Critical role of carbon support in metal nanoaggregate facilitating Fe-N-C catalyst for PEM fuel cell application

Metal nanoaggregates can simultaneously enhance the activity and stability of Fe-N-C catalysts in proton-exchange-membrane fuel cells(PEMFC).Previous studies on the relevant mechanism have focused on the direct interaction between FeN_(4)active sites and metal nanoaggregates.However,the role of carbon support that hosts metal nanoaggregates and active sites has been overlooked.Here,a Fe-N-C catalyst encapsulating inactive gold nanoparticles is prepared as a model catalyst to investigate the electronic tuning of Au nanoparticles(NPs)towards the carbon support.Au NPs donate electrons to carbon support,making it rich inπelectrons,which reduces the work function and regulates the electronic configuration of the FeN_(4)sites for an enhanced ORR activity.Meanwhile,the electron-rich carbon support can mitigate the electron depletion of FeN_(4)sites caused by carbon support oxidation,thereby preserving its high activity.The yield and accumulation of H_(2)O_(2)are thus alleviated,which delays the oxidation of the catalyst and benefits the stability.Due to the electron-rich carbon support,the composite catalyst achieves a top-level peak power density of 0.74 W/cm^(2) in a 1.5 bar H_(2)-air PEMFC,as well as the improved stability.This work elucidates the key role of carbon support in the performance enhancement of the FeN-C/metal nanoaggregate composite catalysts for fuel cell application.

Precious trimetallic single-cluster catalysts for oxygen and hydrogen electrocatalytic reactions:Theoretical considerations

Single cluster catalysts(SCCs),which exhibit remarkable catalytic performance due to their high metal loading and synergy effect between metal atoms,have attracted great attention in research.Herein,by means of density functional theory calculations,the oxygen reduction reaction(ORR),oxygen evolution reaction(OER),hydrogen evolution reaction(HER)performances of precious metal(Pt,Pd,Rh,Ir)trimetallic single-cluster electrocatalyst(U_(x)V_(y)W_(z)-NG)are investigated.The calculation results show that Pt,Pd,Ir have significant effect on ORR,OER,HER,respectively,all the calculated U_(x)V_(y)W_(z)-NG structures are thermodynamically stable due to the negative formation energies and binding energies.The Pt_(3)-NG,Pd_(3)-NG,Ir_(3)-NG show the lowest ORR,OER,HER overpotentials of 0.63,0.77,−0.02 V,respectively,among all combinations of U_(x)V_(y)W_(z)-NG.These overpotentials are lower than that of precious metal single atom catalysts(SACs),which indicate better activities of precious trimetallic SCCs than those of SACs.The electronic structure reveals that the O-2p orbital shows strong hybridization strength with Pt-3d orbitals in the system of OH adsorbed Pt_(3)-NG and thus facilitates the electrocatalytic reactions.The results are helpful for the rational design of high-performance triatomic catalysts.

Enhancing carbon dioxide reduction electrocatalysis by tuning metal-support interactions: a first principles study

The electrochemical reduction of CO_(2) is an extremely potential technique to achieve the goal of carbon neutrality,but the development of electrocatalysts with high activity,excellent product selectivity,and long-term durability remains a great challenge.Herein,the role of metal-supports interaction(MSI)between different active sites(including single and bimetallic atom sites consisting of Cu and Ni atoms)and carbon-based supports(including C_(2) N,C_(3)N_(4),N-coordination graphene,and graphdiyne)on catalytic activity,prod-uct selectivity,and thermodynamic stability towards CO_(2) reduction reaction(CRR)is systematically investi-gated by first principles calculations.Our results show that MSI is mainly related to the charge transfer behavior from metal sites to supports,and different MSI leads to diverse magnetic moments and d-band centers.Subsequently,the adsorption and catalytic performance can be efficiently improved by tuning MSI.Notably,the bimetallic atom supported graphdiyne not only exhibits a better catalytic activity,higher product selec-tivity,and higher thermodynamic stability,but also effectively inhibits the hydrogen evolution reaction.This finding provides a new research idea and optimization strategy for the rational design of high-efficiency CRR catalysts.

