A large number of porous carbon materials with different properties in terms of porosity, surface chemistry and electrical conductivity, were prepared and systematically studied as electric double layer capacitors in aqueous medium with H 2 SO 4 as electrolyte. The precursors used are an anthracite, general purpose carbon fibres and high performance carbon fibres, which were activated by KOH, NaOH, CO 2 and steam at different conditions. Among all of them, an activated anthracite with a BET surface area close to 1500 m 2 /g, presents the best performance, reaching a value of 320 F/g, using a three-electrode system. The results obtained for all the samples, agree with the well-known relationship between capacitance and porosity, and show that the CO-type oxygen groups have a positive contribution to the capacitance. A very good correlation between the specific capacitance and this type of oxygen groups has been found.
Antimony and antimony-platinum doped tin dioxide electrodes supported on titanium have been prepared by thermal decomposition. Ti/SnO 2 -Sb electrodes have a cracked-mud structure, typical of oxide electrodes prepared by thermal decomposition. The introduction of platinum in the oxide layer has a packing effect in the coating morphology. The electrochemical characterization of these electrodes has been performed in acid medium, and a relation between the roughness factor (measured from electrode capacitance) and electrochemical porosity (related to the voltammetric charge) has been established. The mechanism for the oxygen evolution reaction has been determined by Tafel measurements indicating that the electrodes prepared are nonactive electrodes. The electrocatalytic activity strongly depends on geometric factors, since the activity toward oxygen evolution increases with the electrochemical porosity. Anodic stability of Ti/SnO 2 electrodes has been checked with accelerated service life tests. The introduction of platinum in the oxide coating increases the service life by 2 orders of magnitude.
10 Abstract 11Chemical and electrochemical techniques have been used in order to asses surface functionalities of porous carbon materials. An 12 anthracite has been chemically activated using both KOH and NaOH as activating agents. As a result, activated carbons with high 13 micropore volume (higher than 1 cm 3 /g) have been obtained. These samples were oxidized with HNO 3 and thermally treated in N 2 flow 14 at different temperatures in order to obtain porous carbon materials with different amounts of surface oxygen complexes. Thermal treat-15 ment in H 2 was also carried out. The sample treated with H 2 was subsequently treated in air flow at 450°C. Thus, materials with very 16 similar porous texture and widely different surface chemistry have been compared. The surface chemistry of the resulting materials was 17 systematically characterized by TPD experiments and XPS measurements. Galvanostatic and voltammetric techniques were used to dee-18 pen into the characterization of the surface oxygen complexes. The combination of both, chemical and electrochemical methods provide 19 unique information, regarding the key role of surface chemistry in improving carbon wettability in aqueous solution and the redox pro-20 cesses undergone by the surface oxygen groups. Both contributions are of relevance to understand the use of porous carbons as electro-21 chemical capacitors. 22
Here we present two types of all-printable, highly stretchable, and inexpensive devices based on platinum (Pt)-decorated graphite for glucose determination in physiological fluids. Said devices are: a non-enzymatic sensor and an enzymatic biosensor, the latter showing promising results. Glucose has been quantified by measuring hydrogen peroxide (H2O2) reduction by chronoamperometry at -0.35 V (vs pseudo-Ag/AgCl) using glucose-oxidase immobilized on Pt-decorated graphite. The sensor performs well for the quantification of glucose in phosphate buffer solution (0.25 M PBS, pH 7.0), with a working range between 33 μM and 0.9 mM, high sensitivity and selectivity, and a low limit of detection (LOD). Thus it provides an alternative non-invasive and on-body quantification of glucose levels in human perspiration. This biosensor has been successfully applied on real human perspiration samples and results also show a significant correlation between glucose concentration in perspiration and glucose concentration in blood measured by a commercial glucose meter.
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