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## Creator

Abin Sebastian, [Atanu Panda](https://orcid.org/0000-0003-4049-3885), Ravi Nandan, [Joel Henzie](https://orcid.org/0000-0002-9190-2645), [Ovidiu Cretu](https://orcid.org/0000-0002-1822-8172), [Jian Xu](https://orcid.org/0000-0002-1040-5090), Nadiia Velychkivska, [Renzhi Ma](https://orcid.org/0000-0001-7126-2006), Pooja Gakhad, Abhishek Kumar Singh, Gary J. Richards, [Koji Kimoto](https://orcid.org/0000-0002-3927-0492), [Lok Kumar Shrestha](https://orcid.org/0000-0003-2680-6291), [Katsuhiko Ariga](https://orcid.org/0000-0002-2445-2955), Yusuke Yamauchi, [Jonathan P. Hill](https://orcid.org/0000-0002-4229-5842)

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Publishers Copyright, Royal Society of Chemistry[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

## Other metadata

[Scalable nanoarchitectonics with microporous polymer composite for methanol-tolerant ORR electrocatalysts](https://mdr.nims.go.jp/datasets/16cd43a5-2590-4aa8-aadc-b5e98a1ab96d)

## Fulltext

Scalable Synthetic Approach to Inexpensive Methanol-Tolerant ORR Electrocatalysts Using Microporous Polymer Composite Abin Sebastian1, Atanu Panda1, Ravi Nandan1, Joel Henzie1, Ovidiu Cretu2, Jian Xu3, Nadiia Velychkivska1, Renzhi Ma1, Pooja Gakhad4, Abhishek Kumar Singh4, Gary J. Richards5, Koji Kimoto2, Lok K. Shrestha1,6, Katsuhiko Ariga1,7, Yusuke Yamauchi8,9,10, and Jonathan P. Hill*,1  1Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba 305-0044, Ibaraki, Japan 2Center for Basic Research on Materials (CFRM), National Institute for Materials Science (NIMS), Tsukuba 305-0044, Ibaraki, Japan 3International Center for Young Scientists (ICYS), National Institute for Materials Science (NIMS), Tsukuba 305-0044, Ibaraki, Japan 4Materials Research Centre, Indian Institute of Science, Mathikere, Bengaluru, Karnataka 560012, India 5Department of Applied Chemistry, Graduate School of Engineering and Science, Shibaura Institute of Technology, Fukasaku 307, Minuma-ku, Saitama-shi, Saitama 337-8570, Japan 6Department of Materials Science, Faculty of Pure and Applied Sciences, University of Tsukuba 1-1-1, Tennodai, Tsukuba 305-8573, Ibaraki, Japan 7Department of Advanced Materials Science, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan 8Department of Materials Process Engineering, Graduate School of Engineering, Nagoya University, Nagoya 464−8603, Japan 9Department of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, South Korea 10Australian Institute for Bioengineering and Nanotechnology (AIBN) and School of Chemical Engineering, The University of Queensland, Brisbane, Queensland 4072, Australia  Email: Jonathan.Hill@nims.go.jp    mailto:Jonathan.Hill@nims.go.jpTOC Graphic     Abstract The oxygen reduction reaction (ORR) is vital for renewable energy conversion and storage technology and requires effective electrocatalysts for its operation. Platinum-containing amorphous carbon-based materials are the current benchmark industrial catalysts for ORR so that the development of noble-metal-free electrocatalyst alternatives would be advantageous for the wider application of these technologies. Here, we report an efficient ORR electrocatalyst containing cobalt single atom and cobalt nanoparticle active sites embedded in a porous nitrogen-doped graphitic carbon network whose synthesis involves controlled thermolysis of metallated microporous porphyrin polymers. The properties of the resulting material relies on the coexistence of cobalt nanoparticles and cobalt single atom catalysts in an N-doped carbon matrix presenting a graphitic carbon protective layer, which acts as a prophylactic against oxidation of the Co-containing catalytically active sites. The robust electrocatalyst exhibits superior electrochemical ORR activity with onset and halfwave potentials of 0.96 V and 0.87 V (vs RHE), respectively. The electrocatalyst also shows excellent durability and methanol tolerance compared to the commercial benchmark Pt/C catalyst further enhancing the potential of this system for practical applications. Computational methods were used to assess the roles of the material components.  Keywords: Oxygen reduction reaction electrocatalyst, microporous porphyrin polymer, cobalt nanoparticle, cobalt single-atom catalyst.   