most cases, the final hybrid material retains the intrinsic adsorbing properties of the pristine MOF coupled with other interesting synergistic features which are sometimes superior to their pristine counterparts. In this regard, the use of porous polymers of intrinsic microporosity (such as PIM-1) has proved to be of interest. However, most of these polymers lack some other important properties such as conductivity, which is of paramount importance in a hydrogen storage system. It is on this basis that our study aimed at direct anchoring of a PIM-1/MOF viscous solution onto a carbon foam (CF) substrate. The effects of PIM-1/UiO-66(Zr) inclusion into CF to the resulting thermal properties (thermal conductivity, thermal diffusivity and volumetric heat capacity) as well as hydrogen uptake capacity was investigated. Contrary to our expectations, the incorporation of PIM-1/UiO-66(Zr) into CF only offered better handling but did not lead to the enhancement of thermal conductivity.The Department of Science and Innovation (DSI) of South Africa towards HySA Infrastructure, National Research Foundation (NRF) for SA/France collaboration funding and the Royal Society—DFID Africa Capacity Building Initiative Programme Grant.http://link.springer.com/journal/109042021-08-09hj2020Chemistr

Utilization of waste tyres pyrolysis oil vapour in the synthesis of zeolite templated carbons (ZTCs) for hydrogen storage application

In this study, we investigated the potential for use of waste tyre pyrolysis oil vapour as a carbon precursor in the synthesis of zeolite templated carbons (ZTC). With Zeolite 13X as the template, the ZTCs were synthesised using two methods namely: 1-step process which involved the carbonization of gaseous carbon precursor in the zeolite template (in this case, ethylene and pyrolysis oil vapour) and the 2-step synthesis method involved the impregnation of zeolite pores with furfural alcohol prior to carbonization of the gaseous carbon precursor. The replication of the zeolite 13X structural ordering was successful using both methods. The 2-step synthesized ZTCs were found to possess the highest specific surface area (3341 m2 g−1) and also had the highest H2 storage capacity (2.5 wt.%). The study therefore confirmed an additional novel strategy for value-addition of waste tyre pyrolysis by-products.The South African Department of Science and Technology (DST) for the financial support towards HySA Infrastructure (Grant No. EIMH01X), the Council for Sci-entific and Industrial Research (CSIR) for providing facilities and National Research Foundation (NRF) for funding the SA-Poland collaborative proj-ect (EIMH04X).http://www.tandfonline.com/loi/lesa202019-05-18hj2018Physic

Polymer-based shaping strategy for zeolite templated carbons (ZTC) and their metal organic framework (MOF) composites for improved hydrogen storage properties

Porous materials such as metal organic frameworks (MOFs), zeolite templated carbons (ZTC), and some porous polymers have endeared the research community for their attractiveness for hydrogen (H2) storage applications. This is due to their remarkable properties, which among others include high surface areas, high porosity, tunability, high thermal, and chemical stability. However, despite their extraordinary properties, their lack of processability due to their inherent powdery nature presents a constraining factor for their full potential for applications in hydrogen storage systems. Additionally, the poor thermal conductivity in some of these materials also contributes to the limitations for their use in this type of application. Therefore, there is a need to develop strategies for producing functional porous composites that are easy-to-handle and with enhanced heat transfer properties while still retaining their high hydrogen adsorption capacities. Herein, we present a simple shaping approach for ZTCs and their MOFs composite using a polymer of intrinsic microporosity (PIM-1). The intrinsic characteristics of the individual porous materials are transferred to the resulting composites leading to improved processability without adversely altering their porous nature. The surface area and hydrogen uptake capacity for the obtained shaped composites were found to be within the range of 1,054–2,433 m2g−1 and 1.22–1.87 H2 wt. %, respectively at 1 bar and 77 K. In summary, the synergistic performance of the obtained materials is comparative to their powder counterparts with additional complementing properties.The Department of Science and Technology (DST) of South Africa toward HySA Infrastructure (Grant No. ENMH01X), National Research Foundation (NRF) for SA/France collaboration funding (Grant No. ENMH20X) and the Royal Society—DFID Africa Capacity Building Initiative Programme Grant (Grant No. AQ150029).http://www.frontiersin.org/Chemistryam2020Chemistr

Preparation of carbon nanofibers/tubes using waste tyres pyrolysis oil and coal fly ash derived catalyst

In this study, two waste materials namely; coal fly ash (CFA) and waste tyres pyrolysis oil, were successfuly utilized in the synthesis of carbon nanofibers/tubes (CNF/Ts). In addition, Fe-rich CFA magnetic fraction (Mag-CFA) and ethylene gas were also used for comparison purposes. The carbons obtained from CFA were found to be anchored on the surface of the cenosphere and consisted of both CNTs and CNFs, whereas those obtained from Mag-CFA consisted of only multi-walled carbon nanotubes (MWCNTs). The study further showed that the type of carbon precursor and support material played an important role in determining the nanocarbon growth mechanism. The findings from this research have demonstrated that it is possible to utilize waste tyres pyrolysis oil vapor as a substitute for some expensive commercial carbonaceous gases.The South African Department of Science and Technology (DST) for the financial support towards HySA Infrastructure (Grant No. HTC004X), the Council for Scientific and Industrial Research (CSIR) for providing facilities and National Research Foundation (NRF) for funding the SA-Poland collaborative project (HTC071X).http://www.tandfonline.com/loi/lesa202019-05-29hj2018Physic

Carbon nanotube-enhanced photoelectrochemical properties of metallo-octacarboxyphthalocyanines

The photoelectrochemistry of metallo-octacarboxyphthalocyanines (MOCPc, where M = Zn or Si(OH)2) integrated with MWCNTs for the development of dye-sensitized solar cells (DSSCs) is reported. The DSSC performance (obtained from the photo-chronoamperometric and photo-impedimetric data) decreased as ZnOCPc > (OH)2SiOCPc. The incorporation of the MWCNTs on the surface of the TiO2 film (MOCPc–MWCNT systems) gave higher photocurrent density than the bare MOCPc complexes. Also, from the EIS results, the MOCPc–MWCNT hybrids gave faster charge transport kinetics (approximately three times faster) compared to the bare MOCPc complexes. The electron lifetime was slightly longer (ca. 6 ms) at the ZnOCPc systems than at the (OH)2SiOCPc system (ca. 4 ms) meaning that the presence of the MWCNTs on the surface of the TiO2 film did not show any significant improvement on preventing charge recombination process

Electrocatalysis Research for Fuel Cells and Hydrogen Production

AbstractThe CSIR undertakes research in the Electrocatalysis of fuel cells and for hydrogen production. The Hydrogen South Africa (HySA) strategy supports research on electrocatalysts due to their importance to the national beneficiation strategy. The work reported here presents choice methods for the production of Platinum Group Metals (PGM) electrocatalysts, which are characterized for their performance. Investigations on the commercial feasibility of such electrocatalysts in the fuel cells including hydrogen production continue to be subject of global interest, to ensure energy security of supply. The paper aims to present possible synthesis routes for PGM electrocatalysts for commercial gains