Stepping Into Renewable Energy Materials: Developing State-of-art Nanocatalysts For Fuel Cells

As renewable promising power generators and having portable nature, the fuel cells have drawn attractions because of their potential in the further development of highlyefficient sustainable energy devices. The deterioration of anode and as well cathode performances suffered by CO poisoning, lower efficiency of accumulative cell performance and economical unfriendly durable materials of such devices hindered their commercialization and world-wide usage. In order to neutralize and cross the huge hump of above all faced challenges, in this thesis we have developed economically favorable, highly efficient and durable nanostructured electrocatalysts for fuel cells, such as direct formic acid fuel cells (DFAFCs) and direct methanol fuel cells (DMFCs).The study includes four parts; in the first part, efficient anode material catalysts for DMFCs have synthsisized. Herein, single phase PtAg bimetallic alloy highly dispersed electrocatalyst on reduced graphene oxide (rGO) by a facile wet chemical co-reduction method. Different kinds of catalysts have been prepared with varying atomic ratios of Pt and Ag. Structural and morphological characterizations of as-synthesized catalysts are performed by transmission electron microscopy (TEM), HRTEM and X-ray diffraction (XRD) and X-ray photoelectron diffraction (XPS) analysis. It is found that single phase PtAg bimetallic nanoparticles are successfully synthesized that are uniformly dispersed and attached on rGO sheets. High-angle annular dark-field scaning TEM (HAADF-STEM) and energy dispersive X-ray spectroscopic (EDX) analysis have also been performed, which confirm the single phase synthesis of uniformly dispersed PtAg bimetallic catalyst. MOR activity and durability has significantly increased by mutual coordination of both the metals in bimetallic nanocatalyst in comparison with the monometallic commercial Pt/C catalyst. The results can be attributed to the collective effects of the PtAg nanoparticles and the enhanced electron transfer characteristics of rGO sheets.In the second part, efficient anode material catalysts for DMFCs have synthsisized.The selectivity and sensitivity of support material can highly improve the catalytic performance of approachable catalysts. As excellent electron transfer material and having intercalation characteristics, reduced graphene oxide/multiwalled carbon nanotubes (rGO/MWCNTs) composite provides synergistic effect on enhancing the electrocatalytic performance of most reliable power devices, the direct formic acid fuel cells. Herein, we reported the synthesis of palladium nanocubes (NCs) supported on rGO/MWCNTs composite, rGO and MWCNTs. The electrocatalytic performance for formic acid oxidation (FAOR) reaction is tested by detailed electrochemical techniques such as cyclic voltametry (CV), chronoamperometery (CA) and electrochemical impadence spectroscopy (EIS) for all supported Pd-NCs catalysts and compared with unsupported Pd-NCs. The significant, systematic and desired improvement in the activity of FAOR is found for Pd-NCs/rGO/MWCNTs catalyst. The order of activity is observed to be Pd-NCs<Pd-NCs/MWCNTs<Pd-NCs/rGO<Pd-NCs/rGO/MWCNTs. The results can be attributed to the synergistic effect induced by the hybrid support material on enhancing the activity of Pd-NCs catalyst.In the third part, we developed a series of ideal electrocatalysts that are highly efficient and durable as anode and cathode material for DMFCs.The highly efficient and durable smart composite material comprising CeO2 grafted homogeneous PtPd bimetallic nanoparticles dispersed on conductive carbon matrix have synthesized. A facile surfactant free synthetic approach has been adopted to develop clean nanocomposite catalysts. The ex-situ and in-situ spectroelectrochemical techniques such as, CV. in-situ FTIR and online DEMS studies respectively verified the excellent catalytic activity of as-developed catalyst towards electro-oxidation of methanol. In addition, the critical and detailed analysis of RDE experimental results proved the superiority of present material for electro-reduction of oxygen along cathode side. The as-synthesized electrocatalyst has proved itself as better substitute over commercial Pt/C catalyst, with enhanced and durable performance as cathodic and anodic catalyst for direct-methanol fuel cells (DMFCs). The obtained remarkable performance of catalysts in present work can be attributed to the accumulative effects of PtPd bimetallic NPs and the enhanced synergistic factors of CeO2 in hybrid material.In the last and fourth part, we developed an ideal electrocatalyst that is highly efficient and durable as anode and cathode material for DFAFCs. The hetero-nanostructures proved to be hot materials due to their multi-functionalities in various catalytic applications. Herein, the basic focus has been devoted on interface chemistry among different domains in the field of catalysis to develop outstanding composite material with exceptional redox and catalytic properties in energy devices such as DFAFCs. The unique nano hybrid material is synthesized by growth of monometallic Pd NPs on MnOx/CeO2 mixed oxides. The complete study as anode and cathode material in DFAFCs was investigated. The strong synergistic effect of mixed oxides improved the performance of monometallic Pd catalyst. The as-designed nanocomposite depicts high profile catalytic efficiency with low cost economical standards.