Catalysis stability enhancement of Fe/Co dual-atom site via phosphorus coordination for proton exchange membrane fuel cell

Non-precious metal catalysts(NPMCs)are promising low-cost alternatives of Pt/C for oxygen reduction reaction(ORR),which however suffer from serious stability challenge in the devices of proton-exchange-membrane fuel cells(PEMFC).Different from the traditional strategies of increasing the degree of graphitization of carbon substrates and using less Fenton-reactive metals,we prove here that proper regulation of coordination anions is also an effective way to improve the stability of NPMC.N/P cocoordinated Fe-Co dual-atomic-sites are constructed on ZIF-8 derived carbon support using a molecular precursor of C_(34)H_(28)Cl_(2)CoFeP_(2)and a“precursor-preselected”method.A composition of FeCoN_(5)P1 is infered for the dual-atom active site by microscopy and spectroscopy analysis.By comparing with N-coordinated references,we investigate the effect of P-coodination on the ORR catalysis of Fe-Co dual-atom catalysts in PEMFC.The metals in FeCoN_(5)P1 have the lower formation energy than those in the solo N-coordinated active sites of FeCoN6 and FeN_(4),and exhibits a much better fuel cell stability.This anion approach provides a new way to improve the stability of dual-atom catalysts.

High-throughput screening of carbon-supported single metal atom catalysts for oxygen reduction reaction

Carbon-supported transition metal single atoms are promising oxygen reduction reaction(ORR)electrocatalyst.Since there are many types of carbon supports and transition metals,the accurate prediction of the components with high activity through theoretical calculations can greatly save experimental time and costs.In this work,the ORR catalytic properties of 180 types single-atom catalysts(SACs)composed of the eight representative carbon-based substrates(graphdiyne,C_(2)N,C_(3)N_(4),phthalocyanine,C-coordination graphene,N-coordination graphene,covalent organic frameworks and metal-organic frameworks)and 3d,4d,and 5d transition metal elements are investigated by density functional theory(DFT).The adsorption free energy of OH^(*) is proved a universal descriptor capable of accurately prediction of the ORR catalytic activity.It is found that the oxygen reduction reaction overpotentials of all the researched SACs follow one volcano shape very well with the adsorption free energy of OH^(*).Phthalocyanine,N-coordination graphene and metal-organic frameworks stand out as the promising supports for single metal atom due to the relatively lower overpotentials.Notably,the Co-doped metal-organic frameworks,Ir-doped phthalocyanine,Co-doped N-coordination graphene,Co-doped graphdiyne and Rh-doped phthalocyanine show extremely low overpotentials comparable to that of Pt(111).The study provides a guideline for design and selection of carbon-supported SACs toward oxygen reduction reaction.

Morphology evolution of SmCox permanent magnetic nanoparticles

Sm-Co nanoparticles (NPs) are promising candidates for preparing superstable magnets and exchange-coupled nanocomposite magnets with unprecedented magnetic properties.However,the morphology evolution of the NPs remains unclear.Here,single crystalline SmCox(x=4.07,4.79,6.94,and 8.61) NPs with dimensions below the critical size of a single magnetic domain were synthesized.These NPs consist of Sm_(2)Co_(7),SmCo_(5),and Sm2Co17phases with divergent typical morphologies.An evolution model for the different morphological characteristics was proposed based on phase-structure changes and surface-energy calculations using the density functional theory.The results show that these SmCo_(4.79) NPs can be well aligned along the easy magnetization axis and exhibit an ultrahigh coercivity of 5.7 T,thus enabling to advance the control of NP morphology and to facilitate their use in superstable or nanocomposite magnets.

Rational design of bimetallic atoms supported on C3N monolayer to break the linear relations for efficient electrochemical nitrogen reduction

Linear relations between the adsorption free energies of nitrogen reduction reaction(NRR)intermediates limit the catalytic activity of single atom catalysts(SACs)to reach the optimal region.Significant improvements in NRR activity require the balance of binding strength of reaction intermediates.Herein,we have investigated the C_(3)N-supported monometallic(M/C_(3)N)and bimetallic(M_(1)M_(2)/C_(3)N)atoms for the electrochemical NRR by using density functional theory(DFT)calculations.The results show that this linear relation does exist for SACs because all the intermediates bind to the same site on M/C_(3)N.But the synergistic effect of the two atoms in M_(1)M_(2)/C_(3)N can create a more flexible adsorption site for intermediates,which results in the decoupling of adsorption free energies of key intermediates.Subsequently,the fundamental limitation of scaling relations on limiting potentials is broken through.Most notably,the optimal limiting potential is increased from−0.63 V for M/C_(3)N to−0.20 V for M_(1)M_(2)/C_(3)N.In addition,the presence of bimetallic atoms can also effectively inhibit the hydrogen evolution reaction(HER)as well as improve the stability of the catalysts.This study proposes that the introduction of bimetallic atoms into C_(3)N is beneficial to break the linear relations and develop efficient NRR electrocatalysts.