Synthesis Of Ni And Co-based Electrocatalysts For Oxygen Electrodes

With the rapid development of human society and world economy,the consumption of energy and the deteriorating environment have become a serious issue.It is urgen to exploit clean and renewable energy technologies in order to reduce our dependence on conventional energy sources based on fossil fuels.Electrochemical energy conversion and storage technologies(such as fuel cell,metal-air battery and water splitting,etc.)have been attracted much attention due to the high energy conversion efficiency and environmental benignity.The core of these technologies is a series of electrochemical reaction process which including oxygen reduction reaction,hydrogen oxidation reaction and hydrogen or oxygen evolution reaction.In general,the kinetically sluggish oxygen reduction reaction and oxygen evolution reaction constrain the overall performance and commercialization of the entire electrochemical device.The synthesis and design of oxygen electrocatalysts with excellent activity are vitally important to accelerating these reaction processes.To date,commercial oxygen electrocatalysts are precious metal-based materials(such as platinum,palladium,iridium,etc.),the high cost and scarity impede their commercial application for aforementioned technologies.In recent years,highly efficient non-noble metal nanocatalysts considering their low cost and earth-abundant resources have been widely developed as alternatives to noble metal nanocatalysts for oxygen electrode reaction enhancement.In this regard,we synthesize the oxygen electrocatalyst with low cost,high catalytic activity,good stability.The main contents are summarized as follow:1.We propose a "top-down" synthesis strategy for achieving stable Co single atoms on nitrogen-doped porous carbon with high metal loading over 4wt%.The strategy is based on an in-situ pyrolysis process of pre-prepared bimetallic Zn/Co metal-organic frameworks,during which Co can be reduced by carbonization of the organic linker and Zn is selectively evaporated away at high temperatures above 800?.The doping of Zn is regarded as a "fence" to expand the spatial distance of adjacent Co atoms to prevent the formation of Co-Co during the pyrolysis process.The obtained Co single atoms exhibit superior performance in alkaline electrolyte with a half-wave potential(0.881 V)that is more positive than commercial Pt/C.In this research,we use spherical aberration correction electron microscopy and X-ray fine absorption spectrum to reveal a clear information of the structure of the catalyst at the atomic level,so as to explore the structure and performance related to the physical chemistry.This method opens up a new avenue and strategy for synthesis of single atoms catalysts.2.The design and synthesis of electrocatalyst plays an important role in the electrochemical renewable energy conversion technology.In this section,we utilize graphene oxide directly dispersed pristine CNTs as substrate to support OER-active NiCo-LDH through a facile and simple hydrolysis method.The graphene oxide can be recognized as an amphoteric surfactant to directly disperse the CNTs without any functional process or surfacrants,which is consisted by hydrophilic areas of the ionizabled edge containing carboxylic acid groups and hydrophobic polyaromatic regions of unoxidized benzene rings on the basal plane.GO should be able strong interact with the surface of CNTs through ?-? attraction because of many 7r-conjugated aromatic domains in its basal plane.Therefore,the excellent water solubility of GO could be inherited by forming complexes with CNTs,while CNTs can remain the electronic structure without no additives or functionalization of CNTs.The insert CNTs not only can prevent the aggregation of GO but also enhance the conductivity.By varying the ratio of GO and CNT,we can obtain the optimal OER activity of the LDH/CNT-GO complexes while the ratio is 1:1.In 0.1M KOH,the onset potential of LDH/GO-CNT is only 1.42V,which demonstrated a more negative onset potential than other sample.The current density of the composite retain 90%after 1000-cycle durability test.The LDH/GO-CNT exhibit excellent activity and good durability for OER electrocatalysis is attributed to the synergistic effect of GO-CNT and LDH.