Transition Metal Doped Cannabis Catalysts for the Oxygen Reduction Reaction in Hydrogen Fuel Cells

Abstract

The global climate crisis demands a rapid uptake of alternatives to fossil fuels to alleviate further damage to the planet. To this end, supercapacitors, batteries and fuel cells have been identified as critical enabling technologies to overhaul the current energy system. As the demand for these energy storage and conversion devices increases, so does the need to produce sustainable, low-cost and high-performing components for them.Currently, platinum is used to catalyse the sluggish oxygen reduction reaction (ORR) in hydrogen fuel cells. It is generally deposited on a carbon support and forms an electrode that is vital in determining electrochemical performance (namely activity and durability); however, this presents a two-pronged challenge. Traditionally, the carbon used is synthesised via energy-intensive and time-consuming processes involving the incomplete combustion of heavy petroleum products or coal. Secondly, platinum scarcity lends to issues of high cost, which is often ascribed to being the largest hindrance in large-scale commercialisation of this technology. To mitigate these issues, an electrocatalyst based on transition metals and a biomass precursor can be effectively used instead.1 A very promising biomass precursor is hemp. Also known as industrial hemp, it is one of two strains of the cannabis plant. It is one of the oldest domesticated crops in the world, known for its sustainability, high yield and ability to grow on marginal land with low water and pesticide requirements. It is carbon-negative, low-cost and biodegradable - making it the ideal choice in the current climate crisis. Through thermal carbonisation and activation, it yields 3-dimensional hierarchical structures with high conductivity, surface area and porosity.2 Here we report on using nitrogen, iron and cobalt together with cannabis-derived carbon to produce a high functioning and low-cost electrocatalyst to replace Pt/C at the cathode, as shown by a suite of characterisation and electrochemical techniques. With a uniform mesoporous texture and good distribution of metal species, the material displays properties beneficial to catalysing the ORR with a much lower environmental and monetary cost than traditional Pt/C. This forms an excellent basis for further work in this field to achieve the overarching goals of high performance coupled with environmental sustainability. Borghei M., Lehtonen J., Liu L. and Rojas O. J. 2018 Advanced Biomass-Derived Electrocatalysts for the Oxygen Reduction Reaction. Adv. Mater. 30 1703691Rana Z. I., Shah A. R., Llewellyn A. V., Mazloomian K., McAlernon P., Miller T. S., Cullen P. L., Shearing P.R. and Brett D. J. L. B. 2022 A new high: Cannabis as a budding source of carbon-based materials for electrochemical power sources. Curr. Opin. Electrochem. 31 100860