Rational Design And Accurate Preparation Of Durable Catalysts With Ultralow Noble Metal For Hydrogen Evolution In PEM Water Electrolysis

Proton exchange membrane water electrolysis(PEMWE)has the advantages of high efficiency,high purity of hydrogen,and high working current density.It has been regarded as one of the important technical routes for the development of hydrogen economy.Hydrogen evolution catalyst is a key material for the production of hydrogen by water electrolysis with proton exchange membrane,and its performance,as well as cost,is a crucial factor for the popularization and application of this technology.Therefore,the development of a high-activity,long-term stable,low-cost hydrogen evolution catalyst is an important research component in the field of hydrogen production by PEMWE.This thesis is dedicated to the in-depth research on the rational design,preparation,active center and structure-activity relationship of non-Pt-based hydrogen evolution catalysts,specifically including:1.Tuning the oxidation state of Ru to surpass Pt in hydrogen evolution reactionAs a cheaper alternative to Pt,ruthenium is considered an inferior hydrogen evolution reaction(HER)catalyst than Pt due to its high susceptibility to oxidation and loss of activity.Herein,we elaborately selected a N,P containing threedimensional(3D)polymer,in which the Ru3+ is coordinated with the linkers(phytic acid-P),as a template,to design N and P codoped carbon-coating ruthenium phosphide(RuP@NPC)nanocatalyst.This strategy leads to the formation of RuP clusters that are uniformly and densely encapsulated into N,P-doped carbon(NPC)layers.We reveal that the HER activity on Ru based catalysts could surpass Pt via tuning Ru oxidation state.Specifically,RuP clusters encapsulated in few layers of N,P-doped carbon(RuP@NPC)display a minimum over potential of 15.6 mV to deliver 10 mA cm-2.Moreover,we for the first time show that a Ru based catalyst could afford current density up to 4 A cm-2 in a practical water electrolysis cell,with voltage even lower than the Pt/C-based cell,as well as high robustness during 200 h operation.Using a combination of experiment probing and calculation,we postulate that the suitably charged Ru(?+2.4)catalytic center is the origin for its superior catalytic behavior.While the moderately charged Ru is empowered with optimized H adsorption behavior,the carbon encapsulation layers protect RuP clusters from over oxidation,thereby conferring the catalyst with high robustness.2.Pregulates the electronic structure of Pd with Palladium Phosphide as Efficient Electrocatalyst for Hydrogen Evolution ReactionAiming at the solution to the problem that the adsorbed H atoms(Had)and Pd forms a strong Pd-H bond,which hinders the electrochemical desorption of hydrogen.Using the strong coordination between the phosphorous polymer precursor and Pd,a palladium phosphide nano-(Pd3P/NPC)catalyst supported on nitrogen and phosphorus co-doped carbon materials was prepared by pyrolysis.The introduction of P can adjust the ratio of Pd in different valence states,change the electronic structure of Pd,weaken the binding energy of Pd-H,and make it more conducive to the occurrence of HER,thereby increasing the intrinsic activity.The three-dimensional structure of the polymer will provide it with a large specific surface area and increase the utilization of precious metals.The overpotential of this catalyst is only 11 mV when the current density is 10 mA cm-2,which is lower than that of commercial Pd/C and Pt/C catalysts.Compared with other Pd-based catalysts,the inherent activity of Pd3P/NPC has been significantly improved.3.Dentification of active sites in multicomponent carbon-based noble metel catalysts with ultralow matal loading and high hydrogen evolution activityIn order to improve the catalytic activity,increase noble metal utilization and reduce the loading of the catalyst,the coordination and anchoring effect of the polymer containing macrocyclic porphyrin structure on Ru and Ir was used to prepare ultra-low loading Ru/NPCS and Ir/NPCS catalyst by pyrolysis.In these two samples,the strong M-N4 bond formed by N and metal clusters changes the electronic structure of the surface metal,balances the strength of hydrogen absorption and desorption,and improves the hydrogen evolution activity.With ultra-low noble metal content(Ru 3.3%,Ir 2%),the performance of Ru/NPCS and Ir/NPCS exceeds the commercial Pt/C catalyst;and the strong interaction between the support and the metal clusters endows it excellent stability.Although clusters and single-atom sites exist in the catalyst simultaneously,no synergy between them can be found,and single-atom sites hardly catalyze HER.