| Oxygen reduction reaction(ORR)is of great significance for the development and application of fuel cells,but its kinetics is slow,so a catalyst needs to be added to promote the reaction.Currently,the mainstream catalyst used commercially is Pt/C,but it is limited by shortcomings such as scarce platinum reserves,poor specific mass activity and long-term stability.For this reason,reducing the amount of platinum and improving its activity and stability have become the key to actual research.Sub-nanoscale platinum clusters have a high atomic dispersion and specific surface area,which allow a large number of active catalytic sites to be exposed.The application prospect is very broad.In this subject,a radish-derived nitrogen-doped porous carbon was used as a stabilizing material,and then sub-nanometer platinum clusters and bimetallic clusters were prepared by photochemical reduction method.The main research results obtained are as follows:(1)Using the nitrogen-doped porous radish-based carbon as the carrier,the atomically precise platinum clusters with scalable atoms(Ptx,x=1～43)were prepared by the industrially scalable ultraviolet irradiation reduction method.Among them,the 0.75 nm platinum clusters obtained by five times of UV irradiations show excellent ORR electrocatalytic activity(E1/2 is 0.93 V vs RHE,MA is 1.45 A mgpt-1),which exceeds the commercial Pt/C catalyst(E1/2 is 0.87 V vs RHE,MA is 0.14 A mgpt-1).(2)The stable structure and formation mechanism of metal clusters were studied at the atomic level:DFT calculations revealed that 0.8 nm micropores modified with pyridine nitrogen atoms are the active sites for anchoring[PtCl6]2-;the subsequently reduced Pt atoms will gradually spontaneously grow on the surface of carbon and become a 0.75 nm stable cluster with close-packed facecentered cubic.This work provides a possible way to synthesize atomically precise clusters of other precious metals.(3)Based on the advantages of alloying on the electronic control and structure regulation of Pt,a bottom-one-atom tailoring strategy was proposed.The isolated copper atom and cobalt atom were modified on the surface of radish-derived carbon by ammonia-assisted solid phase thermal transfer method,and then the bimetallic sub-nano clusters Cu1Ptx and Co1Ptx were obtained by UV directional deposition.The MA of them reach 2.10 A mgpt-1 and 2.27 A mgPt1,respectively,better than the pure Pt clusters Ptx(1.45 A mgpt-1)and commercial Pt/C(0.14 A mgpt-1).The compression effect caused by the cluster size and the electronic coordination effect produced by the guest metal are the main reasons that lead to the significant improvement of the electrocatalytic performance of oxygen reduction. |
