Investigation Of Pt Nanoparticle Decorated Polyaniline Derivatives Modified Carbon-based Composite Electrode And Its Application On Electrocatalytic Oxidation Of Methanol And Formic Acid

Fuel cells have long been recognized as a promising technology because it can be operated at a low working temperature,have high energy conversion efficiency and emit a low amount of pollutants.The liquid fuels for transportation application and simplicity of storage have encouraged examination of small organic molecules as alternative energy carriers.Direct methanol fuel cell?DMFC?and direct formic acid fuel cell?DFAFC?have attracted more and more attention due to its several advantages such as the absence of C-C bonds along with the high hydrogen-to-carbon ratio in methanol and formic acid which offers the prospect of reasonable oxidation kinetics and the complete conversion to CO₂ at low operating temperature.Platinum has been considered as the best catalysts for methanol and formic acid oxidation reaction at the anode of DMFC and DFAFC in an acidic medium.However it is well known that Pt is expensive material and limited supply.So to move towards their successful commercialization focusing solely on their catalytic activity is not sufficient enough.Instead,more effort is also required to decrease cost.Up to now,a great deal of interests exists in the development of less expensive materials used as substrates for dispersing platinum nanoparticles.In recent years,carbon materials are very favorable supports for Pt catalysts because of their large specific surface area,good electricity and relative stability.Besides,polyaniline derivates given their high accessible surface area,low resistance and high stability can also act as suitable supports for low temperature fuel cell catalysts.In the present work,carbon paste electrode?CPE?and activated battery carbon doped carbon paste electrode?YBCPE?were prepared.Both CPE and YBCPE were modified by poly?o-anisidine??POA?.These POA-modified CPE and YBCPE electrodes were directly used as substrates for Pt,and then their electrocatalytic activity towards methanol oxidation was studied.Moreover,we have been successfully prepared by the electrodeposition of Pt onto YBCPE and glassy carbon?GC?electrode modified with POA and poly?o-aminophenol??POAP?,respectively.And yielded Pt/POA/YBCPE,Pt/POA/GC,Pt/POAP/YBCPE and Pt/POAP/GC were used for the electrocatalytic oxidation of formic acid.The effect of different electrodes as well as polyaniline derivates matrixs and the prepared ways towards formic acid oxidation were also analyzed and discussed.The main investigations of the work are presented herein.?1?Promoting influence of activated battery carbon in carbon paste electrode on platinum nanoparticles efficiency in methanol electrooxidationThe preparation of activated battery carbon?YBC?doped carbon paste electrode?YBCPE?and carbon paste electrode?CPE?were carried out.The electrochemical properties of YBCPE and CPE were investigated by electrochemical impedance spectroscopy.The electrodes of Pt/YBCPE and Pt/CPE were prepared by electrodeposition of platinum on YBCPE and CPE,respectively.The behavior of electrodeposition of platinum on YBCPE and CPE was studied through the application of theoretical models and the morphology of Pt/YBCPE and Pt/CPE were characterized by SEM.The electrochemical activities of these catalysts towards methanol electrooxidation were examined by cyclic voltammetry.The influence of YBC percentages in YBCPE on the electrode activity and long-term stability of electrodes in methanol electrooxidation was studied.It was shown that the addition of activated battery carbon improved the electrocatalytic activity of Pt catalysts on corresponding YBCPE towards methanol oxidation.?2?Fabrication of Pt/POA/YBCPE composite electrodes and their electrocatalytic activities for methanol oxidationThe POA/CPE and POA/YBCPE?14%?were prepared by electropolymerization of the OA monomer on CPE and YBCPE?14%?electrodes.Pt nanoparticles were incorporated into the electrodes by immersion of the POA modified electrode in H₂PtCl₆ solution.Cyclic voltammetric and electrochemical impedance spectroscopy?EIS?experiments were used for the electrochemical study of Pt/POA/CPE and Pt/POA/YBCPE?14%?electrode.TEM analysis was conducted in order to obtain the shapes of the dispersed Pt nanoparticles on the POA/CPE and POA/YBCPE?14%?.The electrocatalytic oxidation of methanol at the surface of the Pt/POA/YBCPE?14%?and Pt/POA/CPE electrodes were studied.The TEM results demonstrated that Pt nanoparticles deposited on POA matrix were smaller in size and showed better dispersion in comparison with those deposited on YBCPE?14%?and CPE.The fabricated POA/YBCPE?14%?and POA/CPE electrodes significantly enhanced the catalytic efficiency of Pt nanoparticles for methanol oxidation.Moreover,the Pt/POA?16mC?/YBCPE?14%?electrode showed the highest catalytic activity for methanol electrocatalytic oxidation.?3?Formic acid electrocatalytic oxidation on the Pt/CPOA/GC,Pt/CPOA/YBCPE,Pt/POA/GC,Pt/POA/YBCPE composite electrodesThe poly?o-anisidine?was produced by cyclic voltammetry technique?CPOA?and potentiostatic method?POA?for construction of the CPOA/GC,CPOA/YBCPE,POA/GC and POA/YBCPE.Electrodeposition of Pt nanoparticles from 0.5 M H₂SO₄ solution containing 3 mM H₂PtCl₆ solution by using potentiostatic method to fabricate the Pt/CPOA/GC,Pt/CPOA/YBCPE,Pt/POA/GC and Pt/POA/YBCPE.Impact of carbon supported electrode on the electrooxidation activity in a formic acid electrooxidation reaction was investigated.The fabricated electrode Pt/CPOA/YBCPE showed better electrocatalytic activity toward formic electrocatalytic oxidation than Pt/CPOA/GC and the Pt/POA/GC showed better electrocatalytic activity toward formic electrooxidation than Pt/POA/YBCPE.It is found that Pt/POA?40mC?/GC and Pt/POA?40mC?/YBCPE?14%?had better catalytic activity than others.The superior activity was attributed to the preference for the direct oxidation and elimination of the indirect oxidation.?4?The effect of poly?o-anisidine?preparation method on the electrooxidation of formicEffect of poly?o-anisidine?preparation method on the catalysts morphology as well as activity in a formic acid electrooxidation reaction was investigated.The fractal dimension was evaluated by the method of the impedance spectroscopy measurements.It was observed that the the fractal dimension of CPOA/YBCPE and CPOA/GC was higher than the POA/YBCPE and POA/GC,the Pt nanoparticles deposited on POA film were smaller and more homogeneous than Pt nanoparticles deposited on CPOA film.The Pt/POA/GC and Pt/POA/YBCPE showed better electrocatalytic activity than Pt/POA/GC and Pt/CPOA/YBCPE.?5?GC and YBCPE electrodes modified by platinum incorporated in poly?o-aminophenol?film for electrocatalytic oxidation of formic acidCPOAP was potentiodynamically deposited on GC and YBCPE electrodes and then used as the supports for Pt deposition.The electrochemical activity of the as-synthesized composite electrodes for formic acid electrooxidation was investigated by cyclic voltammetry.The formic acid electrooxidation on Pt/CPOAP/GC and Pt/CPOAP/YBCPE electrodes has been compared with that on Pt/CPOA/GC and Pt/CPOA/YBCPE electrodes.The obtained results showed the Pt nanoparticles encapsulated CPOA film were smaller and more homogeneous,and had higher electrocatalytic activity than Pt nanoparticles deposited on CPOAP film.Therefore,it can be specified that Pt/POA catalyst had some advantages such as low cost and stability,ease of preparation,regeneration and stable response.