Nitrogen‐Doped Nanoporous Carbon/Graphene Nano‐Sandwiches: Synthesis and Application for Efficient Oxygen Reduction

Abstract

A zeolitic‐imidazolate‐framework (ZIF) nanocrystal layer‐protected carbonization route is developed to prepare N‐doped nanoporous carbon/graphene nano‐sandwiches. The ZIF/graphene oxide/ZIF sandwich‐like structure with ultrasmall ZIF nanocrystals (i.e., ≈20 nm) fully covering the graphene oxide (GO) is prepared via a homogenous nucleation followed by a uniform deposition and confined growth process. The uniform coating of ZIF nanocrystals on the GO layer can effectively inhibit the agglomeration of GO during high‐temperature treatment (800 °C). After carbonization and acid etching, N‐doped nanoporous carbon/graphene nanosheets are formed, with a high specific surface area (1170 m2 g−1). These N‐doped nanoporous carbon/graphene nanosheets are used as the nonprecious metal electrocatalysts for oxygen reduction and exhibit a high onset potential (0.92 V vs reversible hydrogen electrode; RHE) and a large limiting current density (5.2 mA cm−2 at 0.60 V). To further increase the oxygen reduction performance, nanoporous Co‐Nx/carbon nanosheets are also prepared by using cobalt nitrate and zinc nitrate as cometal sources, which reveal higher onset potential (0.96 V) than both commercial Pt/C (0.94 V) and N‐doped nanoporous carbon/graphene nanosheets. Such nanoporous Co‐Nx/carbon nanosheets also exhibit good performance such as high activity, stability, and methanol tolerance in acidic media.

Recent Progress on MOF-Derived Nanomaterials as Advanced Electrocatalysts in Fuel Cells

“…By delicate design of MOFs precursors, together with careful post-treatment, the advantages and catalytic activity of MOFs materials can be fully inherited by the MOF-derived nanomaterials. For example, MOF-derived heteroatom-doped nanocarbon [28][29][30][31], transition metal/metal oxide-carbon hybrids and composites (as shown in Figure 2) [26,[32][33][34][35][36], with high surface area and porosity, have been reported to exhibit excellent catalytic activity and stability, while also displaying outstanding bifunctional activity toward ORR and oxygen evolution reaction (OER). It should be noted that MOFs precursors employed in developing heteroatom-doped nanocarbon can be conveniently tailored by coupling them with a second heteroatom-containing precursor.…”

“…Thus far, the functional porous heteroatom-doped nanocarbon materials have been considered as promising metal-free electrocatalsyts in fuel cells because of their unique physical and chemical characteristics, pronounced electrocatalytic activity, long-term stability, and relatively low costs [40][41][42]. Among them, single-doped nanocarbon (e.g., N-C) [37], multi-doped nanocarbon (e.g., NS-C, NPS-C) [43][44][45][46], as well as nanocarbon composites (e.g., nanocarbon/CNTs, nanocarbon/graphene) [28][29][30][31], have been researched as effective electrocatalysts in fuel cells. …”

“…Previous reports have demonstrated that incorporation of an ultrathin layer of MOF-derived nanocarbon on graphene oxide sheets could lead to the formation of a nanocarbon /graphene oxide/nanocarbon sandwich-like structure with high specific surface area and excellent electronic conductivity [28][29][30][31]. Initial efforts toward developing such a composite were conducted by Wang [29] and Zhang [31], via pyrolyzing ZIF-8/graphene oxide composite at a temperature of 800˝C.…”

Carbon skeleton doped with Co, N, S and P as efficient electrocatalyst for oxygen evolution reaction

“…The N 1s spectra can be fit well with four kinds of N species. Peaks at about 398.8, 400.0, 401.0 and 404.9 eV correspond to pyridinic nitrogen, pyrrolic nitrogen, graphitic nitrogen, and pyridinic N + -O − , respectively [39,40]. Besides these four peaks, an additional peak locates at 398.6 eV, which is ascribed to the pyridinic nitrogen or P=N/P-N bond [41,42].…”

Porous yolk–shell microspheres as N–doped carbon matrix for motivating the oxygen reduction activity of oxygen evolution oriented materials

“…Interestingly, our NCYS catalyst was also active and durable for ORR when tested in acidic solution. The ORR polarization curve ( figure 4(a)) exhibited E onset of 0.86 V and E 1/2 of 0.70 V, comparable to commercial Pt/C and even superior to many state-of-art catalyst materials recently reported in top publications [7,[39][40][41][42][43]. Kinetic currents derived from the mass transport corrected ORR currents ( figure 4(b)) showed a little lower Tafel slope than that of the commercial Pt/C catalyst, indicating a similar electrochemical reaction rate between the catalysts.…”