Improving The Electrocatalytic Performances Of Catalysts By Engineering The Electronic Structures

Fuel cell is an electrochemical device which can convert chemical energy into to electricity.Compared with internal combustion engine and steam engine the fuel cell has higher conversion efficiency and lower pollution.The energy conversion in fuel cells is dependent on the oxidation of fuel and reduction of oxygen,both of which need.electrocatalysts to catalyze the reactions.However,the oxygen reduction reaction(ORR)is kinetically sluggish.Therefore,high potential ORR catalyst is essential to the overall performance of the fuel cell.State-to-art ORR electrocatalyst are those based on Pt and its alloys.Therefore,developing new inexpensive electrocatalysts for ORR is very demanding.This thesis is committed to develop palladium based ORR catalysts.The research comprises synthesis of Pd nano cubes,W doping on the surface of the Pd nanocubes,characterization and electrochemical test.The first chapter of the thesis is focused on the basics of electrochemistry.The second chapter of the thesis is about W doped Pd catalyst i.e.boosting the Electrocatalytic Activities of Pd-Based Electrocatalyst by Surface-Doping Engineering.As the development of active and durable Pd-based electrocatalysts with well-defined microstructure is of great importance to both the catalytic applications and fundamental understanding.Herein,we report a surface-doping process to prepare well-defined W-doped Pd nanocubes with the tunable atomic percent of W from 0 to 1.5%by using the Pd nanocubes as seeds.The obtained 1.2%W-doped Pd nanocubes/C exhibited greatly enhanced electrocatalytic performance toward oxygen reduction reaction(ORR)in alkaline media,presenting an enhancement factor of 4.7 in specific activity and 2.5 in mass activity with respect to those of commercial Pt/C catalyst,respectively.The downshift of d-band center due to the negative charge transfer from W to Pd intrinsically accounts for such improvement in activity by weakening the adsorption of reaction intermediates.Besides,the 1.2%W-doped Pd nanocubes/C showed a superior catalytic properties toward ethanol oxidation reaction,showing a great potential to serve as a bifunctional electrocatalyst in fuel cells.The third chapter is about electrochemical reduction of CO2 over metal and metal free catalyst;recent progress and future perspective.Research in the area of electrocatalytic reduction of CO2 to value-added products has grown briskly in the past few decades.This is due to the increasing amount of CO2 in the atmosphere and a steady rise in global fuel demand.Serious efforts are urgently needed to minimize to CO2 emission and enhance sources of global energy demand.Electrochemical reduction(ECR)of CO2 is considered to be the best solution which not only reduces the increasing CO2 accumulation but also produces fuels and chemicals.Sluggish kinetics,high over potential,low selectivity,low durability and competitive side reactions are the focal issues,to overcome these problems an efficient electrocatalyst is needed.Here in this mini review we had tried to discuss the fundamental factors that greatly influences catalytic activity of the catalyst in the light of updated experimental and computationaldata,which include size,crystal plane,grain boundary,metal metal-oxide interface and finally a brief note on metal free catalyst and future perspective of ECR of CO2.In the fourth chapter we report a doping process to prepare well-defined Fe-doped NiOOH nanosheets with the tunable molar ratio of Fe from 0 to 0.4 by using single pot synthesis.The obtained Ni0.7Fe0.3OOH nanosheets/C exhibited greatly enhanced electrocatalytic performance toward oxygen evolution reaction(OER)in alkaline media with overpotential of 265 mV to generate 10 mA cm-2 current density in 1 M KOH and is able to retain excellent performance over 15 hours without obvious degradation.The Tafel slope for Ni0.7Fe0.3OOH was 44.8 mV/decade.