Preparation, Structure And Properties Of ORR And OER Catalysts Based On Sodium Alginate

Abundant and environmental biomass has great potential applications in electrochemical catalysis. Sodium alginate(SA) is commonly known as a kind of natural polysaccharide extracted from brown algae. The SA can covert to hydrogels followed by coordinating with the multivalent metal cations and be confined within an “egg-box” structure. In this thesis, we have used SA as precursors and done the following different three part research:Hydrogels with the mixed ions Co2+ and Ni2+ were prepared by using SA and carbon nanotubes as raw materials and introduing Co and Ni metal precersors. Then, aerogels was obtained by dehydrated hydrogels via a freeze-drying process. Finally, after calcined in NH3 atmosphere and oxidized in air, a metal and metal oxide carbon aerogels(Ni/NiO/NiCo2O4/N-CNT-As) was obtained. Apparently, the Ni/NiO/NiCo2O4 nanoparticles(NPs) are supported on the highly porous 3D N-CNT-As and N-doped amorphous carbon is also observed in Ni/NiO/NiCo2O4/N-CNT-As. We tested their catalytic performance as bifunctional electrocatalyst including both OER and ORR and as air electrode of Zn–air battery. The resultant hybrid shows bifunctional catalytic activities. Moreover, the Zn–air battery fabricated with the hybrid nanoaerogel displays very high energy efficiency(58.5%) and long-term stability.Hydrogels with the Fe3+, Co2+, Ni2+ were prepared by using SA and carbon nanotubes as raw materials and introduing Fe, Co, Ni metal precersors. Then, aerogels was obtained by dehydrated hydrogels via a freeze-drying process. Finally, after calcined in NH3 atmosphere, a metal or metal nitride carbon aerogels(Fe2N/N-CNTAs, Co/N-CNTAs, Ni/N-CNTAs) was obtained. Fe2 N, Co and Ni NPs are supported on the highly porous 3D N-CNT-As. Interestingly, the Fe-alginate, Co-alginate and Ni-alginate “egg-box” were converted to the high-density N-doped amorphous carbon shell to encapsulate Fe2 N, Co and Ni NPs. We tested their catalytic performance as cathode catalysts of fuel cell. The Fe2N/N-CNTAs and Co/N-CNTAs show similar onset potential(0.02 and 0 V) and half-wave potential(-0.147 and-0.159 V) with the commercially available Pt/C(0.02 V,-0.133 V). Furthermore, the Fe2N/N-CNTAs and Co/N-CNTAs exhibit very good methanol-crossover and durability, which are better than the commercial Pt/C.1D nanomaterials of different mass of alginate were prepared by using SA and AAO membrane, which were used to prepared hydrogels with ethanol or ultra-pure water solution of Co2+. Then, 1D nanomaterials were obtained by dehydrating hydrogels via a drying process. and calcining in NH3 atmosphere. We tested their ORR catalytic performance. Interestingly, 1 wt% SA solution and Co2+ treated by ethanol(1-SA-Co/ethanol) displayed substantially the highest activity of ORR.