My Tesla Runs on Banana Peels

These days there is a lot of interest in biomass as a substitute for fossil fuels, the idea being to get off the 500-million-year savings account and into the checking account that comes from sunshine in order to stop screwing with the atmosphere.

This likely won’t work if the biomass is grown in lieu of either food or forested ecosystems. It has to come from carbon wastes. Fortunately there is no shortage. It also won’t work if the biomass is just burned, sending long-lived greenhouse gases skyward. The only way it can work is if the biomass is converted to stable biochar, with energy and potentially food as (profitable) byproducts.

Put biochar in the ground, and regardless who the next farmer is, or what the weather decides to do, the biochar carbon will stay in the ground. That is possibly our strongest asset in relation to other options that are only as good as the management that maintains them. Forests can be bulldozed, soils can be ripped up and oxidized, biochar is stable in soil.
— Josiah Hunt

The amount of thermal energy or electricity produced during that conversion is variable, depending on the energy potential of the biomass and the process. The types of machines used are typically divided between CHAP (combined heat and power) and CHAB (combined heat and biochar). CHAP is mostly carbon neutral (depending on transportation distances) and CHAB is carbon negative, or net drawdown, as long as the product — biochar — is not reused as a fuel.

from The Biochar Solution: Carbon Farming and Climate Change

In many production systems the waste heat is used to good advantage. Thomas Harttung’s farm in Denmark — the largest subscription farm in Europe — uses it to heat greenhouses. The Pyreg unit in Stockholm uses it to warm air in the winter and water in the summer for district air conditioning.

Some biomass energy equipment also produces pyrolysis oil, also known as wood vinegar, biocrude or bio-oil, that can be burned in boilers, furnaces or turbines, or transformed into useful chemicals, plastics and adhesives.

Wood gas, also called producer gas, is a type of synthesis gas (syngas) that can directly power internal combustion engines, gas furnaces and stoves the way gasoline or diesel does. Syngas can generate electricity with lower emissions than fossil fuels, although with full cycle costing you can’t say its carbon negative.

Biomass can also be gasified chemically. Argonne National Labs discovered that adding small amounts of biochar to anaerobic digesters can boost both the quantity and the quality of methane. This process led to municipalities being able to reduce contaminants from sewage sludge, and that’s led to pipeline-quality methane for power and transportation fuel.

Bronson Griscom: a second shameless plug

At the COP23 summit in Bonn, Bronson Griscom told a crowd that the maximum drawdown potential of all natural pathways, over and above what they already accomplish, could be as much as 37.4 gigatons of CO2-equivalent at a 2030 reference year. All human activity today releases about 37 gigatons, so Griscom said, essentially, we can neutralize that with biochar, forests, and wetlands. Then, cut emissions and we can return the atmosphere to the way it was before fossil fuels came into widespread use.

The economics of Griscom’s plan, however, do not pencil out. This is true of many such plans. Planting new, climate-hardy forests over the available 1780 million hectares of marginal lands is not an inexpensive undertaking. Also, applying biochar to soil rejuvenation at the rate of several billion tons per year would likely run out of forestry wastes, at least in the near term.

Adding sensitive plantations (willow, bamboo, vetiver, miscanthus) or ecosystem-optimized forestry rotations (milpa, coppice, step-harvest low-grading) would expand the feedstock reservoir. That strategy is more about social permaculture and community building than legions of government-paid tree-planters.

But here is the kicker. If you put your biochar in concretes, asphalts, composites, or electronics you can then employ municipal wastes and industrial wastes that greatly expand the available biomass supply. In our forthcoming book we call these carbon cascade enterprises. They make carbon drawdown so profitable as to eliminate the need for credit exchanges. Consider a few examples.

The quest for larger and longer storage capacity has researchers and investors frothing because batteries are the key to kissing fossil fuels good-bye once and for all. Besides capacity and discharge time, batteries need to be durable, fast charging and cheap. They also need to operate at ambient temperatures year-round, in nearly all climates.

