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

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.Le pr\ue9sent article fait \ue9tat de la synth\ue8se d\u2019un catalyseur binaire sur carbone, soit le FeCo\u2013N/C, en utilisant comme ligand la tripyridyl-triazine (TPTZ). Le complexe FeCo\u2013TPTZ a ensuite subi un traitement thermique \ue0 diverses temp\ue9ratures (600, 700, 800 et 900 \u25e6C) pour optimiser son activit\ue9 d\u2019oxydor\ue9duction (ORR). On a constat\ue9 que le catalyseur FeCo\u2013N/C produit une activit\ue9 maximale d\u2019ORR dans le cas du traitement thermique \ue0 700 \u25e6C. Les techniques de diffraction des rayons X, de spectroscopie des rayons X par dispersion d\u2019\ue9nergie, de microscopie \ue9lectronique \ue0 transmission, de spectroscopie XPS et de voltamp\ue9rom\ue9trie cyclique ont permis de caract\ue9riser les changements de structure de ces catalyseurs apr\ue8s le traitement thermique, la charge de m\ue9tal totale, le rapport molaire FE/Co du catalyseur, les structures possibles des sites actifs de la surface, ainsi que l\u2019activit\ue9 \ue9lectrochimique. L\u2019analyse par spectroscopie XPS montre la pr\ue9sence de Co\u2013Nx, de Fe\u2013Nx et de C\u2013N \ue0 la surface des particules de catalyseur. Pour \ue9valuer l\u2019activit\ue9 d\u2019ORR du catalyseur, on a effectu\ue9 des analyses quantitatives au moyen de la technique de l\u2019\ue9lectrode \ue0 disque tournant et de celle de l\u2019\ue9lectrode \ue0 disque tournant et anneau, ce qui a permis d\u2019obtenir plusieurs param\ue8tres cin\ue9tiques, dont le nombre de transferts d\u2019\ue9lectrons global, le coefficient de transfert d\u2019\ue9lectrons dans l\u2019\ue9tape cin\ue9tiquement limitante (RDS pour rate determining step), la constante de vitesse de transfert d\u2019\ue9lectrons dans la RDS, la densit\ue9 de courant d\u2019\ue9change et le pourcentage molaire de H2O2 produit par l\u2019ORR catalys\ue9e. Le nombre de transferts d\u2019\ue9lectrons global pour l\u2019ORR catalys\ue9e est d\u2019environ 3,88 et la production de H2O2 est inf\ue9rieure \ue0 10 %, ce qui suppose que l\u2019ORR catalys\ue9e par le catalyseur FeCo\u2013N/C est domin\ue9e par une voie de transfert de 4 \ue9lectrons qui produit du H2O. On a \ue9galement v\ue9rifi\ue9 la stabilit\ue9 du catalyseur binaire FeCo\u2013N/C en utilisant, comme r\ue9f\ue9rences, les catalyseurs Fe\u2013N/C et Co\u2013N/C s\ue9par\ue9ment. D\u2019apr\ue8s les r\ue9sultats exp\ue9rimentaux obtenus, il est clair que le catalyseur binaire FeCo\u2013N/C accro\ueet l\u2019activit\ue9 et la stabilit\ue9 de l\u2019ORR. Compte tenu des r\ue9sultats exp\ue9rimentaux, on propose et examine un m\ue9canisme possible de performance accrue de l\u2019ORR en utilisant le catalyseur binaire FeCo\u2013N/C.Peer reviewed: YesNRC publication: Ye