Nitrogen (N)‐doped carbons are potential nonprecious metal catalysts to replace Pt for the oxygen reduction reaction (ORR). Pyridinic‐N‐C is believed to be the most active N group for catalyzing ORR. In this work, using zinc phthalocyanine as a precursor effectively overcomes the serious loss of pyridinic‐N, which is commonly regarded as the biggest obstacle to catalytic performance enhancement upon adopting a second pyrolysis process, for the preparation of a 3D porous N‐doped carbon framework (NDCF). The results show only ≈14% loss in pyridinic‐N proportion in the Zn‐containing sample during the second pyrolysis process. In comparison, a loss of ≈72% pyridinic‐N occurs for the non‐Zn counterpart. The high pyridinic‐N proportion, the porous carbon framework produced upon NaCl removal, and the increased mesoporous defects in the second pyrolysis process make the as‐prepared catalyst an excellent electrocatalyst for ORR, exhibiting a half‐wave potential (E1/2 = 0.88 V) up to 33 mV superior to state‐of‐the‐art Pt/C and high four‐electron selectivity (n > 3.83) in alkaline solution, which is among the best ORR activities reported for N‐doped carbon catalysts. Furthermore, only ≈18 mV degradation in E1/2 occurs after an 8000 cycles' accelerating stability test, manifesting the outstanding stability of the as‐prepared catalyst.
Structural design and self‐assembly at the molecular level provide feasible strategies for constructing materials with novel and unique properties. Cellulose is one of the most abundant bioresources and is renewable, biodegradable, biocompatible, and environmentally friendly. The formation of hydrogen‐bonding networks between the cellulose molecular chains on the one hand gives cellulose a rigid crystalline region and high mechanical strength and on the other hand it causes inconvenience to material design based on the molecular scale. The emergence of eco‐friendly solvents such as ionic liquids and alkali/urea solutions breaks the hydrogen bonds and allows the design of various cellulose‐based functional materials, such as membranes, gels, fibers, and nano/microspheres via structural optimization and molecular self‐assembly. Such functional materials have promising applications in flexible electronic devices, such as electrochemical energy storage devices, sensors, biomimetic electronic skins, and optoelectronic devices. In this review, green solvents for cellulose, the dissolution–recombination process, molecular self‐assembly strategies, advanced applications, and future development prospects for high‐performance cellulose‐based functional materials with unique structures are presented.
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