An official website of the United States government
Despite the various strategies for achieving metal–nitrogen–carbon (M–N–C) single-atom catalysts (SACs) with different microenvironments for electrochemical carbon dioxide reduction reaction (CO 2 RR), the synthesis–structure–performance correlation remains elusive due to the lack of well-controlled synthetic approaches. Here, we employed Ni nanoparticles as starting materials for the direct synthesis of nickel (Ni) SACs in one spot through harvesting the interaction between metallic Ni and N atoms in the precursor during the chemical vapor deposition growth of hierarchical N-doped graphene fibers. By combining with first-principle calculations, we found that the Ni-N configuration is closely correlated to the N contents in the precursor, in which the acetonitrile with a high N/C ratio favors the formation of Ni-N 3 , while the pyridine with a low N/C ratio is more likely to promote the evolution of Ni-N 2 . Moreover, we revealed that the presence of N favors the formation of H-terminated edge of sp 2 carbon and consequently leads to the formation of graphene fibers consisting of vertically stacked graphene flakes, instead of the traditional growth of carbon nanotubes on Ni nanoparticles. With a high capability in balancing the *COOH formation and *CO desorption, the as-prepared hierarchical N-doped graphene nanofibers with Ni-N 3 sites exhibit a superior CO 2 RR performance compared to that with Ni-N 2 and Ni-N 4 ones.
more »
« less
Recent progress in electrochemical reduction of carbon dioxide on metal single‐atom catalysts
Abstract Electrochemical reduction reaction of CO2(CO2RR) is a promising technology for alleviating the global warming caused by the emission of CO2. This technology, however, is still in the stage of finding efficient catalysts. The catalysts must be able to convert CO2to other carbon‐based products with high activity and selectivity to valuable chemicals. In this review, previous development of heteroatom‐doped metal‐free carbon materials (H‐CMs) is briefly summarized. Recent progress of CO2RR promoted by metal single‐atom catalysts (M‐SACs) is then discussed with emphasis on the synthesis of M‐SACs, the catalytic performance, and reaction mechanisms. The high temperature pyrolysis method and electrodeposition are attracting attentions recently to prepare M‐SACs with high metal loading on N‐doped carbon materials, a very active M‐SACs system for the CO2RR. Theoretical calculations of free energy change on active sites, the Operando X‐ray absorption near edge structure (XANES), and Bader charge analysis reveal a significant role of metal oxidation state and charge transfer between metal atoms and absorbed CO. The challenges and perspectives for the extensive applications of M‐SACs in CO2RR are also discussed in this review.
more »
« less
- Award ID(s):
- 1804949
- PAR ID:
- 10367043
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Energy Science & Engineering
- Volume:
- 10
- Issue:
- 5
- ISSN:
- 2050-0505
- Format(s):
- Medium: X Size: p. 1584-1600
- Size(s):
- p. 1584-1600
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Carbon‐supported nitrogen‐coordinated single‐metal site catalysts (i.e., M−N−C, M: Fe, Co, or Ni) are active for the electrochemical CO2reduction reaction (CO2RR) to CO. Further improving their intrinsic activity and selectivity by tuning their N−M bond structures and coordination is limited. Herein, we expand the coordination environments of M−N−C catalysts by designing dual‐metal active sites. The Ni‐Fe catalyst exhibited the most efficient CO2RR activity and promising stability compared to other combinations. Advanced structural characterization and theoretical prediction suggest that the most active N‐coordinated dual‐metal site configurations are 2N‐bridged (Fe‐Ni)N6, in which FeN4and NiN4moieties are shared with two N atoms. Two metals (i.e., Fe and Ni) in the dual‐metal site likely generate a synergy to enable more optimal *COOH adsorption and *CO desorption than single‐metal sites (FeN4or NiN4) with improved intrinsic catalytic activity and selectivity.more » « less
-
Abstract Developing high performance nonprecious metal‐based electrocatalysts has become a critical first step towards commercial applications of metal‐air batteries. Herein, nanocomposites based on Co/Co2P nanoparticles encapsulated within hierarchically porous N, P, S co‐doped carbon are prepared by controlled pyrolysis of zeolitic imidazolate frameworks (ZIF‐67) and poly(cyclotriphosphazene‐co‐4,4’‐sulfonyldiphenol) (PZS). The resulting Co/Co2P@NPSC nanocomposites exhibit apparent oxygen reduction reaction (ORR) and evolution reaction (OER) catalytic performance, and are used as the reversible oxygen catalyst for zinc‐air batteries (ZABs). Density functional theory (DFT) calculations exhibit that Co2P could provide active sites for the ORR and promote the conversion between the adsorbed intermediates, and porous N,P,S co‐doped carbon with Co2P nanoparticles also improves the exposure of actives sites and endows charge transport. Liquid‐state ZABs with Co/Co2P@NPSC as the cathode catalysts demonstrate the greater power density of 198.1 mW cm−2and a long cycling life of 50 h at 10 mA cm−2, likely due to the encapsulation of Co/Co2P nanoparticles by the carbon shell. Solid‐state ZABs also display a remarkable performance with a high peak power density of 74.3 mW cm−2. Therefore, this study indicates the meaning of the design and engineering of hierarchical porous carbon nanomaterial as electrocatalyst for rechargeable metal‐air batteries.more » « less
-
Abstract Cu is the most promising metal catalyst for CO2electroreduction (CO2RR) to multi-carbon products, yet the structure sensitivity of the reaction and the stability versus restructuring of the catalyst surface under reaction conditions remain controversial. Here, atomic scale simulations of surface energies and reaction pathway kinetics supported by experimental evidence unveil that CO2RR does not take place on perfect planar Cu(111) and Cu(100) surfaces but rather on steps or kinks. These planar surfaces tend to restructure in reaction conditions to the active stepped surfaces, with the strong binding of CO on defective sites acting as a thermodynamic driving force. Notably, we identify that the square motifs adjacent to defects, not the defects themselves, as the active sites for CO2RR via synergistic effect. We evaluate these mechanisms against experiments of CO2RR on ultra-high vacuum-prepared ultraclean Cu surfaces, uncovering the crucial role of step-edge orientation in steering selectivity. Overall, our study refines the structural sensitivity of CO2RR on Cu at the atomic level, highlights the self-activation mechanism and elucidates the origin of in situ restructuring of Cu surfaces during the reaction.more » « less
-
Enhanced Solar CO2 Reduction Using Single Cobalt Sites on Carbon Nitride Modified with a DianhydridePhotoactive single-atom catalysts (SACs) are among the most exciting catalytic materials for solar fuel production. Different SACs, including our own Co SACs, have been prepared on graphitic carbon nitride (C3N4) for use in photocatalysis. Building on our prior success, we report here doped C3N4 using various supplemental carbon dopants as the support for Co SACs. The Co SAC on a dianhydride doped C3N4 showed the highest activity in photocatalytic CO2 reduction. Catalyst characterization was carried out to explore the origin of the enhanced activity of this particular Co SAC. The dianhydride doped C3N4 possesses unique microstructural features, including large inter-layer space and fibrous morphology, that could contribute to the enhanced photocatalytic activity. Our results further indicate that the dianhydride is the most effective dopant to incorporate aromatic moieties in C3N4, which resulted in improved charge separation and enhanced activity in photocatalysis.more » « less
