Global climate change is one of the greatest challenges facing the world today. While many Canadians certainly wouldn’t complain about a few more warm summer days, unchecked climate change will bring many undesirable consequences, including more frequent extreme weather events, poor crop growth due to unpredictable seasons, and rising sea levels. The international community set a goal at the Paris Climate Conference to keep the average global temperature increase below 2°C, a threshold which sounds small but exceeds the range experienced in the past 100,000 years.
The question now becomes: how do we avoid passing this 2°C mark? To do so, we will have to eliminate our carbon dioxide (CO2) emissions. Not reduce them by a quarter, or by a half, but completely eliminate CO2 emission by the year 2100. While improvements in efficiency and conservation can reduce emissions, our remaining energy needs will need to be met with clean sources of energy, like solar, to eliminate emissions altogether.
One issue with current renewable energy sources is that they are not as readily available as traditional fuels. Wind and sunlight vary day to day and with the seasons, but energy demand doesn’t necessarily follow the same patterns. For instance, at night, when the sun isn’t shining, more energy is required for lighting. Energy storage is therefore a very important part of the equation for increasing renewable energy usage.
In the Sargent group at the University of Toronto, we are exploring more efficient methods of storing renewable electricity in chemical form. When renewable generation outpaces demand, the excess electricity can be used to power the synthesis of renewable fuels that can then be stored. This is especially important for northern countries such as Canada; the long days in the summer can be used to generate chemical fuels that can be used in the cold, dark wintertime. For example, renewable electricity can be used to break water, H2O, into oxygen (O2) and hydrogen (H2). Hydrogen fuel cells can then be used to generate electricity when needed. We recently demonstrated a new material that performs the oxygen generation part of this reaction very efficiently, and is much less expensive than previous materials based on precious metals.
A new material promotes highly efficient water-splitting, generating bubbles of oxygen gas.
CO2 as friend and foe
We are now looking at making fuels not just from water, but from CO2 itself. Renewable electricity provides the energy to convert CO2 to a conventional carbon-based fuel, through a process known as electrocatalysis. This is similar to how plants use sunlight to convert CO2 into sugars and biomass. Burning these renewable fuels still releases CO2, of course, since the fuels are chemically identical to conventional fuels. However, the CO2 can be captured and converted into fuel again, essentially recycling CO2 without net generation of greenhouse gases.
Besides the generation of fuels for storage, electrocatalysis can be used to convert CO2 into other useful products. Carbon is an important component of many products we use which are typically produced from petroleum-based chemicals. By using CO2 as the source of carbon, we could produce polymers and plastics which have a negative carbon footprint.
Climate change is a very big and very important challenge, but it’s one we can address through advances in clean energy generation and storage. Our research aims not to avoid CO2, the main villain in climate change, but to turn it into a resource that we can use for energy storage and for building useful products.