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Graphite pencil stroked electrodes for paper-based Microfluidic devices are gaining immense attention due to their electrochemical properties, cost efficiency, and ease-of-use. However, their widespread use has been hindered by the challenges associated with their manual fabrication such as non-uniformity in graphite deposition, applied pressure, etc. This work presents the design and development of an automated graphite pencil stroking device for graphite electrode fabrication with high efficiency through a compact, inexpensive and automatic process, with reduced fabrication time and human intervention leading to more uniformity. The motion platform of Graphtec plotter was used to create multiple strokes with the help of the proposed device. Such inexpensive graphite electrodes (less than the US $1) have been observed to be porous in nature, acting as diffusion agents. The automated graphite electrodes were used to study the performance of microfluidic paper fuel cells (MPFCs) with formic acid, oxygen, and sulphuric acid acting as fuel, oxidising agent and electrolyte respectively. From this configuration, the maximum current density and power density were measured to be 1,305.5 µA cm −2 and 135.5 µW cm −2 , respectively at 0.3 V stable OCP at 100 strokes. Overall, the study enumerates the development of an automated pencil stroke device for fabricating graphite electrodes, which can potentially be harnessed in numerous miniaturized paper based applications. Microfluidic devices with integrated electrodes, or electromicrofluidic devices, have attained essential roles in diverse areas, including energy harvesting for portable applications and sensing devices 1-3. Paper-pencil based microfluidic fuel cell is one of the most recent vital advancements to develop point of the source (POS) and point of care (POC) devices owing to the well-proven benefits of microfluidic environment and graphite electrodes 4,5. In recent years, graphite pencils are being used as electrodes and have shown encouraging outcomes and promising features of MPFCs when compared with the existing approaches. Initially approaches on graphite electrodes, Aoki et al. demonstrated the first use for of graphite material (pencil lead), as electrodes 6. Bandapati et al. investigated the performance of membraneless glucose biofuel cell with various grades of graphite pencils act as electrodes 7,8. Rewatkar et al. examined 3D printed enzymatic biofuel cell performance with graphite pencil as an electrodes 9. In spite of the numerable benefits of such devices, they come with an inherent setback of the physically fabricated electrodes with non-uniform deposition of graphite due to the subjective nature of the applied pressure and manual counting of the number of strokes. Most of the recent researches in the field of paper-pencil based microfuel cells employ manual deposition of graphite on the paper for fabricating the electrode. Arun et al. reported formic acid microfluidic fuel cell with manual graphite pencil electrodes with diverse grades of pencils 1...

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Summary Miniaturization of devices, combined with other features such as portability, proneness to automation, rapid performance, amenability to integration, multiplexing, and cost‐effectiveness, is rapidly increasing for various sensing and energy harvesting applications. One such emerging area is the development of microfluidic fuel cell on cellulose papers, which has enormous scope to optimize its performance. This is primarily because such devices eliminate the need for membranes as well as external pumps since they have built‐in colaminar flow embedded capillaries. Such peripherals are usually used in conventional microfluidic fuel cells, which are fabricated using methods like photolithography, PDMS lithography, and 3D printing. This paper presents investigations on microfluidic paper–based fuel cells (MPFCs) with different cellulose absorbent pads for their performance optimization. Herein, the MPFC utilizes formic acid as fuel, oxygen from quiescent air as oxidant, and sulfuric acid as electrolyte for conducting ionic exchange under colaminar flow. The electrodes are realized through simple pencil strokes depositing a thin layer of graphite. The porous graphite electrodes act as diffusion agents breathing oxygen directly from the atmospheric air. Such an MPFC configuration, costing less than US $1, was optimized to achieve maximum energy density by examining various combinations of absorbent pads with different grades of cellulose papers. It is seen that the maximum open circuit potential is 0.46 V, while the maximum current and power densities are 1505.66 μAcm−2 and 173.97 μWcm−2, respectively, with a grade 6 absorbent pad. Such performance can be further enhanced by investigating MPFCs with various graphite pencils with a diverse number of strokes at different concentration levels.

Topology optimization is a powerful method of material minimization in structural design problems. The obtained topology and the compliance values by this method are very sensitive to each of the input parameters such as, applied force, volume fraction, dimensions, and support-rigidity. In real-life situations, these parameters may vary due to material uncertainty, manufacturing imperfections, and operating conditions. Hence, the topology obtained during the conceptual design phase may not suffice the actual working condition. Thus, it is desirable to explore individual and the combined effects of the parametric variations and uncertainties. This study describes a systematic approach utilized to investigate the effect of different input parameters on compliance values along with material and load uncertainties for a topologically optimized structure. In this paper, applied force, volume fraction, and aspect ratio of the domain are treated as input parameters and their effects are analyzed. Proposed work modifies the solid isotropic microstructure with penalization method to incorporate the effect of uncertainties and uses design of experiments approach to investigate statistically significant input parameters. Four different benchmark problems available in the literature are analyzed and the results are obtained for aforesaid input parameters along with uncertainties. Results obtained from this investigation will help designers/practitioners to select suitable input parameters combination to achieve targeted compliance.

This paper reports on single step and rapid fabrication of interdigitated electrodes (IDEs) using an inkjet printing-based approach. A commercial inkjet-printed circuit board (PCB) printer was used to fabricate the IDEs on a glass substrate. The inkjet printer was optimized for printing IDEs on a glass substrate using a carbon ink with a specified viscosity. Electrochemical impedance spectroscopy in the frequency range of 1 Hz to 1 MHz was employed for chemical sensing applications using an electrochemical workstation. The IDE sensors demonstrated good nitrite quantification abilities, detecting a low concentration of 1 ppm. Taste simulating chemicals were used to experimentally analyze the ability of the developed sensor to detect and quantify tastes as perceived by humans. The performance of the inkjet-printed IDE sensor was compared with that of the IDEs fabricated using maskless direct laser writing (DLW)-based photolithography. The DLW–photolithography-based fabrication approach produces IDE sensors with excellent geometric tolerances and better sensing performance. However, inkjet printing provides IDE sensors at a fraction of the cost and time. The inkjet printing-based IDE sensor, fabricated in under 2 min and costing less than USD 0.3, can be adapted as a suitable IDE sensor with rapid and scalable fabrication process capabilities.

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