| Portable and flexible fuel cells,due to their superior energy densities to batteries,are of cardinal significance and have drawn increasing attentions in the field of flexible electronics.Although various fuel cells based on lightweight materials and miniaturized design of overall structure have been fabricated recently and reached certain level of portability and miniaturization,these devices often suffer from fuel crossover,poor flexibility and difficulty in fuel storage,giving rise to flexibility challenges as well as limitations of practical use.Among all types of fuel cells,the direct ethanol fuel cell?DEFC?using liquid ethanol is one of the best candidates in portable and flexible devices.Distinguished by its non-toxicity and low-cost,it is deemed to be a commendable energy conversion device for a generation or more.However,there are still no flexible DEFC devices that can actually be used so far.The major difficulties in their practical application have not been solved:ethanol-crossover-induced catalyst poisoning,and failed polyelectrolyte caused by the harsh alkaline environment.On one hand,although Pt-based materials are considered to be the most efficient ORR electrocatalysts,the key challenge for their application in flexible DEFC is catalytic inactivation by inevitable ethanol crossover.Thus,searching for anti-ethanol toxic,highly efficient and low-cost non-noble metal ORR catalysts is extremely urgent.Among various types of catalysts,heteroatom-doped carbon materials are very promising on account of all features mentioned above due to their intrinsically unique electronic structure characteristics.Although many progresses have achieved on carbonaceous catalysts doped by various elements,many of them still suffer from inferior ORR activities,which could make the running environment of DEFC harsher?e.g.,higher temperatures and/or pressure?.Moreover,the tedious process of fabrication and additional activation treatment is also a fatal flaw.Therefore,it is crucial to fabricate an anti-ethanol toxic,highly catalytic and low-cost heteroatom-doped carbon catalyst via one-step synthesis.On the other hand,the ORR catalytic activity of most catalysts,especially carbon based metal-free catalysts,is much higher under alkaline condition than under acidic condition.Additionally,some evidences reveal that the ethanol oxidation rate of noble metal catalysts such as Pt-and Pd-based is much faster in alkaline environment than in acid.However,the most widely used Nafion membrane in medium-low temperature fuel cells is proton-conductive,hampering its application in high-performance flexible DEFCs.Therefore,it is primarily important to develop an alkali-compatible polyelectrolyte with long-time stable and high ionic conductivity.Sodium polyacrylate hydrogel?PANa?possesses superior and stable ionic conductivity in high-concentration alkaline corrosive media due to its super-absorbing and water-retaining capabilities.Besides,it keeps good mechanical properties even when saturated with highly concentrated alkali.These are in line with the afore-mentioned needs of flexible DEFC and thus,guarantee PANa hydrogel as an excellent hydroxyl-ion-conductive membrane for the DEFC.Herein,we synthesized an anti-ethanol toxic,highly catalytic and low-cost porous N,S co-doped carbon catalyst?NSDC?as well as a highly conductive and durable PANa alkaline membrane to fabricate a novel flexible DEFC for the first time to our best knowledge.Notably,it delivers high power and energy densities of21.48 mW cm-22 and 1.41 mWh cm-2,respectively.Moreover,it possesses excellent flexibility to even 180°bending and unique function of drop-and-play,which solve the shortcomings of the previous rigid DEFCs. |
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