Jonathan Winfield

The overshoot phenomenon as a function of internal resistance in microbial fuel cells.

A method for assessing the performance of microbial fuel cells (MFCs) is the polarisation sweep where different external resistances are applied at set intervals (sample rates). The resulting power curves often exhibit an overshoot where both power and current decrease concomitantly. To investigate these phenomena, small-scale (1 mL volume) MFCs operated in continuous flow were subjected to polarisation sweeps under various conditions. At shorter sample rates the overshoot was more exaggerated and power generation was overestimated; sampling at 30 s produced 23% higher maximum power than at 3 min. MFCs with an immature anodic biofilm (5 days) exhibited a double overshoot effect, which disappeared after a sufficient adjustment period (5 weeks). Mature MFCs were subject to overshoot when the anode was fed weak (1 mM acetate) feedstock with low conductivity (<100 μS) but not when fed with a higher concentration (20 mM acetate) feedstock with high conductivity (>1500 μS). MFCs developed in a pH neutral environment produced overshoot after the anode had been exposed to acidic (pH 3) conditions for 24 h. In contrast, changes to the cathode both in terms of pH and varying catholyte conductivity, although affecting power output did not result in overshoot suggesting that this is an anodic phenomenon.

Investigating a cascade of seven hydraulically connected microbial fuel cells

Seven miniature microbial fuel cells (MFCs) were hydraulically linked in sequence and operated in continuous-flow (cascade). Power output and treatment efficiency were investigated using varying organic loads, flow-rates and electrical configurations. When fed synthetic wastewater low in organic load (1mM acetate) only the first MFC operated stably over a 72-h period. Acetate feedstock at 5mM was enough to sustain the first four MFCs, and 10mM acetate was sufficient to maintain all MFCs at stable power densities. COD was reduced from 69 to 25mg/L (64%, 1mM acetate), 319-34mg/L (90%, 5mM acetate) and 545-264mg/L (52%, 10mM acetate). Fluctuating flow-rates improved performance in downstream MFCs. When connected electrically in parallel, power output was two-fold and current production 10-fold higher than when connected in series. The results suggest cascades of MFCs could be employed to complement or improve biological trickling filters.

Comparing the short and long term stability of biodegradable, ceramic and cation exchange membranes in microbial fuel cells

The long and short-term stability of two porous dependent ion exchange materials; starch-based compostable bags (BioBag) and ceramic, were compared to commercially available cation exchange membrane (CEM) in microbial fuel cells. Using bi-directional polarisation methods, CEM exhibited power overshoot during the forward sweep followed by significant power decline over the reverse sweep (38%). The porous membranes displayed no power overshoot with comparably smaller drops in power during the reverse sweep (ceramic 8%, BioBag 5.5%). The total internal resistance at maximum power increased by 64% for CEM compared to 4% (ceramic) and 6% (BioBag). Under fixed external resistive loads, CEM exhibited steeper pH reductions than the porous membranes. Despite its limited lifetime, the BioBag proved an efficient material for a stable microbial environment until failing after 8 months, due to natural degradation. These findings highlight porous separators as ideal candidates for advancing MFC technology in terms of cost and operation stability.

Urine-activated origami microbial fuel cells to signal proof of life

The adaptability and practicality of microbial fuel cells (MFCs) are highly desirable traits in the search for alternative sources of energy. An innovative application for the technology could be to power portable emergency locator transmitters (ELTs). Such devices would ideally need to be lightweight, robust and fast-in terms of response. Urine is an abundant resource, and with MFCs, could be the ideal fuel for powering ELTs, with the compelling advantage of also indicating proof of life. We developed novel origami tetrahedron MFCs (TP-MPFCs) using photocopier paper to test different urine-based inoculants. When inoculated with urine extracted from the anode chambers of working MFCs a stack of 6 abiotic MFCs produced a usable working voltage after just 3 h 15 min; enough to energise a power management system. The anodes of established TP-MFCs were then removed and air-dried for 7 days before being inserted into new paper reactors and refrigerated. After 4 weeks, these MFCs displayed an immediate response to fresh urine and achieved a functional working voltage in just 35 minutes. Two paper MFCs connected in parallel were able to transmit 85 radio signals and in a series configuration 238 broadcasts over 24 hours. These findings demonstrate that simple, inexpensive, lightweight paper MFCs can be employed as urine-activated, “proof of life” reporting systems.

A review into the use of ceramics in microbial fuel cells.

Microbial fuel cells (MFCs) offer great promise as a technology that can produce electricity whilst at the same time treat wastewater. Although significant progress has been made in recent years, the requirement for cheaper materials has prevented the technology from wider, out-of-the-lab, implementation. Recently, researchers have started using ceramics with encouraging results, suggesting that this inexpensive material might be the solution for propelling MFC technology towards real world applications. Studies have demonstrated that ceramics can provide stability, improve power and treatment efficiencies, create a better environment for the electro-active bacteria and contribute towards resource recovery. This review discusses progress to date using ceramics as (i) the structural material, (ii) the medium for ion exchange and (iii) the electrode for MFCs.

Small Scale Microbial Fuel Cells and Different Ways of Reporting Output

The present study, reports on the findings of connecting 2 stacks of 48 MFCs and the importance of maturity and acclimation for the anodic biofilms. Furthermore, an attempt is made to emphasize the importance of a universal unit for quantifying power output. Finally, this paper presents data from the smallest MFCs, specifically designed for wastewater treatment. The main aims of this study were to (1) configure a high number of small-scale MFCs (48) to run as a stack for a long period of time (2-years); (2) repeat this process with a new set of MFCs configured as a stack of equal dimensions (units) and compare individual as well as stack performances of both old and new MFC, through polarization experiments under identical conditions; (3) normalize and compare the recorded power output according to the plethora of methods reported in the literature; (4) design even smaller MFCs and investigate their performance.

