Closing the Carbon Loop with Artificial Photosynthesis

Energy production fuels global growth and prosperity, but worldwide, the majority of energy continues to be generated from fossil fuel combustion, which contributes to climate change through the production of carbon dioxide (CO₂) emissions. The increase in the atmospheric concentration of CO₂ is causing our world to warm, alongside numerous related and adjacent effects. Extreme weather events are increasing, biodiversity is decreasing, and all across the globe people’s everyday lives are being disrupted or uprooted by the changing climate.

Thankfully, renewable energy sources such as solar, wind, hydro, and geothermal can mitigate CO₂ concentrations by generating emissions-free electricity. Fossil fuels, after all, are simply liquefied and pressured sunlight that has accumulated over millions of years. Renewable energy simply cuts out the middle step: the growth of plants and organic matter that die, decompose, accumulate, and liquefy underground over millennia.

Beyond just energy production, nearly all everyday goods are somehow implicated in fossil fuel production. From the carbon in your phone’s plastic components, to the synthetic fibres in your shirt, to the fertilizers used in industrial food production—all of these goods are linked to processes that emit high amounts of CO₂. The comfortable lives many people enjoy is only possible because of our addiction to fossil fuels.

There is another way. Nature’s elegant solution is photosynthesis, which synthesizes water, sunlight, and CO2 into energy, in the form of sugars. However, photosynthesis is less than one percent efficient, and it takes years to grow a tree. By comparison, solar cells are now twenty-two percent efficient in turning sunlight to electricity.22National Renewable Energy Library, “Best Research-Cell Efficiency Chart,” 2019, https://www.nrel.gov/pv/cell-efficiency.html. The amount of CO₂ emitted in the atmosphere annually through human activity is vastly larger than what photosynthesis can sequester alone.

In research labs around the world, scientists and engineers are working on a technology called artificial photosynthesis. This process replicates what nature does: it combines energy, CO₂, and water, and then engineers that process to make chemicals and fuels. For example, CO₂ can be electrochemically converted into a variety of hydrocarbons such as ethylene (the precursor to every major consumer plastic), methane (natural gas), and ethanol (a fuel). In doing so, artificial photosynthesis generates usable materials from air pollution. The idea is simple: can we make fuels and chemicals, the building blocks of our society, from the CO₂ in the air rather than from crude oil in the ground? The successful deployment of this process would allow us to convert excess renewable energy into a stable chemical form (as fuels) for long-term seasonal energy storage, thereby solving the problem of intermittency. In addition, fuels made from artificial photosynthesis could integrate into existing and costly energy infrastructure—such as pipelines, tankers, and even your car’s gas tank. This is the idea of a truly circular economy, of engineering the carbon cycle, of working towards a renewably powered future.

There are two steps to artificial photosynthesis: capturing CO₂ from the air, and then converting it into something useful. Carbon capture technologies, which address the first step, are beginning to enter the market. Vancouver-based company Carbon Engineering is one leader in this emerging technology. My PhD research was focused on the second step of artificial photosynthesis: converting CO₂ into something useful. I led a team to the finals of the Carbon XPRIZE, a $20M competition which challenges entrants to capture CO₂ and convert it into a valuable good. Our team, Carbon Electrocatalytic Energy Toronto, focused on generating carbon-based fuels, and base chemicals used in the production of everyday goods.

Artificial photosynthesis is an energy-intensive process. The energy sources powering this process need to be renewable in order for it to close the carbon cycle. At the heart of this technology is a catalyst—a material that combines renewable electricity and CO₂, transforming them into fuels and chemicals. Catalysts come in a variety of materials, like copper, silver, or gold, and are synthesized and engineered in the lab. Catalysts lower the energy required for the electrosynthetic reaction to occur—they accelerate the process by making it more efficient. Although research is ongoing, catalyst materials are not yet at the point of industrial commercialization. Stability issues (or how long the catalyst can last before being deactivated) continue to pose challenges to researchers. The issue of selectivity, or being able to control which exact fuel or chemical you make from CO₂ (and to make as pure of an output stream as possible), is also a hurdle to overcome.

Phil De Luna is Program Director of the Materials for Clean Fuels Challenge Program at the National Research Council Canada, where he leads a seven-year collaborative program on CO2 conversion and hydrogen technologies. De Luna received his PhD from the University of Toronto, where he was awarded the Governor General’s Gold Medal. His research on artificial photosynthesis has been published in Science and Nature. He was included in Forbes Magazine’s 2019 Top 30 Under 30 list in the Energy category, was an NRG COSIA Carbon XPRIZE finalist, and serves on the board of directors for Carbon Management Canada.