Introduction The increasing global demand for energy resources, coupled with escalating environmental challenges, has stimulated an intensive research effort in the development of renewable energy conversion and storage technologies, including fuel cells and metal-air batteries, where the cathodic oxygen reduction reaction (ORR) plays a pivotal role.1,2  However, the poor kinetic characteristics of the available ORR materials has impeded any practical realization of the related applications on an industrial scale. Platinum group metal (PGM) catalysts have been used to address the difficulties associated with ORR operation, but the poor availability and high cost of PGMs make their widespread usage impractical.3 Based on their low cost, high activities, and excellent stabilities, nitrogen-doped porous carbons incorporating transition metals (Fe, Cu, Co, and Ni) in different states are promising replacement materials for Pt-based ORR systems.4–10 In these materials, the introduction of different metal-nitrogen (M-Nx) coordination sites is a critical factor in determining their overall efficiency, and also helps establish structure-activity relationships.11–14 M-Nx coordination sites can be conveniently introduced to the relevant materials by using appropriate coordination complexes such as porphyrins or phthalocyanines, which provide four nitrogen atoms in an M-Nx coordination structure with a suitable geometry not only to bind transition metal cations but also to maintain a state of coordination unsaturation.15,16 While M-Nx porphyrins and phthalocyanines have been incorporated into different materials for the construction of various composite electrocatalysts,17–22 there remain several disadvantages associated with this approach including their low affinity for the conductive scaffolds and their strong tendency to aggregate, both of which lead to poor charge and mass transfer rates, low mass efficiency, and low stability of the resulting materials. M-Nx-type molecules can also be incorporated as linkers or monomers in the construction of metal-organic framework (MOFs),23,24 covalent organic polymers (COPs)25–29 or covalent organic frameworks (COFs).30,31 Porous porphyrin polymers have also been studied for the construction of M-Nx systems32–35  with the resulting nitrogen-doped carbon materials being porous and conductive promoting their usefulness in oxygen reduction reaction (ORR) applications. In addition, the use of N-doped graphene supports containing pyridinic N or graphitic N states can enhance the oxygen reduction reaction (ORR) performance of the relevant materials,36,37 and the use of highly porous conducting carbon supports having numerous exposed active sites facilitates electrocatalytic reactions. Other important potential components of oxygen reduction electrocatalysts are based on cobalt compounds whose electrochemical activities have been enhanced by preparing innovative architectures,38–40 introduction of heteroatoms including boron,41 nitrogen,42,43 sulphur,39,44–46 and/or oxygen,47 or by the preparation of multimetallic systems.45,48–51 The construction of single-atom catalysts (SACs) with multiple active sites also offers a promising strategy to improve ORR performance, while the use of multiple metal sites (including clusters or nanoparticles) anchored on N-doped carbon substrates allows optimized adsorption-desorption behavior during ORR due to synergistic effects between the metal sites and locally unsymmetrically distributed electron density.49,52,53  Consequently, the copresence in the relevant materials of single metal atoms and nanoparticles holds significant potential for the optimization of ORR catalytic performance. However, an easily implementable approach to synthesize these materials based on combining single atom catalysts and metal nanoparticles on conducting N-doped graphene is lacking. In this work, we have developed a simple synthesis protocol to prepare cobalt-based electrocatalysts based on an inexpensive porous porphyrin polymer precursor. Porous porphyrin polymer containing multiple transition metal binding sites is prepared in high yield using Friedel-Crafts cross-coupling polymerization of meso-tetraphenylporphyrin (TPP). Subsequently, cobalt cations are introduced by coordination in the porphyrin polymer. Controlled thermolysis of the resulting metallated porphyrin polymer results in materials incorporating face-centered cubic (fcc) metallic cobalt nanoparticles (Co-NP) as well as cobalt single-atom catalysts (Co-SA) confined in porous N-doped graphitic carbon (NPC), which has been confirmed by using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and other X-ray absorption techniques (XANES, EXAFS). Of the materials prepared, the Co-NP/Co-SA@NPC electrocatalyst exhibits remarkable oxygen reduction reaction (ORR) performance with an onset potential (Eonset) of 0.96 V vs RHE and a half-wave potential (E1/2) of 0.865V vs RHE, surpassing the performances of control samples and the state-of-the-art reference material Pt/C (20 wt%). Co-NP/Co-SA@NPC catalyst also exhibits substantial methanol tolerance during operation, emphasizing its superiority over Pt/C, and has high durability making it an excellent candidate for implementation in the relevant applications.   Results and Discussion  Fig. 1. Preparation of cobalt nanoparticle/cobalt single atom catalyst incorporated in nitrogen doped mulilayered graphitic carbon.  Porous porphyrin polymer (PPP) was prepared using meso-tetraphenylporphyrin (TPP) monomer by aryl-aryl Scholl coupling/solvent knitting Friedel-Crafts polymerization using aluminum chloride as Lewis acid catalyst in dichloromethane (See Fig. 1).54 The reaction gives an insoluble brown powder as product, whose infrared spectrum (FT-IR; Fig. S1) contains broadened absorption bands signifying the polymeric structure of PPP. Cobalt cations were introduced to PPP by its reaction with CoCl2.6H2O in refluxing DMF yielding PPP-Co confirmed by the appearance of the characteristic N-Co stretching vibration band at 1004 cm-1 in its FTIR spectrum.55 PPP-Co was subjected to thermolysis under constant nitrogen gas flow at different temperatures in the range 500 – 1000 oC. Cobalt nanoparticle (Co-NP)/cobalt single atom (Co-SA) catalytic sites deposited in nitrogen doped porous graphitic carbon (NPC) Co-NP/Co-SA@NPC materials were obtained upon thermolyzing PPP-Co at 1000 °C. Free base porphyrin polymer thermolyzed under the same conditions (PPP-1000), cobalt single-atom-only Co-SA@NPC and cobalt nanoparticle-only Co-NP@NPC (prepared by solvothermal treatment) in nitrogen doped porous carbon were also prepared as control materials for comparative purposes.  Surface areas and porosities of the materials were measured using nitrogen adsorption/desorption isotherms. (Fig. S2a) The relatively large adsorption of nitrogen at 77 K at low relative pressure (P/P0 0.01) for PPP, PPP-Co indicates that micropores contribute significantly to the total pore volume. Following thermolysis, there is a predictable decline in the surface area due to the partial collapse of the porous structure, although a substantial surface area is retained; Co-NP/Co-SA@NPC maintained 478 m2 g-1 while PPP-Co maintained 970 m2 g-1. Variation in surface area of Co-NP/Co-SA@NPC with increasing temperature corresponds approximately to the weight-loss according to thermogravimetry (Fig S2b)  The excellent acid/base and thermal stability (more than 85% mass remains after pyrolysis) and retention of the porous structure can be attributed to the robust network aromatic polymer structure, which provides an additional advantage over, for instance, materials prepared by direct pyrolysis of the porphyrin monomer.56 The large surface areas and tailored pore size distributions of the materials are favorable to promote electrochemical processes, in particular facilitating ion diffusion.    Fig. 2. Electron microscopy analyses of Co-NP/Co-SA@NPC. (a) Scanning transmission electron microscopy (STEM) image (bright field mode). (b) STEM image (dark field). (c) Selected area electron diffraction (SAED) pattern with indices. (d) High resolution TEM image with important lattice fringes indicated for C and Co.  (e) STEM and (f-h) EDX elemental mapping of the area shown in (e).   (i) Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (ac-HAADF-STEM) images of Co-NP/Co-SA@NPC. Sites of single Co atoms are marked with yellow circles.  