Study On Electrocatalytic Activityand Application Of Nitrogen–Doped Porous Carbon Materials For Catalytic Oxygen Reduction

With the development of economy,the environment is becoming more and more serious,and the energy is becoming more and more urgent.Resource starvation and environmental pollution have become the two prominent problems.In this regard,the fuel cell technology shows many advantages because of its high energy in efficiency and environmetantly friendly characterization.Cathodic oxygen reduction reaction?ORR?catalyst has become a key factor limiting the development of fuel cells,the commercialization of the ORR catalyst is mainly platinum catalyst in the present.Platinum based catalysts have limited the development of fuel cells because of the high price,easy poisoning and poor stability.Development ORR catalysts with low cost,high catalytic activity,high stability is the primary task of the development of fuel cells.Porous carbon material,like a shining star,has been noticed by scientists in many non noble catalysts.Porous carbon with high specific surface area and pore size,controllable morphology,is a strong contender for oxygen reduction catalyst.However,due to its low catalytic activity,the catalyst is not scientific alone.Similar reports about hybrid mesoporous carbon with transition metal atoms and other elements emerge in an endless stream.The main principle is that the atomic hybrid doping changes the electron cloud distribution of carbon atoms,which makes it easy to be absorbed by the carbon material to improve the catalytic performance of mesoporous carbon.Nitrogen doping is reported to be the most frequently,however,the reported ORR catalysts are main limited to one kind of medium,the catalyst with high catalytic activity and high stability in acid and alkaline medium is rare.Therefore,it is very important to prepare the catalyst with high catalytic activity and highstability in acid and alkali medium.This paper intends to construct a new type of stable and highly efficient nitrogen doped porous carbon oxygen reduction catalyst.Small molecular compounds were used as nitrogen and carbon sources,valence stable transition metal salt as metal source,the catalyst was synthesized by homogeneously dispersing metal source and precursors onto the surface of the template.The electrochemical properties of the catalysts were studied by linear scanning?LSV?,cyclic voltammetry?CV?and rotating disk electrode technique?REDE?.Scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray powder diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,low temperature nitrogen adsorption desorption curve,and inductively coupled plasma atomic emission spectrometry?ICP?were used to analysis and compare the microstructure of the catalyst.The main conclusions are summarized as follows:?1?With chitosan as the precursor,the catalysts were obtained at the same process except for the pyrolysised temperature,respectively at 700??800??900?.As a result,the catalyst obtained at 800? exhibited better ORR performance.In addition,the transferred number was close to 4,revealing that the 4e-reaction path was mainly approach in the oxygen reduction reaction.?2?With chitosan,melamine and aminopyrine as nitrogen rich precursor,catalysts were achieved respectively.The obtained catalysts were analyzed using electrochemical characterization and the kinetics of the reaction.The results showed that the catalyst come from the precursor aminopyrine,showed the most excellent performance,and he transferred number was is more than 3.96,showing great effect on the activity of catalyst.?3?Two times leaching and reheating played an important role in improving ORR activity.With the same synthesis process,aminopyrine as precursor,two times leaching and reheating intend to compare the influence on ORR performance.The result showed that the ORR performance had a great improvement after the twp times eaching and reheating.The peak potential increased from 0.86 V to 0.98 V,the half wave potential increased from 0.58 V to 0.82 V,the maximum current density also has a lot of improvement?from 3.58 mA cm-2 to 5.80 mA cm-2?.?4?With aminopyrine as precursor,this paper made three catalysts: AP,AP/BP2000 and AP/SiO₂.AP/SiO₂ stand for the catalyst using SiO₂ as template,AP/BP2000 stand for the catalyst using BP2000 as support,and AP stand for bare comparison.The peak potential of AP/SiO₂ was 1.04 V,higher than the other twocatalysts?0.94 V and 0.86V?,the half wave potential were 0.58 V,0.81 V and 0.83 V respectively.SEM,TEM,XRD,low temperature N2 absorption and XPS results showed that AP/SiO₂ had porous structure and higher surface area,932.68 m2 g-1.In addition,the peak separation of N indicated AP/SiO₂ had no inactive site pyrrolic-N.Therefore,the large surface area and the prohibited inactive sites made AP/SiO₂ good performance for ORR.?5?With AP/SiO₂ as the optimal catalyst,further studies of the catalysts were researched,the catalyst in acid electrolyte showed good performance.The catalyst exhibited excellent stability in both acid and alkalinity electrolyte.In the alkalinity electrolyte with methanol,it showed good resistance to methanol.Single cell performance of AP/SiO₂ showed that the OCV and the largest power density were0.874 V and 90 m W cm-2 respectively.