N-doped Carbon Electrocatalysts Research Articles

Impact of Local Structure and Spin on the ORR Performance of Single Atom M-N-C Catalysts

Transition metal single-atom catalysts supported on N-doped graphene (M-N-Cs) offer significant advantages in metal utilization and uniformity of active sites compared to traditional heterogeneous catalysts. They are particularly notable for their superior electrocatalytic Oxygen Reduction Reaction (ORR) performance. Various modifications have been explored, including different metal combinations, different first shell elements (N, C, S, B), and coordination numbers, to enhance electrocatalytic ORR activities. Another emerging focus is the link between their local structure and spin state. The Zhenan Bao and Jaramillo groups recently found that the catalytic activity of the NiNx moiety stems from its tetrahedrally distorted structure because it stabilizes the high-spin Ni state more than the low-spin state.[1] The local structure and its distortion can be modified by adjusting the carbon nanotube diameter,[2] pore size,[3] layering,[4] or by adding ligands at the first or second shell.[5]In this study, we have conducted a computational screening of M-N-Cs with 3d, 4d, and 5d metals and local structures including square planar, tetragonal pyramidal, and tetrahedral symmetries. Metals in their divalent states within the MN4 units exhibited a V-shaped trend in formation energy correlated with increasing atomic numbers across each series. This pattern appears to be linked to the interaction between the two electrons of the N4 ligand and the d electron count of the metals, and it also emerged in the *O/*OH adsorption energy plots. Additionally, the preferred spin state varied with the metal type and structural symmetry, influencing electron distribution and crystal field splitting. These factors collectively impacted the binding energies with adsorbents, subsequently altering oxygen reduction reaction (ORR) activity. Further, we explored the adsorption energies of various intermediates (*CO, *H, *Cl, and *N2H) relevant to carbon dioxide reduction reaction (CO2RR), hydrogen evolution reaction (HER), chlorine evolution reaction (ClER), and nitrogen reduction reaction (NRR), respectively. Our primary objective was to identify optimal metal-structure combinations for enhanced catalytic performance. To achieve this, we considered several descriptors including partial Integrated Crystal Orbital Hamilton Population (ICOHP), metal d-band center, Madelung energy, and metal ionization potential. Moving forward, we aim to extend these findings by incorporating distorted coordination environments and integrating experimental synthesis strategies to induce such distortions, potentially unlocking new pathways for catalytic efficiency enhancement.[1] Koshy, David M., et al. "Investigation of the Structure of Atomically Dispersed NiNx Sites in Ni and N-Doped Carbon Electrocatalysts by 61Ni Mössbauer Spectroscopy and Simulations." Journal of the American Chemical Society 144.47 (2022): 21741-21750.[2] Cepitis, Ritums, et al. "Surface curvature effect on dual-atom site oxygen electrocatalysis." ACS Energy Letters 8.3 (2023): 1330-1335.[3] Glibin, Vassili P., et al. "Non-PGM electrocatalysts for PEM fuel cells: thermodynamic stability and DFT evaluation of fluorinated FeN4-based ORR catalysts." Journal of The Electrochemical Society 166.7 (2019): F3277.[4] Wu, Yahui, et al. "Boosting CO2 electroreduction over a cadmium single‐atom catalyst by tuning of the axial coordination structure." Angewandte Chemie International Edition 60.38 (2021): 20803-20810.[5] Choi, Daeeun, et al. "Bridging the Catalytic Turnover Gap Between Single‐Atom Iron Nanozymes and Natural Enzymes by Engineering the First and Second Shell Coordination." Advanced Materials (2023): 2306602.

Customizing pyridinic nitrogen coordination in Ni–N–C for electrocatalytic CO2 reduction towards CO

