Research On Synthesis And Properties Of Ultrafine PT-CO NWs As Cathode Catalyst For PEMFC

Proton exchange membrane fuel cell（PEMFC）are considered to be one of the solutions to solve the global energy crisis and environmental pollution due to their high energy conversion efficiency,fast startup at low temperatures,and zero emissions.As the most promising type of fuel cell in the commercialization stage,countries attach increasing importance to hydrogen energy and supporting industries,but the application of PEMFC is still limited by its high cost and catalyst durability.Therefore,improving the catalytic activity,utilization efficiency and stability of Pt-based catalysts is a hot topic for scientific researchers.Although studies show that Pt alloyed with second-phase metal is an important way to reduce the amount of Pt and improve catalytic activity,poor durability and stability due to degradation of the non-precious metal,particle agglomeration and Ostwald ripening have become the main limitations.Traditional Pt nanowires have higher structural stability but lower activity.Therefore,the design and synthesis of ultrafine Pt M alloy nanowires（NWs）can not only improve the catalytic activity and utilization efficiency of Pt,but also improve the durability of the catalyst.In this paper,a simple and effective solvothermal method has developed to prepare ultrafine Pt-Co alloy NWs and the application of the NWs as an oxygen reduction reaction（ORR）catalyst in cathode of PEMFC to study its cell performance is also realized.First,the formation factors and growth mechanisms of Pt-Co alloy nanowires were investigated,and the effects of different reaction conditions on the nanowire morphology were compared.After the precursor was kept at 180°C for five hours in the reactor,the nanocrystals were observed to exhibit a uniform nanowire morphology with a diameter of 2 nm and a length of 30 nm,with an aspect ratio of 15.Chromium hexacarbonyl plays a significant role in making Pt and Co forming an alloyed NWs,which acts as both a reducing agent and a structure directing agent.From a kinetic point of view,the corner of the fused nuclei becomes an autocatalytic site,absorbing more nuclei and eventually growing into a nanowire structure.Next,after exploring the optimal loading method,a uniformly dispersed carbon-supported Pt-Co alloy nanowire（Pt-Co NWs/C）catalyst was obtained.In the half-cell test,the mass activity of the Pt-Co NWs/C catalyst was 291.4 m A·mg _Pt^-1,which was significantly better than the 85.5 m A·mg _Pt^-1 of the commercial Pt/C catalyst.Further characterization found that nanowires have a Pt-rich surface,which improves the utilization and reduces the use of Pt,reducing costs effectively.After the accelerated durability test（ADT）,the electrochemical active surface area（ECSA）loss of Pt-Co NWs/C was 19.1%,while that of commercial catalyst was 41.8%,indicating that this one-dimensional nanowire structure effectively improves the durability of the catalyst.Finally,Membrane Electrode Assembly（MEA）was fabricated using Pt-Co NWs/C as the cathode catalyst,and the single-cell performance research was performed.After exploring the influence of different test conditions on the single cell,the power generation performance of MEA was studied.The MEA with Pt-Co NWs/C as the cathode catalyst layer has a cell voltage of 0.675 V at a current density of 1000 m A cm^-2 and a maximum power density of 952 m W·cm^-2,which are better than the MEA prepared by commercial Pt/C catalyst.The stability of the single cell was tested by running at 1000 m A·cm^-2 for 100hours using a galvanostatic method.The maximum power density decay rates of MEA prepared with Pt-Co NWs/C and Pt/C were 11.5%and 16.1%,respectively.These results indicate that an innovative and effective method for the preparation of ultrafine Pt-Co NWs has been developed and can be used as a cathode catalyst for PEMFC.This not only improves the activity and durability of the catalyst at the half-cell level,but also realizes the application of the catalyst in MEA level.More importantly,this efficient and simple preparation method can be expanded in grams,which provides a reference for production.