Monovacancy Coupled Pyridinic N Site Enables Surging Oxygen Reduction Activity of Metal-Free CN_x Catalyst

Abstract

Nitrogen-doped carbon (CN x ) nanostructures are appealing metal-free electrocatalysts for some key electrochemical processes such as oxygen reduction reaction (ORR), due to their low cost, exceptional stability, and desirable selectivity. However, the precise configuration engineering of N-related active sites still remains a big challenge. Herein, we report a concept of monovacancy coupled pyridinic N (MV-c-PN) active site, which is designed and successfully fabricated by the pyrolysis of welldesigned precursor. This unique active site couples the features of pyridinic N and topological monovacancy defect, synergistically tuning the electronic properties of CN x moiety. This tuning induces stronger adsorption of oxygen-containing intermediates on the MV-c-PN sites and alters the ORR kinetics pathway. Additionally, the hierarchical porous nature of CN x nanostructure facilitates the penetration of electrolyte and the transportation of O 2 . Accordingly, the CN x nanomaterial with such MV-c-PN sites shows outstanding ORR activity in alkaline solution, surpassing most of the reported metal-free catalysts, with its intrinsic turnover frequency (TOF) 7.26 times higher than conventional pyridinic N. The assembled zinc-air battery reaches a maximum power density even 40.3% higher than that with the benchmark Pt/C. Our fine configuration engineering of CN x active sites provides a novel strategy for developing efficient carbon-based metal-free ORR catalysts.

Designing a Hierarchical Porous Carbon with Optimized Nitrogen Doping for Efficient Oxygen Reduction Reaction

“…The electrocatalytic performance, as assessed from half‐wave potential (E 1/2 ), increased successively for HPC, KOAc/HPC, Zn(OAc) 2 /HPC and Zn(OAc) 2 ‐DCD/HPC with the E 1/2 values of 0.844, 0.862, 0.892 and 0.909 V, respectively. The E 1/2 for Zn(OAc) 2 /HPC and Zn(OAc) 2 –DCD/HPC samples with optimal hierarchical porous structures and higher active N‐doping was more positive than most of the recently reported metal‐free carbon‐based catalysts (Table S4 [4,12, 19–20, 28, 37, 46, 51–53] ) and even obviously higher than tha4 of Pt/C (E 1/2 =0.872 V). In particular, the ultimate current density of the Zn(OAc) 2 –DCD/HPC sample was able to approach around 5 mA cm −2 even with a catalyst loading of only 0.106 mg cm −2 (Figure S10).…”

“…[35] Various attempts have been made to introduce mesoporous structures in ZIF-8-derived NCs by the combination of ZIF and hard template method to expose the N-doped active sites located in the micropores as much as possible. [36][37][38] Nevertheless, as the hard template is usually independent of ZIF structure, the mesopore generated by hard templates are difficult to link up micropores well, so a large number of active sites still cannot be fully utilized. In this regard, it would be an effective way to balance mass transport and nitrogen doping if the unique M-N x structures in ZIF-8 could be introduced into the porous structure.…”

“…However, the very limited mesoporous structure of the ZIF‐derived NC material severely hampers the efficient use of the internal active sites [35] . Various attempts have been made to introduce mesoporous structures in ZIF‐8‐derived NCs by the combination of ZIF and hard template method to expose the N‐doped active sites located in the micropores as much as possible [36–38] . Nevertheless, as the hard template is usually independent of ZIF structure, the mesopore generated by hard templates are difficult to link up micropores well, so a large number of active sites still cannot be fully utilized.…”

Boosting Oxygen Reduction Catalysis with Hierarchically Porous Fe-Doped Carbon by Chemical Vapor Deposition in Zn–Air Batteries

“…The degrees of graphitization for the three samples were further studied by a Raman spectrometer. As illustrated in Figure b, Raman spectra collected on all carbon-based materials unveil a D band (1340 cm –1 ) and a G band (1590 cm –1 ), which are characteristic of graphitic carbon and defective carbon, respectively. , The I D / I G of FeNC-CVD (1.05) was lower than those of NC (1.10) and FeNC-MIX (1.22) in raman spectral results, demonstrating the CVD-assisted Fe doping, facilitating the graphitization of carbon and further promoting the charge transfer during electrochemical oxygen reduction. , …”

Material design and surface chemistry for advanced rechargeable zinc–air batteries

“…60,61 Heteroatom doping strategies have been widely studied as an efficient way to improve the catalytic properties of metal-free carbon-based electrocatalysts. 56,57,[62][63][64] Many studies demonstrated that heteroatom doping can change the sp 2 electronic structures of carbon materials and electrocatalytically active sites could be formed between elements with a different electronegativity. 51,53,54,61,65 For example, Zhang et al fabricated graphite-analogous nitrogen-doped carbon nanoake using sandwich-like zeolitic imidazolate framework (ZIF)-8/MnO 2 materials as the precursor.…”