Morphological analyses of the materials are shown in Fig. 2 and Fig. S3-S5 in the Supporting Information. Scanning electron microscopy (SEM; Fig. S3) reveals an irregular aggregated particle structure of the polymers, a morphology that hardly varies during metalation and thermolysis. Transmission electron microscopy (TEM) images (Fig. S4) of PPP-Co indicate that there are no cobalt nanoparticles present and selected area electron diffraction (SAED) patterns contain no reflections because the polymers are amorphous with no long-range crystallographic order due to their irregular chemical structure.26 Energy-dispersive X-ray spectroscopy (EDX; Fig. S6) confirms the presence of C, N, and Co distributed uniformly in PPP-Co. TEM imaging of Co-NP/Co-SA@NPC (Fig. 2a) reveals its nanometric porous morphology and the STEM image (Fig. 2b) contains bright spots due to the presence of cobalt nanoparticles (Co-NP) in the carbon matrix. The selected area electron diffraction (SAED) pattern (Fig. 2c) contains (111) and (220) planes assigned to fcc Co-NPs. EDX (Fig. 2d-g) of Co-NP/Co-SA@NPC establishes the presence of Co (apparently in nanoparticulate form) and a uniform distribution of N consistent with the proposed structure: Co-NP embedded in N-doped carbon. HR-TEM imaging (Fig. 2h) reveals that Co-NPs are coated with layers of graphitic carbon and the lattice fringes at 0.34 and 0.20 nm can be assigned to (002) interplane distances of graphitic carbon and the (111) plane of metallic Co, respectively, the latter which supports the formation of Co-NP. Co-NPs catalyze the conversion of amorphous carbon to graphitic carbon during the high temperature thermolysis process thus improving intercomponent electron transfer with graphitic carbon also acting as a protective barrier preventing aerial oxidation of metallic cobalt of Co-NPs.57 Atom-level structural features of Co-NP/Co-SA@NPC were investigated using aberration-corrected high-angle annular dark-field scanning TEM (ac-HAADF-STEM). As shown in Fig. 2i, a moderate number of scattered bright dots (indicated by yellow circles, see also Fig. S5) are present corresponding to cobalt single atom (Co-SA) sites (identified as being CoN4 species; vide infra) distributed throughout the carbon matrix. HR-TEM (Fig. S5a) of Co-SA@NPC shows graphitic nanorings about pores formed by acid etching of the cobalt nanoparticles. For comparison, see Fig. S5b where Co-NP immobilized between several layers of graphitic carbon can be observed for Co-NP@NPC. Lattice fringes consistent with the proposed structures were observed at 0.21 and 0.34 nm respectively corresponding to Co(111) and graphitic C(002). PPP-Co exhibited no SAED or XRD peaks consistent with its essentially amorphous structure and lack of Co-NP. Fig. 3. Spectroscopic analyses of different Co-NP/Co-SA@NPC materials. (a) Powder X-ray diffraction (pXRD) patterns. (b) Raman spectra.  (c,d) High resolution X-ray photoelectron spectroscopy (XPS) spectra of Co-NP/Co-SA@NPC, Co-SA@NPC, Co–NPC:  (c) Co2p (d) N1s. (e) Temperature dependency of nitrogen content of PPP-Co. (f) Normalized K-edge XANES spectra, (g) first derivative XANES spectra. (h) FT-EXAFS spectra of Co-NP/Co-SA@NPC and standard samples.  Other salient analyses of the materials are shown in Fig. 3. The PXRD pattern of Co-NP/Co-SA@NPC (Fig. 3a) contains two broad peaks at 26° and 43° due to the (002) and (101) lattice planes of graphitic carbon.58 Peaks at 44.1° and 51.4° are respectively associated with the (111) and (200) planes of metallic fcc Co-NP (JCPDS No. 15-0806). Peaks due to Co-NP are absent in samples pyrolyzed below 1000 °C indicating that nanoparticle formation occurs only at or above this temperature. Graphitic carbon peaks are also absent in samples thermolyzed between 500-700 °C indicating the importance of higher temperature (900 °C and above) for graphitization (Fig. S6a) Additionally, absence of graphitic structures in PPP-1000 suggests that cobalt promotes graphitization.(Fig. S7) The pXRD pattern of Co-NP@NPC is similar to that of Co-NP/Co-SA@NPC indicating the presence of graphitic carbon and Co-NP, and the pXRD pattern of Co-SA@NPC contains only broad peaks assignable to graphitic carbon confirming the absence of Co-NP. Thus, the form and composition of Co-NP/Co-SA@NPC is strongly affected both by the presence of cobalt and by the thermolysis temperature, which both promote graphitization.    