Nickel anchored N-doped carbon electrocatalysts (Ni–N–C) are rapidly developed for the electrochemical reduction reaction of carbon dioxide (CO2RR). However, the high-performanced Ni–N–C analogues design for CO2RR remains bewilderment, for the reason lacking of definite guidance for its structure-activity relationship. Herein, the correlation between the proportion of nitrogen species derived from various nitrogen sources and the CO2RR activity of Ni–N–C is investigated. The x-ray photoelectron spectroscopy (XPS) spectrum combined with the CO2RR performance results show that pyridinic-N content has a positive correlation with CO2RR activity. Moreover, density functional theory (DFT) demonstrates that pyridinic-N coordinated Ni–N4 sites offers optimized free energy and favorable selectivity towards CO2RR compared with pyrrolic-N. Accordingly, Ni–Na–C with highest pyridinic-N content (ammonia as nitrogen source) performs superior CO2RR activity, with the maximum carbon monoxide faradaic efficiency (FECO) of 99.8% at −0.88 V vs. RHE and the FECO surpassing 95% within potential ranging of −0.88 to −1.38 V vs. RHE. The building of this parameter for CO2RR activity of Ni–N–C give instructive forecast for low-cost and highly active CO2RR electrocatalysts.

Design of high-performance wood-derived N-doped ECR electrocatalysts based on Marcus theory

Electrochemical reduction of CO2 over wood-derived metal-free N-doped carbon electrocatalysts provides a new route for converting CO2 into value-added fuels However, it is a challenge to efficiently design and screen high-performance electrocatalysts. In this paper, we combined the Marcus equation with the theory of thermal-kinetic correlation to successfully predict the optimal N-C doping ratio. Poplar wood -derived 3D N-doped graphitized carbon with optimal N doping content (pyridine-N 1.87 at%, pyrrole-N, 1.52 at%), high specific surface area (471.2 m2 g−1), and abundant nanopores were successfully obtained with the assistance of melamine (N source), which exhibited a high ECR activity of 86.78 % at a low applied potential of −0.71 V (vs. RHE) and long-term stability of at least 10 cycles. This extends the application of the Marcus equation and improves new ideas for the future design of high-performance electrocatalysts.

Controllable synthesis of a hybrid mesoporous sheets-like Fe0.5NiS2@ P, N-doped carbon electrocatalyst for alkaline oxygen evolution reaction

Owing to the high cost of precious metal catalysts for the oxygen evolution reaction (OER), the production of highly efficient and affordable electrocatalysts is important for generating pollution-free and renewable energy via electrochemical processes. A facile hydrothermal approach was employed to synthesize hybrid mesoporous iron-nickel bimetallic sulfides @ P, N-doped carbon for the OER. The prepared Fe0.5NiS2@C exhibited an overpotential (η) of 250 mV at 10 mA/cm2. This exceeded the overpotentials recently reported for surface-modified P, N-doped carbon-based catalysts for the OER in a 1 M KOH medium. Moreover, the Fe0.5NiS2@C catalyst showed a notable Tafel slope of 90.5 mV/dec with long-dated stability even after 24 h at 10 mA/cm2. The superior OER performance of the Fe0.5NiS2@C catalysts may be due to their large surface area, sheet-like morphology with abundant active sites, fast transfer of mass and electrons, control of the electronic structure by co-treatment with heteroatoms (e.g., P and N), and the synergistic effect of bimetallic sulfides, making them favorable catalysts for the oxygen evolution reaction. Density functional theory (DFT) calculations showed that the Fe0.5NiS2@C catalyst exhibited strong H2O-adsorption energy. The enhanced OER activity of Fe0.5NiS2@C was attributed to its higher surface area, favorable H2O adsorption energy, improved electron transfer efficiency, and lower Gibbs free energy compared to those of the other proposed catalysts.

Enhancing Hydrogen Peroxide Production through Modulating the Morphology of N-doped Mesoporous Carbon Electrocatalysts

Enhancing Hydrogen Peroxide Production through Modulating the Morphology of N-doped Mesoporous Carbon Electrocatalysts

In Situ Construction of a Co2P/CoP Heterojunction Embedded on N-Doped Carbon as an Efficient Electrocatalyst for a Hydrogen Evolution Reaction.

Noble metal-free electrocatalysts have received widespread attention in a hydrogen evolution reaction (HER) due to the importance of renewable energy development. Herein, a Co2P/CoP heterojunction embedded on an N-doped carbon (Co2P/CoP/NC) electrocatalyst was prepared via an in situ pyrolysis method. The as-prepared electrocatalyst exhibited efficient electrocatalytic activity for HER in an acidic solution. The Co2P/CoP/NC catalyst displayed an overpotential of 184 mV at 10 mA cm-2 and a low Tafel slope of 82 mV dec-1, which could be attributed to the tight Co2P/CoP heterojunction and the synergetic effect of Co2P/CoP and N-doped carbon. In addition, the electrochemical active surface area of Co2P/CoP/NC was 75.2 m2 g-1, which indicated that more active regions can be applied for the HER process. This report may pave a new way for the design of efficient and low-cost N-doped-carbon-supported 3d transition metal phosphide electrocatalysts.

