Artificial plant guzzles carbon and produces electricity

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Image from Maryam Rezaie and Seokheun Choi. Cyanobacterial Artificial Plants for Enhanced Indoor Carbon Capture and Utilization, Advanced Sustainable Systems, 2024.: Operating principle of cyanobacterial artificial plants for indoor carbon capture and utilization. a) An artificial plant converting captured CO2 into O2 and bioelectricity during photosynthesis. b) An artificial plant utilizing indoor light, water, and nutrients to convert CO2 into O2, thereby enhancing indoor air quality. c) A photograph of the artificial leaf of the plant, showing five biosolar cells attached to a stem. The cells are electrically connected outside the stem, which transports fluids. d) A schematic illustration of the biosolar cell, consisting of a cyanobacteria-infused anode, a cathode, and an ion exchange membrane. The electrogenic cyanobacteria generate electricity during photosynthesis. (AC: Activated carbon).

 

Made of tiny bacteria, the new fake plant soaks up more carbon than its natural cousins, and produces electricity to boot
By Anthropocene Team
October 10, 2024

In an effort to one-up nature, engineers have created an artificial plant that captures carbon dioxide ten times more efficiently than its natural counterparts. And it generates enough electricity to power a lamp.

The fake plant is built with bacteria-based solar cells, and looks odd. But it offers a fun, novel concept to tackle two important issues: carbon dioxide removal and clean electricity generation.

Carbon dioxide is the main planet-warming greenhouse gas. It is also an important indoor air pollutant that threatens human health, write Maryam Rezaie and Seokheun Choi, electrical and computer engineers at the State University of New York at Binghamton, in their Advanced Sustainable Systems paper.

The European standard for a safe carbon dioxide threshold indoors is 800 parts per million (ppm). But studies report that carbon dioxide levels in indoor environments often exceed 2,500 ppm.

So the researchers set out to develop a small, maintenance-free indoor version of the expensive carbon capture systems that are being developed for outdoor capture. They decided to harness cyanobacteria, which are photosynthetic bacteria that convert carbon dioxide and water into oxygen. Choi and others have been using these organisms to make bacteria-based biobatteries.

Now, they put the bacteria into artificial leaf-shaped devices to make biological solar cells that absorb indoor light. They feed on carbon dioxide to produce oxygen and generate a small amount of electricity.

The engineers constructed an artificial plant made of five of these leaves. The leaves are connected to each other electrically via metal wires, and via channels through which water and nutrients can flow. The porous stem of the plant brings up water and nutrients from a plate below, just like in natural plants.

Researchers have made fake plants before that produce electricity by harvesting motion. The cyanobacteria-based plants used the energy from indoor light to drive photosynthesis. They reduced indoor carbon dioxide levels by 90%, from 5000 to 500 ppm, much higher than the 10% reduction that natural plants achieve. The fake plants also produced 140 microwatts of energy, enough to power an LED light.

Choi said in a press release that they want to achieve a power output of over one milliwatt. He also wants to integrate the plant with lithium-ion batteries or other type of energy-storage system.

Source: Maryam Rezaie and Seokheun Choi. Cyanobacterial Artificial Plants for Enhanced Indoor Carbon Capture and Utilization, Advanced Sustainable Systems, 2024.

Image: ©Anthropocene Magazine

Cyanobacterial Artificial Plants for Enhanced Indoor Carbon Capture and Utilization