Raman spectra of the materials (Fig. 3b) contain two intense peaks around 1350 and 1580 cm-1 assigned as D and G bands, respectively (‘D’ indicates disordered carbon, ‘G’ is due to in-plane vibrations of sp2 graphitic carbon). An additional peak at 2750 cm-1 corresponds to the 2D band of multilayered graphitic structures.59 Materials thermolyzed below 1000 °C or without Co contained very weak or no 2D peak confirming the necessity of the two conditions for the formation of the multilayered graphitic structure. Raman spectra of Co-SA@NPC and Co-NP@NPC similarly contain D, G and 2D bands. The relative intensity ratio of D and G (Id/Ig) indicates the degree of disorder in the carbon structure with values of 1.02, 1.01 and 1.0 calculated for Co-SA@NPC, Co-NP/Co-SA@NPC and Co-NP@NPC respectively. The small increase in Id/Ig is due to nanoparticle formation.60,61  To gain insight into the chemical composition and oxidation states of the materials’ components, X-ray photoelectron spectroscopy XPS measurements were performed. Peaks due to carbon, nitrogen and cobalt are found in the XPS survey spectrum. Fig. S8a shows the XPS survey spectrum of PPP-Co including Co 2p1/2 and Co 2p3/2 at 795.7 and 780.3 eV, respectively (Fig. S8b). The N1s spectrum (Fig. S8c) is dominated by a peak at 399.16 eV peak which corresponds to the nitrogen-cobalt coordinate bond.58 Fig. 3c,d shows the high-resolution Co 2p and N 1s XPS spectra of Co-NP/Co-SA@NPC where peaks at 778.7 and 794.6 eV correspond to Co 2p3/2 and 2p1/2 of metallic cobalt Co0. Peaks at 780.5 and 796.4 eV correspond to Co2+ at cobalt single atom sites (CoN4) with those at 784.04 and 802.8 eV being shakeup satellite peaks. Samples thermolyzed at lower temperatures and Co-SA@NPC contained no XPS peaks due to metallic Co consistent with the absence of nanoparticles found by pXRD. (Fig. S7) XPS spectra of Co-NP@NPC contain peaks due to metallic cobalt (Co-NP) at 778.7 and 794.6eV for Co 2p3/2 and Co 2p1/2, respectively. The XPS spectrum of Co-NP/Co-SA@NPC was deconvoluted with five peaks (Fig. 3d) at 398.4, 399.1, 400.9, 402.5, 404.4 eV corresponding respectively to pyridinic N, N-Co, pyrrolic nitrogen, graphitic nitrogen, N oxide, confirming nitrogen coordination of cobalt at single atom sites. (Fig. S9) Variation in the nitrogen contents with increasing temperature (Fig. 3e) revealed a decrease in N-Co and an increase in pyrrolic nitrogen above 900 °C due to aggregation of cobalt as cobalt nanoparticles and the resulting decline in availability of Co-SA single atom sites. An increase in the graphitic nitrogen content is found as the temperature increases from 500-900 °C (Fig. S10a). Interestingly, in the case of Co-NP@NPC, nitrogen content was found to be significantly reduced. This is likely due to loss of nitrogen during thermolysis due to the absence of single atom sites where the nitrogen might be retained in NPC. Furthermore, the absence of an N-Co peak confirms the absence of single-atom catalysts in Co-NP@NPC. In contrast, deconvolution of the nitrogen peaks in Co-SA@NPC revealed a similar pattern to that of Co-NP/Co-SA@NPC due to the retention of nitrogen in the structure and cobalt single atoms after etching of cobalt nanoparticles.  To investigate the electronic structure and coordination environment of Co-NP/Co-SA@NPC at the atomic level, X-ray absorption near-edge structure (XANES) and extended X-ray absorption structure (EXAFS) experiments were conducted at the Co K-edge. Fig. 3f shows the XANES spectrum of Co-NP/Co-SA@NPC which has a characteristic Co K-edge absorption located between those of Co foil and LiCoO2 indicating Co oxidation states ranging from Co0 to Co2+.  Furthermore, the first derivative of the XANES pre-edge data (Fig. 3g) shows a distinctive peak in the energy range 7710 to 7715 eV, corresponding to the 1s→4pz transition of in-plane CoII-N4 moieties.62 The EXAFS spectrum (Fig. 3h) contains a characteristic peak due to Co0-Co0 bonds configured at 2.1 Å, which further confirms the presence of Co metallic nanoparticles.  A characteristic Co-N peak was also observed at 1.37 Å.  A slight shift in the Co0-Co0 peak (relative to Co foil) in EXAFS and a XANES peak 7727eV for Co-NP/Co-SA@NPC is probably due to the strong interaction between Co-NP and Co-SA sites. Overall, the physical and chemical analyses suggest a close integration of cobalt single atom species and metallic cobalt nanoparticle in Co-NP/Co-SA@NPC which is combined within a graphitic porous structure. These are key features of Co-NP/Co-SA@NPC to promote its catalytic activity for ORR with a strong likelihood for the occurrence of synergetic effects.63,64  Fig. 4. Electrochemical characterization of Co-NP/Co-SA@NPC. (a) Cyclic voltammograms under N2 (dashed line) and O2 (solid line). (b) Linear sweep voltammetry (LSV) curves and (c) corresponding Tafel plots. (d) E1/2 and Jk for the materials and Pt/C. (e) Electrical double layer capacitance, Cdl (f) Nyquist plot of the electrocatalysts at 1600 rpm in a 0.1 M KOH electrolyte. (g) %HO2¯and