Synthesis Of Carbon-based Single-metal-site Catalysts And Study On Electrocatalytic Performance Towards Oxygen Evolution Reaction

Electrochemical oxygen evolution reaction(OER)as half reaction plays an important role in energy conversion and environmental protection.Currently,great efforts have been devoted in pursuit of robust OER electrocatalysts based on earth-abundant transition metal elements.Single-metal-site catalysts(SMSCs)with isolated metal atoms dispersed on solid supports have emerged as a new frontier in the catalysis science,because of their unique properties and great potential for a variety of applications.Despite extensive efforts have been made in the preparation and application of SMSCs,there are many deficiencies in macro preparation of SMSCs.Many difficulties exist in expanding the substrate types to improve the performance of SMSCs and building multifunctional SMSCs.In addition,there is also much room for understanding the correlations between structure and special catalytic performance by utilizing the features of SMSCs.The main study contents in this thesis are listed as follow:(1)Study on preparation and performance of cheap carbon-based nickel-iron bimetallic sites electrocatalystAn atomically dispersed nickel-iron bimetallic sites on carbon substrate electrocatalyst(Ni Fe-O/C)was successfully synthesized via a simple coordination design strategy.The structural characteristics of as-prepared Ni Fe-O/C electrocatalyst were revealed by a series of microscopy and spectroscopy analysis.The electrocatalytic performance for the OER was facilitated by as-prepared Ni Fe-O/C electrocatalyst.As a result,Ni Fe-O/C showed excellent electrocatalytic performance with a low overpotential of 260 m V at a current density of 10 m A cm^-2,outdistancing the performance of single Fe sites on carbon substrate electrocatalyst(Fe-O/C).Furthermore,as-prepared Ni Fe-O/C electrocatalyst also exhibited a good stability for electrocatalytic water oxidation.This coordination design strategy presents a promising potential to realize the large-scale application of SMSCs.(2)A general design strategy for carbon-based bimetallic sites electrocatalystsBased on the studying and analyzing the molecular structures of different polyphenols,a series of atomically dispersed bimetal sites on carbon substrates electrocatalysts were synthesized and evaluated by electrocatalytic OER performance.Compared with Fe-O/C,all of as-prepared bimetal sites electrocatalysts exhibited significantly improved catalytic OER activity.As a result,the performance differences of as-prepared cobalt-iron double sites electrocatalysts(Co Fe-O/C)are mainly attributed to the adsorption capacity of water molecules on the catalyst surface and purity of organic ligands.In addition,the contributions of different introduced metal atoms of electrocatalysts for the performance were also summarized from practical electrochemical measurements.(3)Study on construction and OER mechanism of nickel sulphide@carbon-based single-iron-site composite electrocatalystsnickel sulphide@carbon-based single-iron-site(Ni S2 NS@Fe-O/C)composite electrocatalysts was firstly synthesized by utilizing the advantages of SMSCs and composites.The obtained Ni S2 NS@Fe-O/C composite has an average 4 nm of thin carbon layers on the surface that contain single Fe sites.During OER,the Ni S2 NS@Fe-O/C shows an obvious performance improvement over both pure Ni S2 NS and Fe-O/C.This robust catalytic activity can be attributed to the unique coordination chemistry of Fe in form of distorted Fe O4 and the synergy between Fe and Ni that optimize single Fe sites in changing to better configurations for reducing reaction barriers.This work provides a new perspective for the studying of the active site of Ni Fe-based materials in the electrocatalytic OER.(4)The universal construction of high-performance carbon-based single-iron-site composite electrocatalystsA series of well-formed and high-performance nickel(cobalt)composite electrocatalysts with single Fe sites were successfully synthesized via a universal ink-assisted strategy by the utilization of ductile and adherent Fe-GA precursor.Among these,the best composite is(Ni0.33Fe0.67)2P@Fe-O/C,requiring an overpotential of only183 m V for the OER at a current density of 30 m A cm^-2.And the highest performance improvement is about 22%of the Ni S2 NP@Fe-O/C compared with pure Ni S2 NP.Such outstanding electrocatalytic activities originate from the improved hydrophilicity and fast charge transfer on the surface of composite catalysts.This work firstly proposed the concept of good hydrophilicity for single metal sites catalysts,which provides a new design thought for constructing advanced catalysts.