Search for: All records

Abstract Iron- and nitrogen-doped carbon (Fe-N-C) represents a promising class of alternative electrocatalysts to noble metals for the oxygen reduction reaction (ORR) in acidic environments. To make Fe-N-C active, one of the most critical parameters is microporosity, which must be controlled to maximize the active site density. However, the use of microporosity must be optimized for the requirement of high-flux mass transport. Here, we synthesized and demonstrated gyroidal mesoporous Fe-N-C with microporous pore walls as an avenue to combine a high active-site density with favorable mass transport at high flux. The gyroidal mesoporous Fe-N-C catalysts have competitive gravimetric and volumetric ORR activities, comparable to the ORR activity obtained in purely microporous configurations despite having mesoporous features. Our result suggests that the ORR activity of microporous Fe-N-C electrocatalysts can be combined with mesoporosity through the use of mesoporous Fe-N-C with microporous pore walls. We further investigate effects of the nitrogen incorporation method on mesoporous N-doped carbon electrocatalysts. We find that despite having ∼2 × higher N concentration, nitrogen incorporationviaNH₃yields similar ORR activity to incorporationviaa chemical additive, a finding we attribute to the role of pyridinic and quaternary N in the ORR. 

Abstract Materials combining an asymmetric pore structure with mesopores everywhere enable high surface area accessibility and fast transport, making them attractive for e.g., energy conversion and storage applications. Block copolymer (BCP)/inorganic precursor co‐assembly combined with non‐solvent induced phase separation (NIPS) provides a route to materials in which a mesoporous top surface layer merges into an asymmetric support with graded porosity along the film normal and mesopores throughout. Here, the co‐assembly and non‐solvent‐induced phase separation (CNIPS) of poly(isoprene)‐b‐poly(styrene)‐b‐poly(4‐vinylpyridine) (ISV) triblock terpolymer and titanium dioxide (TiO₂) sol‐gel nanoparticlesare reported. Heat‐treatment in air results in free‐standing asymmetric porous TiO₂. Further thermal processing in ammonia results in free‐standing asymmetric porous titanium nitride (TiN). processing changes alter structural membrane characteristics is demonstrated. Changing the CNIPS evaporation time results in various membrane cross‐sections ( finger‐like to sponge‐like). Oxide and nitride material composition, crystallinity, and porosity are tuned by varying thermal processing conditions. Finally, thermal processing condition effects are probed on phase‐pure asymmetric nitride membrane behavior using cyclic voltammetry to elucidate their influence, e.g., on specific capacitance. Results provide further insights into improving asymmetric and porous materials for applications including energy conversion and storage, separation, and catalysis and motivate a further expansion of CNIPS to other (in)organic materials.