Abstract

Indoor carbon dioxide (CO2) levels are often significantly higher than those outdoors, which is a growing health concern, particularly in urban areas where people spend over 80% of their time indoors. Traditional CO2 mitigation methods, such as ventilation and filtration, are becoming less effective as outdoor CO2 levels increase due to global warming. This study introduces a novel solution: cyanobacterial artificial plants that enhance indoor carbon capture while converting CO2 into oxygen (O2) and bioelectricity. These artificial plants use indoor light to drive photosynthesis, achieving a 90% reduction in indoor CO2 levels, from 5000 to 500 ppm—far surpassing the 10% reduction seen with natural plants. In addition to improving air quality, the system produces O2 and enough bioelectricity to power portable electronics. Each artificial leaf contains five biological solar cells that generate electricity during photosynthesis, with water and nutrients supplied through transpiration and capillary action, mimicking natural plant systems. The system generates an open circuit voltage of 2.7 V and a maximum power output of 140 µW. This decentralized approach offers a sustainable, energy-efficient solution to indoor environmental challenges, providing improved air quality and renewable electricity amid rising global CO2 levels.

1 Introduction

The World Health Organization (WHO) has designated poor air quality as the foremost environmental threat to public health worldwide.[1] It is alarming that 90% of people globally are exposed to air that does not meet the WHO’s recommended quality standards. Indoor air quality is often significantly poorer than outdoor air quality because of persistent pollution sources within buildings.[1, 2] Those sources include materials used in construction and household products, as well as human activities such as cooking, heating, and cleaning.[3] Additionally, the human metabolism contributes to indoor pollution, particularly in tightly sealed environments designed to maintain stable indoor temperatures.[4] With most people now spending more than 80% of their time indoors, both the duration and intensity of exposure to poor air quality have markedly increased.[1–3] Furthermore, the COVID-19 pandemic has underscored the critical importance of maintaining good indoor air quality.[5] Identified indoor air pollutants encompass a wide range of substances, including particulate matter, biological organisms, allergens, and organic and inorganic chemical compounds.[1–3] Additionally, various reactive chemicals such as ozone and sulfur dioxide are present.[1]

Among various air pollutants, carbon dioxide (CO2) stands out as the primary greenhouse gas, contributing to 80% of all human-caused climate-changing emissions globally.[1, 2] Additionally, as CO2 levels typically correlate with the presence of other pollutants, they are often used as an indicator of indoor air quality.[6] However, CO2 is a direct indoor pollutant that threatens human health.[1, 2, 4] Elevated concentrations ranging from 1000 to 3000 parts per million (ppm), even for just a few hours, can significantly impair cognition and decision-making.[2] Exposure levels of 2000 to 4,000 ppm for several hours can trigger inflammatory responses and lead to health issues such as headaches, drowsiness, and fatigue.[1] Chronic exposure to very elevated levels of CO2 may result in more severe conditions including bone demineralization, kidney calcification, obesity, and in extreme cases, respiratory failure and loss of consciousness.[2, 4] Several regulations and standards define acceptable CO2 concentrations to ensure indoor air quality. For example, the European Standard recommends a maximum of 800 ppm, while countries such as France, the U.K., and Portugal typically accept an average concentration of 1,000 ppm.[1, 2] The American Society of Heating also uses 1,000 ppm as a benchmark, making it a common threshold.[1] Despite the guidelines, studies frequently report that CO2 levels in indoor environments such as schools, offices, and underground transportation often exceed 2,500 ppm, with peaks sometimes surpassing 5,000 ppm.[1, 6]

Carbon capture and storage (CCS) technology has become a crucial research focus in the 21st century, aimed at capturing CO2 emissions from fossil fuels and securely storing them.[7–9]Despite their promise, that technology has been met with skepticism because of the significant financial investment and energy required for the separation, transportation, and storage of CO2, coupled with uncertainties about the permanence of storage. Consequently, there has been a shift toward carbon capture and utilization (CCU) technology, where captured CO2 is converted into high-value products or chemicals through methods such as thermochemical, biochemical, photochemical, and electrochemical processes.[1, 9–11] The new approach reduces emissions and harnesses CO2 as a renewable resource for energy and resource recovery. However, CCS and CCU are primarily focused on large-scale outdoor CO2 emissions and have not been effectively adapted for indoor CO2 management because of their great expense and substantial space and energy requirements.

