Instant power generation from an air-breathing paper and pencil based bacterial bio-fuel cell

Pencil graphite electrodes for in-situ spectroelectrochemical sensing of reaction intermediates and products in organic solvents

BACKGROUND

Spectroelectrochemistry (SEC) is a valuable analytical tool providing insights to reaction mechanisms and the structure of species involved in charge transfer reactions. Most of commercial SEC setups are based on platinum working electrodes where the adsorption of species involved in reactions often complicates their analysis.

RESULTS

In this work, we employ an array of pencil graphite rods as an optically transparent working electrode in a custom-made air-tight thin-layer cell suitable for the SEC analysis performed here in acetonitrile as a representative non-aqueous solvent. The functionality of the device was demonstrated by UV-Vis SEC sensing of charge transfer reactions of ruthenium acetylacetonate, ferrocene and ethylviologen dibromide redox probes performed employing the cyclic voltammetry. The SEC response obtained for all three probes confirmed no adsorption and the absence of oxygen in the cell. Furthermore, we have developed and utilized finite element method numerical simulations considering charge transfer reactions coupled with the diffusional mass transport to model the cyclic voltammetric response and the reaction conversion in the thin-layer SEC cell.

SIGNIFICANCE

Our work paves the way for easy-to-assemble customized air-tight adsorption-free SEC devices with the manufacturing costs well below those of commercially available platforms. Developed computational approaches have the predictive power for optimizing reaction conditions and the geometry of the SEC cell.

Bio-electrochemical frameworks governing microbial fuel cell performance: technical bottlenecks and proposed solutions

Microbial fuel cells (MFCs) are recognized as a future technology with a unique ability to exploit metabolic activities of living microorganisms for simultaneous conversion of chemical energy into electrical energy. This technology holds the promise to offer sustained innovations and continuous development towards many different applications and value-added production that extends beyond electricity generation, such as water desalination, wastewater treatment, heavy metal removal, bio-hydrogen production, volatile fatty acid production and biosensors. Despite these advantages, MFCs still face technical challenges in terms of low power and current density, limiting their use to powering only small-scale devices. Description of some of these challenges and their proposed solutions is demanded if MFCs are applied on a large or commercial scale. On the other hand, the slow oxygen reduction process (ORR) in the cathodic compartment is a major roadblock in the commercialization of fuel cells for energy conversion. Thus, the scope of this review article addresses the main technical challenges of MFC operation and provides different practical approaches based on different attempts reported over the years.

Sustainable operation requires addressing key MFC-bottleneck issues. Enhancing extracellular electron transfer is the key to elevated MFC performance.

Microfluidic Microbial Bioelectrochemical Systems: An Integrated Investigation Platform for a More Fundamental Understanding of Electroactive Bacterial Biofilms

It is the ambition of many researchers to finally be able to close in on the fundamental, coupled phenomena that occur during the formation and expression of electrocatalytic activity in electroactive biofilms. It is because of this desire to understand that bioelectrochemical systems (BESs) have been miniaturized into microBES by taking advantage of the worldwide development of microfluidics. Microfluidics tools applied to bioelectrochemistry permit even more fundamental studies of interactions and coupled phenomena occurring at the microscale, thanks, in particular, to the concomitant combination of electroanalysis, spectroscopic analytical techniques and real-time microscopy that is now possible. The analytical microsystem is therefore much better suited to the monitoring, not only of electroactive biofilm formation but also of the expression and disentangling of extracellular electron transfer (EET) catalytic mechanisms. This article reviews the details of the configurations of microfluidic BESs designed for selected objectives and their microfabrication techniques. Because the aim is to manipulate microvolumes and due to the high modularity of the experimental systems, the interfacial conditions between electrodes and electrolytes are perfectly controlled in terms of physicochemistry (pH, nutrients, chemical effectors, etc.) and hydrodynamics (shear, material transport, etc.). Most of the theoretical advances have been obtained thanks to work carried out using models of electroactive bacteria monocultures, mainly to simplify biological investigation systems. However, a huge virgin field of investigation still remains to be explored by taking advantage of the capacities of microfluidic BESs regarding the complexity and interactions of mixed electroactive biofilms.

Automated pencil electrode formation platform to realize uniform and reproducible graphite electrodes on paper for microfluidic fuel cells

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.

