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).

We report a high-performance bi-functional electrocatalyst composed of 3D crumpled graphene (CG)–cobalt oxide nanohybrids. This is the first report on using CG coupled with nanocrystals as both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts. The nitrogen-doped CG–CoO hybrid exhibits excellent catalytic activity and durability, making it a high-performance non-precious metal-based bi-functional catalyst for both ORR and OER.