WREN 2016

The Workshop on Renewable Energy Sources and Nanotechnology

SEMINARS

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Seminar 1: Value-Added Electrochemical and Photochemical Remediation of Carbon Dioxide

Speaker: Krishnan Rajeshwar

 

Summary: Benign substitutes such as oxygenates (e.g., ethanol), burning of any fuel generates the greenhouse gas, carbon dioxide (CO2). In the specific case o Brazil, combustion of sugarcane-derived alcohol fuel will pose long-term climate issues with the inevitable generation of CO2. Thus it is imperative that solutions be quickly found for the remediation of CO2 emissions. This R&D problem becomes especially attractive if value-added products can be generated during the remediation process itself. This talk will specifically

focus on two such related approaches, namely: electrochemical (EC) and photoelectrochemical (PEC) conversion of CO2 to products such as C1-C3 hydrocarbons (e.g., methane) and oxygenates such as alcohols.Of the myriad electrode materials that have been used for the EC and PEC reduction of CO2 in aqueous media, copper oxide/copper interfaces have shown a remarkable range of hydrocarbon and oxygenated products including acids, aldehydes, ketones, and alcohols. This perspective talk highlights experimental evidence for the fact that both EC and PEC reduction scenarios have similar chemical and morphological underpinnings in the in situ formation of copper nanocubes on the (photo) cathode surface. Recent rapid developments in our fundamental understanding of these interfaces and areas requiring further studies are discussed in the light of recent studies in the authors’ laboratories and elsewhere.

Muhammad N. Huda

Seminar 2: Prediction and pure-phase stability of complex solar absorber materials.

Speaker: Muhammad N. Huda

 

Summary: To make solar energy competitive with fossil fuels, sustainable and cost effective solar absorber materials are needed. In this regards, we are particularly interested in multi-cation complex alloy materials as they offer flexible pathways to tune their electronic and optical properties. However, once the material is selected, the primary challenge is to predict whether the material (pristine or doped) can be synthesized as pure-phase in thermodynamic equilibrium conditions. We will present density functional theory (DFT)

studies on three such examples for solar absorber materials: (i) Prediction of new solar absorber materials: CuSnW2O8 (CTTO), (ii) Cu2ZnSnS (Se) (CZTS) and (ii) Bi2Ti2O7 (BTO). We’ll fist present new solar absorber material, CTTO, predicted by our materials discovery protocol. We’ll discuss its electronic and optical properties, and analyze its stability. Chemical potential landscape analysis revealed that CTTO can be synthesized at flexible experimental growth conditions. Finally, like other Cu-based compounds, the formation of Cu vacancies is highly probable, even at Cu-rich growth condition, which could introduce p-type activity in CTTO. Next we’ll show from the chemical potential landscape analysis that the formation of stoichiometric CZTS is practically impossible under thermodynamic equilibrium condition. Our study justifies the experimental growth conditions of CZTS (Zn rich and Cu-poor) for higher solar-to-current conversion efficiency. Growth condition for p-type CZTS and suitable reaction pathways will be presented.In the third example, a resent experiment showed that a transition metal, such as Fe doping, can enhanced photo-current in bismuth titanate (Bi2Ti2O7) up to an impurity concentration of ~1%. Beyond this impurity concentration the photocurrent decreased due to the formation of Fe2O3 phase. Our theoretical study predicted the doping configurations and suitable chemical potential ranges to avoid formation of the Fe2O3 phase in Fe- doped BTO in order to increase the photo -current.

Edson A. Ticianelli

Seminar 3: Structure, performance and stability of cathode and anode nanocatalysts for low-temperature fuel cell reactions.

Speaker: Edson A. Ticianelli

 

Summary: Fuel cells are efficient and nonpolluting electrical power sources based on the oxidation of a fuel (hydrogen, small organic molecules) in the anode and the reduction of oxygen in the cathode. Among several types, the proton exchange membrane (PEMFC) and the alkaline (AFC) systems appear as very promising candidates for applications on automotive, portable or stationary devices. However, there are still significant challenges for their full development, one of them corresponding to the large potential loss at the cathode

caused by the slow rate of the oxygen reduction reaction (ORR). Another is the strong poisoning of the hydrogen oxidation reaction (HOR) in the anode caused by low levels of carbon monoxide when reformed hydrogen is used as fuel. In this presentation, results of characterization of the structure and electronic properties of nanocatalysts formed by Pt-M (M is a 3d or 4d transition metal), supported on WC/C, MoC/C, MoOx/C and MnO2/C and of their performance for the promotion of the ORR and HOR in acid and alkaline electrolytes will be discussed. Materials have been prepared by several techniques and characterized by high-resolution transmission electron microscopy, X-ray diffraction and in situ X-ray absorption near edge structure. The observed electrocatalytic activity of the platinum alloys for the ORR will be discussed in terms of different factors related to the Pt-Pt bond distance, the number of nearest neighbors, the electronic density of states of the Pt 5d band, and the nature and degree of coverage of surface oxide layers. On the other hand, the CO tolerance of the alloyed materials will be discussed in terms of the so-called electronic, bifunctional, partial oxidation, or water gas shift mechanisms. Here, the analyses are made with the used of OLEMS (on line electrochemical mass spectrometry) technique to follow the formation of CH4 and/or CO2 at the fuel cell anode.

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