electron transfer number determined by RRDE at a scan rate of 10 mV s-1. (h) Methanol crossover and (i) evaluation of durability based on the i–t chronoamperometric responses of Co-NP/Co-SA@NPC and Pt/C. ORR catalytic activities of the Co-NP/Co-SA@NPC catalyst and other materials were evaluated by using electrochemical methods (Fig. 4) Cyclic voltammetry (CV) of Co-NP/Co-SA@NPC measurements at a scan rate of 25 mV s-1 in 0.1 M KOH solution (Fig. 4a) in nitrogen or oxygen saturated electrolyte using a three-electrode setup. For N2 saturated electrolyte, no significant redox peaks were observed. However, for O2 saturated electrolyte, a strong cathodic response was observed demonstrating the excellent intrinsic catalytic activity of Co-NP/Co-SA@NPC catalyst for ORR. To further investigate, linear sweep voltammetry (LSV; Fig. 4b, Table S1) was conducted in an oxygen-saturated 0.1 M KOH solution using a rotating disk electrode (RDE) as the working electrode. Optimum thermolysis temperature for the materials was determined by comparing the ORR performance of electrocatalysts prepared at different temperatures. (Fig. S11, Table S2) Of the materials prepared, Co-NP/Co-SA@NPC prepared at 1000 °C, exhibits superior ORR catalytic performance with an onset potential (Eonset) of 0.96 V vs RHE (reversible hydrogen electrode) and a half-wave potential (E1/2) of 0.865 V vs RHE, the latter value being similar to Pt/C (20 wt%). However, as observed from the polarization curve, the mixed (kinetic + diffusion) region potential window for Co-NP/Co-SA@NPC is narrower than that of Pt/C.  Of the other materials tested, PPP-Co and PPP-Co/500 exhibit low ORR activity due to ineffective development of the materials’ structures especially a lack of graphitization. PPP-1000 (Fig. S12) shows a 75 mV lower halfwave potential compared to Co-NP/Co-SA@NPC reflecting the importance of cobalt for efficient electrocatalysis by boosting ORR activity. The effects of cobalt single atoms and nanoparticles were studied using the control electrocatalysts, Co-SA@NPC and Co-NP@NPC. Considering the LSV curves (Fig. 4b), it was found that Co-NP/Co-SA@NPC exhibits a 50 mV more positive half-wave potential than Co-SA@NPC (0.815 V vs RHE) indicating that cobalt nanoparticles enhance significantly the electrocatalytic activity. E1/2 of nanoparticle only Co-NP@NPC is 45 mV lower than Co-NP/Co-SA@NPC emphasizing the importance also of the copresence of cobalt single atoms and cobalt nanoparticles including possible synergetic effects. The excellent ORR activity of Co-NP/Co-SA@NPC can be further confirmed by Tafel plots (Fig. 4c) and considering kinetic current density (Jk). As shown in Fig. 4d, Co-NP/Co-SA@NPC exhibits an excellent Jk value of 57 mA/cm2 at 0.8 V, which is more than double that of Pt/C. Also, the Tafel slope of Co-NP/Co-SA@NPC is 54.5 mV dec-1, significantly lower than that of Pt/C (102 mV dec-1), suggesting a significantly faster electron transfer rate for Co-NP/Co-SA@NPC (Fig. 4c) Interestingly, Co-SA@NPC has a Tafel slope (56.6 mV dec-1) similar to Co-NP/Co-SA@NPC, while that of Co-NP@NPC (100 mV dec-1) denotes comparatively slow electron transfer and is similar to Pt/C. This suggests that, while both Co-SA and Co-NP improve ORR efficiency, the role of Co-SA is to increase electron transfer rate. Intrinsic electrocatalytic activity was investigated using impedance spectroscopy and electrochemical double layer capacitance (Cdl) based on the cyclic voltammetry (CV) curves at different scan rates. (Fig. S13) Co-NP/Co-SA@NPC exhibits a high Cdl value of 23 mF cm-2, indicating a larger electrochemical surface area than for Co-SA@NPC (Cdl = 14.3 mF cm-2), although it is lower than that of Co-NP@NPC (Cdl = 36.7 mF cm-2).(Fig. 4e) This indicates a larger number of catalytically active sites for Co-NP/Co-SA@NPC over Co-SA@NPC due to the etching of cobalt nanoparticles. Nyquist plots of the materials (Fig. 4f) indicate that Co-NP/Co-SA@NPC has the lowest charge transfer resistance (58 Ω), compared to Co-NP@NPC (91.4Ω) and Co-SA@NPC (90.18Ω) suggesting faster charge transfer than occurs in the other materials under the same conditions.  