Carbon Based Transition Metal Catalysts For Fuel Cells Based On First Principle Methods Design

The development of efficient and non-noble metal or low noble metal catalysts for oxygen reduction reactions（ORR）in proton exchange membrane fuel cells（PEMFCs）and hydrogen oxidation reactions（HOR）in alkaline exchange membrane fuel cells（AEMFCs）is of great significance for the large-scale commercial use of fuel cells.Carbon based transition metal catalysts are widely used for catalyzing various electrochemical reactions due to their low cost and have excellent performance.Traditional research and development catalysts generally use experimental trial-and-error methods,which lack theoretical basis,have high blindness,uncertainty,and low efficiency.Moreover,due to insufficient understanding of catalytic mechanisms by researchers,it is often difficult to conduct targeted research on catalyst modification.Nowadays,the mainstream design method for catalysts is gradually shifting towards using theoretical calculations to assist and guide experimental personnel in developing new catalysts.For example,by constructing descriptors related to the electronic or geometric structure of catalytic materials and catalytic performance through theoretical calculations,high-performance materials can be directly screened from millions of such configurations in a short period of time.This work systematically explores the performance of carbon-based transition metal materials（including single atom catalysts and armor catalysts）used for catalyzing electrode reactions in fuel cells based on first principles quantum chemistry theory calculation methods.The impact mechanism of different modification methods on the catalytic performance of the materials is analyzed in detail,and structural descriptors are constructed to screen and evaluate high-performance catalysts,providing guidance for experimental personnel.The main research content is as follows:1.Defect regulation:We explored the effects of 555777,5775,and 585defects in three shell layers of FeN₄ sites on the ORR activity of Fe centers,and demonstrated that the pre-adsorption of*OH and the distance between Fe SAC and defects significantly affect the orbital hybridization of Fe(d_xz)-O（p_x）,Fe(d_yz)-O（p_y）and Fe（d_z2）-O（p_z+s）between Fe SAC and*OH intermediates,thereby regulating the ORR activity of defect Fe-N-C accordingly.An intrinsic structural descriptor was established to accurately and quantitatively predict the activity of defect Fe-N-C ORR without the need for DFT calculations.With the help of the structural descriptor,we found that 5775 and 585 large ring defects adjacent to Fe-N-C pentagonal ring usually increase the length of Fe-OH bonds and the distance between Fe-OH defects.This effectively adjusts the peak position of Fe d_yz orbitals above the Fermi level to approach the optimal energy level,thereby improving ORR performance.This work reveals the ORR activity origin of defective Fe-N-C materials,providing intuitive guidance for improving the ORR performance of Fe-N-C materials through defect engineering,and will help researchers quickly screen for defective Fe-N-C catalysts.2.Support regulation:We explored ORR activity of T-graphene anchored TM SA（including TMN₄-Tgra and TMC₄-Tgra,TM=Sc～Zn）and their corresponding graphene anchored TM SA.We proved that the hybridization of TM(d_xz)-O（p_x）,TM(d_yz)-O（p_y）and TM（d_z2）-O（p_z+s）orbitals between the active center metal and*OH intermediate determines the ORR activity of TM-Tgra materials.Compared to graphene,the unique bond angle in T-graphene causes the d-band center（especiallyβ-spin state）of central metal undergoes a slight positive shift,which weakens the adsorption strength of the central metal on intermediates,thereby improving the ORR performance of the left branch catalyst located in the ORR active volcano.Importantly,we found that for catalysts with different metals anchored on the same supports,the adsorption strength of oxygen intermediates increases with the increase of the d-band center of the active metal site.On the contrary,for catalysts with the same metal anchored on different supports,the adsorption strength of oxygen intermediates weakens with the increase of d-band centers of active metal sites,which can be used as the d-band center dependence law for designing ORR catalysts for supports and active sites.3.Interface regulation:We explored the alkaline HOR performance of commonly used 3d transition metal armored catalysts coated with graphene shell（TM@C,TM=Cr～Zn）,and elucidated that graphene shell coating improves the stability of the catalyst by inhibiting its chemical dissolution.We demonstrated that HBE is an effective descriptor for alkaline HOR activity of TM@C.Cr@C～Co@C have surface configurations with outer carbon atoms as active sites.The electron transfer of inner metal leads to an increase in graphene electrons and a positive shift in the center of p_z orbital,improving the adsorption strength of graphene for*H.Ni@C～Zn@C have confined configurations with inner metal atoms as active sites.Graphene shell coating leads to a decrease in metal electrons and a negatively shift in the center of d_z2orbital,weakening the adsorption strength of the inner layer metal surface on*H.The modulation of trace noble metal can transform the surface configuration into confined configuration,with significant HOR performance comparable to Pt.4.Alloy regulation:We investigated the HOR/ORR performance of graphene shell coated 3d TM-Co and TM-Ni alloy armored catalysts（collectively marked as TM-Co/Ni@C,TM=Cr～Zn）,and proposed surface/confined configuration determination criteria based on the type and proportion of metal elementary.We demonstrated that surface and confined configurations only exhibit efficient catalytic activity for ORR and HOR,respectively.It is worth mentioning that during experimental synthesis,heterogeneity may lead to different alloy specific surfaces in one material,resulting in two possible surface/confined configurations（marked as heterogeneous TM-Co/Ni@C）for one material.In heterogeneous TM-Co/Ni@C,the surface configuration provides carbon atoms with stronger adsorption ability,which are more electron rich and have a positive shift in the p-band center,as efficient active sites for catalyzing ORR.The confined configuration provides metal atoms with stronger adsorption ability,which are more electron rich and have a positive shift in the d-band center,as efficient active sites for catalyzing HOR.Therefore,heterogeneous TM-Co/Ni@C has efficient dual functional catalytic performance of HOR/ORR.This work elucidates the influence of alloying on HOR/ORR catalytic performance of graphene shell armored catalysts,and proposes the element composition and structural requirements of graphene shell armored catalysts with dual-functional catalytic performance,providing new ideas for the development of dual functional catalysts.