Graphene Based Catalysts and Electrodes for Fuel Cells
Despite enormous progress in polymer electrolyte membrane (PEM) fuel cells, development of catalysts with maximum activity and durability and minimum loading are still the core challenges. Catalyst supports are also very important in this respect. Generally, proper catalyst support materials must have large specific surface areas to support catalyst nanoparticles, high electrical conductivity to promote fast electron transfer, strong affinity towards the nanoparticles and stability under the operating conditions to provide stable catalyst structures. We employ various carbon materials such as graphene, carbon black, carbon fibers and their hybrids as the catalyst support. We develop graphene based electrodes and electrode fabrication methods to enhance the dispersion, utilization and the durability of the Pt catalyst at the same time to reduce the Pt loading. The reduction of catalyst amount in the electrode without sacrificing the performance and thus lowering the cost of fuel cell is the ultimate goal. Highly uniform and well dispersed graphene supported Pt (Pt/graphene) catalyst nanoparticles are chemically synthesized to be used as the catalyst layer of fuel cell electrodes. Synthesized Pt/graphene electrocatalysts are applied via air-spray or electro-spray to have electrode structure. By the improved technique of our group, PEM fuel cell efficiency increased. That work is carried out as a part of Graphene Flagship Project
Radiation Grafted Membranes for Low Temperature Fuel Cells
Fuel cells are one of the most promising electrochemical power sources both for mobile and stationary applications. Among others, the polymer electrolyte membrane (PEM) fuel cell has received great attention due to their high power density, quick start-up time, pollution free operation and compact structure. The development of cost effective proton exchange membranes to replace the state-of-the-art high cost perfluorinated membranes is an important challenge. The radiation induced grafting, a versatile technique allowing the functionalization of the base material for the introduction of a desired property, offers several advantages. Homogenous, highly conducting and low cost proton exchange membranes have been developed for fuel cells having comparable performance with that of Nafion®.
Radiation Grafted Membranes for High Temperature Fuel Cells
Most of those shortcomings arise when the operation temperature is limited to below 100 °C (typically 60-80 °C), at atmospheric pressure which is in turn limited by the current state-of-the-art membranes such as Nafion® because of its water assisted conduction mechanism. Nafion® membranes have advantages such as high mechanical and chemical stability at temperatures below 100 °C and high proton conductivity in hydrated form as well. However, the water requirement in the membrane limits the operation temperature to below 100 °C in theory. Thus, the synthesis and characterization of proton conducting membranes constitutes a significant step for the development of high temperature PEM fuel cells. Our focus is the preparation of phosphoric acid doped proton exchange membranes to operate at high temperature (especially above boiling point of water) and water free conditions for PEM fuel cells. Owing to a simple manufacturing process, radiation-induced grafting, the procedure that is offered to fabricate high temperature membranes is able to overcome casting (or manufacturing) problems of other high temperature membrane candidates. Nitrogen containing monomers are selected since strong interaction with phosphoric acid to create N-H interaction to operate at high temperature is expected. The resultant membranes exhibit promising thermal and mechanical properties, lower water uptake and encouraging proton conductivity. Moreover, both the ex situ proton conductivity measurements and fuel cell testing prove that these membranes are very promising to operate at high temperature and dry fuel cell operation conditions.
Mixed Cation- and Anion-Exchange Hybrid Membranes for Fuel Cell Applications
Bipolar membrane fuel cells (BPMFCs) can self-humidify to ensure high ionic conductivity and allow the use of non-Pt catalysts. This novel membrane electrode assembly (MEA) represents bipolar (hybrid) membranes composing of both cation (proton) and anion exchange membranes laminated together. Self-humidification is created at the bipolar membrane interface. Anion exchange membranes are the most critical components of a bipolar membrane. Hence, in addition to proton exchange membranes, we report on the design and development of crosslinked anion exchange membranes (AEMs) which are synthesized by radiation grafting and subsequent functionalization (amination and crosslinking). The aim is to verify one-step synthesis of crosslinked AEM for bipolar membrane fuel cells (BPMFCs).
Alp YürümEmre Biçer
Li-ion batteries are the most used electrochemical battery type in mobile applications. In near future, the demand for high energy, high power batteries will increase due to the increasing demand for electric vehicles and renewable energy resources. Therefore, the high energy and high power batteries will be provided by the developments in cathode active materials. Lithium-air (Li-air) batteries are one of the most promising candidates of energy storage for portable applications and electrical vehicles due to their high energy density. However, there are still various problems to be solved and several limitations to overcome for commercialization of Li-air batteries. In this regard, especially the development of catalysts and electrodes, which influence significantly the battery performance, is an important issue. As the battery group here in Sabanci University, we are mainly working on the development and synthesis of novel anode and cathode materials for Li-ion and Li-air batteries. Our competence is on carbon, and metal/metal oxide materials. With our extensive experience in material synthesis, we are able to synthesize unique composite materials and morphologies. These materials, thanks to their structures, perform better and have much higher activities.
Graphene nanocomposites have been cited as a promising candidate for energy conversion and storage applications. We focused on the hydrogen adsorption behavior of these nanocomposites at room temperature and low pressures that are relevant for practical on-board storage systems.
MCM-41, a mesoporous silica material has been also considered for hydrogen storage due to its high surface area, uniform pore size and good adsorption properties.To improve the hydrogen storage capacity of the pure MCM-41, samples were loaded with Pd that is known with its affinity to hydrogen.
Biomass is a sustainable energy source therefore reasearch about extracting raw materials and energy from fast growing plants like grass by thermal and catalytic methods has a significant potential to aid economic and environmental progress.
M. Baysal, K. Bilge, B. Yılmaz, M. Papila, Y. YÜRÜM
Preparation of high surface area activated carbon from waste-biomass of Sunflower piths:
Kinetics and equilibrium studies on the methylene blue adsorption,
Journal of Environmental Chemical Engineering, 6, 1702-1713, 2018.
Sunflower pith (SP), a vast agricultural waste is herein used as a precursor material for highly porous low density activated carbon production. Porosity and flake-like microstructure of the SP in its natural form are shown by micro-computed tomography (Micro-CT). Carbonization process turns the SP into thin, separated carbon flakes of 200 nm thickness. Two types of alkaline based chemical activation with KOH and NaOH are performed to yield SP based activated carbon (AC), K-SPAC and N-SPAC, respectively. Microstructural changes upon carbonization and activation process are elaborated by RAMAN, FTIR and SEM analyses. BET Surface area of the NaOH-activated N-SPAC was calculated as 2690m2/g and was higher than KOH-activated K-SPAC with 2090m2/g. Maximum adsorption capacity of N-SPAC was calculated as 965 mg/g whereas it was 580 mg/g for K-SPAC. Adsorption kinetic studies for N-SPAC revealed that at a low initial concentration of dye (500 mg/L), the pseudo first-order kinetic model was predictive. On the other hand, at high initial MB concentration (1000 mg/ L), the results indicate that the adsorption kinetics follow the Elovich model with intraparticle diffusion as one of the rate-determining steps. In conclusion, overall results suggest that thanks to its highly porous microstructure, the SP is an alternative renewable AC precursor choice for dye removal applications.