Rotating ring disk electrode (RRDE) tests (Fig. 4g) show an electron transfer number for ORR by Co-NP/Co-SA@NPC at 3.8, indicating a nearly four-electron pathway for ORR. Notably, the peroxide yield calculated for Co-NP/Co-SA@NPC is 14.9 %, within the potential window 0.2 to 0.8 V. Compared to other cobalt electrocatalysts derived from porphyrins, 56,65,66 Co-NP/Co-SA@NPC exhibits a higher electron transfer number and lower peroxide yield, probably based on the presence of cobalt nanoparticles. As expected, Co-SA@NPC also shows a higher peroxide yield compared to Co-NP/Co-SA@NPC further confirming that cobalt single atom sites from the porphyrin moiety tends weakly to the two-electron pathway for ORR.    To elucidate the direct involvement of single atom active sites in promoting the ORR activity, a poisoning test was performed using NaCN which is known to block M–Nx centers.67,68  As shown in Fig. S14, poisoning leads to a decrease in the halfwave potential and limiting current density for Co-NP/Co-SA@NPC, Co-NP@NPC and Co-SA@NPC. Co-NP/Co-SA@NPC undergoes an 86 mV drop in its halfwave potential; for Co-SA@NPC, a 69 mV reduction is observed. Also, it is interesting to note that the reduction in diffusion limited current is prominent for Co-SA@NPC (27% drop) and Co-NP@NPC (13.7%) compared to Co-NP/Co-SA@NPC (7.5% drop), suggesting excellent poisoning tolerance of the electrocatalyst. Poisoning tolerance might arise from a higher density of active sites, which can compensate for the losses caused by poisoning. Additionally, the graphitic carbon structure provides a physical barrier, preventing direct contact between the poisoning agent and the active sites.  These results suggest that the high ORR activity of Co-NP/Co-SA@NPC can be attributed to a synergetic effect, due to the copresence of single atom centers and cobalt nanoparticles. Methanol tolerance and durability of the catalyst are also important aspects for practical implementation of the catalyst. Fig. 4h shows that Co-NP/Co-SA@NPC maintains a stable current density even after injection of 3 M methanol, whereas Pt/C exhibits a sharp decrease in current density due to methanol oxidation. Additionally, as shown in Fig. 4i, Co-NP/Co-SA@NPC retains a significant percentage of its initial current density after 10 h of continuous operation, indicating the excellent durability of the catalyst. High durability of the catalyst is attributed to its resistance to peroxide and effective protection especially of the Co-NP sites provided by the multilayered graphitic structure. The remarkable methanol tolerance and excellent durability of the Co-NP/Co-SA@NPC electrocatalyst along with superior performance compared to other cobalt based catalysts (Table S3) highlight its strong potential for practical applications.  Although Co-NP/Co-SA@NPC is a mixed component material having a broad range of environments for each of its active elements including wide-ranging separating distances of the active sites, we have assessed their relative contributions, especially Co-NP and Co-SA, using computational methods. In particular, synergies between active sites are not easy to detect even if experimental data indicates that such mechanisms are operating. For computational purposes, an N-doped graphene (NPC) structure containing the three most common nitrogen defects observed in graphene (pyrrolic, pyridinic and graphitic) was constructed (see Figure S15a). Cobalt single atom catalyst (SA) sites can be formed by incorporating a Co atom into a void provided by an N4 defect (Figure S15b), which represents a remnant of the starting porphyrin materiaal. A thirteen Co atom icosahedral nanoparticle was also constructed using the Atomic Simulation Environment (ASE) toolkit and was incorporated on NPC. The formation energies of NPC and Co-SA on N-doped graphene (Co-SA@NPC) and Co-NP on NPC (Co-NP@NPC) were calculated using the following equations: Ef (NPC) = Etotal (NPC) - E(graphene) - 3.5 * E(N2) [1] Ef (Co-SA@NPC) = Etotal (Co-SA@NPC) - Etotal(NPC) - E(Co) [2] Ef(Co-NP@NPC) = Etotal(Co-NP@NPC) - Etotal (NPC) - Eicosahedron(Co) [3] where, Etotal (NPC), Etotal (Co-SA@NPC) and Ef (Co-NP@NPC) are the total energies obtained during relaxation of NPC, Co-SA@NPC and Co-NP@NPC structures, respectively. E(N2), E(Co) and Eicosahedron(Co) are the energies of nitrogen molecules, Co atom in the nanoparticle structure and one unit of Co13 icosahedron, respectively. Ef (NPC), Ef (Co-SA@NPC) and Ef(Co-NP@NPC) are the formation energies of NPC, Co-SA@NPC and Co-NP@NPC, respectively. To study the oxygen reduction reaction (ORR) activity on the resulting systems, an associative mechanism involving a 4e– transfer process in alkaline medium was explored69: