Hemin-based Catalytic Layer Materials And Gel-electrolyte For Al-air Batteries

As a kind of metal-air batteries,Al-air batteries（AABs）have attracted much attention by many researchers because of their high theoretical energy density,environmentally friendly discharge products,and low cost of Al sheets.Alkaline electrolytes are mainly used in AABs at present,however,it faces many challenges,such as expensive noble metal-based catalysts,corrosive passivation of Al sheets,hydrogen evolution,serious self-discharge,and weak carbon dioxide resistance,limiting the commercialization of AABs.In this thesis,the materials and devices are developed to address some of the above-mentioned problems.1.Design and synthesis of Hemin-based trinity catalytic layer materials.Hemin-based trinity catalytic layer materials were designed and synthesized.Hemin is a natural iron porphyrin,with Fe-N-C structure to catalyze the oxygen reduction reactions（ORR）.At the same time,the porphyrin ring can conduct electrons,and the carboxyl functional group can conduct ions,in a Hemin molecule.The Fe-N-C catalytic center,the electron transfer ability,as well as the ion conducting functional groups,endows all the characteristics of a successful ORR.Therefore,Hemin and Norbornene（NBE）were used as the raw materials,to copolymerize Hemin-based trinity catalytic layer materials,named as Poly（NBE-co-Hemin）X.Hemin can be fixed in the polymer skeleton to provide a stable and reliable ORR catalytic activity,electron and ion conduction channels.The NBE monomers can provide oxygen access channel after the ring-opening polymerization.In an alkaline system,Poly（NBE-co-Hemin）10 possesses E_onset 0.683V,E_1/2 0.456V,a limiting current density j 4.44 m A cm^-2,and electron transfers number of 3.7.Meanwhile,the Poly（NBE-co-Hemin）10 can provide significant high Al-air battery performances.The discharge test of the AABs was carried out under6M KOH electrolyte,and the peaking power density can reach as high as 163.5 m W cm^-2,which is 29 m W cm^-2 higher than the commercial 20%Pt/C catalyst battery.2.Development of the PVA-PAA gel electrolyte and its application in AABsWhen the liquid electrolyte is applied in AABs,shortcomings will be encountered,such as battery sealing difficulties,and additional battery weights.In this regard,gel electrolytes,as a kind of solid-state electrolyte,are expected to solve these problems.Polyvinyl alcohol（PVA）and acrylic acid（AA）as raw materials,KOH as the electrolyte were used to prepare the alkaline gel electrolyte PVA-PAA-KOH.The abundant hydroxyl functional groups in the PVA matrix are beneficial to water storage;carboxyl groups provided by AA are excellent polydentate ligands,to capture and enriche Al³⁺ions.The assembled solid-state Al-air battery with PVA-PAA-KOH and Poly（NBE-co-Hemin）10air electrode,can deliver a peaking power density of 205.1 m W cm^-2.The specific energy of this solid-state Al-air battery can reach to 899.7 m Ah g_Al^-1.under a current of 20 m A cm^-2.In addition,the neutral Al-air battery system with better corrosion resistance.When using PVA-PAA-1M Na Cl neutral gel electrolyte,the battery’s open-circuit voltage is0.718 V,with a power density of 21.7 m W cm^-2.An AB-type gel electrolyte（PVA-PAA-Na Cl|PVA-PAA-KOH）is further designed by optimizing the batteries’performance.The open-circuit voltage of the Al-air battery can be increased to 1.456 V,with a peak power density of 33.5 m W cm^-2,which is among the state-of-the-art neutral Al-air battery performances.