Synthesis of carbon-supported binary FeCo\u2013N non-noble metal electrocatalysts for the oxygen reduction reaction

摘要

In this paper, a carbon-supported binary FeCo\u2013N/C catalyst using tripyridyl triazine (TPTZ) as the complex ligand was successfully synthesized. The FeCo\u2013TPTZ complex was then heat-treated at 600 \ub0C, 700 \ub0C, 800 \ub0C, and 900 \ub0C to optimize its oxygen reduction reaction (ORR) activity. It was found that the 700 \ub0C heat-treatment yielded the most active FeCo\u2013N/C catalyst for the ORR. XRD, EDX, TEM, XPS, and cyclic voltammetry techniques were used to characterize the structural changes in these catalysts after heattreatment, including the total metal loading and the mole ratio of Fe to Co in the catalyst, the possible structures of the surface active sites, and the electrochemical activity. XPS analysis revealed that Co\u2013Nx, Fe\u2013Nx, and C\u2013N were present on the catalyst particle surface. To assess catalyst ORR activity, quantitative evaluations using both RDE and RRDE techniques were carried out, and several kinetic parameters were obtained, including overall ORR electron transfer number, electron transfer coefficient in the ratedetermining step (RDS), electron transfer rate constant in the RDS, exchange current density, and mole percentage of H2O2 produced in the catalyzed ORR. The overall electron transfer number for the catalyzed ORR was ~3.88, with H2O2 production under 10%, suggesting that the ORR catalyzed by FeCo\u2013N/C catalyst is dominated by a 4-electron transfer pathway that produces H2O. The stability of the binary FeCo\u2013N/C catalyst was also tested using single Fe\u2013N/C and Co\u2013N/C catalysts as baselines. The experimental results clearly indicated that the binary FeCo\u2013N/C catalyst had enhanced activity and stability towards the ORR. Based on the experimental results, a possible mechanism for ORR performance enhancement using a binary FeCo\u2013N/C catalyst is proposed and discussed.