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Top diagram: The NiFeMo-PC catalyst is made by mixing an aqueous solution of metal salts and sodium hypophosphite, the sodium salt of a phosphorus-containing acid, with treated nickel foam and subjecting the solution to a simple, low-cost hydrothermal reaction that increases the temperature and pressure of the solution in the reaction vessel. The intermediate product (scanning electron microscopy image of the middle (SEM)) is then loaded with an alloy and metal phosphide through H2/Ar (hydrogen/argon) pyrolysis (addition of electrons to metal ions using hydrogen and heat) to create the final catalyst product (right SEM image). Bottom graphs: graphs depicting linear sweep potentiometry, or current density of the working electrode in a hydrogen evolution reaction (left graph) and an oxygen evolution reaction (right graph) at different potentials, depending on the catalyst used. NiFeMo-PC performance is highlighted in red. Image source: Nanoenergy Research, Tsinghua University Press
Hydrogen gas is a clean, renewable alternative to fossil fuels, but current industrial production methods used to produce hydrogen release carbon into the atmosphere and pollute the environment.
The new catalyst, a carbon-nickel-iron-molybdenum-phosphide composite stabilized on nickel foam (NiFeMo-PC), has significantly reduced the amount of electricity needed to generate both hydrogen and oxygen from water, providing a clean and efficient way to produce hydrogen gas.
A team of leading chemical engineers has created a cost-effective, easy-to-manufacture catalyst designed to reduce the amount of energy required for water electrolysis, which splits water molecules into hydrogen and oxygen using electricity.
Hydrogen and oxygen gas are separated from water through the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER), respectively. A transition metal alloy, or mixture containing at least one metal, nickel-iron-molybdenum (NiFeMo) has been used as a catalyst for the electrolysis of water due to the incomplete filling of electron orbitals in the nickel-iron transition metal atoms, making it a perfect electron. Donor and acceptor in chemical reactions. Phosphide has been added to the catalyst to improve corrosion resistance in an alkaline, or basic pH, electrolyte solution.
The team published the results of their study in Nano research energy on July 7th.
“Hydrogen is recognized as the most ideal alternative to fossil fuels due to its high energy density, high heat conversion efficiency and zero carbon emission. However, hydrogen production methods commonly applied in industry, including steam reforming of natural gas, methanol and hydrogen gasification, said Jingjingtang, supervisor. According to the study and associate professor at Central South University in Changsha, China, coal consumes fossil fuels and causes serious pollution to the environment.
“Water electrolysis uses water as a raw material to produce high-purity hydrogen by converting electricity into chemical energy, which is a clean and promising hydrogen production technology,” Tang said.
The catalysts used to lower the energy required for both the HER and the OER existed previously, but used platinum and iridium oxide, which are valuable elements that are expensive and in short supply. Creating an affordable catalyst that lowers the activation energy for both reactions reduces overall manufacturing costs and improves the commercial viability of producing clean hydrogen gas.
One of the challenges in designing a bifunctional stimulus was the special requirements of OER. He said, “Because OER is a four-electron transfer reaction with slow kinetics, it generally performs better in alkaline solutions. It was necessary to search for non-noble metal-based electrocatalysts with excellent bifunctional performance in alkaline electrolyte” . Tang. The team created the alloy and metal phosphide to maintain the integrity of the catalyst in these alkaline conditions.
To test the composition and valence state of the generated NiFeMo-PC catalyst, the synthesizing team subjected X-ray photoelectron spectroscopy (XPS) to confirm the presence of Ni, Fe, Mo, P, C and O. The nickel resolution spectrum also determined the 2p3/2 and 2p1/2 spin orbitals, which indicate the state of electrons in the nickel atoms in the catalyst.
In general, the newly developed NiFeMo-PC electrocatalyst requires very low overpotentials, or energy required to split water, for HER (87 mV to achieve a current density of 10 mA cm-2) and OER (196 mV to achieve a current density of 10 mA cm-2). The cell potential, or potential difference between two electrodes, required for the electrolysis of water using the catalyst is also only 1.50 V at 10 mA cm-2.
The team is optimistic that their discovery will make clean hydrogen production a reality. “Unlike most bifunctional catalysts, NiFeMo-PC can achieve excellent catalytic performance without complicated preparation steps and complex nanostructures. Moreover, the superior durability without any attenuation (effort) within 50 hours… makes NiFeMo-PC an ideal device (non-precious metal) “The catalyst is a candidate for … large-scale hydrogen production,” Tang said.
Other contributors include Xiangyang Zhu, Tingting Yang, Ting Li, Yougu Ze, Sijing Zhang, Li Yang, Yingkang Liu and Juan Yang from the School of Mineralogy and Environment of Central South University in Changsha, China.
more information:
Xiangyang Zhou et al., In situ fabrication of a NiFeMo-P carbon composite immobilized on a nickel foam as a bifunctional catalyst for overall water splitting enhancement. Nano research energy (2023). doi: 10.26599/NRE.2023.9120086
Provided by Tsinghua University Press