As the energy sector and transport industry seek to mitigate their environmental impact, green hydrogen will likely play a major role in achieving carbon neutrality. Green hydrogen is produced by the electrolysis of water using renewable energy sources, such as solar or wind power. Electrolyzers based on polymer electrolyte membrane (PEM) technology provide an efficient pathway for producing green hydrogen through water electrolysis. By inverting the process, PEM fuel cells (PEMFCs) can be used to generate electricity using hydrogen as fuel, in combination with oxygen (which acts as an oxidizing agent). Fuel cells have the potential to make hydrogen a viable replacement for fossil fuels in energy, transport, and other industrial sectors. However, to achieve this on a large scale, their performance and cost must be optimized.
The catalytic material used to produce PEMFC electrodes is the main component in determining both the performance and the cost of fuel cells. The catalytic ink is typically composed of a mixture of a catalytic active material, an ionomer, and a dispersion solvent. Within the ink, the catalyst – usually platinum-on-carbon (Pt/C) – is a composite of platinum (Pt)-metal group nanoparticles deposited on activated carbon, which serves as a support matrix. The catalyst’s activity and stability are the two key parameters that determine the PEMFC’s ultimate performance. Catalytic activity, in turn, is governed by the size, dispersion, and morphology of the Pt-metal group nanoparticles. Equally important are the structural, textural, and surface chemistry properties of the carbonaceous agglomerates during ink drying, upon deposition on the proton exchange membrane. The optimized pore structure of the C-support matrix can significantly reduce the amount of Pt needed, and the optimization of its distribution and maximization of the availability of the catalytic points for the oxygen reduction reaction (ORR) and hydrogen-oxidation reaction (HOR) in fuel cells reduces the overall cost of the process.
Catalytic activity and stability can be optimized in several ways: by developing novel Pt-alloy cathode materials, controlling the particle size for maximum mass activity, controlling the inter-crystallite distance, or ensuring uniform dispersion of Pt nanoparticles on the carbonaceous support.