Regulating N Species in N-Doped Carbon Electro-Catalysts for High-Efficiency Synthesis of Hydrogen Peroxide in Simulated Seawater.

Electrochemical oxygen reduction reaction (ORR) is an attractive and alternative route for the on-site production of hydrogen peroxide (H2 O2 ). The electrochemical synthesis of H2 O2 in neutral electrolyte is in early studying stage and promising in ocean-energy application. Herein, N-doped carbon materials (N-Cx ) with different N types are prepared through the pyrolysis of zeolitic imidazolate frameworks. The N-Cx catalysts, especially N-C800 , exhibit an attracting 2e- ORR catalytic activity, corresponding to a high H2 O2 selectivity (≈95%) and preferable stability in 0.5m NaCl solution. Additionally, the N-C800 possesses an attractive H2 O2 production amount up to 631.2mmolg-1 h-1 and high Faraday efficiency (79.8%) in H-type cell. The remarkable 2e- ORR electrocatalytic performance of N-Cx catalysts is associated with the N species and N content in the materials. Density functional theory calculations suggest carbon atoms adjacent to graphitic N are the main catalytic sites and exhibit a smaller activation energy, which are more responsible than those in pyridinic N and pyrrolic N doped carbon materials. Furthermore, the N-C800 catalyst demonstrates an effective antibacterial performance for marine bacteria in simulated seawater. This work provides a new insight for electro-generation of H2 O2 in neutral electrolyte and triggers a great promise in ocean-energy application.

Zinc-Mediated Template Synthesis of Hierarchical Porous N-Doped Carbon Electrocatalysts for Efficient Oxygen Reduction.

The development of highly active and low-cost catalysts for use in oxygen reduction reaction (ORR) is crucial to many advanced and eco-friendly energy techniques. N-doped carbons are promising ORR catalysts. However, their performance is still limited. In this work, a zinc-mediated template synthesis strategy for the development of a highly active ORR catalyst with hierarchical porous structures was presented. The optimal catalyst exhibited high ORR performance in a 0.1 M KOH solution, with a half-wave potential of 0.89 V vs. RHE. Additionally, the catalyst exhibited excellent methanol tolerance and stability. After a 20,000 s continuous operation, no obvious performance decay was observed. When used as the air-electrode catalyst in a zinc-air battery (ZAB), it delivered an outstanding discharging performance, with peak power density and specific capacity as high as 196.3 mW cm-2 and 811.5 mAh gZn-1, respectively. Its high performance and stability endow it with potential in practical and commercial applications as a highly active ORR catalyst. Additionally, it is believed that the presented strategy can be applied to the rational design and fabrication of highly active and stable ORR catalysts for use in eco-friendly and future-oriented energy techniques.

Durable N-doped carbon electrocatalysts derived from NH3-activated coffee waste for the oxygen reduction reaction

Polymer electrolyte membrane fuel cells typically use expensive electrocatalysts comprising Pt-group metals (PGMs), particularly for the oxygen reduction reaction (ORR). However, PGMs can undergo surface poisoning resulting in severe performance deactivation. Therefore, metal-free electrocatalysts have been investigated as alternatives. In this study, N-doped carbon electrocatalysts for the ORR were derived from coffee waste (CW), which originates from carbonaceous natural resources. The electrocatalysts by CW recycling and simple thermal activation under NH3 improve the electrocatalytic activity toward ORR and exhibit excellent durability in 40,000 cycles of accelerated stability tests. Although further investigation is required to optimize the electrochemical performance and gain deeper insights into the mechanistic roles of active sites, this simple strategy can promote cost-effective waste recycling and valorization for carbon neutrality.