Fade to Green: A Biodegradable Stack of Microbial Fuel Cells

The focus of this study is the development of biodegradable microbial fuel cells (MFCs) able to produce useful power. Reactors with an 8 mL chamber volume were designed using all biodegradable products: polylactic acid for the frames, natural rubber as the cation-exchange membrane and egg-based, open-to-air cathodes coated with a lanolin gas diffusion layer. Forty MFCs were operated in various configurations. When fed with urine, the biodegradable stack was able to power appliances and was still operational after six months. One useful application for this truly sustainable MFC technology includes onboard power supplies for biodegradable robotic systems. After operation in remote ecological locations, these could degrade harmlessly into the surroundings to leave no trace when the mission is complete.

Here today, gone tomorrow: biodegradable soft robots

One of the greatest challenges to modern technologies is what to do with them when they go irreparably wrong or come to the end of their productive lives. The convention, since the development of modern civilisation, is to discard a broken item and then procure a new one. In the 20th century enlightened environmentalists campaigned for recycling and reuse (R and R). R and R has continued to be an important part of new technology development, but there is still a huge problem of non-recyclable materials being dumped into landfill and being discarded in the environment. The challenge is even greater for robotics, a field which will impact on all aspects of our lives, where discards include motors, rigid elements and toxic power supplies and batteries. One novel solution is the biodegradable robot, an active physical machine that is composed of biodegradable materials and which degrades to nothing when released into the environment. In this paper we examine the potential and realities of biodegradable robotics, consider novel solutions to core components such as sensors, actuators and energy scavenging, and give examples of biodegradable robotics fabricated from everyday, and not so common, biodegradable electroactive materials. The realisation of truly biodegradable robots also brings entirely new deployment, exploration and bio-remediation capabilities: why track and recover a few large non-biodegradable robots when you could speculatively release millions of biodegradable robots instead? We will consider some of these exciting developments and explore the future of this new field.One of the greatest challenges to modern technologies is what to do with them when they go irreparably wrong or come to the end of their productive lives. The convention, since the development of modern civilisation, is to discard a broken item and then procure a new one. In the 20th century enlightened environmentalists campaigned for recycling and reuse (R&R). R&R has continued to be an important part of new technology development, but there is still a huge problem of non-recyclable materials being dumped into landfill and being discarded in the environment. The challenge is even greater for robotics, a field which will impact on all aspects of our lives, where discards include motors, rigid elements and toxic power supplies and batteries. One novel solution is the biodegradable robot, an active physical machine that is composed of biodegradable materials and which degrades to nothing when released into the environment. In this paper we examine the potential and realities of biodegradable robotics, consider novel solutions to core components such as sensors, actuators and energy scavenging, and give examples of biodegradable robotics fabricated from everyday, and not so common, biodegradable electroactive materials. The realisation of truly biodegradable robots also brings entirely new deployment, exploration and bio-remediation capabilities: why track and recover a few large non-biodegradable robots when you could speculatively release millions of biodegradable robots instead? We will consider some of these exciting developments and explore the future of this new field.

Biodegradable and edible gelatine actuators for use as artificial muscles

The expense and use of non-recyclable materials often requires the retrieval and recovery of exploratory robots. Therefore, conventional materials such as plastics and metals in robotics can be limiting. For applications such as environmental monitoring, a fully biodegradable or edible robot may provide the optimum solution. Materials that provide power and actuation as well as biodegradability provide a compelling dimension to future robotic systems. To highlight the potential of novel biodegradable and edible materials as artificial muscles, the actuation of a biodegradable hydrogel was investigated. The fabricated gelatine based polymer gel was inexpensive, easy to handle, biodegradable and edible. The electro-mechanical performance was assessed using two contactless, parallel stainless steel electrodes immersed in 0.1M NaOH solution and fixed 40 mm apart with the strip actuator pinned directly between the electrodes. The actuation displacement in response to a bias voltage was measured over hydration/de-hydration cycles. Long term (11 days) and short term (1 hour) investigations demonstrated the bending behaviour of the swollen material in response to an electric field. Actuation voltage was low (<10 V) resulting in a slow actuation response with large displacement angles (<55 degrees). The stability of the immersed material decreased within the first hour due to swelling, however, was recovered on de-hydrating between actuations. The controlled degradation of biodegradable and edible artificial muscles could help to drive the development of environmentally friendly robotics.

Eating, Drinking, Living, Dying and Decaying Soft Robots

Soft robotics opens up a whole range of possibilities that go far beyond conventional rigid and electromagnetic robotics. New smart materials and new design and modelling methodologies mean we can start to replicate the operations and functionalities of biological organisms, most of which exploit softness as a critical component. These range from mechanical responses, actuation principles and sensing capabilities. Additionally, the homeostatic operations of organisms can be exploited in their robotic counterparts. We can, in effect, start to make robotic organisms, rather than just robots. Important new capabilities include the fabrication of robots from soft bio-polymers, the ability to drive the robot from bio-energy scavenged from the environment, and the degradation of the robot at the end of its life. The robot organism therefore becomes an entity that lives, dies, and decays in the environment, just like biological organisms. In this chapter we will examine how soft robotics have the potential to impact upon pressing environmental pollution, protection and remediation concerns.