The big challenging issues in photocatalytic H 2 evolution are efficient separation of the photoinduced carriers, the stability of the catalyst, enhancing quantum efficiency, and requiring photoinduced electrons to enrich on photocatalysts' surface. Herein, Ti 3 C 2 MXene quantum dots (QDs) possess the activity of Pt as a co-catalyst in promoting the photocatalytic H 2 evolution to form heterostructures with g-C 3 N 4 nanosheets (NSs) (denoted g-C 3 N 4 @Ti 3 C 2 QDs). The photocatalytic H 2 evolution rate of g-C 3 N 4 @Ti 3 C 2 QD composites with an optimized Ti 3 C 2 QD loading amounts (100 mL) is nearly 26, 3 and 10 times higher than pristine g-C 3 N 4 NSs, Pt/g-C 3 N 4 , and Ti 3 C 2 MXene sheet/g-C 3 N 4 , respectively. The Ti 3 C 2 QDs increase the specific surface area of g-C 3 N 4 and boost the density of the active site. Besides, metallic Ti 3 C 2 QDs possess excellent electronic conductivity, causing the improvement of carrier transfer efficiency. KEYWORDS: photocatalytic H 2 production, Ti 3 C 2 MXene quantum dots, g-C 3 N 4 nanosheets, co-catalysts

High mass loading and fast charge transport are two crucial but often mutually exclusive characteristics of pseudocapacitors. On conventional carbon supports, high mass loadings inevitably lead to sluggish electron conduction and ion diffusion due to thick pseudocapacitive layers and clogged pores. Here we present a design principle of carbon supports, utilizing self-assembly and microphase-separation of block copolymers. We synthesize porous carbon fibers (PCFs) with uniform mesopores of 11.7 nm, which are partially filled with MnO2 of <2 nm in thickness. The uniform mesopores and ultrathin MnO2 enable fast electron/ion transport comparable to electrical-double-layer-capacitive carbons. At mass loadings approaching 7 mg cm−2, the gravimetric and areal capacitances of MnO2 (~50% of total mass) reach 1148 F g−1 and 3141 mF cm−2, respectively. Our MnO2-coated PCFs outperform other MnO2-based electrodes at similar loadings, highlighting the great promise of block copolymers for designing PCF supports for electrochemical applications.

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High mechanical strength, thermal stability, and flame retardancy are three crucial criteria for highperformance polymers to be suitable for aerospace applications. Most polymers, however, cannot meet the three criteria simultaneously. Herein, phosphonium bromide-terminated poly(ether imide)s (PEI-PhPPh 3 Br) simultaneously possessing high mechanical strength, thermal stability, and flame retardancy were synthesized by functionalizing dianhydrideterminated poly(ether imide)s (PEI-DA) with triphenyl-4aminophenylphosphonium bromide. With the judiciously designed end group, PEI-PhPPh 3 Br exhibited excellent tensile properties, thermal stability, and flame retardancy. Importantly, PEI-PhPPh 3 Br with a molecular weight of 12 kDa [PEI-PhPPh 3 Br (12k)] showed a tensile strength of 109 ± 4 MPa and a Young's modulus of 2.75 ± 0.12 GPa, much higher than those of the noncharged PEI analogue. Additionally, PEI-PhPPh 3 Br (12k) showed outstanding flame retardancy, better than the state-of-the-art commercial PEIs, as evidenced by the high limiting oxygen index of 51% and high char yield of 60% at 980 °C. The study herein provides a highly effective strategy to simultaneously improve mechanical strength, thermal stability, and flame retardancy, which are three important properties rarely possessed by most polymers.