Phenylenediamine-based Non-precious Metal Catalyst For Oxygen Reduction In Fuel Cell

Fuel cell is an environment-friendly power supply, which could be the substitution for internal-combustion engine and reduce carbon emissions. However, the large-scale application of fuel cell is severely hindered by high prices, and the high cost is primarily due to platinum catalyst used in the cathode. Recently, non-precious metal catalysts for cathodic oxygen reduction reduction(ORR) have attracted great research interests as alternatives to platinum-based materials. And aniline derivatives are constantly used as the nitrogen source of non-precious metal catalyst, because of the favorable structure of aromatic rings connected via imino group, which could promote the incorporation of nitrogen containing active sites into the graphitized carbon framework. In this paper, phenylenediamine-baesd Fe/N/C catalyst and nitrogen-doped carbon material are prepared. The physical characterization and electrochemical performance tests are carried out, and the durability of catalysts are studied.The Fe/N/C catalyst, which is a typical non-precious metal catalyst, is the most likeliest candidate in acid medium. Solid phase polymerization of phenylenediamine with ZnO template toward self-supported Fe/N/C catalyst is prepared. Transmission electron microscopy shows that the morphology of poly-p-phenylenediamine change from bulk to thin layer. Nitrogen adsorption-desorption tests show that BET surface of poly-p-phenylenediamine increases from 122 m2/g to 1215 m2/g after the addition of ZnO. X-ray diffraction and X-ray photoelectron spectroscopy reveal that ZnO can be removed completely after acid leaching. Rotating disc electrode tests in O2-saturated 0.1 mol/L HClO4 solution show that the ORR activity is radically enhanced after the addition of ZnO, the half wave potential of which is only 40 mV lower than that of Pt/C.However, the durability of the self-supported Fe/N/C catalyst is not as good as its activity. As a result, CeO2 doped Fe/N/C catalyst is prepared. The reaction between Ce3+ and H2O2 can reduce the production of·OH and improve the durability of catalyst. Accelerative aging tests in O2-saturated 0.1 mol/L HClO4 solution show that a slight change in the half wave potential (-25 mV) is observed after 1000 cycles, indicating the good stability of CeO2 doped Fe/N/C catalyst.On the other hand, nitrogen-doped carbon materials are prepared via the pyrolysis of the poly-p-phenylenediamine/carbon black composite. The optimized catalyst outperforms commercial Pt/C in 0.1 mol/L KOH solution, the half wave potential of which is 40 mV higher than that of Pt/C. Scanning electron microscopy shows that carbon particles aggregate on the surface of poly-p-phenylenediamine. N2 adsorption-desorption analyses indicate that a composite structure, in which the N-rich surface of the poly-p-phenylenediamine has an increased active center concentration and the high external surface area of the carbon black is conducive to the mass transport, is highly beneficial in terms of promoting the oxygen reduction reaction. However, the activity of this catalyst undergo an obvious decrease following exposure to air for 30 d. X-ray photoelectron spectroscopy shows that the oxygen content in the catalyst increases by 1%, which means that oxygen reacts with the catalyst, leading to the deactivation of active sites and the decrease of ORR activity.