| Energy is the main concern in the modern world because no development can be made without or with less energy.Due to the abrupt increase of population and industrial revolutions,the demand for renewable energy has been greatly boosted worldwide.Severe environmental pollution problems and diminishing trend of fossil fuels inspired the researchers,scientists,and policy makers for many decades to explore alternative energy sources to meet the increasing energy demand of the world's population.Hydrogen(H2)as a fuel is considered as clean,sustainable,and environmental friendly fuel concerning renewable energy resources perspectives.Thus,hydrogen production from electrochemical water splitting is considered as one of the important renewable source of energy to reduce the environmental pollution complications and escalate the energy supply and storage from renewables.H2 is used to generate the clean energy with the help of polymer electrolyte membrane water electrolyzers(PEMWE)and fuel cells.But,the H2 production from electrolytic cells is greatly inhibited due to the slow kinetics of oxygen evolution reaction(OER)occurring in the anodic compartment of the electrolytic cell.The OER is a complex and key half-reaction that requires the four electron to complete the reaction followed by the requirement of large overpotential as compared to standard thermodynamic value i.e.,1.23 volts.Currently,noble metal oxides specially,iridium di-oxide(IrO2)and ruthenium di-oxide(RuO2)proved as a state of the art OER catalysts beneficial for the production of hydrogen.These noble metals are very expensive,and scarce elements that obstruct the commercialization of this technology on the industrial scale.Therefore,the minimum utilization of noble metal contents along with the improved activity and durability of the OER composites are considered a great challenge.It needs to be addressed to make the electrocatalysts more and more economical.This will help in making the renewable sources of energy as a primary source in the result of which dependency on conventional fuels will be reduced.In this dissertation,we have used the different transition metal oxides to reduce the amount of noble metal contents in corrosive environment by employing the different facile routes.The systematic summary of all the research findings is given below,High valance transition metal oxide i.e.,MoO3 has been used first time as an anodic catalysts in electrochemistry successfully to the best of our knowledge.OER beneficial mixed oxide composites of molybdenum and iridium oxides have been synthesized by using facile hydrothermal method.Adhered IrO2 nanoparticles over the large particles of MoO3,synergistically possessed the robust nature towards harsh acidic water electrolysis.Mass specific OER activity of iridium active centers was greatly increased by seven-folds,twice the current density and was attributed to electronic modulation of noble metal.Increased surface area and the existence of highly oxidative species in O-1s spectra of IrO2 and two doublet regions in XPS spectra of molybdenum metal were found,accountable for the robust performance of the best composite.Moreover,prepared composite possessing only 30%by weight of the noble metal presented the excellent long term stability for 40,000 seconds.Reduction in the value of the Tafel slope for IM-30 and IrO2 from 77 to 57 mV dec-1 respectively were calculated.The iridium free,acidic-stable,cost-effective,and efficient oxygen evolution reaction electrocatalyst is prepared which is considered as a bottleneck in the quest of high pressure energy production/storage devices worldwide.I have successfully provided the facile approach to synthesize the mixed oxide composite of RuO2 tailored with MoO3.The results showed the 50%percent reduction of noble metal content,2 times enhanced of the activity and showed an excellent durability as compared to pure homemade and commercial state of the art RuO2 have been affirmed by numerous characterization techniques.Enhanced electrochemical performance of best-mixed composite is observed due to the increasing number of oxygen vacancies,electronic distortion and lower oxidation state of noble metal verified by X-ray photoelectron spectroscopy,and reduced value of the Tafel slope.Furthermore,the best composite showed the 7-fold increase in electrochemical surface area,3.2 times improvement in the bulk mass activity,and less value of overpotential.In the continuation of research study,I have synthesized the earth-abundant WO3 coupled with IrO2 as a mixed oxide composite by a two-step chemical method.The 50%reduction in noble metal contents(IW-50)usage followed by twice enhancement in activity,four-folds increase in bulk mass specific activity along with the stability of mixed oxide composite as compared to state of the art IrO2 catalyst were evaluated.The superior performance of mixed oxide composites was perceived due to four times increase in electrochemical surface area,reduction of Tafel slope value,four-fold increase of turn over frequency,electronic distortion in Ir-4f spectrum of IW-50 along with the bridging of lattice oxygen atoms between iridium and tungsten metals.We believe that the conducted research studies in this dissertation will pave the new routes for applicability of the high valance transition metal oxides,i.e.,molybdenum oxide,Tungsten oxide and their derived oxides to cheap and rational designing of electrocatalysts in the field of electrochemistry. |
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