Rational Design of Single Atomic Co in CoN_x Moieties on Graphene Matrix as an Ultra‐Highly Efficient Active Site for Oxygen Reduction Reaction

Abstract

The sharp increase in current energy consumption needs the development of fuel cells (FCs) as one of sustainable, renewable, efficient and eco-friendly electrochemical conversion systems of energy. The performance of electrocatalysts is crucially important for commercialization of FCs. Commercial Pt based catalysts are used due to their high catalytic activity. However, widespread commercialization is impossible because of the scarcity and poor durability of Pt based catalysts. We are on our quest to find a more stable and affordable alternative catalyst of Pt based catalysts. In particular, single-atom catalysts supported on graphene are greatly attractive because of their unique characteristic and high catalytic activity. In this work, graphene is hydrothermally treated by sulfuric acid to introduce the ion-exchanging sites. Then, Co 2 + ion-exchanging, 2-methylimidazole coordination and pyrolysis process are subsequently conducted to prepare highly-dispersed single-atom Co species catalyst with outstanding ORR activity and durability. This work presents a new direction for a rational design of single-atom catalyst on carbon matrix.

Recent advances in graphene‐based materials for fuel cell applications

“…For example, Zhang et al 83 reported that atomically dispersed Ru on N‐doped graphene exhibited higher ORR activity, better durability, and tolerance toward methanol and CO poisoning than commercial Pt/C catalyst in 0.1 mol/L HClO 4 . Shu et al 84 dispersed single‐atom Co species on to sulfuric acid‐treated N‐doped graphene, demonstrating higher durability (94% of the initial current density remained after 7200 seconds operation in 1 mol/L methanol) than that (87% remained) of Pt/C due to the strong covalent bonding between CoN x species and graphene. Mou et al 85 reported that the ORR active sites on atomically dispersed Cu atoms confined in N‐doped graphene are a mixture of Cu‐N 2 and Cu‐N 4 moieties.…”

Activity Origin and Catalytic Mechanism of the M–N–C Catalysts for the Oxygen Reduction Reaction

“…Pyridinic N could reduce electron localization around Co centers, thereby lowering the energy barrier and facilitating the 4e – ORR process (Figure e and f). Shu et al . hydrothermally treated graphene with sulfuric acid to introduce Co ion-exchanging sites (−SH) to prepare highly dispersed single atom Co species catalysts with excellent ORR activity and durability.…”

“…Pyridinic N could reduce electron localization around Co centers, thereby lowering the energy barrier and facilitating the 4e − ORR process (Figure 6e and f). Shu et al 180 hydrothermally treated graphene with sulfuric acid to introduce Co ion-exchanging sites (−SH) to prepare highly dispersed single atom Co species catalysts with excellent ORR activity and durability. Gao et al 70 designed a novel ZIF using an acetic acid (OAc)-assisted strategy, in which the Co ion had two forms of coordination, one was the known Co-imidazole 182 However, the application of Mn-based catalysts in acidic ORR is limited due to the low metal loadings.…”