skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Defect-rich and ultrathin N doped carbon nanosheets as advanced trifunctional metal-free electrocatalysts for the ORR, OER and HER
Title: Defect-rich and ultrathin N doped carbon nanosheets as advanced trifunctional metal-free electrocatalysts for the ORR, OER and HER
Rational design and facile preparation of non-noble trifunctional electrocatalysts with high performance, low cost and strong durability for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) are highly demanded, but remain as a big challenge. Herein, we report a spontaneous gas-foaming method to prepare nitrogen doped ultrathin carbon nanosheets (NCNs) by simply pyrolysing a mixture of citric acid and NH 4 Cl. Under the optimized pyrolysis temperature (carbonized at 1000 °C) and mass ratio of precursors (1 : 1), the synthesized NCN-1000-5 sample possesses an ultrathin sheet structure, an ultrahigh specific surface area (1793 m 2 g −1 ), and rich edge defects, and exhibits low overpotential and robust stability for the ORR, OER and HER. By means of density functional theory (DFT) computations, we revealed that the intrinsic active sites for the ORR, OER and HER are the carbon atoms located at the armchair edge and adjacent to the graphitic N dopants. When practically used as a catalyst in rechargeable Zn–air batteries, a high energy density (806 W h kg −1 ), a low charge/discharge voltage gap (0.77 V) and an ultralong cycle life (over 330 h) were obtained at 10 mA cm −2 for NCN-1000-5. This work not only presents a versatile strategy to develop advanced carbon materials with ultrahigh specific surface area and abundant edge defects, but also provides useful guidance for designing and developing multifunctional metal-free catalysts for various energy-related electrocatalytic reactions.  more » « less
Award ID(s):
1736093
PAR ID:
10106996
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Energy & Environmental Science
Volume:
12
Issue:
1
ISSN:
1754-5692
Page Range / eLocation ID:
322 to 333
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, Journal of Materials Chemistry A)
    null (Ed.)
    Iridium oxide (IrO 2 ) is one of the best known electrocatalysts for the oxygen evolution reaction (OER) taking place in a strongly acidic solution. IrO 2 nanocatalysts with high activity as well as long-term catalytic stability, particularly at high current densities, are highly desirable for proton exchange membrane water electrolysis (PEM-WE). Here, we report a simple and cost-effective strategy for depositing ultrafine oxygen-defective IrO x nanoclusters (1–2 nm) on a high-surface-area, acid-stable titanium current collector (H-Ti@IrO x ), through a repeated impregnation–annealing process. The high catalytically active surface area resulting from the small size of IrO x and the preferable electronic structure originating from the presence of oxygen defects enable the outstanding OER performance of H-Ti@IrO x , with low overpotentials of 277 and 336 mV to deliver 10 and 200 mA cm −2 in 0.5 M H 2 SO 4 . Moreover, H-Ti@IrO x also shows an intrinsic specific activity of 0.04 mA cm catalyst −2 and superior mass activity of 1500 A g Ir −1 at an overpotential of 350 mV. Comprehensive experimental studies and density functional theory calculations confirm the important role of oxygen defects in the enhanced OER performance. Remarkably, H-Ti@IrO x can continuously catalyze the OER in 0.5 M H 2 SO 4 at 200 mA cm −2 for 130 hours with minimal degradation, and with a higher IrO x loading, it can sustain at such a high current density for over 500 hours without significant performance decay, holding substantial promise for use in PEM-WE. 
    more » « less
  2. ; ; ; ; (, Journal of Materials Chemistry A)
    Oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) are three critical reactions for energy-related applications, such as water electrolyzers and metal-air batteries. Graphene-supported single-atom catalysts (SACs) have been widely explored; however, either experiments or density functional theory (DFT) computations cannot screen catalysts at high speed. Herein, based on DFT computations of 104 graphene-supported SACs (M@C3, M@C4, M@pyridine-N4, and M@pyrrole-N4), we built up machine learning (ML) models to describe the underlying pattern of easily obtainable physical properties and limiting potentials (errors = 0.013/0.005/0.020 V for ORR/OER/HER, respectively), and employed these models to predict the catalysis performance of 260 other graphene-supported SACs containing metal-NxCy active sites (M@NxCy). We recomputed the top catalysts recommended by ML towards ORR/OER/HER by DFT, which confirmed the reliability of our ML model, and identified two OER catalysts (Ir@pyridine-N3C1 and Ir@pyridine-N2C2) outperforming noble metal oxides, RuO2 and IrO2. The ML models quantitatively unveiled the significance of various descriptors and fast narrowed down the potential list of graphene-supported single-atom catalysts. This approach can be easily used to screen and design other SACs, and significantly accelerate the catalyst design for many other important reactions. 