Nickel single atom overcoordinated active sites to accelerate the electrochemical reaction kinetics for Li-S cathode

Porous 2D N-doped carbon electrocatalyst consisting of atomically disperse Ni active centers with Ni-N 4 -O coordinated structure which act as efficient polysulfides traps and highly LiPSs conversion catalysts. Lithium-sulfur (Li-S) batteries with high theoretical energy density are promising advanced energy storage devices. However, shuttling of dissolute lithium polysulfide (LiPSs) and sluggish conversion kinetics impede their applications. Herein, single nickel (Ni) atoms on two-dimensional (2D) nitrogen(N)-doped carbon with Ni-N 4 -O overcoordinated structure (SANi-N 4 -O/NC) are prepared and firstly used as a sulfur host of Li-S batteries. Due to the efficient polysulfides traps and highly LiPSs conversion effect of SANi-N 4 -O/NC, the electrochemical performance of Li-S batteries obviously improved. The batteries can well operate even under high sulfur loading (5.8 mg·cm -2 ) and lean electrolyte (6.1 μL·mg -1 ) condition. Meanwhile, density functional theory (DFT) calculations demonstrate that Ni single atom’s active sites decrease the energy barriers of conversion reactions from Li 2 S 8 to Li 2 S due to the strong interaction between SANi-N 4 -O/NC and LiPSs. Thus, the kinetic conversion of LiPSs was accelerated and the shuttle effect is suppressed on SANi-N 4 -O/NC host. This study provides a new design strategy for a 2D structure with single-atom overcoordinated active sites to facilitate the fast kinetic conversion of LiPSs for Li-S cathode.

Synergies of Ru/Co nanoparticles and Co single atoms active sites toward efficient electrocatalysis of oxygen reduction reaction for Zn-Air battery

The development of metal-nitrogen-codoped carbon catalysts for oxygen reduction reaction (ORR) is highly desired for the practical applications of energy conversion technologies, but there remains a challenge in elucidating mechanisms of structure–activity relationship for enhancing electrocatalytic performance. Herein, we propose a general approach for the synthesis of metallic RuCo nanoparticles and CoNx species embedded in N-doped carbon electrocatalysts (RuCo@CoNC). Benefiting from the synergistic effect of chemical compositions and 3D hierarchical structures, RuCo@CoNC exhibits high ORR activity and superior durability, outperforming Pt/C catalysts. Density functional theory further reveals that Ru@CoNx possesses stronger reactant adsorption ability and a lower dissociation energy barrier than Co@CoNx, which is conducive to accelerating ORR kinetics. Moreover, the Zn-air battery using RuCo@CoNC as the air cathode presents higher power densities, larger specific capacities and stronger cycling stability, outperforming the Pt/C + RuO2 counterparts. This work presents a perspective for the controllable design of highly-efficient electrocatalysts for energy storage applications.

FeNC Oxygen Reduction Electrocatalyst with High Utilization Penta-Coordinated Sites.

Atomic Fe in N-doped carbon (FeNC) electrocatalysts for oxygen (O2 ) reduction at the cathode of proton exchange membrane fuel cells are the most promising alternative to platinum-group-metal catalysts. Despite recent progress on atomic FeNC O2 reduction, their controlled synthesis and stability for practical applications remain challenging. A two-step synthesis approach has recently led to significant advances in terms of Fe-loading and mass activity; however, the Fe utilization remains low owing to the difficulty of building scaffolds with sufficient porosity that electrochemically exposes the active sites. Herein, this issue is addressed by coordinating Fe in a highly porous nitrogen-doped carbon support (≈3295m2 g-1 ), prepared by pyrolysis of inexpensive 2,4,6-triaminopyrimidine and a Mg2+ salt active site template and porogen. Upon Fe coordination, a high electrochemical active site density of 2.54×1019 sitesgFeNC -1 and a record 52% FeNx electrochemical utilization based on in situ nitrite stripping are achieved. The Fe single atoms are characterized pre- and post-electrochemical accelerated stress testing by aberration-corrected high-angle annular dark field scanning transmission electron microscopy, showing no Fe clustering. Moreover, ex situ X-ray absorption spectroscopy and low-temperature Mössbauer spectroscopy suggest the presence of penta-coordinated Fe sites, which are further studied by density functional theory calculations.

Construction of a Co/MnO Mott-Schottky Heterostructure to Achieve Interfacial Synergy in the Oxygen Reduction Reaction for Aluminum-Air Batteries.

