Making hydrogen production more sustainable
Though hydrogen gas is a clean and renewable alternative to fossil fuels, current industrial production methods used to produce it release carbon into the atmosphere, polluting the environment. A new catalyst, carbon compound nickel-iron-molybdenum-phosphide anchored on nickel foam (NiFeMo-P-C), has decreased the amount of electricity required to generate both hydrogen and oxygen from water, providing a clean and efficient means to produce hydrogen gas.
A team of chemical engineers recently synthesised this catalyst designed to lower the amount of energy required for the electrolysis of water, which splits water molecules into hydrogen and oxygen using electricity. Through the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, hydrogen and oxygen gas can be split from water. The transition metal alloy, nickel-iron-molybdenum (NiFeMo), was used as a catalyst for water electrolysis due to the incomplete filling of electron orbitals in transition metal atoms nickel and iron, making it a suitable electron donor and acceptor in chemical reactions. Phosphide was added to the catalyst to improve corrosion resistance in an alkaline electrolyte solution.
According to Jingjing Tang, Central South University associate professor and supervisor of the study, hydrogen is recognised as the most ideal alternative to fossil fuels; however, commonly used methods to produce hydrogen consume fossil fuels and cause pollution.
“Water electrolysis takes water as raw material to produce high-purity hydrogen by converting electricity into chemical energy, which is a clean and promising hydrogen production technology,” Tang said.
Catalysts used to lower the energy required for both the HER and OER previously existed, but they utilised platinum and iridium oxide — valuable elements that are both expensive and in short supply. To reduce overall manufacturing costs and improve the commercial viability of clean hydrogen gas production, an affordable catalyst had to be created.
A challenge in designing a bifunctional catalyst was the special requirements of the OER, which generally performs better in an alkaline solution because it is a four-electron transfer reaction with sluggish kinetics. Researching non-noble, metal-based electrocatalysts with excellent bifunctional performance in an alkaline electrolyte was critical. The team created the alloy and metal phosphide to maintain catalyst integrity in these alkaline conditions.
To test the composition and valence state of the generated NiFeMo-P-C catalyst, the team used X-ray photoelectron spectroscopy (XPS) measurement to confirm the presence of Ni, Fe, Mo, P, C and O. The high-resolution spectrum of nickel also identified 2p3/2 and 2p1/2 spin orbits, which refers to the state of electrons in the nickel atoms of the catalyst.
The newly developed NiFeMo-P-C electrocatalyst requires very low overpotentials, or energy required to split water for HER and OER. The cell voltage required for water electrolysis using the catalyst is 1.50 V at 10 mA·cm–2.
The team hopes their discovery will make clean hydrogen production a reality as it can achieve catalytic performance without complicated preparation steps and elaborate nanostructures.
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