Highly Efficiency Low/Non-Platinum Electrocatalysts Of Cathodic Oxygen Reduction Reaction For Fuel Cells

The increasing consumption of fossil fuels leads the environmental problems such as the greenhouse effect and smog.It is one of great challenges human facing to find a clean and pollution-free alternative energy.Fuel cell is widely used new energy source due to their various types among kinds of clean energy.Proton exchange membrane fuel cell?PEMFC?is a developed device that uses a reaction of H₂/O₂ fuels to form water.Oxygen reduction reaction?ORR?is an extremely important half-reaction in PEMFC that combines a clean energy conversion unit with an electrolytic cell to deliver electricity to the public.A high loading of Pt-based catalyst is required to accrelate the reaction due to the slow kinetic of ORR,so the electrochemical kinetic loss and cost of the cathode account for the largest proportion of fuel cell systems.Due to the scarcity of Pt,the search of catalysts is one of the main tasks of fuel cell technology.The thesis mainly studies low Pt/non-Pt catalysts for ORR.The contents are listed as follows:?1?The development of supports can enhance activity and stability of Pt-based catalyst while reduce costs.TiO₂ is supported on N-doped carbon material by sol-gel method as a carrier of Pt nanoparticles.The highly dispersed Pt nanoparticles are uniformly dispersed on TiO₂,the higher oxygen reduction reaction and hydrogen elvution reaction activities of Pt/TiO₂-NC catalyst are attributed to the enhanced interaction between the metal,the support,and the coordination of the N atoms.Compared with commercial Pt/C,the half-wave potential of Pt/TiO₂-NC has 41 mV positive shift,the electrochemically active area?ECSA?is 1.36 times and mass activity is 3.5 times than that of commercial Pt/C.At the same time,the stability of the catalyst is significantly improved.After 10000 cycles of CV,the Pt/TiO₂-NC presents a long-term stability with no half-wave potential shift and only 2.5%decrese of ECSA.For the HER reaction,it exhibits lower overpotential and higher stability superior to Pt/C.Our findings indicate that the synergy between Pt nanoparticles and TiO₂-NC,as well as the N-doped carbon support plays a key role in improving the electrochemical performances of the Pt/TiO₂-NC composite materials.?2?The development of efficient,inexpensive and stable metal-free electrocatalysts to replace commercial Pt/C still remains a great challenge for application in fuel cells and batteries.In contrast to single-component carbon materials,the ideal heterostructures are highly desired due to the possibility of combining the conductive carbon with porous carbon to simultaneously achieve the good conductivity and large surface area.Herein,an acidification-assisted assembly strategy is presented for embedding the activated carbon spheres into polymer-drived porous carbon networks to the formation of oxygen-functionalized carbon heterostructure with well-contacted interface and ultrahigh surface area of 2042 m² g^-1.The as-obtained heterostructure,only containg elements of C and O,exhibits the remarkably enhanced ORR activity relative to single-component carbons and its excellent performance can be comparable to commercial Pt/C.The enhancement can be attributed to the activation of local sites with oxygenic groups and defects as well as the improved conductivity and enlarged surface area for electron and mass transport.Finally,the successful extension of this strategy suggests its feasibility and universality in constructing various heterostructures,may not be limited for carbon and polymer materials,applicable in versatile fields.