Aerogels offer a great platform for heterogeneous electrocatalysis owing to their high surface area and porosity. Atomically dispersed transition metal ions can be imbedded in these platforms at ultra‐high site density to make them catalytically active for various reactions. Herein, the synthesis of a new class of conjugated microporous organic aerogels that are used as covalent 3D frameworks for the electrocatalysis of oxygen reduction reaction (ORR) is reported. Modified aerogels functionalized with bipyridine ligands enable copper ion complexation in a single‐step synthesis. The aerogels’ structures are fully characterized using a wide array of spectroscopic and microscopic methods, and heat‐treated in order to make them electronically conductive. After heat treatment at 600 °C, the aerogels maintained their macrostructure and became active ORR catalysts in alkaline environment, showing high mass activity and ultra‐high site density.
Oxygen reduction reaction (ORR) is considered the bottleneck reaction in fuel cells. Its sluggish kinetics requires the use of scarce and expensive platinum group metal (PGM) catalysts. Significant efforts have been invested in trying to find a PGM-free catalyst to replace Pt for this reaction or reduce its loadings.One interesting family of materials that has shown great promise in doing so is aerogels, which are based on covalent frameworks. The aerogels' high surface area and porosity enable good mass transport and high catalyst utilization that is expected to lower PGM loadings or replacing them completely. This review summarizes recent research in this field, introducing methods of using aerogels as cathodes for ORR, from carbon to metal aerogels. The catalytic sites vary from nanoparticles to atomically dispersed metal ions embedded in carbon aerogels that form all-in-one platform which can serve as both the support and the catalyst.
Carbon aerogels have been studied in the context of fuel cell electrodes mainly as catalyst support materials due to their high surface area, porosity, and electrical conductivity. Recently, aerogels composed solely of inorganic molecular complexes have shown to be promising materials for the electrocatalysis of oxygen reduction reaction (ORR). These aerogels consist of atomically dispersed catalytic sites. Herein, we report on the synthesis and characterization of an aerogel-based catalyst: iron phthalocyanine aerogel. It was synthesized by coupling of ethynylterminated phthalocyanine monomers and then heat-treated at 800 °C to increase its electrical conductivity and catalytic activity. The aerogels reported here were tested as catalysts for ORR in acidic conditions for the first time and found to have a ultra-high number of atomically dispersed catalytic sites (7.11 × 10 20 sites g −1 ) and very good catalytic activity (E onset = 0.9 V vs RHE and TOF = 9.2 × 10 −3 e − s −1 site −1 at 0.8 V vs RHE). The iron phthalocyanine aerogel was also studied in a proton exchange membrane fuel cell, reaching a peak power density of 292 mW cm −2 and an open circuit voltage of 0.83 V.
Stimuli-responsive polymers were synthesized by atom transfer radical polymerization (ATRP) using a photoresponsive self-immolative bifunctional initiator. The photoactivated self-immolative junctions allow transforming nonresponsive polymers into photocleavable polymers that can be split into two equally sized fragments when exposed to the stimulation. We demonstrate this modular approach by preparing a series of photoresponsive poly(benzyl methacrylate) and polystyrene polymers of various molecular weights. Taking advantage of the well-defined architecture of the polymers, we studied their photoresponse as thin films and examined the effect of irradiation time and solvent addition on the degree of response and splitting. The results show that the polymers can be split in the solid phase, confirming that the self-immolative quinone methide elimination can occur in solid phase. Importantly, we could also obtain insights into the role of the mobility of the polymer chains in the solid phase and in the presence of solvent molecules on the responsiveness of the films and degree of splitting. The potential to introduce such modular self-immolative units into different types of widely used of polymers will allow the utilization of this approach to create wide range of responsive materials that can undergo vast structural changes by relatively minor synthetic modifications.
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