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Two-dimensional (2D) layered materials have attracted significant attention for device applications because of their unique structures and outstanding properties. Here, a field-effect transistor (FET) sensor device is fabricated based on 2D phosphorene nanosheets (PNSs). The PNS sensor exhibits an ultrahigh sensitivity to NO2 in dry air and the sensitivity is dependent on its thickness. A maximum response is observed for 4.8-nm-thick PNS, with a sensitivity up to 190% at 20 parts per billion (p.p.b.) at room temperature. First-principles calculations combined with the statistical thermodynamics modelling predict that the adsorption density is ∼1015 cm−2 for the 4.8-nm-thick PNS when exposed to 20 p.p.b. NO2 at 300 K. Our sensitivity modelling further suggests that the dependence of sensitivity on the PNS thickness is dictated by the band gap for thinner sheets (<10 nm) and by the effective thickness on gas adsorption for thicker sheets (>10 nm).

A novel hybrid electrocatalyst consisting of nitrogen‐doped graphene/cobalt‐embedded porous carbon polyhedron (N/Co‐doped PCP//NRGO) is prepared through simple pyrolysis of graphene oxide‐supported cobalt‐based zeolitic imidazolate‐frameworks. Remarkable features of the porous carbon structure, N/Co‐doping effect, introduction of NRGO, and good contact between N/Co‐doped PCP and NRGO result in a high catalytic efficiency. The hybrid shows excellent electrocatalytic activities and kinetics for oxygen reduction reaction in basic media, which compares favorably with those of the Pt/C catalyst, together with superior durability, a four‐electron pathway, and excellent methanol tolerance. The hybrid also exhibits superior performance for hydrogen evolution reaction, offering a low onset overpotential of 58 mV and a stable current density of 10 mA cm−2 at 229 mV in acid media, as well as good catalytic performance for oxygen evolution reaction (a small overpotential of 1.66 V for 10 mA cm−2 current density). The dual‐active‐site mechanism originating from synergic effects between N/Co‐doped PCP and NRGO is responsible for the excellent performance of the hybrid. This development offers an attractive catalyst material for large‐scale fuel cells and water splitting technologies.

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...

A cost-effective route for the preparation of Fe(3) C-based core-shell structured catalysts for oxygen reduction reactions was developed. The novel catalysts generated a much higher power density (i.e., three times higher at R(ex) of 1 Ω) than the Pt/C in microbial fuel cells. Furthermore, the N-Fe/Fe(3)C@C features an ultralow cost and excellent long-term stability suitable for mass production.