Self-Assembly Synthesis of Cobalt- and Nitrogen-Coembedded Trumpet Flower-Like Porous Carbons for Catalytic Oxygen Reduction in Alkaline and Acidic Media

Abstract

Developing highly cost-effective catalysts for an oxygen reduction reaction (ORR) in fuel cells is highly significant but still full of challenges. In this work, cobalt-and nitrogen-coembedded threedimensional (3D) trumpet flower-like porous carbons (CoNC) have been prepared by a simple two-step self-assembly technique, using carbon quantum dots (CQDs) as the carbon precursor and a supermolecular gel of self-assembled melamine and Co 2+ ions as the nitrogen and cobalt sources. The resultant CoNC catalysts possess unique 3D trumpet flowerlike structures, efficient charge transfer ability, and abundant Co−N x active sites. As a catalyst for ORR, the optimized CoNC-800 (pyrolyzed at 800 °C) exhibits efficient electrocatalytic activities, longer-term stability, and strong endurance to methanol both in acidic and alkaline media. It can be worked as a prospective substitute for a commercial Pt/C catalyst for ORR in the widespread implementation of fuel cells.

Co Nanoparticles Confined in 3D Nitrogen‐Doped Porous Carbon Foams as Bifunctional Electrocatalysts for Long‐Life Rechargeable Zn–Air Batteries

“…Figure a shows a broad diffraction peaks at 2θ ≈ 25.5°, which is related to the (002) face of graphite carbon . Other three well‐defined peaks at ≈44.1°, 51.4°, and 75.7° are corresponding to the face‐centered metallic Co, which is in good agreement with JCPDS card 15‐0806 . More holes, edges, and broken fringe usually mean more defect locations exist in the CoNCF, which were further verified by Raman spectra.…”

“…Besides, the metallic Co NPs with the size of ≈30 nm were firmly enwrapped by the onion‐like carbon shells and uniformly confined in the N‐doped porous carbon foams. A lattice spacing of 0.203 nm can be observed from the high‐resolution TEM (HRTEM) image of CoNCF‐1000‐80 (Figure d), which is corresponding to the (111) plane of metallic Co . Figure e–i displays the STEM image and corresponding elemental mapping images of CoNCF‐1000‐80, indicating the evenly distribution of C, O, N, and Co elementals in this sample.…”

“…In particular, the CoNCF‐1000‐80 shows an ultrahigh specific surface area of 1641 m 2 g −1 , which is much higher than that of CoNCF‐900‐80 (968 m 2 g −1 ) and CoNCF‐900‐80 (460 m 2 g −1 ). More importantly, the specific surface area of CoNCF‐1000‐80 also outperforms the vast majority of other M–N–C catalysts, e.g., N‐doped graphitic carbon supported Fe 3 C nanoclusters and Fe NPs (1100 m 2 g −1 ), Fe‐, N‐doped porous carbons (1060 m 2 g −1 ), Fe‐, N‐doped porous carbon networks (862 m 2 g −1 ), Fe‐, N‐doped nanocarbon intercalated graphene (457 m 2 g −1 ), Co‐, N‐doped graphene (365 m 2 g −1 ), and Co‐, N‐embedded trumpet flower‐like porous carbons (177 m 2 g −1 ) . The corresponding pore size distribution curves further indicated that the CoNCF catalysts possess large pore volume and are dominated by mesopore and micropore (Figure d; Table S1, Supporting Information).…”

“…Figure e–i displays the STEM image and corresponding elemental mapping images of CoNCF‐1000‐80, indicating the evenly distribution of C, O, N, and Co elementals in this sample. The obtained 3D porous foam architecture of CoNCF‐1000‐80 is not only beneficial to expose more potential active sites to the electrolyte, but also can protect the Co NPs from agglomeration and corrosion during the long‐term electrochemical process …”

“…Then, FeCo alloy NPs adhered on the inside wall of N‐doped carbon nanotubes were prepared by Ci and co‐workers and achieved a peak power density of 152 mW cm −2 in rechargeable Zn–air battery . This is because porous carbon materials typically possess excellent conductivity and rich porous structure, and thereby can facilitate the transfer of electrons and prevent the agglomeration of transition metal NPs . In addition, it was demonstrated that doping porous carbon materials with transition metal and nitrogen can form more effective active catalytic sites and further enhance the bifunctional catalytic activity .…”