Prediction And Preparation Of Carbon-based Mono-dispersed Metal Catalysts With High Electro-Reduction Activity

Due to the progressive development of human society,environmental pollution has become more serious,and the demand for energy has continued to rise.To reduce mankind’s dependence on traditional fossil fuels has been a major concern today.In our surroundings,there are amount of small molecules such as N2,CO2 and NO.Developing and utilising these small molecules can not only alleviate the problem of environmental pollution,but also greatly reduce mankind’s dependence on conventional fuels.So far,a variety of strategies have been developed to reduce small molecules,such as industrial synthetic ammonia,but these methods are also accompanied by problems environmental pollution and resource consumption,and the electrochemical reduction method is a good alternative method,because electricity is a renewable energy source,and the products obtained by the reduction of small molecules can be achieved by controlling the voltage.As N2,CO2 and NO are all relatively stable in the environment,they need to be activated using a suitable catalyst.Single-atom catalysts have become a hot research topic due to their high atom utilisation and their ability to interact with ligand atoms to form special catalytic sites.By modulating the local environment of single-atom catalysts,we can point out the influence of different coordination environments on the activity and selectivity of catalysis.The main findings are as follows.(1)The single-atom Ni stabilised and activated molecular catalyst FePc was investigated,enabling the catalyst,which is otherwise inert to CO2RR,to have a high current density and excellent selectivity over a wide potential range(-0.2 V to-0.8 V vs.RHE),with a maximum fractional current density of～270 mA/cm2 for CO and a Faraday efficiency of over 90%.Combining the XAFS technique with density flooding theory calculations,we suggest that Ni SA@FePc is a three-dimensional heterostructure connecting metal Fe and metal Ni atoms through the axial action of O atoms,a three-dimensional heterostructure that deactivates the metal centre due to the axial action of the O atoms,which makes the Fe atoms depressed downwards,however,the N atoms near the Fe atoms have the activity of CO2RR.This modulation strategy illustrates that modulating the coordination environment of the catalytic centre affects the catalytic activity in the pursuit of efficient electrocatalysts at the atomic level,and guides the direction for subsequent in-depth studies.(2)A series of 3d metals were investigated to influence the NRR activity of Co@C2N.while Co@C2N can effectively bind N2,there is still a large potential barrier to carry out subsequent protonation to form NNH*intermediates.The use of a 3d transition metal assisted means of embedding a transition metal in another pore site of C2N to provide electrons to the original metal Co centre forms a TM2@C2N type catalyst and effectively reduces the potential barrier to N2 formation of NNH*.The increase in charge from the surface to the N2 molecule illustrates the enhanced activation,as indicated by the bader charge and differential charge density together.Furthermore,the electronic structure of such catalysts bound to N2,i.e.,the fractional wave state density and COHP,shows that the more antibonding orbital components,the lower the binding capacity,and the more bonding components,the higher the binding capacity.It is confirmed that the TM2@C2N catalyst has good NRR activity,indicating the feasibility of enhancing electron transfer by other metals and providing a corresponding guide for the synthesis of subsequent catalysts for NRR.(3)Ten carbon-based monoatoms(TM=V,Cr,Mn,Fe,Co,Ni,Cu,Ru,Rh,Ta)formed by pyrrole-type N were systematically investigated for NORR activity by DFT calculations.Our study revealed that FeN4,CoN4 and RhN4 all have good activity towards NORR.Also,the selective reaction of the catalysts showed that FeN4 can effectively inhibit the HER side reaction,resulting in high NORR Faraday efficiency.In addition,by linearly fitting the adsorption free energy of the adsorbed intermediates involved in NORR,we propose an N*intermediate adsorption energy as a descriptor to describe and screen the optimal performance catalysts.The correlation between the catalyst and the adsorption intermediate N*was explored using the COHP method,and a linear fit between ICOHP and the adsorption free energy of the N*adsorption intermediate using the bonding integral of COHP could be obtained with a better linear relationship,from which the relationship between the bonding strength of the intermediate and the NORR activity was inferred.This provides guidance for the rational design of NORR catalysts.