Low‐Coordinated CoNC on Oxygenated Graphene for Efficient Electrocatalytic H₂O₂ Production

Abstract

Electrochemical H2O2 production through the 2‐electron oxygen reduction reaction (ORR) is a promising alternative to the energy‐intensive anthraquinone process. Herein, by simultaneously regulating the coordination number of the atomically dispersed cobalt sites and the nearby oxygen functional groups via a one‐step microwave thermal shock, a highly selective and active CoNC electrocatalyst for H2O2 electrosynthesis that exhibits a high H2O2 selectivity (91.3%), outstanding mass activity (44.4 A g−1 at 0.65 V), and large kinetic current density (11.3 mA cm−2 at 0.65 V) in 0.1 m KOH is obtained. In strong contrast to the typical CoN4 moieties for the 4‐electron ORR, the present CoNC catalyst possesses a low‐coordinated CoN2 configuration and abundant epoxide groups, which work in synergy for promoting the 2‐electron ORR, as demonstrated by a series of control experiments and theoretical simulations. This study may provide an effective avenue to modulating the composition and structure of electrocatalysts at the atomic scale, leading to the development of new electrocatalysts with unprecedented reactivity.

Tuning Two‐Electron Oxygen‐Reduction Pathways for H2O2 Electrosynthesis via Engineering Atomically Dispersed Single Metal Site Catalysts

“…In a recent work, the simultaneous tuning of OFGs and coordination numbers in a Co–N–C catalyst was successfully realized via a microwave irradiation treatment method (Figure 6e). [ 172 ] In particular, a solid mixture of amine‐functionalized graphene oxide (AGO) and Co cations was prepared as a precusor. An instant microwave irradiation was employed to synthesize a Co–N 2 –C/HO catalyst, which facilitates the mitigation of atom migration/aggregation compared to traditional high‐temperature heating treatment.…”

“…e) Schematic diagram of the synthesis route, f) schematic of the optimal Co-N 2 configuration with four epoxy groups and one O solvent species (CoN 2 H 6 -4O-O), the plot of η as a function of ΔG *OOH for g) CoN 2 H x (x = 4, 6, 8, 12, 14) moieties, h) CoN 2 H 6 with epoxy groups (CoN 2 H 6 -θ), and i) CoN 2 H 6 with four epoxy groups (CoN 2 H 6 -4O-ω, ω = H, H 2 O, OH, or O). Reproduced with permission [172]. Copyright 2021, Wiley-VCH.…”

Engineering the Morphology and Microenvironment of a Graphene‐Supported Co‐N‐C Single‐Atom Electrocatalyst for Enhanced Hydrogen Evolution

“…As shown in the Co K‐edge XANES (Figure 3b), CoN 3 ‐CSG and CoN 4 ‐CSG show similar profiles and the positions at the half of the edge maximum intensity are between those of the references (Co foil and CoO) and closer to CoO, indicating that the valence states of Co are ≈+2. [ 32 ] In order to verify the atomic dispersion of the Co species, EXAFS wavelet transform (WT) analysis was conducted as it can provide both radial distance and k ‐space resolution of backscattering atoms. [ 14 ] As shown in Figure S10 (Supporting Information), CoN 3 ‐CSG and CoN 4 ‐CSG display only one intensity maximum at ≈4.0 Å −1 , which is different from the Co‐Co scattering at ≈7.0 Å −1 present in Co foil, and it can be assigned to the Co‐N contributions, excluding the possible formation of Co‐derived nanoparticles.…”

Tailoring the selectivity and activity of oxygen reduction by regulating the coordination environments of carbon-supported atomically dispersed metal sites

“…5j–l). 46 High-resolution Co 2p XPS spectra showed the low-coordinated Co–N 2 sites shifted slightly to lower binding energy compared to the ordinary thermal treatment derived Co–N 4 catalyst, indicating the lower oxidation state of the Co moiety in Co–N 2 –C. EXAFS characterization results were in line with the XANES results revealing that Co–N 2 presented an evidently lower peak intensity of the Co–N moiety compared to Co–N 4 , manifesting a lower N coordination number.…”