| Rapid development of human material civilization is based on abundant resources.Due to population explosion and industrial production expanding,human have to treat with resource crisis and environment problems caused by excessive consumption of fossil fuel.It is urgent to decrease consumption of energy in industry and develop clean renewable power.Through electrochemical method,some available materials could be converted to high-value energy storage molecules and industrial chemicals.For instances,N2 and CO2 could be reduced to NH3,CH4,and CH3OH,respectively.Among them,NH3 is greatly important for agricultural production,energy conversion or storage,and industrial manufacture.By method of electrocatalysis,N2 reduction reaction(NRR)could be carried out under mild conditions.Therefore,this approach is expected to replace energy-intensive Haber-Bosch technology.Conversion of CO2 to hydrocarbon fuels could decrease concentration of CO2 in atmosphere and provide power and chemicals,which forms a relatively stable carbon cycle.Along this approach,resource crisis and environmental problems could be alleviated.Catalyst is a crucial factor to determine the efficiency of electrocatalysis.Therefore,researchers focus on screening cheap,efficient and durable electrocatalysts for N2 and CO2 reaction reaction.For electrocatalytic N2 reduction reaction(NRR),there are some disadvantages of traditional catalysts,including high overpotentials with intensive energy consumption,and competitive hydrogen evolution reaction(HER).The process of CO2 reduction reaction(CO2RR)is complicated and the products are diverse.Therefore,electrocatalysts with high activity and selectivity are important for CO2RR to achieve low energy input and gain high purity of product.According to recent reports,single transition metal atoms supported by 2D nanomaterials exhibit superior performances.2D nanomaterials possess many advantages,including large area/surface rate,high stability,unique electronic properties and surface modification.Combing the virtues of 2D nanomaterials with that of metal particles,such as good activity and high conductivity,is a promising idea to design catalysts.Herein,we untilized density functional theory(DFT)to investigate catalytic performance of a series of 2D metal-organic frameworks(MOFs)as single-atom catalysts(SACs)applied in NRR and CO2RR.The main contents are as follows:(1)Noval 2D MOFs were succefully synthesized in experiment,which were consisted of transition metal and hexaaminobenzene.Low coordination metal atoms distribute on the surface of MOFs regularly and stably,which is typical characteristic of excellent SACs.We tested catalytic performances of Co,Ni,Cu,and Mo-based MOFs applied in NRR through density functional theory(DFT).By contrasting N2 activation effects on various MOFs,we picked Mo-based MOF as the electrocatalyst for NRR Under mild conditions,the Mo-based MOF show excellent catalytic performance for N2 fixation with a very low overpotential,whose value is 0.18 V.The hydrogen evolution reaction(HER)is the competive reaction,whose energy barrier is 0.65 V,which means the Mo-based MOF is an efficient electrocatalyst for NRR.(2)The Mo-based MOF is also suitable for CO2RR.The Mo-based MOF could catalyze CO2 reducing to CH4 selectively,and limiting potential(Ulimiting)is only-0.42 V(vs-0.65 V/HER).Once MOF oxidated,namely active sites are covered by oxygen atoms,the catalytic performance of the Mo-based MOF does not decrease but futher improves.On the surface of MoO-based MOF,CO2 still be converted to CH4 with high selectivity,and the limiting potential decreased to-0.27 V.The energy cost of Mo-based MOF catalyzing CO2RR is much less than traditional pure metal catalysts and some SACs based on precious metal.This study based on atomic level proposes that Mo-based MOF can efficiently catalyze CO2 reduction reactions under mild conditions.Mo-based MOF based on an earth abundant metal presents greater catalytic performance than some noble metal catalysts. |
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