The rational design of non-noble metal-based electrocatalysts for an efficient oxygen reduction reaction (ORR) is an important research topic to promote the advancement of aluminum-air batteries. In this work, heterostructural Co/MnO nanoparticles encapsulated in a N-doped carbon electrocatalyst were prepared via one-step pyrolysis utilizing different reduction potentials of Co and Mn ions, and the heterointerface between the two phases was confirmed. The prepared catalyst displays Pt/C competitive ORR performance because of the interfacial synergy of a Co/MnO Mott-Schottky (M-S) heterostructure, which leads to boosted conductivity, formation of an M-S barrier, and a reduced oxygen reduction energy barrier for excited electrons. Furthermore, the Co/MnO-based aluminum-air battery displays good discharge performance, demonstrating good feasibility for practical application.

Zn(II)-MOF derived N-doped carbons achieve marked ORR activity in alkaline and acidic media.

A highly efficient metal-free N-doped carbon electrocatalyst toward oxygen reduction was obtained by one-pot pyrolysis of a single Zn(II)-MOF with mixed azolate and terephthalate ligands, demonstrating E1/2 of 0.88 V (vs. RHE) in 0.1 M KOH, and 0.79 V (vs. RHE) in 0.5 M H2SO4. It represents one of the best metal-free N-doped carbon electrocatalysts for the acidic ORR.

Waste silk fabric derived N-doped carbon as a self-supported electrocatalyst for hydrogen evolution reaction

Developing a highly efficient, stable and cost-effective electrocatalyst is critical for Hydrogen Evolution Reaction (HER). Herein, we present a facile approach for constructing self-supported N-doped carbon electrocatalysts derived from waste silk fabric for HER. After activation of KCl and the thermal carbonization process, the resulting catalysts present a unique porous three-dimensional(3D) structure that can expose more active sites and will promote the efficient diffusion of the electrolyte. As an N-rich and self-supported HER catalyst, the synthetic materials exhibit outstanding electrocatalytic performance with the overpotential of 336.33 ± 26.22 mV to achieve a current density of 10 mA cm−2 and long-term stability (more than 24 h). This work will explore a completely novel approach to prepare a variety of self-supporting 3D electrodes from biomass for various applications.

Investigation of the Structure of Atomically Dispersed NiNx Sites in Ni and N-Doped Carbon Electrocatalysts by 61Ni Mössbauer Spectroscopy and Simulations.

Ni and nitrogen-doped carbons are selective catalysts for CO2 reduction to CO (CO2R), but the hypothesized NiNx active sites are challenging to probe with traditional characterization methods. Here, we synthesize 61Ni-enriched model catalysts, termed 61NiPACN, in order to apply 61Ni Mössbauer spectroscopy using synchrotron radiation (61Ni-SR-MS) to characterize the structure of these atomically dispersed NiNx sites. First, we demonstrate that the CO2R results and standard characterization techniques (SEM, PXRD, XPS, XANES, EXAFS) point to the existence of dispersed Ni active sites. Then, 61Ni-SR-MS reveal significant internal magnetic fields of ∼5.4 T, which is characteristic of paramagnetic, high-spin Ni2+, in the 61NiPACN samples. Finally, theoretical calculations for a variety of Ni-Nx moieties confirm that high-spin Ni2+ is stable in non-planar, tetrahedrally distorted geometries, which results in calculated isotropic hyperfine coupling that is consistent with 61Ni-SR-MS measurements.

Tafel Slope Analysis from Inherent Rate Constants for Oxygen Reduction Reaction Over N-doped Carbon and Fe–N-doped Carbon Electrocatalysts

Tafel Slope Analysis from Inherent Rate Constants for Oxygen Reduction Reaction Over N-doped Carbon and Fe–N-doped Carbon Electrocatalysts

Synthesizing MOF-derived Ni[sbnd]N[sbnd]C catalyst via surfactant modified strategy for efficient electrocatalytic CO2 to CO