Hydrogen has long been looked upon as a promising energy storage medium for transportation but the special qualities of hydrogen — the lightest and easiest-to-combine of all elements — have proven challenging. Fortunately, we now know that hydrogen stored in the pores of a biochar sponge is less likely to escape its confines and even less likely to combust in the tank (or body panels) of your car or the wing-reservoir of a commercial jetliner.

Supercapacitors (also known as ultracapacitors or supercaps) store energy as static charge rather than chemical charge. They are quickly replacing chemical batteries because they are lighter, faster charging and longer lasting. They can be recharged thousands of times without much capacity loss, and they have a broader temperature performance range.

This kind of storage is particularly good for products that require many charge/discharge cycles for relatively short-term power needs — consumer electronics, braking systems, and data storage, for instance. Graphene and activated carbon are already used in capacitors but biochar is coming in at a lower price point. This is helpful for biomass energy producers and indirectly for farmers and foresters.

What makes low-tech, easily sourced biochar economically viable without government subsidies or carbon credits are the carbon cascades. The same biochar might first filter out heavy metals such as nickel in wastewater. Charged this way, it is twice as effective as plain biochar as the dialectic between the two metal conducting plates. It shows almost no loss of capacity after 1000 cycles.

Biochar from pyrolyzed alligator weed, an aquatic invasive species found across the globe, shows even longer durability, lasting more than 5000 cycles without losing capacity.

Storing energy electrochemically has been dominated by lithium ion batteries for more than two decades. They power Nike+ FuelBands, Apple Watches and Teslas. They move electrons from one side, or electrode, to the other to charge, then reverse the direction to power. The negative side is known as an anode and is generally made of carbon. The positive side is called a cathode and is usually a metal oxide. The catalyst is called an electrolyte — in this case lithium salt in an organic solvent. Although Li-ions have a fairly long life (~1200 cycles), they are pricey and have a relatively low energy density so using them for larger applications has been difficult.

The new kid on the electrochemical battery block is the lithium sulfur battery. It packs five times more energy, is lighter and cheaper, but there’s a catch. Li-S suffers rapid capacity fade. It can only charge/recharge 50 to 100 times due to something called the shuttle effect — basically a meet-up of polysulfides.

Carbon to the rescue! High porosity carbon such as cherry pit biochar activated with phosphoric acid is beginning to improve the prospects for longer lived Li-S batteries. Cherry char traps polysulfides.

Quantitative analysis by McKinsey & Co (2009), as amended

Batteries from carbonized biomass can come from sources as simple and abundant as green algae, bamboo, olive pits, and banana peels. All those feedstocks have been optimized in trials to increase surface area at lower cost, producing anodes with better conductivity and less charging time.

The world of 3D printing materials is changing by the day. Filament materials are no longer limited to just plastics and metals but might include ceramics, paper, sugar — even seaweed. Today carbon in its various forms is a versatile and regenerative feedstock. For its part, 3D printing helps put carbon where it needs to be.

We are about to dive into the weeds here, so a quick chemistry lesson:

Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom or ion; reduction is the gain of electrons or a decrease in oxidation state. As an example, during the combustion of wood, oxygen from the air is reduced, gaining electrons from the carbon. Although oxidation reactions are commonly associated with oxides, oxygen is not necessary. Other chemical species can serve the same function.

The reaction can occur relatively slowly, as in the case of rust, or more quickly, as in the case of fire. The oxidation of carbon to yield carbon dioxide (CO2) or the reduction of carbon by hydrogen to yield methane (CH4), and more complex processes such as the oxidation of glucose (C6H12O6) in the human body are all examples of this oxidation-reduction reaction.

Microbial fuel cell technology captures the exudates of microorganisms to generate electricity, even while they serve their essential function of digesting and transforming organic matter. First discovered a century ago, MFCs only began to leave the lab and find practical applications in the 1970s. Most MFCs contain a membrane to separate the compartments of an anode (where oxidation takes place) and a cathode (where reduction takes place). The electrons produced during oxidation — when the microbes break down oxygen-containing food — are transferred directly to an electrode or to a redox (short for reduction–oxidation reaction) mediator. The electron flux is moved to the cathode and stored as useful power.

