Development of non-noble (Co-N/MWCNT) and polybenzimidazole-modified (Pt-PBİ/MWCNT) electrocatalysts for high-temperature PEM fuel cell applications

2020
Eren, Enis Oğuzhan
Due to the extremely high cost of platinum group metals, the development of highly efficient, non-noble electrocatalysts, especially for the oxygen reduction reaction (ORR) is essential for the commercialization. In recent studies, state-of-the-art Metal-N-C (Metal = Fe or Co) catalysts are considered as promising alternatives to expensive Pt/C catalysts because of their excellent electrochemical and physical properties. They can somehow provide decent mass activity and electrochemical performance with considerably low material and synthesis cost. In this thesis, the main course is the development of a non-noble, high-performance Co-N/MWCNT electrocatalyst for high-temperature proton exchange membrane fuel cell (HT-PEMFCs) application, and the second course is the development of polybenzimidazole (PBI) modified carbon-nanotubes as a support material for platinum-based electrocatalysts to increase catalytic durability at elevated temperatures. Upon completion of the studies, synthesis of the Co-N/MWCNT catalyst with a high-temperature pyrolysis method was successfully demonstrated by XPS, ToF- SIMS, XRD, Raman, and HR-TEM analysis. Results showed that the uniform dispersion of Co nanoparticles and the formation of active pyridinic Co-N4 sites v were appropriately achieved. It is believed that the formation of stable Pyridinic-N sites could promote more electron pathways through the ORR, and increases the catalyst’s stability. Rotating disc electrode (RDE) analysis demonstrated that the kinetics of the Co-N/MWCNT catalyst is sufficient enough to operate as a cathode for a typical PEM fuel cell operation. From the HT-PEMFC test results, at the 150°C and 160°C, the peak current/power density of the cobalt-based MEA was somehow higher than that of the commercial Pt/C. The only drawback is the stability issue at higher temperatures (170°C or more) in an acidic medium. Results partially confirmed that the Co-N/MWCNT catalyst could be the promising alternative to replace noble Pt/C catalysts at the cathode side. In the sub-study, polybenzimidazole wrapped carbon-nanotubes and microwave- assisted reduction of Pt nanoparticles were successfully characterized by TGA, XPS, XRD, and TEM analysis. Modifying carbon-nanotubes through the polybenzimidazole film ensured fine (about 2 – 5 nm) and uniform dispersion of Pt nanoparticles. Cyclic voltammetry (CV) analysis concluded that the Pt- PBI/MWCNT catalyst had a 43 m2·g-1 of electrochemically active surface area (ECSA) to catalyze hydrogen oxidation, which is parallel to the literature but slightly lower than that of commercial Pt/C and Pt/MWCNT catalysts due to hydrophobic behavior of PBI molecules in an aqueous electrolyte. On the other hand, it has shown superior durability compared with the commercial Pt/C and Pt/MWCNT. After the 1000th CV, it has retained almost 80% of its initial ECSA, which makes the Pt-PBI/MWCNT is much more durable than the Pt/C and Pt/MWCNT. However, HT-PEMFC tests indicated that the peak current/power density values of the PBI-modified catalyst were lower than that of commercial- grade Pt/C, suggesting that some balance between durability and performance has to be taken into consideration.

Suggestions

Development of anodes for direct oxidation of methane fuel in solid oxide fuel cells
Akdeniz, Yelda; Timurkutluk, Bora; Timurkutluk, Cigdem (2016-06-22)
In addition to pure hydrogen, solid oxide fuel cells (SOFCs) can utilize hydrocarbons as a fuel. However, conventional Ni-based anodes exhibit an excellent catalytic activity towards the hydrocarbon cracking reaction and thus the carbon deposition occurs in the anode. The deposited carbons quickly deactivate the anode irreversibly by covering the active surface of the anode catalyst. As a result, a significant degradation in the cell performance can be seen. In this study, the anode structure is modified by...
Modeling and sensitivity analysis of high temperature PEM fuel cells by using Comsol Multiphysics
Sezgin, Berna; Caglayan, Dilara Gulcin; DEVRİM, YILSER; Steenberg, Thomas; Eroğlu, İnci (2016-06-22)
The objective of this study is to observe the effect of the critical design parameters, velocities of inlet gases (hydrogen and air) and the conductivity of polymer membrane, on the performance of a high temperature PEM fuel cell. A consistent and systematic mathematical model is developed in order to study the effect of these parameters. The model is applied to an isothermal, steady state, three-dimensional PEM fuel cell in order to observe concentration profiles, current density profiles and polarization ...
MODELING OF BIPOLAR PLATES FOR PROTON EXCHANGE MEMBRANE FUEL CELLS
Ekiz, Ahmet; Camci, Talha; Turkmen, Ibrahim; SANKIR, MEHMET; USLU, SITKI; Baker, Derek Keıth; Agar, Ertan (2011-09-01)
Fuel cell technology is one of the most economic and efficient ways to utilize hydrogen energy. Various types of fuel cells are present regarding the fuel type and amount of power produced. Among these, proton exchange membrane fuel cells (PEMFCs) are very promising. In this work, a 2D proton exchange membrane fuel cell unit cell was modeled using Comsol Multiphysics software. Cell section was taken parallel to flow direction. Obstacles with various geometries were placed in the flow channel in order to for...
Development of non-noble Co–N–C electrocatalyst for high-temperature proton exchange membrane fuel cells
Eren, Enis Oğuzhan; Özkan, Necati; Devrim, Yılser (Elsevier BV, 2020-11-27)
© 2020 Hydrogen Energy Publications LLCThe development of a non-noble Co–N/MWCNT (MWCNT = multi-walled carbon nanotubes) electrocatalyst is achieved through the high-temperature pyrolysis method and successfully characterized by five-step physico-chemical analysis. By utilizing high-resolution analytical surface characterization methods, the chemical states of elements are determined, and the presence of Co-Nx sites is confirmed. ORR activity of a Co–N/MWCNT is found to be auspicious. The maximum number of ...
Modeling of a high temperature PEM fuel cell
Sezgin, Berna; Eroğlu, İnci; Devrim, Yılser; Department of Chemical Engineering (2016)
High temperature polymer electrolyte membrane fuel cells (HT-PEMFC) are considered as the next generation of fuel cells since high temperature operation for PEM fuel cells has several advantages such as single phase operation, high carbon monoxide tolerance, low or zero carbon emission and removal of some equipment from the system. In order to obtain high performances, HT-PEMFC systems should be optimized in terms of dimensions, materials, operating conditions and other parameters. Modeling can help to pre-...
Citation Formats
E. O. Eren, “Development of non-noble (Co-N/MWCNT) and polybenzimidazole-modified (Pt-PBİ/MWCNT) electrocatalysts for high-temperature PEM fuel cell applications,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Polymer Science and Technology., Middle East Technical University, 2020.