Carbon-based Electrocatalysts Derived From Functionalized N-containing Polymer:Synthesis And Performance Research

The extensive developments of green and sustainable energy technologies have been largely driven by the rapid expansion of global energy demand and the ever-growing concentration of carbon dioxide,which could promote clean energy,energy conservation and emission,and the implementation of carbon neutrality.Among diverse energy technologies,fuel cells,metal-air batteries and the recycling of CO2 are widely considered as promising energy conversion and storage devices.However,the widespread use of these technologies is limited by the inefficiency of key chemical reactions(such as oxygen reduction,oxygen evolution,and carbon dioxide reduction).Electrocatalysis is of vital importance to facilitate the developments of energy conversion storage devices.Towards electrocatalysis of devices,ORR/OER/CO2RR are kinetically sluggish,and thus hold the decisive key to the efficiency of energy conversion.To date,noble metal catalysts have been regarded as the state-of-the-art electrocatalysts.Unfortunately,the prohibitive cost and scarcity have impeded their widespread commercial application.In recent years,carbon material have attracted considerable attention in electrochemical energy storage and conversion due to their typical advantages including abundant sources,high conductivity,tailorable structures and good chemical stability.For carbon-based electrocatalysts,the composition and physicochemical properties of carbon precursors have a critical impact on catalytic performance.Notably,the nitrogen-containing polymers are excellent carbon precursors.The introduction of abundant nitrogen heteroatoms into the carbon network could induce the modification of electronic properties and possess the ability to harvest more active sites.The presence of N group is beneficial to forming metal-nitrogen coordination structures or anchoring the metal particles.Besides,multi-dimensional carbon materials are constructed by tailoring composition and structure of nitrogen-containing polymer.These integrated favorable factors endow nitrogen-containing polymer as carbon precursors with a possibility for designing high-efficiency carbon-based electrocatalysts.In this context,our work aims to design and tailor the composition and structure of nitrogen-containing polymers at the molecular level,which could engender highly active carbon-based catalysts and optimize catalytic performances for energy conversion and storage.The main research contents are as follows:1.We developed a facile method for crafting a low molecular weight liquid polyacrylonitrile as carbon precursor with in-situ doped nitrogen and sulfur elements through the radical polymerization,which achieved effective regulation of the components.Owing to the fluid property of as-prepared PAN,it was easily miscible with the metal salts(ZnCl3 as a volatile porogen agent and FeCl3 as a metal precursor).By capitalizing on ZnCl2 salts,Fe-Nx species on N/S codecorated hierarchically porous carbon with with a large specific surface area of up to 1730 m2 g-1 was synthesized.This sample strategy expands the methods for preparing porous carbon using polyacrylonitrile.The optimal porous carbon exhibited excellent oxygen reduction reaction activity and robust durability.Finally,the implementation of porous carbon as the air-cathode catalyst for primary Zn-air batteries yields an open-circuit potential of 1.49 V,a high peak power density of 168 mW cm-2,a large specific capacity 778 mAh gZn-1 and a remarkable durability.2.We designed an effective synthesis strategy,which could modify polyethylenimine by amidation reaction.The abundant pyridinic-nitrogen structures were introduced through composition tailoring,and nitrogen-containing groups were beneficial to the formation of coordination structures between metals and nitrogen.The modified polyethyleneimine could retain considerable carbon yield after high-temperature heat treatment due to good thermal stability.We have prepared atomically dispersed Co-N-C Species by introducing transition metal salt into the modified polyethyleneimine to let the atomic dispersion of dense metal sites isolated by rich multiple nitrogen-containing group,resulting in excellent bifunctional OER/ORR catalysts.The oxygen electrode activity(?E)was performed by difference between half-wave potential(0.88 V)of ORR and the potential(1.62 V)at 10 mA cm-2 current density in OER.A rechargeable Zn-air battery was prepared using Co-N-C catalysts as air electrodes,which exhibited a high power density,low charge and discharge overpotential,and good stability.This work provides a viable strategy for preparing carbon-based electrocatalysts by tailoring composition of nitrogen-containing polymers.3.We used a simple soft template method to prepare an aniline-pyrrole copolymer with a hollow structure as carbon precursors.Structure tuning of N-containing polymer was obtained via the micelle-induced preparation,which is the copolymerization of aniline and the pyrrole monomer to form a hollow structure.N,S dual-doped high-surface-area hollow carbon materials were synthesized by a one-step pyrolysis of copolymer and sulfur powder.Notably,high specific surface areas and porous structures with homogeneously effective N/S doping could be beneficial for CO2RR activity arising from enhanced accessibility of active sites and transport of related species.These integrated favorrange able factors endow catalysts with a superior CO2RR activity and a high CO Faradaic efficiency(-93%)as well as long-term stability,This work further expands the of carbon-based materials for carbon dioxide reduction by tuning the structure of nitrogen-containing polymers.