Oxygen-Reconstituted Active Species of Single-Atom Cu Catalysts for Oxygen Reduction Reaction

Abstract

Identification of an active center of catalysts under realistic working conditions of oxygen reduction reaction (ORR) still remains a great challenge and unclear. Herein, we synthesize the Cu single atom embedded on nitrogen-doped graphene-like matrix electrocatalyst (abbreviated as SA-Cu/NG). The results show that SA-Cu/NG possesses a higher ORR capability than 20% Pt/C at alkaline solution while the inferior activity to 20% Pt/C at acidic medium. Based on the experiment and simulation calculation, we identify the atomic structure of Cu-N2C2 in SA-Cu/NG and for the first time unravels that the oxygen-reconstituted Cu-N2C2-O structure is really the active species of alkaline ORR, while the oxygen reconstitution does not happen at acidic medium. The finding of oxygen-reconstituted active species of SA-Cu/NG at alkaline media successfully unveils the bottleneck puzzle of why the performance of ORR catalysts at alkaline solution is better than that at acidic media, which provides new physical insight into the development of new ORR catalysts.

What Is the Real State of Single-Atom Catalysts under Electrochemical Conditions—From Adsorption to Surface Pourbaix Plots?

“…Overall, the results presented here and in previously published experimental findings [12,16,44] indicate that theoretical models for SACs should be carefully set to match realistic operating conditions. Moreover, UHV characterization results must be taken with care when interpreting the electrochemical performance of SACs.…”

“…The obtained results have implications in terms of both the theoretical modelling of SACs and their practical applications. While the current study is restricted to the metal embedded in the graphene single vacancy site, it should be noted that recently, it was shown that oxygen reconstitutes the Cu-N 2 C 2 site in Cu-based SACs and that Cu-N 2 C 2 -O site is the actual active species of alkaline ORR, while the oxygen reconstitution process is not operative at a low pH [12]. Such oxygen reconstitution is seen here as well (Figures 5 and 6) for Cu@vG.…”

“…Since virtually every atom possesses catalytic function, even SACs based on Pt-group metals are attractive for practical applications. So far, the use of SACs has been demonstrated for numerous catalytic and electrocatalytic reactions, including energy conversion and storage-related processes such as hydrogen evolution reactions (HER) [4][5][6][7][8][9], oxygen reduction reactions (ORR) [7,[10][11][12], oxygen evolution reactions (OER) [8,13,14], and others. Moreover, SACs can be modeled relatively easily, as the single-atom nature of active sites enables the use of small computational models that can be treated without any difficulties.…”

“…The concept of Pourbaix plots has not been widely utilized for SACs, although there are some examples of their construction [12,28]. However, their use would be exceptionally helpful for understanding the nature of the active sites in SACs under operating conditions and the proper modelling of SACs using computational approaches of different complexity.…”

Rapid Controllable Synthesis of Atomically Dispersed Co on Carbon under High Voltage within One Minute

“…[ 10–14 ] In particular, metal single sites embedded in N‐doped carbon ( M /N‐C) ( M = Co, Fe, Ni, etc.) are promising electrocatalysts for oxygen reduction, [ 15–19 ] water splitting, [ 20,21 ] and carbon dioxide reduction. [ 22 ] The typical bottom‐up strategies to fabricate carbon‐supported ADMCs usually involve an annealing process after the wet‐chemistry pre‐treatment, [ 23 ] or the direct pyrolysis of metal‐containing precursors, such as organometallics, [ 24 ] polymers, [ 25 ] and especially metal‐organic frameworks (MOFs).…”