Suchergebnisse

Sodium-oxygen batteries (SOBs) have the potential to provide energy densities higher than the state-of-the-art Li-ion batteries. However, controlling the formation of sodium superoxide (NaO2) as the sole discharge product on the cathode side is crucial to achieve durable and efficient SOBs. In this work, the discharge efficiency of two graphene-based cathodes was evaluated and compared with that of a commercial gas diffusion layer. The discharge products formed at the surface of these cathodes in a glyme-based electrolyte were carefully studied using a range of characterization techniques. NaO2 was detected as the main discharge product regardless of the specific cathode material while small amounts of Na2O2⋅2H2O and carbonate-like side-products were detected by X-ray diffraction as well as by Raman and infrared spectroscopies. This work leverages the use of X-ray diffraction to determine the actual yield of NaO2 which is usually overlooked in this type of batteries. Thus, the proper quantification of the superoxide formed on the cathode surface is widely underestimated; even though is crucial for determining the efficiency of the battery while eliminating the parasitic chemistry in SOBs. Here, we develop an ex-situ analysis method to determine the amount of NaO2 generated upon discharge in SOBs by transmission X-ray diffraction and quantitative Rietveld analysis. This work unveils that the yield of NaO2 depends on the depth of discharge where high capacities lead to very low discharge efficiency, regardless of the used cathode. We anticipate that the methodology developed herein will provide a convenient diagnosis tool in future efforts to optimize the performance of the different cell components in SOBs. ; M.E., L.M and N.O.-V. thank the European Union (Graphene Flagship-Core 3, Grant number 881603) for the financial support of this work. J.I.P. acknowledges funding by the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN), Agencia Estatal de Investigación (AEI) and the European Regional Development Fund (ERDF) through project RTI2018-100832-B-I00. R.Y. acknowledges financial support from StandUp for Energy and the Swedish Energy Agency. ; Peer reviewed

Graphene aerogels derived from a biomolecule‐assisted aqueous electrochemical exfoliation route are explored as cathode materials in sodium–oxygen (Na–O2) batteries. To this end, the natural nucleotide adenosine monophosphate (AMP) is used in the multiple roles of exfoliating electrolyte, aqueous dispersant, and functionalizing agent to access high quality, electrocatalytically active graphene nanosheets in colloidal suspension (bioinks). The surface phenomena occurring on the electrochemically derived graphene cathode is thoroughly studied to understand and optimize its electrochemical performance, where a cooperative effect between the nitrogen atoms and phosphates from the AMP molecules is demonstrated. Moreover, the role of the nitrogen atoms in the adenine nucleobase of AMP and short‐chain phosphate is unraveled. Significantly, the use of such cathodes with a proper amount of AMP molecules adsorbed on the graphene nanosheets delivers a discharge capacity as high as 9.6 mAh cm−2 and performs almost 100 cycles with a considerably reduced cell overpotential and a coulombic efficiency of ≈97% at high current density (0.2 mA cm−2). This study opens a path toward the development of environmentally friendly air cathodes by the use of natural nucleotides which offers a great opportunity to explore and manufacture bioinspired cathodes for metal–oxygen batteries. ; M.E., J.L.G.‐U., D.C., and N.O.‐V. thank the European Union (Graphene Flagship‐Core 3, Grant number 881603) and the Spanish Ministry of Science and Innovation (MICINN/FEDER) (RTI2018‐096199‐B‐I00) for the financial support of this work. J.M.M., J.I.P., and S.V.‐R. gratefully acknowledge funding by the Spanish Ministerio de Ciencia, Innovación y Universidades (MICINN), Agencia Estatal de Investigación (AEI), and the European Regional Development Fund (ERDF) through project RTI2018‐100832‐B‐I00, as well as Plan de Ciencia, Tecnología e Innovación (PCTI) 2013‐2017 del Principado de Asturias and the ERDF (project IDI/2018/000233). J.L.G.‐U. is very thankful to the Spanish Ministry of Education, Science and Universities (MICINN) for the FPU grant (16/03498) ; Peer reviewed

Integrated approaches that expedite the production and processing of graphene into useful structures and devices, particularly through simple and environmentally friendly strategies, are highly desirable in the efforts to implement this two-dimensional material in state-of-the-art electrochemical energy storage technologies. Here, we introduce natural nucleotides (e.g., adenosine monophosphate) as bifunctional agents for the electrochemical exfoliation and dispersion of graphene nanosheets in water. Acting both as exfoliating electrolytes and colloidal stabilizers, these biomolecules facilitated access to aqueous graphene bio-inks that could be readily processed into aerogels and inkjet-printed interdigitated patterns. Na-O2 batteries assembled with the graphene-derived aerogels as the cathode and a glyme-based electrolyte exhibited a full discharge capacity of ∼3.8 mAh cm–2 at a current density of 0.2 mA cm–2. Moreover, shallow cycling experiments (0.5 mAh cm–2) boasted a capacity retention of 94% after 50 cycles, which outperformed the cycle life of prior graphene-based cathodes for this type of battery. The positive effect of the nucleotide-adsorbed nanosheets on the battery performance is discussed and related to the presence of the phosphate group in these biomolecules. Microsupercapacitors made from the interdigitated graphene patterns as the electrodes also displayed a competitive performance, affording areal and volumetric energy densities of 0.03 μWh cm–2 and 1.2 mWh cm–3 at power densities of 0.003 mW cm–2 and 0.1 W cm–3, respectively. Taken together, by offering a green and straightforward route to different types of functional graphene-based materials, the present results are expected to ease the development of novel energy storage technologies that exploit the attractions of graphene. ; Funding by the Spanish Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (ERDF) through project MAT2015-69844-R and by the Spanish Ministerio de Ciencia, Innovación y Universidades and ERDF through project RTI2018-100832-B-I00 is gratefully acknowledged. Partial funding by Plan de Ciencia, Tecnología e Innovación (PCTI) 2013-2017 del Principado de Asturias and the ERDF through project IDI/2018/000233 is also acknowledged. J.M.M. is grateful to the Spanish Ministerio de Educación, Cultura y Deporte (MECD) for his pre-doctoral contract (FPU14/00792). J.N.C. acknowledges the ERC Adv. Gr. FUTUREPRINT. This work was also financially supported by the European Union (Graphene Flagship, Core 2, Grant number 785219). ; Peer reviewed