Study On Electrocatalytic Properties Of Non-noble Metal Layered Materials By Surface Modification

With the development of new sustainable energy systems including fuel cell,metal-air battery and electrochemical water decomposition system,researchers have shown great interest and carried out a lot of basic and applied research.These applications mainly involve a common oxygen electrode reaction,oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?.Electrocatalytic ORR and OER are two important components of fuel cells,metal-air batteries.At the same time,OER is also an important half reaction of hydrogen production by electrocatalytic water decomposition.However,for ORR and OER,they have high reaction barrier and slow reaction kinetics which seriously restricts the development of sustainable energy.Therefore,developing high efficient electrocatalysts to accelerate the process of ORR and OER is very important.At present,Pt and RuO₂ have exhibited excellent electrocatalytic ORR and OER properties,respectively.However,these materials are expensive,limited reserves,poor stability,vulnerability to poisoning and inactivation which hinder their large-scale commercial applications.In this paper,carbon materials and transitional metal CoS were selected as the research objects which were used to electrocatalytic ORR and OER,respectively.Firstly,based on the model of carbon materials,the electronic structure of carbon materials is regulated by introducing double heteroatom doping to improve the intrinsic activity of carbon materials.At the same time,a large number of holes are introduced into the double heteroatom doped materials to increase the number of catalytic sites.Combining these two aspects,the ORR electrocatalytic properties of carbon materials is further improved.Secondly,bulk CoS nanosheets intercalated by TETA?CoS-TETA?was used as the research model.Bulk CoS-TETA nanosheets were exfoliated into ultrathin CoS nanosheets by low temperature Ar plasma technology,which increased the number of active sites of electrocatalysts.At the same time,defects and holes were introduced on the surface of as-synthesized ultrathin CoS nanosheets by the strong etching of plasma,which can optimize the electronic structure of the catalysts,improve the intrinsic activity of the catalysts,and ultimately enhance the OER performance of the CoS electrocatalysts.The research details are as follows:?1?N and P double doped carbon materials with trace Co doping and abundant edge sites were prepared.In the presence of Co²⁺,melamine and phytic acid self-assemble into melamine-phytic acid supramolecular aggregates?MPSA?.Then,MPSA was pyrolyzed in Ar/H₂ atmosphere to prepare precursor?MPSA-Co-900?.Subsequently,the synthesized precursor was washed with acid to remove the metal Co in the precursor,and a large number of holes were formed on the surface of the precursor.Finally,the catalyst was successfully synthesized?MPSA-Co-900-Acid?.The microstructure of the synthesized catalyst were observed by SEM and TEM.The specific surface area of the catalyst was tested by BET.XPS was used to study the surface chemical composition and bonding type of the catalyst.The morphology,BET specific surface area and surface element composition of MPSA-Co-900-Acid catalyst were studied by these characterization methods.The results showed that many holes were formed in the MPSA-Co-900-Acid nanosheets leading to exposing more active sites.N and P were successfully doped into layered carbon materials.Doping atoms can adjust the electronic structure of carbon atoms and produce more ORR active sites.In addition,the formation of Co-N-C active substances in carbon materials by trace Co doping can further improve the ORR performance.Finally,the ORR electrocatalytic activity of Co-doped and N,P-doped carbon materials with abundant edge sites was evaluated by electrochemical measurement.In 0.1 mol dm^-33 KOH,combining the trace level Co doping and rich edge sites in the dual doped carbon nanosheets,the MPSA-Co-900-Acid showed very good ORR activity and was close to thatofPt/C.Andinaddition,theelectrochemicalresultsshowedthat MPSA-Co-900-Acid had much better fuel selectivity and higher long-term stability than that of commercially available Pt/C electrode.?2?Bulk CoS-TETA nanosheets were used as the research model.CoS-TETA nanosheets were exfoliated by Ar plasma technology to form ultrathin CoS nanosheets?Ar-CoS-TETA-10?.At the same time,defects and holes were introduced into the ultrathin Ar-CoS-TETA-10 nanosheets.SEM,TEM were used to observe the changes of the morphology and thickness of catalysts;XRD was used to characterize the changes of the crystal structure of the materials before and after treatment,and XPS was used to analyze the changes of element composition and valence of the catalyst surface before and after treatment.The OER electrocatalytic activity of the catalyst before and after treatment was evaluated by electrochemical teat.Based on the above characterization and measurement,the effects of Ar plasma treatment on the microstructures,thickness and size,crystal structure,valence states of elements and the electrocatalytic activity of CoS-TETA catalysts were studied and explored.The results show that After Ar plasma treatment,the thickness and size of bulk CoS-TETA nanosheets decrease significantly and they are successfully exfoliated into ultrathin porous CoS nanosheets?Ar-CoS-TETA-10?with rich defects and edges.The formation of ultrathin CoS nanosheets expose more surface active sites,the introduction of defect and edge sites changes the electronic structure of CoS surface which is more facilitate to the adsorption of OER reaction intermediates and ultimately improves the OER electrocatalytic properties of Ar-CoS-TETA-10 samples.Compared with CoS-TETA nanosheets,Ar-CoS-TETA-10 samples showed better OER electrocatalytic properties.In the 1 mol dm^-33 KOH electrolyte,when the current density reaches 10 mA cm^-2,the required overpotential is 341 mV.The synthesized Ar-CoS-TETA-10 samples were coated onto the three-dimensional conductive foam nickel,the overpotential was only291 mV at the current density of 10 mA cm^-2.