O2(g) + * → O2* [4] O2* + H2O (l) + e– → HOO* + OH– [5] HOO* + e– → O* + OH– [6] O* + H2O (l) + e– → HO* + OH– [7] HO* + e– → OH– + * [8] Initially, the key intermediates for ORR reaction O*, OH* and OOH* are adsorbed on Co-SA@NPC at five distinct sites, namely C1, C2, C3, C4 and C5 (Figure 15b). The adsorption energies for all five sites were calculated using the following equations:  ΔEads(HOO*) = Etotal(HOO*) − [E* + 2E(H2O) − 1.5E(H2)] [9] ΔEads(O*) = Etotal(O*) − [E* + E(H2O) − E(H2)] [10] ΔEads(HO*) = Etotal(HO*) − [E* + E(H2O) − 0.5E(H2)] [11] where ΔEads(HO*), ΔEads(O*) and ΔEads(HOO*) are the adsorption energies of HO*, O* and HOO* intermediates, respectively. Etotal(HO*), Etotal(O*) and Etotal(HOO*) are the total energies of the system, E* is the energy of the system without intermediate, E(H2O) and E(H2) are the energy of the reference molecules. Figure S16 shows adsorption energy profile of ORR intermediates adsorbed over five distinct sites. However, the adsorption energy is quite high for all the cases. This is expected because of the electronegative nature of nitrogen which inhibits adsorption on carbon as well as at Co. In view of these matters, new structures to study reactions on Co–SA@NPC and Co-NP@NPC were prepared (Figure S17) involving binding of Co-SA at a single pyridinic-N defect site. Intermediates species *OH, *O and *OOH were adsorbed over Co site in reconstructed Co-SA@NPC (Figure S17a) and reconstructed Co-NP@NPC (Figure S17b). The free energy profile is shown in Figure 5. Free energy of the O* intermediate over Co in Co-NP@NPC is lower than that in Co-SA@NPC (Figure 5) with Bader charges of –0.79 and –0.58, respectively (Table S3). Oxygen intermediate is strongly bound at the hollow site formed by three cobalt atoms of Co-NP (Figure S18). Hence, it experiences greater charge accumulation than its Co-SA counterpart. Similarly, O atoms in HO* and HOO* intermediates are saturated with three Co atoms (Figure S18). This saturation leads to stronger interaction of these intermediates with Co-NP making desorption difficult. This is reflected in the free energy plots where overpotential for Co-NP@NPC is greater than for Co-SA@NPC. However, both systems show negative free energy at U = 1.23 V. Hence, structures comprising Co-SA and Co-NP can accelerate the ORR process more effectively than the individual systems.  Figure 5. Gibbs free energy plots for oxygen reduction reaction for Co-SAC@NPC (left) and Co-NP@NPC (right).  Conclusion In summary, we have developed a facile, low-cost synthesis of ORR-active electrocatalyst, which is not only highly scalable based on its ease of operation, but also produces poisoning-resistant materials with ORR performance ostensibly superior to Pt/C.  The synthesis protocol involves Friedel-Crafts polymerization/metalation/thermolysis and leads to the electrocatalyst Co-NP/Co-SA@NPC consisting of N-doped graphene embedded with single cobalt atoms in the copresence of cobalt nanoparticles and with an ultralow loading of Co (0.3 at%). The composition of the material has been investigated in-depth allowing a deeper understanding of its electrochemical properties and usefulness as an electrocatalyst. Remarkably, Co-NP/Co-SA@NPC catalyst exhibits an ORR half-wave potential of 0.865 V vs RHE, surpassing the performance of commercial 20 wt% Pt/C catalyst and competitive with other reported ORR catalysts (see Table S4). Furthermore, the Co-NP/Co-SA@NPC electrocatalyst exhibits superior durability and methanol tolerance compared to Pt/C. Computational analysis supports possible synergetic effects in Co-NP/Co-SA@NPC where copresence of Co-NP/Co-SA can accelerate ORR processes. Overall, the scalable synthesis method and excellent properties of this catalyst paves the way for the future development of high-performance cobalt-based electrocatalysts for ORR in industrial applications, especially alkaline fuel cell devices.  Declaration of Competing Interests The authors declare that there are no competing financial interests.  Acknowledgements The authors are grateful to JST-ERATO Yamauchi Materials Space-Tectonics Project (JPMJER2003) and the Queensland Node of the Australian National Fabrication Facility (ANFF-Q). J.X. is grateful to the National Institute for Materials Science, International Center for Young Scientists, Japan (ICYS, NIMS) for an ICYS fellowship and research funds). 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