Metal−Organic Framework‐Derived Nitrogen‐Doped Core‐Shell‐Structured Porous Fe/Fe₃C@C Nanoboxes Supported on Graphene Sheets for Efficient Oxygen Reduction Reactions

Abstract

synthesis of MOFs-derived porous Fe, N-based carbon catalysts supported on NRGO sheets as ORR catalysts.Here, we report the fabrication of novel nitrogen-doped coreshell-structured porous Fe/Fe 3 C@C nanoboxes supported on RGO sheets (N-doped Fe/Fe 3 C@C/RGO) by a simple pyrolysis process using graphene oxide (GO) and PB nanocubes as precursors. Such a unique structure not only offers more active sites from both nitrogen-doped Fe/Fe 3 C@C and NRGO sheets, but also shows enhanced electrical conductivity. As a result, the hybrid exhibits much better electrocatalytic activity, long-term stability, and methanol tolerance ability than the commercial Pt/C catalyst (10% Pt on Vulcan XC-72).The fabrication process for the porous N-doped Fe/Fe 3 C@C/ RGO hybrid is demonstrated in Figure 1 a. Highly uniform PB nanocubes were fi rstly synthesized using a hydrothermal method based on previous reports. [ 9a ] The obtained PB nanocubes were further dispersed in the GO solution (PB/GO) under stirring. The resulting PB/GO powders after drying at 80 °C were then annealed at 800 °C in an argon fl ow to form a core-shell-structured porous N-doped Fe/Fe 3 C@C/RGO hybrid. During this process, the continuous decomposition of PB nanocubes was accompanied by releasing nitrogen-containing gases, [ 11 ] which resulted in the formation of a porous structure accompanied with carbide reactions according to the thermogravimetric analysis (TGA) results ( Figure S1, Supporting Information). Simultaneously, the nitrogen-containing species contributed to the reduction of GO and nitrogen doping in both GO and carbon shells, fi nally evolving into nitrogen-doped core-shell-structured porous Fe/Fe 3 C@C/RGO hybrids. The PB nanocubes not only act as templates/precursors, but also provide nitrogen sources for the formation of N-doped Fe/Fe 3 C@C and NRGO.Field-emission scanning electron microscopy (FESEM) images show that uniform PB nanocubes with an edge length of about 500 nm are obtained without any aggregation (Figure 1 b). An enlarged image (inset of Figure 1 b) reveals the very smooth surface over a single box. After the thermal treatment, the PB nanocubes are converted to porous N-doped Fe/Fe 3 C@C nanoboxes with a side length of around 300-400 nm (Figure 1 c). The cubic structure still remained, although its size decreased a little due to the decomposition and shrinkage during the annealing process. [ 12 ] This suggests that the PB nanocubes served as both a template and a self-sacrifi cing precursor for the formation of porous nanoboxes, which are composed of numerous Developing catalytic materials with high activity for oxygen reduction reaction (ORR) is of great signifi cance for commercial fuel cell applications. [ 1 ] Although Pt-based materials are known as the most effi cient ORR catalysts, [ 2 ] they still suffer from several serious problems, including high cost, low abundance, weak durability, crossover effect and CO poisoning; [ 3 ] these obstacles hinder the large-scale application of fuel cells. To solve these issues, numero...

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

“…In addition to Co-based MOFs, other transition metal-based MOFs, like Fe-based MOFs, have also been reported as precursors in the fabrication of Fe-Nx-C and N-doped Fe/Fe 3 C@C/RGO catalysts to activate ORR in alkaline media [17,[59][60][61]66]. Tang and co-workers [17] can be employed to develop Fe-Nx-C nanostructure as an electrocatalyst (Figure 9).…”

“…Additionally, the porosity structure derived from the MOFs particles could promote diffusion of both reactants (O 2 ) and products (OH´), which promises the limiting current density of Fe-Nx-C catalyst is considerably 1.2 times higher than that of Pt/C. using GO as a conductive support and Prussian blue (PB-created from assembly of iron components with N-containing polyvinylpyrrolidone) nanocubes as carbon precursors [61]. During pyrolysis, the continuous decomposition of PB precursor was accompanied by the production of nitrogencontaining gases, resulting in the formation of a PB-nanocarbon with porous and N-doped structure.…”

Long life rechargeable Li-O2 batteries enabled by enhanced charge transfer in nanocable-like Fe@N-doped carbon nanotube catalyst

“…However, they generally suffer from a large overpotential of 1.5 V and low round-trip efficiency (53%-64 %). Heteroatom doping or hybridization with metal species represents an efficient way to enhance the activity of carbon-based catalysts towards oxygen reduction reaction (ORR)/OER reactions [39][40][41][42]. The presence of heteroatoms (e.g., N) and metal species not only reduces the local work function on carbon surface for better O2 adsorption, but also changes the charge density on the carbon surface via electron transfer effect [16,[43][44][45][46][47][48][49][50][51].…”

A facile strategy for ultrasmall Pt NPs being partially-embedded in N-doped carbon nanosheet structure for efficient electrocatalysis

“…4d, the deconvoluted N 1s contains three peaks positioned at 399.2, 400.9 and 402.4 eV, which can be respectively ascribed to pyrrolic N, graphitic N and oxidized N [31] derived from N elements in pyrrole upon heat treatment. Among them, the pyrrolic and graphitic N species can promote the oxygen reduction via changing the chemical/electronic environment of the neighboring carbon atoms [32][33][34]. Besides, a lower binding energy of 398.5 eV may be attributed to the interaction between Pt and N atoms [15,16].…”