13 research outputs found
Ultrathin Nanosheets of Oxoâfunctionalized Graphene Inhibit the Ion Migration in Perovskite Solar Cells
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Towards the Synthesis of Graphene Azide from Graphene Oxide
In the last decades, organic azides haven proven to be very useful precursors in organic chemistry, for example in 1,3-dipolar cycloaddition reactions (click-chemistry). Likewise, azides can be introduced into graphene oxide with an almost intact carbon framework, namely oxo-functionalized graphene (oxo-G1), which is a highly oxidized graphene derivative and a powerful precursor for graphene that is suitable for electronic devices. The synthesis of a graphene derivative with exclusively azide groups (graphene azide) is however still a challenge. In comparison also hydrogenated graphene, called graphene or halogenated graphene remain challenging to synthesize. A route to graphene azide would be the desoxygenation of azide functionalized oxo-G1. Here we show how treatment of azide functionalized oxo-G1 with HCl enlarges the Ï-system and removes strongly adsorbed water and some oxo-functional groups. This development reflects one step towards graphene azide
Towards the Synthesis of Graphene Azide from Graphene Oxide
In the last decades, organic azides haven proven to be very useful precursors in organic chemistry, for example in 1,3-dipolar cycloaddition reactions (click-chemistry). Likewise, azides can be introduced into graphene oxide with an almost intact carbon framework, namely oxo-functionalized graphene (oxo-G1), which is a highly oxidized graphene derivative and a powerful precursor for graphene that is suitable for electronic devices. The synthesis of a graphene derivative with exclusively azide groups (graphene azide) is however still a challenge. In comparison also hydrogenated graphene, called graphene or halogenated graphene remain challenging to synthesize. A route to graphene azide would be the desoxygenation of azide functionalized oxo-G1. Here we show how treatment of azide functionalized oxo-G1 with HCl enlarges the Ï-system and removes strongly adsorbed water and some oxo-functional groups. This development reflects one step towards graphene azide
Origin of Oxygen in Graphene Oxide Revealed by <sup>17</sup>O and <sup>18</sup>O Isotopic Labeling
Wet-chemical oxidation
of graphite in a mixture of sulfuric acid
with a strong oxidizer, such as potassium permanganate, leads to the
formation of graphene oxide with hydroxyl and epoxide groups as the
major functional groups. Nevertheless, the reaction mechanism remains
unclear and the source of oxygen is a subject of debate. It could
theoretically originate from the oxidizer, water, or sulfuric acid.
In this study, we employed 18O and 17O labeled reagents to experimentally
elucidate the reaction mechanism and, thus, determine the origin of
oxo-functional groups. Our findings reveal the multifaceted roles
of sulfuric acid, acting as a dispersion medium, a dehydrating agent
for potassium permanganate, and an intercalant. Additionally, it significantly
acts as a source of oxygen next to manganese oxides. Through 17O solid-state magic-angle spinning (MAS) NMR experiments,
we exclude water as a direct reaction partner during oxygenation.
With labeling experiments, we conclude on mechanistic insights, which
may be exploited for the synthesis of novel graphene derivatives
Focused electron beam based direct-write fabrication of graphene and amorphous carbon from oxo-functionalized graphene on silicon dioxide
Systematic evaluation of different types of graphene oxide in respect to variations in their in-plane modulus
Graphene oxide samples prepared in various laboratories following a diversity of synthesis protocols based on Brodie's (BGO) and Hummers/Offeman's (HGO) methods were compared in respect of their in-plane moduli. A simple wrinkling method allowed for a spatial resolution <1.5Â ?m by converting the wrinkling frequency. Quite surprisingly, a drastic variation of the in-plane moduli was found spanning the range from 600Â GPa for the best BGO types, which is in the region of chemically derived graphene, all the way down to less than 200Â GPa for HGO types. This would suggest that there are no two equal GO samples and GO should not be regarded a compound but rather a class of materials with very variable physical properties. While large differences between Brodie's and Hummers/Offeman's types might have been expected, even within the group of Hummers/Offeman's types pronounced differences are observed that, based on 13C solid-state NMR, were related to over-functionalization versus over-oxidation
Extending the environmental lifetime of unpackaged perovskite solar cells through interfacial design
Solution-processed oxo-functionalized graphene (oxo-G1) is employed to substitute hydrophilic PEDOT:PSS as an anode interfacial layer for perovskite solar cells. The resulting devices exhibit a reasonably high power conversion efficiency (PCE) of 15.2% in the planar inverted architecture with oxo-G1 as a hole transporting material (HTM), and most importantly, deploy the full open-circuit voltage (Voc) of up to 1.1 V. Moreover, oxo-G1 effectively slows down the ingress of water vapor into the device stack resulting in significantly enhanced environmental stability of unpackaged cells under illumination with 80% of the initial PCE being reached after 500 h. Without encapsulation, âŒ60% of the initial PCE is retained after âŒ1000 h of light soaking under 0.5 sun and ambient conditions maintaining the temperature beneath 30 °C. Moreover, the unsealed perovskite device retains 92% of its initial PCE after about 1900 h under ambient conditions and in the dark. Our results underpin that controlling water diffusion into perovskite cells through advanced interface engineering is a crucial step towards prolonged environmental stability