A major concern plaguing the shift towards sustainable and renewable energy is how much the transition will cost.  This is particularly important when considering batteries, water electrolyzers (used to convert water into oxygen and hydrogen), and fuel cells that rely on electrochemistry to function.  At the moment, the majority of these mechanisms rely on expensive noble metals such as platinum, ruthenium, and iridium.  However, in early 2020 a team of chemists based in Finland proposed an alternative using earth-abundant (and therefore cheaper) materials.

Water electrolyzing involves separating oxygen (the red molecule) from hydrogen (the blue molecule). This is particularly useful in making hydrogen based fuel! Picture courtesy of Creative Commons.

The primary function the noble metals serve in each of these mechanisms is to act as a catalyst, or a component used to increase the speed of a reaction/”convince” a reaction to start.  These catalysts are responsible for some of the most important reactions in renewable energy systems: oxygen reduction reactions (ORR) and oxygen evolution reactions (OER).  (While I won’t go into the exact science behind these procedures, it is important to note that these reactions determine how efficiently fuel cells, water electrolyzers, and metal-air batteries work.)

The selected catalyst must be able to adhere to a machine’s electrode, where electricity enters the system, in order to react efficiently.  With this in mind, the team of chemists created a porous surface area that would improve the ability of the catalyst to function.  The pores act as little cubbies for the catalysts, enabling the catalysts to have easier access to active sites where the needed ORR and OER reactions take place.

Once the proper surface material was in place, they set their sights on developing a powerful catalyst that would readily react with the system.  They found their answer in the abundant element of nitrogen.

Fun Fact: Liquid nitrogen to make icecream is a classic chemistry experiment, but some ice cream parlor have added it to their daily repertoire! Picture courtesy of Creative Commons.

Nitrogen “doped” carbon materials can act as non-metallic and cheap catalysts for ORR and OER reactions.  To be more specific, single nitrogen atoms are attached to graphene nano-flakes, tiny pieces of extremely durable carbon.  The process of making these catalysts is one step which makes the system’s cost/energy expenditure even lower and therefore more attractive.

Furthermore, after running tests the chemists discovered they could effectively “tune” how reactive the catalysts are.  This is extremely beneficial as it means the procedure can be modified depending on what other materials are used in the machine.

Better control over important chemical reactions can improve the production of green technology and clean energy.

In the future, the chemistry team hopes their research of catalytic activity regarding porous materials will establish a baseline for future projects, especially those designing electrodes for green energy sources.

Mohammad Tavakkoli, Emmanuel Flahaut, Pekka Peljo, et. al. Mesoporous Single-Atom-Doped Graphene‒Carbon Nanotube Hybrid: Synthesis and Tunable Electrocatalytic Activity for Oxygen Evolution and Reduction Reactions. ACS Catalysis, 2020; DOI: 10.1021/acscatal.0c00352