Construction And Electrocatalytic Properties Of Transition Metal Borides And Low Platinum Alloy Compounds

Renewable and green energy conversion and storage systems such as fuel cells,metal-air batteries,and water electrolyzers have broad prospects in responding to increasing global energy and environmental challenges.However,their energy conversion efficiency and energy utilization are mainly limited by the slow kinetics of electrochemical processes.At present,pure platinum is still the most suitable catalyst for these types of fuel cells in terms of activity,selectivity and stability.However,there are still many problems in the large-scale application of Pt catalysts,because of the high cost and the lack of durability of Pt catalysts due to surface poisoning.Therefore,the development of oxygen reduction catalysts with anti-toxicity,high activity and low cost is of far-reaching significance for the development of fuel cells.Low platinum alloy catalysts and non-precious metal-based electrocatalysts,such as transition metal-based carbides,borides,nitrides,etc.,have been widely studied and exhibit excellent oxygen reduction catalytic performance.In this paper,transition metal borides and low platinum alloy oxygen reduction catalysts were prepared,and their structure and catalytic properties were studied.The main conclusions are as follows:（1）The Fe₂B catalyst precursor was synthesized by a simple chemical reduction method,in which sodium borohydride acted as both a boron source and a reducing agent.Then,the reduced graphene oxide supported Fe₂B（Fe₂B/rGO）oxygen reduction catalyst was successfully synthesized by one-step hydrothermal method.The results of XRD,SEM and TEM show that the synthesized Fe₂B/rGO is a spherical structure.The electrocatalytic oxygen reduction performance of Fe₂B/rGO was studied by cyclic voltammetry,Tafel,RDE and RRDE.The results show that the peak current intensity of ORR catalyzed by Fe₂B/rGO can reach 7.6 m A/cm²,which is higher than that of Pt/C（20 wt.%）catalyst.After long-term operation,the current intensity can be maintained at 82.47%,which is higher than that of Pt/C catalyst（79.4%）.The onset potential is as high as 0.95 V,which is only 0.06 V lower than that of Pt/C（20 wt%）catalyst.Fe₂B/rGO has excellent catalytic activity and electrochemical stability for ORR in alkaline electrolyte.This may be due to the fact that the boron atoms in Fe₂B accelerate the catalytic kinetics of Fe₂B/rGO for ORR,increasing the onset potential and cycle life.（2）The FeNiB catalyst precursor was synthesized by a simple chemical reduction method.Using sodium borohydride as a boron source and a reducing agent,FeNiB/rGO oxygen reduction catalysts with different iron and nickel contents were successfully synthesized by one-step hydrothermal method.The results of XRD,SEM and TEM show that FeNiB/rGO is a spherical structure.The electrocatalytic oxygen reduction performance of Fe₁Ni₁B/rGO catalyst was studied by cyclic voltammetry,Tafel,RDE and RRDE electrochemical tests.The Fe₁Ni₁B/rGO catalyst has high catalytic activity for oxygen reduction reaction in alkaline electrolyte.The reduced graphene oxide in Fe₁Ni₁B/rGO plays a good role in electron transfer,and the surface of iron-nickel-boron can form abundant catalytic active centers for oxygen reduction reaction.The onset potential(E_onset)of ORR was 0.91 V.The good catalytic performance of FeNiB and the good conductivity of reduced graphene oxide make Fe₁Ni₁B/rGO have similar catalytic oxygen reduction performance to Pt/C.At the same time,the boron atom of FeNiB crystallinity accelerates the catalytic kinetics of FeNiB/rGO for ORR,and improves the initial potential and cycle life.（3）A series of PtNi/HCNR catalysts were obtained by calcining PtNi alloy supported on hollow carbon nanorods derived from polydopamine under high temperature N₂ atmosphere.The catalytic oxygen reduction activity was studied by CV,LSV,Tafel curve and current-time curve（i-t）in alkaline electrolyte.The catalytic mechanism was also studied by RDE test and RRDE test.The results show that PtNi/HCNR-2 catalyst has good oxygen reduction catalytic activity.The prepared PtNi/HCNR-2 has good catalytic oxygen reduction performance.Its catalytic ORR onset potential(E_onset)is 0.98 V,which is 0.04 V higher than that of Pt/C（0.94 V）.At the same time,it also has less H₂O₂ yield,which has higher conversion efficiency.