Study Of Nitrogen-Doped Carbon With Non-Precious Metals As Efficient Catalysy For Oxygen Reduction

The development of efficient electrocatalysts for an oxygen diffusion cathode (ODC) is one of the most important projects for enhancing the performance of electrochemical energy conversion including fuel cells, metal-air batteries, and NaCl/Na2CO3 electrolysis. However, the sluggish kinetics of the oxygen reduction reaction (ORR) results in serious cathodic polarization, which leads to low outputs of fuel cells and metal-air batteries, and high input of electrolysis cells. Platinum (Pt)-based materials have long been regarded as the most effective catalysts for the ORR, but they suffer from a prohibitive cost and limited storage. Nowadays, tremendous efforts are devoted to the design and preparation of non-precious metal catalysts (NPMCs) with low cost, high activity, and long-term durability to promote the progress of fuel cells, metal-air batteries, and ODC electrolysis.In view of the abundant pyridinic N and the interaction with ferrous of 1, 10-Phenanthroline, a series of catalysts doped with Fe and N designated as Fe-N@Cs were synthesized by the impregnation method followed by pyrolysis. In the process 1, 10-Phenanthroline was used as nitrogen source, oxidized BP1000 was used as carbon source, and ferrous acetate was added as the catalyst of the synthesis process. All these catalysts have a certain ORR activity but not as competitive as Pt/C. What's more, in the study of ORR-OER, anode current is not sustainable current caused by oxygen evolution, and the initial potential and the half-wave potential of ORR both negatively shift. XPS results suggest that pyridinic N, as one of the effective components for ORR, can be easily destroyed when the potential is relatively high, making Fe-N@Cs not suitable to be bifunctional catalysts for ORR-OER.Then, a series of N-doped carbon materials decorated with one or more non-precious metals (Mn, Fe, Co, and Ni) have been prepared through a simple pyrolysis method. The oxides of Mn and Co can increase ORR activity, as they are involved in the ORR directly. Co and Fe can introduce metal-pyridinic N, which is reported to be one of the most efficient N species for ORR catalysis. Moreover, Fe and Ni can improve the graphitization degree, which is able to enhance the ORR activity indirectly. It is expected that the proper doping of nitrogen and metal species into a carbon matrix can effectively improve the ORR performance of the catalyst. As the pyrolysis temperature will greatly affect the form and content of the nitrogen, and graphitization of carbon, it is also taken into consideration to optimize the experimental conditions.Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) tests show that N-doped carbon decorated with four kinds of non-precious metals and prepared at 800? designated as MFCN/NC-800 has the best ORR activity. Specifically, it has a more positive ORR onset potential (54 mV) and a more positive halfwave potential (46 mV) than commercial Pt/C. Rotating ring-disk electrode (RRDE) result indicates that the MFCN/NC-800 catalyst exhibits a typical four-electron pathway with negligible H2O2 productivity during the ORR process. According to XRD, XPS and HRTEM, pyridinic nitrogen, graphitic carbon, MnO, and Fe-Co-Ni nanoparticles, which are efficient for catalyzing the ORR individually or synergistically, are successfully introduced into the composite catalyst with a high specific surface area (1908 m2·g-1). Moreover, MFCN/NC shows remarkable electrocatalytic activity and longterm stability in Na2CO3 electrolysis. The cell voltages at 10 mA·cm-2 and 100 mA·cm2 are only 0.86 V and 1.45 V, respectively, while the cell voltages of conventional HEC electrolysis in the same condition are 1.90 V and 2.52 V, respectively, suggesting an energy-saving electrolysis of Na2CO3 to regenerate NaHCO3 and NaOH.