    more » « less
  3. ; ; ; (, Journal of Materials Chemistry A)
    Transition metal selenides have attracted intensive interest as cost-effective electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) because of the continuous thrust in sustainable energy conversion. In this article a Mn-based bifunctional electrocatalyst, MnSe, has been identified which shows efficient OER and ORR activity in alkaline medium. The catalytic activity could be further enhanced by using multiwalled carbon nanotubes (MWCNTs) which increases the charge transfer and electronic conductivity of the catalyst composite. This MnSe@MWCNT catalyst composite exhibits a very low overpotential of 290 mV at 10 mA cm −2 , which outperforms state-of-the-art RuO 2 as well as other oxide based electrocatalysts. Furthermore, the composite's facile OER kinetics was evidenced by its small Tafel slope of 54.76 mV dec −1 and low charge transfer resistance, indicating quick transport of the reactant species at the electrode interface. The MnSe@MWCNT also exhibited efficient electrocatalytic activity for ORR with an E onset of 0.94 V, which is among the best reported to date for chalcogenide based ORR electrocatalysts. More importantly, this MnSe-based ORR electrocatalyst exhibits high degree of methanol tolerance, showing no degradation of catalyst performance in the presence of copious quantities of methanol, thereby out-performing the state-of-the-art Pt electrocatalyst. The catalyst composite also exhibited exceptional functional and compositional stability for OER and ORR after a prolonged period of continuous operation in alkaline medium. The surface Raman analysis after OER revealed the retention of manganese selenide surface with evidence of oxo coordination, confirming the formation of an (oxy)selenide as the active surface for OER. Such efficient bifunctional OER and ORR activity makes this MnSe based catalyst attractive for overall electrolysis in regenerative as well as direct methanol fuel cells. 
    more » « less
  4. ; ; ; ; ; ; ; ; (, Chemical Engineering Journal)
    Low-cost, high-performance oxygen catalysts are critical for electrochemical water splitting and metal-air batteries. Herein, carbon aerogels with skeletons consisting of few-layer graphene are derived pyrolytically from a hydrogel precursor using an array of NaCl crystals as the template, exhibiting a high electrical conductivity (869 S m−1) and an ultralow mass density (11.1 mg cm−3). The deposition of NiFe layered double hydroxide (NiFeLDH) nanocolloids renders the aerogels active towards both the oxygen reduction/evolution reactions (ORR/OER), with the performances highly comparable to those of commercial benchmarks in both alkaline and neutral media. Results from operando Raman spectroscopy measurements and first principles calculations suggest that Fe(OH)3 colloids facilitate the oxidation of Ni2+, which lowers the energy barrier to 0.42 eV for OER, whereas the nitrogen-doped carbon aerogels are responsible for the ORR activity. With the composites used as bifunctional oxygen catalysts for electrochemical water splitting and rechargeable zinc-air batteries, the performances in both alkaline and neutral media are markedly better than those based on the mixture of commercial Pt/C and RuO2. Results from this study highlight the unique advantages of ultrathin graphene aerogels in the development of effective catalysts for electrochemical energy devices. 
    more » « less
  5. ; ; ; ; ; ; ; (, Small)
    Abstract It is essential but still challenging to design and construct inexpensive, highly active bifunctional oxygen electrocatalysts for the development of high power density zinc–air batteries (ZABs). Herein, a CoFe‐S@3D‐S‐NCNT electrocatalyst with a 3D hierarchical structure of carbon nanotubes growing on leaf‐like carbon microplates is designed and prepared through chemical vapour deposition pyrolysis of CoFe‐MOF and subsequent hydrothermal sulfurization. Its 3D hierarchical structure shows excellent hydrophobicity, which facilitates the diffusion of oxygen and thus accelerates the oxygen reduction reaction (ORR) kinetic process. Alloying and sulfurization strategies obviously enrich the catalytic species in the catalyst, including cobalt or cobalt ferroalloy sulfides, their heterojunction, core–shell structure, and S, N‐doped carbon, which simultaneously improve the ORR/OER catalytic activity with a small potential gap (ΔE = 0.71 V). Benefiting from these characteristics, the corresponding liquid ZABs show high peak power density (223 mW cm−2), superior specific capacity (815 mA h gZn−1), and excellent stability at 5 mA cm−2for ≈900 h. The quasi‐solid‐state ZABs also exhibit a very high peak power density of 490 mW cm−2and an excellent voltage round‐trip efficiency of more than 64%. This work highlights that simultaneous composition optimization and microstructure design of catalysts can effectively improve the performance of ZABs. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email