Recently, Ni, N-doped carbon (NiNC) electrocatalysts synthesized using metal–organic frameworks (MOFs) as templates have demonstrated attractive catalytic performances in the CO2 reduction reaction (CO2RR). However, most of the reported preparations of MOFs-based precursors are carried out in organic solvents, and the resulting NiNC materials have relatively low metal loadings and mainly exhibit microporous structures, which is unfavorable for the mass transport. Herein, Ni, N-doped meso-microporous carbon electrocatalysts with a range of Ni loadings (M−NiNCx/CNTs) were prepared by the pyrolysis of MOFs-based precursors synthesized in aqueous solution using the surfactant cetyltrimethylammonium bromide (CTAB) as a modifier to promote the adsorption of Ni2+ ions and the formation of mesopores. Owing to the unique morphology, porous structure and high contents of Ni-Nx sites and pyrrolic-N, the optimal catalyst (M−NiNC2/CNTs) shows superior electrocatalytic activity for the CO2RR with a maximum CO Faradaic efficiency (FECO) of 98 % at −0.7 V vs. reversible hydrogen electrode (RHE), and the FECO can reach over 80 % in a wide potential range of −0.5 to −1.0 V vs. RHE. This work develops a facile and environmentally friendly strategy to obtain high-performance and low-cost transition metal-nitrogen-doped porous carbon electrocatalysts for the CO2RR.

Synergistically coupling of Ni3Mo3C/Mo2C/Ti3C2Tx MXene/N-doped carbon electrocatalyst towards enhanced hydrogen evolution activity

The development of highly active electrocatalysts is of great significance to improve hydrogen production technology and promoting the development of the hydrogen energy economy. Herein, we report an electrocatalyst consisting of bimetallic carbide nanoparticles encapsulating by an N-doped carbon (NC) layer deposited on the multilayer Ti3C2Tx (denoted as Ni3Mo3C/Mo2C/Ti3C2Tx/NC) for hydrogen evolution reaction (HER) using Ti3C2Tx MXene as a conductively catalytic carrier, polyoxometalates (POM) as a soft template, in which bimetallic carbides interact with hybrid carbon. Profiting from the bimetallic character and multi-aperture structure, the Ni3Mo3C/Mo2C/Ti3C2Tx/NC catalyst represents an overpotential of 99 mV in acidic medium and 98 mV in alkaline medium at 10 mA cm−2 with extended durability for 24 h. The turnover frequency (TOF) at 100 mV overpotential for Ni3Mo3C/Mo2C/Ti3C2Tx/NC electrocatalyst is 0.188 s−1. The remarkable catalytic activity for Ni3Mo3C/Mo2C/Ti3C2Tx/NC electrocatalyst can be attributed to the synergistic effects of bimetallic carbides. In addition, the introduction of Ti3C2Tx MXene further strengthened the conductivity of the catalyst as well as accelerated proton transport. Moreover, the protective effect of the porous carbon layer and the adulteration of the N atom increased the active site, resulting in improved HER properties. This simple preassembly-thermal conversion strategy offers a novel approach for the designing of superior electrocatalysts for HER.

Modulating the electrocatalytic activity of N-doped carbon frameworks via coupling with dual metals for Zn\u2013air batteries

N-Doped carbon electrocatalysts are a promising alternative to precious metal catalysts to promote oxygen reduction reaction (ORR). However, it remains a challenge to design the desired active sites on carbon skeletons in a controllable manner for ORR. Herein, we developed a facile approach based on oxygen-mediated solvothermal radical reaction (OSRR) for preparation of N-doped carbon electrocatalysts with a pre-designed active site and modulated catalytic activity for ORR. In the OSRR, 2-methylimidazole reacted with Co and Mn salts to form an active site precursor (MnCo-MIm) in N-methyl-2-pyrrolidone (NMP) at room temperature. Then, the reaction temperature increased to 140 °C under an oxygen atmosphere to generate NMP radicals, followed by their polymerization with the pre-formed MnCo-MIm to produce Mn-coupled Co nanoparticle-embedded N-doped carbon framework (MnCo-NCF). The MnCo-NCF showed uniform dispersion of nitrogen atoms and Mn-doped Co nanoparticles on the carbon skeleton with micropores and mesopores. The MnCo-NCF exhibited higher electrocatalytic activity for ORR than did a Co nanoparticle only-incorporated carbon framework due to the improved charge transfer from the Mn-doped Co nanoparticles to the carbon skeleton. In addition, the Zn–air battery assembled with MnCo-NCF had superior performance and durability to the battery using commercial Pt/C. This facile approach can be extended for designing carbon electrocatalysts with desired active sites to promote specific reactions.Graphical