Theoretical insights on the catalytic activity and mechanism for oxygen reduction reaction at Fe and P codoped graphene

Abstract

The non-precious metal graphene catalyst doped with Fe-Px are recently proposed as a promising candidate in substituting Pt for catalyzing oxygen reduction reaction (ORR) in fuel cells. Systematic DFT calculations are performed to investigate the catalytic activity and the ORR mechanism on the Fe-Px (x = 1-4) system in acid medium in this work. Our results indicated that the configuration with one Fe and two P atoms codoped at zigzag edge site (Fe-P2-zig-G) is the most stable, in excellent agreement with the experimental observation that the ratio of Fe and P is nearly 1 : 2. The four-electron reduction mechanism for ORR on the Fe-P2-zig-G is via the competing OOH hydrogenation pathways (to form either OH + OH or O + H2O). The rate determining step is the O2 hydrogenation with an energy barrier of 0.43 eV, much smaller that of calculated 0.80 eV for pure Pt. In addition, the highest energy barrier of the studied ORR mechanism is the O2 dissociation with an energy barrier of 0.70 eV, a value also smaller than that of pure Pt. This demonstrated that the zigzag edge site of the Fe-P2 codoped graphene should be active for the ORR.

Theoretical Investigation on the Reaction Pathways of the Oxygen Reduction Reaction on Graphene Codoped with Manganese and Phosphorus as a Potential Nonprecious Metal Catalyst

“…For the single O atom, the most favorable adsorption site is on the Mn top site with an adsorption energy of −5.54 eV (Figure d). The adsorption energy of the single O atom is the strongest among the studied single intermediates, which indicates that the O atom has the strongest binding interaction with the MnP 2 ‐Gra surface, similar to that in previous studies (Table ) …”

“…Compared with MnN 4 ‐, FeP 4 ‐, and CoP 4 ‐doped graphene, the adsorption energies on MnP 2 ‐Gra are stronger for O 2 , O, H, OH, OOH, and H 2 O, except for H in FeN 4 (Table ). In addition, edge‐site FeP 2 shows a much stronger adsorption for O 2 and H 2 O (Table ) …”

“…Theoretical studies on FeP 4 ‐ and CoP 4 ‐doped graphenes indicated that FeP 4 ‐doped graphene is a more efficient electrocatalyst for the ORR in an alkaline medium than CoP 4 ‐doped graphene . For FeP 2 ‐doped graphene at the zigzag edge‐site, the hydrogenation of OOH is the most favorable pathway …”

“…[37] For FeP 2 -doped graphene at the zigzag edge-site, the hydrogenation of OOH is the most favorable pathway. [38] Inspired by these studies, in this work we studied the catalytic activity and the ORR mechanism on divacancy graphene codopedw ith MnP x (x = 1-4). To check the stabilityo ft hese species, we calculated the formation energy using Equation (1):…”

Medium Modulated Oxygen Reduction Activity of Fe/Co Active Centre‐engrafted Electrocatalysts

“…The catalyst showed remarkable stability for 700 h at 0.40 V in a hydrogen fuel cell against the state-of-the-art Pt/C catalyst. The standard reduction potential and equations for the reduction of molecular oxygen in acidic and basic media is given below: [18][19][20][21] a) In basic media: For the direct four-electron pathway [13][14] As the MÀ N x À C catalysts have emerged as a potential substitute for the noble metal catalysts, it is desirable to explore the surface reactions over the active catalyst for developing sustainable and durable devices.…”