Metal-organic Frameworks Derived Nanocomposites And Their Applications In Electrocatalytic Reduction Reaction

The diminishing fossil fuel storage and increasing environmental pollution facilitate the development and popularization of advanced renewable energy technology.To date,sustainable energy technologies mainly include hydrogen-oxygen fuel cell technology,overall water splitting technology and metal-air fuel cell technology.The everlasting but formidable challenge confronting the energy conversion processes lies in the lack of cheap alternatives to precious metal-based electrocatalysts to improve the reaction kinetics.As a renewable and durable fuel with zero-emission,hydrogen is regarded as the most effective carrier for future on-board fuel cells.On the other hand,the commercialization of hydrogen-oxygen fuel cell,zinc-air fuel cell and nitrogen reduction electrolyzers are still bottlenecked by insurmountable demerits associated with the lack of active catalysts to reduce the reaction barrier.For electrocatalytic reduction reaction,Pt displays the highest catalytic performance,efficient as it is,the expensive cost and natural scarcity significantly impede their global technological scalability.The intrinsic activity of a catalyst is determined by the adsorption capacity and electrical conductivity of active center.Modulating the geometric and electronic structure of the material can improve the conductivity while adjusting the band gap.Metal-organic frameworks(MOFs)are periodic coordination polymers with three-dimensional network structure,which are composed of central metal ions(clusters)and corresponding organic ligands.The large specific surface and tunable structure can be employed as an ideal platform for controlling the electronic and geometric structures of catalysts.Governed by a combination of the reduction potential impact,pyrolysis atmosphere and the content of metal ions,we can get metal(alloy)/carbon,metal oxide/carbon and metal oxide composites by pyrolysis of MOFs precursors.The details are as follows:1.Metals or alloys are easily corroded and denatured in strong acidic electrolytes,while implanting the metal/alloy nanoparticles into carbon cages can improve the stability and electrical conductivity at the same time.IrCo nanoalloy encapsulated in nitrogen-doped carbon layers are prepared by one-step pyrolysis of Ir-doped MOFs.The catalyst,with a low Ir content(1.56 wt%),requires an overpotential of 24 mV to drive a 10 mA cm-2 current density.Computational results reveal that the C atoms next to the N dopants are active sites.2.Traditionally,Ru is recognized as the benchmark for OER under basic media,however,the potential for hydrogen generation remains to be developed.Ru-MoO2 nanojunctions are prepared by one-step pyrolysis of Mo-based MOFs modified by Ru in nitrogen atmosphere.To achieve a 10 mA cm-2 current density,the nanocomposites require overpotentials of 55 mV in 0.5 M H2SO4 and 29 mV in 1 M KOH,respectively.Such outstanding catalytic activity in alkaline media even outperforms the state-of-the-art Pt/C catalysts.According to the Sabatier principle,the binding energy of hydrogen on MoO2 is weak bur strong on Ru,thus the binding and interaction between Ru and MoO2 could make ? GH*value close to 0 eV.3.The IrFe nanoalloys supported on N-doped carbon layers are designed and synthesized by pyrolyzing Ir-modified MOFs precursors.The catalyst needs an overpotential of 850 mV to sustain a 1000 mA cm-2 current density in basic media,which surpasses that of commercial Pt/C benchmarks.Such remarkable performance originates from excellent conductivity,the modulated electronic structure as well as large specific surface area.4.In order to regulate the electronic structure of single atom catalyst,the common strategy is to change the distance and interaction between the hetero-atoms and the metal sites.Inspired by the structure of nitrogenase,monodispersed FeNx riveted on nitrogen,sulfur co-doped porous carbon nanospheres(FeSA/NSC)is prepared by one-step pyrolysis of Fe-based MOFs.The catalyst exhibits excellent ORR activity in both acidic and alkaline media,additionally the performance under alkaline conditions is comparable to that of Pt/C,and the maximum output power density of the zinc-air cell is up to 200.8 mW cm-2.Benefiting from the introduction of S into carbon frameworks,which changes the charge distribution around the metal center of Fe,the FeSA/NSC exhibit superior NRR performance in acidic media.