In this work, we demonstrate the first example of fully printed carbon nanomaterials on paper with unique features, aiming the fabrication of functional electronic and electrochemical devices. Bare and modified inks were prepared by combining carbon black and cellulose acetate to achieve high-performance conductive tracks with low sheet resistance. The carbon black tracks withstand extremely high folding cycles (>20 000 cycles), a new record-high with a response loss of less than 10%. The conductive tracks can also be used as 3D paper-based electrochemical cells with high heterogeneous rate constants, a feature that opens a myriad of electrochemical applications. As a relevant demonstrator, the conductive ink modified with Prussian-blue was electrochemically characterized proving to be very promising toward the detection of hydrogen peroxide at very low potentials. Moreover, carbon black circuits can be fully crumpled with negligible change in their electrical response. Fully printed motion and wearable sensors are additional examples where bioinspired microcracks are created on the conductive track. The wearable devices are capable of efficiently monitoring extremely low bending angles including human motions, fingers, and forearm. Here, to the best of our knowledge, the mechanical, electronic, and electrochemical performance of the proposed devices surpasses the most recent advances in paper-based devices.

A simple and fast fabrication method to create high-performance pencil-drawn electrochemical sensors is reported for the first time. The sluggish electron transfer observed on bare pencil-drawn surfaces was enhanced using two electrochemical steps: first oxidizing the surface and then reducing it in a subsequent step. The heterogeneous rate constant was found to be 5.1 × 10 cm s, which is the highest value reported so far for pencil-drawn surfaces. We mapped the origin of such performance by atomic force microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Our results suggest that the oxidation process leads to chemical and structural transformations on the electrode surface. As a proof-of-concept, we modified the pencil-drawn surface with Meldola's blue to electrocatalytically detect nicotinamide adenine dinucleotide (NADH). The electrochemical device exhibited the highest catalytic constant (1.7 × 10 L mol s) and the lowest detection potential for NADH reported so far in paper-based electrodes.

The possibility of current injection and transport in eumelanin films, humans' most common natural pigment, has fascinated physicists and materials scientists since the early '60s. Nowadays, it is accepted that...

Annealing of sugarcane bagasse cellulose or lignin biocarbons under isopropanol vapor has induced an improvement in electrical conductivity of these materials. Remarkably, the sheet resistance dropped nearly three times for lignin biocarbon treated with isopropanol vapors. The use of isopropanol vapor annealing has increased sp2 carbon and decreased oxygenated functionality contents of these biocarbons. These chemical changes were confirmed by X-ray photoelectron and Raman spectroscopy analyses. Transmission electron microscopy images revealed the formation of graphitic domains on samples pyrolyzed in the presence of isopropanol, while electron energy loss spectroscopy mapping at a nanoscale showed an increase in graphitic characteristics of the particles. These chemical and structural changes of biocarbons have improved their electrical conductivity and decreased sheet resistance values of conductive tracks prepared with such materials. As a proof of concept, we fabricated flexible electronic circuits and paper-based electrochemical devices using conductive lignin-based inks prepared with our method.

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