The most common, albeit passive, method for controlling indoor CO2 levels involves manually opening windows or operating building ventilation systems to equalize indoor and outdoor CO2concentrations.[2] While these approaches have been widely used to improve indoor air quality, they are inefficient for precisely controlling CO2 levels and are becoming less effective as outdoor air quality deteriorates as humans pump more global-warming gases into the atmosphere. A more active and reliable alternative involves integrating filters or sorbent materials into ventilation systems, similar to outdoor CCS techniques but designed for temporary CO2 containment.[1–3, 12] However, once these materials become saturated, they require replacement or the captured CO2 needs to be released. This cycle escalates costs, reduces air quality efficiency, and may increase outdoor CO2 emissions. The most economical and environmentally friendly method uses houseplants, which naturally absorb CO2 and release oxygen (O2).[13–16] That strategy mirrors large-scale outdoor CCU techniques that use the natural carbon cycle to convert captured CO2 into beneficial compounds, thus sustainably improving air quality. Additionally, indoor plants help purify the air by eliminating other pollutants and airborne microbes, while effectively regulating indoor humidity levels.[13, 14] However, this approach is constrained by its substantial maintenance demands, which are time-intensive and costly. Furthermore, the presence of indoor plants can increase pollen levels and potential allergenicity, often accompanied by strong fragrances.[3] Challenges such as the need for regular maintenance, coupled with their slow growth and gas exchange rates, hinder the practical implementation of houseplants in indoor environments. Additionally, the limited portability of houseplants and their requirement for specific environmental conditions render them less suitable as a widespread decentralized system for managing indoor air quality.

In this study, we introduce a groundbreaking artificial plant that harnesses cyanobacterial CO2fixation to generate oxygen and bioelectricity during their photosynthesis, acting as a miniaturized version of CCU technology tailored for indoor environments (Figure 1a). This system is designed to be compact, requiring minimal space and maintenance, while offering significantly faster growth and gas exchange rates sustainably. The artificial plant uses indoor light to enable cyanobacteria to convert CO2 and water into oxygen, thereby improving indoor air quality (Figure 1b). This system features artificial leaves, each containing five biological solar cells (called biosolar cells) (Figure 1c). A single biosolar cell comprises a cyanobacteria-infused anode, a cathode, and an ion exchange membrane (Figure 1d). These cells are interconnected electrically, via metallic paths, and fluidically, through a microfluidic channel. The selected cyanobacteria, Synechocystis sp. PCC 6803, is known for its exoelectrogenic properties,[17, 18]enabling it to produce bioelectricity during photosynthesis. Transpiration and capillary action bring water and nutrients to each biosolar cell, mimicking the nutrient distribution systems in living plants and trees. A porous anode effectively captures CO2 molecules and it is decorated with iron oxide nanoparticles (Fe2O3 NPs) to enhance light capture and electrocatalytic activity. Additionally, the cathodic function is augmented by a coating of palladium nanoparticles (Pd NPs). Our innovative integration of material science and biological entities presents a very promising solution for the simultaneous capture and utilization of CO2. This approach offers a valuable decentralized system for enhancing indoor air quality and generating electricity.

Details are in the caption following the image
Figure 1

Open in figure viewerPowerPoint
Operating principle of cyanobacterial artificial plants for indoor carbon capture and utilization. a) An artificial plant converting captured CO2 into O2 and bioelectricity during photosynthesis. b) An artificial plant utilizing indoor light, water, and nutrients to convert CO2 into O2, thereby enhancing indoor air quality. c) A photograph of the artificial leaf of the plant, showing five biosolar cells attached to a stem. The cells are electrically connected outside the stem, which transports fluids. d) A schematic illustration of the biosolar cell, consisting of a cyanobacteria-infused anode, a cathode, and an ion exchange membrane. The electrogenic cyanobacteria generate electricity during photosynthesis. (AC: Activated carbon).

References

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