The commercial Haber-Bosch process for NH3 production not only requires large amounts of energy and hydrogen supply but also generates tremendous greenhouse CO2 emission. To mitigate energy and environmental challenges, renewable ammonia production technologies based on electrochemical and photochemical methods, in particular, photocatalytic nitrogen fixation in aqueous phase for ammonia production is highly desired. In the present work, single-atom Pt anchored at the −N3 sites of stable and ultrathin covalent triazine framework (CTF) nanosheets have been successfully synthesized (Pt-SACs/CTF). The well-defined coordination structure of Pt–N3 sites in the Pt-SACs/CTF catalyst have been characterized using HAADF-STEM and EXAFS, as well as ab initio molecular dynamics simulations. The ammonia production rate over the as-synthesized Pt-SACs/CTF catalyst is 171.40 μmol g–1 h–1 in the absence of sacrificial agent. On the basis of density functional theory calculations, it has been found that the alternating mechanism is energetically more favorable than the distal mechanism over the well-defined Pt–N3 sites. The significance of the present work is to demonstrate that the single-atom metal catalysts are anchored at the two-dimensional stable CTF nanosheets for photocatalytic nitrogen fixation to ammonia.

A flexible, transparent, and renewable mesoporous cellulose membrane (mCel‐membrane) featuring uniform mesopores of ≈24.7 nm and high porosity of 71.78% is prepared via a facile and scalable solution‐phase inversion process. KOH‐saturated mCel‐membrane as a polymer electrolyte demonstrates a high electrolyte retention of 451.2 wt%, a high ionic conductivity of 0.325 S cm−1, and excellent mechanical flexibility and robustness. A solid‐state electric double layer capacitor (EDLC) using activated carbon as electrodes, the KOH‐saturated mCel‐membrane as a polymer electrolyte exhibits a high capacitance of 110 F g−1 at 1.0 A g−1, and long cycling life of 10 000 cycles with 84.7% capacitance retention. Moreover, a highly integrated planar‐type micro‐supercapacitor (MSC) can be facilely fabricated by directly depositing the electrode materials on the mCel‐membrane‐based polymer electrolyte without using complicated devices. The resulting MSC exhibits a high areal capacitance of 153.34 mF cm−2 and volumetric capacitance of 191.66 F cm−3 at 10 mV s−1, representing one of the highest values among all carbon‐based MSC devices. These findings suggest that the developed renewable, flexible, mesoporous cellulose membrane holds great promise in the practical applications of flexible, solid‐state, portable energy storage devices that are not limited to supercapacitors.

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