Energy from bacteria for battery-free electronics

In recent years, there has been an explosion of interconnected electronic devices, from consumer electronics to industrial applications, all aimed at improving quality of life. However, this growth raises serious environmental concerns, especially regarding batteries. Most batteries have a limited number of charge-discharge cycles, leading to resource waste and significant costs, particularly considering the large number of devices installed in hard-to-reach locations.

A strategy to reduce environmental impact is adopting alternative and sustainable energy storage solutions, such as battery-free systems that harness energy from the environment through Energy Harvesting techniques. Among sustainable energy sources, the team composed of Prof. Davide Brunelli, Maria Doglioni (Ph.D. Student), and Dr. Matteo Nardello (RTD A) is exploring Plant Microbial Fuel Cells (PMFC). These are appealing due to their low cost and minimal environmental impact, requiring only fertile soil, a plant, and two eco-friendly conductive terminals, known as electrodes, (as shown in the image below: Schematic representation of a PMFC).

Figure 1: Schematic Representation of a PMFC
PMFCs utilize bacteria naturally present in the soil to extract energy. These bacteria form a biofilm on the anode, consuming organic matter and releasing electrons. The electrons flow to the cathode through an external circuit, generating energy that is stored in a capacitor. The presence of a plant sustains the electroactive microbes, keeping the bacterial colony active. Once stabilized, a PMFC requires minimal maintenance and can produce energy continuously. Even a small, one-liter PMFC can generate approximately 10 mW of power, suitable for wireless sensors or smart cameras within the Internet of Things.

This technology promises sustainable energy while addressing battery-related issues. However, challenges remain, such as the stability and aging of PMFCs, requiring further development to make them a practical and reliable long-term solution.

To bridge the gap between the power requirements of battery-free electronics and the output of PMFCs, the team has outlined a twofold approach:

1. On the battery-free electronics front, they are designing ultra-low-power circuits to extend the autonomy of sensors and digital processors. They are also developing intermittent processing solutions, enabling devices to pause and resume operation instantly, even without power. The team has incorporated a capacitor-based storage mechanism to maximize autonomy.
2. On the PMFC generator side, to increase usable energy, they are exploring techniques for combining multiple cells in series-parallel configurations, akin to a “battery pack,” and implementing continuous optimization of the operating point.

The challenge lies in adapting the power consumption to the capabilities of a “living system” that generates energy and sometimes requires “rest periods.” To address this, the team is integrating electrochemical measurements, such as impedance spectroscopy, to estimate the health of both the bacterial colony and the plant in the PMFC, which sustains the colony.

This commitment to a sustainable future aims to develop innovative energy solutions for electronic devices and make them battery-free. Through the development of ultra-low-power circuits, the implementation of advanced intermittent processing strategies, and the optimization of PMFCs, the team is paving the way for a new energy paradigm in the world of sensors and electronic systems, eliminating the use of polluting batteries and contributing to a greener and more prosperous future.