Electrical Power Generation from Wet Textile Mediated by Spontaneous Nanoscale Evaporation

Developing low-weight, frugal, and sustainable power sources for resource-limited settings appears to be a challenging proposition for the advancement of next-generation sensing devices and beyond. Here, we report the use of centimeter-sized simple wet fabric pieces for electrical power generation by deploying the interplay of a spontaneously induced ionic motion across fabric nanopores due to capillary action and simultaneous water evaporation by drawing thermal energy from the ambient. Unlike other reported devices with similar functionalities, our arrangement does not necessitate any input mechanical energy or complex topographical structures to be embedded in the substrate. A single device is capable of generating a sustainable open circuit potential up to ∼700 mV, which is further scaled up to ∼12 V with small-scale multiplexing (i.e., deploying around 40 numbers of fabric channels simultaneously). The device is able to charge a commercial supercapacitor of ∼0.1 F which can power a white light-emitting diode for more than 1 h. This suffices in establishing an inherent capability of functionalizing self-powered electronic devices and also to be potentially harnessed for enhanced power generation with feasible up-scaling.

Characterization of a new composite membrane for point of need paper-based micro-scale microbial fuel cell analytical devices

Microbial fuel cells (MFCs) can evolve in a viable technology if environmentally sound materials are developed and became available at low cost for these devices. This is especially important not only for the designing of large wastewater treatment systems, but also for the fabrication of low-cost, single-use devices. In this work we synthesized membranes by a simple procedure involving easily-biodegradable and economic materials such as poly (vinyl alcohol) (PVA), chitosan (CS) and the composite PVA:CS. Membranes were chemical and physically characterized and compared to Nafion^®. Performance was studied using the membrane as separator in a typical H-Type MFCs showing that PVA:CS membrane outperform Nafion^® 4 times (power production) while being 75 times more economic. We found that performance in MFC depends over interactions among several membrane characteristics such as oxygen permeability and ion conductivity. Moreover, we design a paper-based micro-scale MFC, which was used as a toxicity assay using 16 μL samples containing formaldehyde as a model toxicant. The PVA:CS membrane presented here can offer low environmental impact and become a very interesting option for point of need single-use analytical devices, especially in low-income countries where burning is used as disposal method, and toxic fluoride fumes (from Nafion^®) can be released to the environment.

Flexible Electronics Based on Micro/Nanostructured Paper

Over the past several years, a new surge of interest in paper electronics has arisen due to the numerous merits of simple micro/nanostructured substrates. Herein, the latest advances and principal issues in the design and fabrication of paper-based flexible electronics are highlighted. Following an introduction of the fascinating properties of paper matrixes, the construction of paper substrates from diverse functional materials for flexible electronics and their underlying principles are described. Then, notable progress related to the development of versatile electronic devices is discussed. Finally, future opportunities and the remaining challenges are examined. It is envisioned that more design concepts, working principles, and advanced papermaking techniques will be developed in the near future for the advanced functionalization of paper, paving the way for the mass production and commercial applications of flexible paper-based electronic devices.

Hydroelectric power plant on a paper strip

We exploit the combinatorial advantage of electrokinetics and tortuosity of a cellulose-based paper network on laboratory grade filter paper for the development of a simple, inexpensive, yet extremely robust (shows constant performance for 12 days) 'paper-and-pencil'-based device for energy harvesting applications. We successfully achieve harvesting of a maximum output power of ∼640 pW in a single channel, while the same is significantly improved (by ∼100 times) with the use of a multichannel microfluidic array (maximum of up to 20 channels). Furthermore, we also provide theoretical insights into the observed phenomenon and show that the experimentally predicted trends agree well with our theoretical calculations. Thus, we envisage that such ultra-low cost devices may turn out to be extremely useful in energizing analytical microdevices in resource limited settings, for instance, in extreme point of care diagnostic applications.

A solvent-free microbial-activated air cathode battery paper platform made with pencil-traced graphite electrodes

We present the fabrication of an ultra-low cost, disposable, solvent-free air cathode all-paper microbial fuel cell (MFC) that does not utilize any chemical treatments. The anode and cathode were fabricated by depositing graphite particles by drawing them on paper with a pencil (four strokes). Hydrophobic parchment paper was used as a proton exchange membrane (PEM) to allow only H⁺ to pass. Air cathode MFC technology, where O₂ was used as an electron acceptor, was implemented on the paper platform. The bioelectric current was generated by an electrochemical process involving the redox couple of microbial-activated extracellular electron transferred electrons, PEM-passed H⁺, and O₂ in the cathode. A fully micro-integrated pencil-traced MFC showed a fast start-time, producing current within 10 s after injection of bacterial cells. A single miniaturized all-paper air cathode MFC generated a maximum potential of 300 mV and a maximum current of 11 μA during 100 min after a single injection of Shewanella oneidensis. The micro-fabricated solvent-free air cathode all-paper MFC generated a power of 2,270 nW (5.68 mW/m²). The proposed solvent-free air cathode paper-based MFC device could be used for environmentally-friendly energy storage as well as in single-use medical power supplies that use organic matter.