Developing Batteries Powered by Human Urine 

Urine–fed microbial fuel cells could help solve two of the world’s most pressing environmental challenges: generating sustainable energy and removing waste.

Microbial Fuel Cell (MFC) is an environmentally friendly technology that harnesses the power of bacteria to convert an energy-rich substrate into electricity. It works by anaerobic bacteria living inside the anode chamber of the battery breaking down a substrate to release electrons.

The technology offers tantalising opportunities to generate sustainable energy from waste products such as biodegradable waste or sewage. The process can continue for as long as the food is available. MFC could prove particularly useful in remote locations where energy infrastructure is poor – and helping with wastewater treatment at the same time.

An Abundant Natural Substrate

Human urine offers several benefits over types of waste currently under investigation as MFC substrates – including its unlimited supply and bioelectrical properties. Urine–fed MFCs have already been created that can charge smartphones and power lighting – opening the possibility of transforming this naturally abundant human waste into useful energy.

Researchers are looking for ways to improve the design and materials of urine–fed MFCs – to improve their power performance and long–term stability and functionality, all of which are important requirements for the practical implementation of the technology. Using conducting polymers as the anode is gaining increasing attention, with poly(3,4–ethylene dioxythiophene) (PEDOT) one of the most successful to date – and adding polystyrene sulfonate (PSS) may help further boost the performance of this material.

PEDOT–PSS Modified Anodes

In a new study, a team of researchers explore the potential of using PEDOT–PSS modified electrodes in urine-fed MFCs.¹ The researchers synthesised PEDOT–PSS anodes by electropolymerization onto the surface of a piece of carbon veil for different times: 30, 60, 120 and 240 seconds. While all the modified anodes outperformed the bare carbon veil electrode, the material created with the shortest electropolymerization time was best – showing a 24.3% higher maximum power output.

The team then evaluated the functionality of the PEDOT–PSS anodes over three months where the systems were continuously fed with neat human urine. The performance of the MFCs was stable, demonstrating that the PEDOT–PSS was successfully deposited onto the surface of the electrodes and stayed attached and unchanged throughout this period.

The researchers prepared all solutions using ultrapure water generated from an ELGA PURELAB® laboratory water purification system, minimising the risk of adding contaminants that might affect the results of their experiments.

Improved Performance and Practicality

This is the first time that PEDOT–PSS anode material has been tested in MFCs continuously fed with neat human urine. The results of the study show that using modified anodes improved the power performance of urine–fed MFCs and had long-term stability and functionality. This suggests that these would be suitable for long–term operating processes, commonly needed in real-world applications.

Further advances in the design of new materials are crucial for the development of this green technology and work towards its practical application.

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Reference:

1. Salar–Garcia, M. J. et al. Improving the power performance of urine–fed microbial fuel cells using PEDOT–PSS modified anodes. Applied Energy 2020; 278:115528

Dr Alison Halliday

After completing an undergraduate degree in Biochemistry & Genetics at Sheffield University, Alison was awarded a PhD in Human Molecular Genetics at the University of Newcastle. She carried out five years as a Senior Postdoctoral Research Fellow at UCL, investigating the genes involved in childhood obesity syndrome. Moving into science communications, she spent ten years at Cancer Research UK engaging the public about the charity’s work. She now specialises in writing about research across the life sciences, medicine and health.