The charge balance of the system is compensated by ionic movement inside the cell, usually across a membrane. Most MFCs use an organic electron donor that is oxidized to produce CO2, protons and electrons. Petroleum hydrocarbons, solvents like vinyl chloride, banana peels, and soil organic matter are all compounds that can be electron donors. The cathode reaction brings together a variety of electron acceptors that can reduce oxides, metals, sulfates or nitrates; or change water to hydrogen and oxygen.

Meghana Rao, who dazzled us as a High School sophomore from Beaverton, Oregon at the Sonoma Biochar Conference in 2012, delivering a PhD level talk on the effect of particle size and feedstock on physical and chemical stability of biochar, returned for an encore at the Amherst Biochar Conference in 2013 as a much older 17-yr-old High School junior, having by then presented in Kyoto, Japan, final-ed at the Intel International Science and Engineering Fair, had 15 minutes with President Obama to better educate him on the climate restoring value of biochar, and then been named Young Naturalist of the Year by the American Museum of Natural History. Her presentation in Amherst, which was again jaw-dropping, was on the “Novel Implementation of Biochar Cathodes in Microbial Fuel Cells — Phase I.”

Having earlier noted the high surface area and cation exchange capacity of biochar, she began conducting a longer study on replacing platinum and rare earths in fuel cells with biocathodes. Preliminary results suggest biochar is somewhat less efficient (10–15 percent) but up to 400 times more cost-effective and of course can be recycled from or to later uses, such as water filtration, toxin-scavenging, or as an organic soil amendment.

This past week the Journal of the Electrochemical Society previewed an article accepted for its May issue entitled Flexible and Self-Healing Aqueous Supercapacitors By Polyampholyte Gel Electrolytes with Biochar Electrodes and Their Unique Low Temperature Properties. You know you are not a bubba when you actually enjoy reading stuff like this, right?

Author Hyun-Joong Chung of the University of Alberta says that he created a flexible and self-healing supercapacitor with 3 times the normal energy density (50 Wh/kg at room temperature) with 90% capacitance retention after 5000 charge-discharge cycles. The electrode material was biochar produced from biological wastes (could be banana peels, but he didn’t say).

Pyrolyzed carbon film is now finding applications as working electrode material for electrochemical impedance biosensors. Batch-fabricated by photolithography, smooth thin film carbon electrodes can be inexpensively produced that have electrical resistivity comparable to that of highly boron-doped polysilicon. This opens new approaches for miniaturization, circuit integration, and low-cost fabrication in electrochemical biosensors.

In microbial fuel cells, carbon can function as both an electron donor and an electron acceptor. This is no small advantage. It means that rather than having to be continuously fed, the MFC can operate on a closed cycle. Biochar is its own redox pair. A 2018 literature review for the journal Bioresource Technology found that:

Biochar can be used as an environmentally-sustainable electron donor, acceptor, or mediator. It can enhance the reduction of oxidized contaminants and participate in elemental cycling in terrestrial, groundwater, or waste water ecosystems. We illustrated that it is possible to tailor the redox characteristics of the biochar by selecting specific feedstocks, pyrolysis temperatures, and post-treatments. Further understanding of the factors impacting these redox properties will allow production of biochars for specific redox applications.

Imagine now that the 3D printers of the future, being designed in the science laboratories of high schools, even as you read this, employ filament feeds and feedstocks made of industrial wastes digested and decontaminated by microbes that in the process supply the electricity required for the printing. And when it is done and the printed object served its purpose, it can go back to feeding more microbes and producing more energy and supplying another printer somewhere to make an entirely different object. This is the way a proper carbon cycle goes: not point A to point Z — petrofuel to pollution. Instead, around and around.

Thanks for reading! If you liked this story, please consider sharing it around. Our open banjo case for your spare change is at Patreon or Paypal. This post was a collaborative effort between Albert Bates and Kathleen Draper and is likely to be included in Carbon Cascades: Redesigning Human Ecologies from Chelsea Green Publishers later this year (the book is free to our sponsors). Since neither of us are physicists, we are hoping you, dear readers, will spot our errors and offer corrections.