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Fuelling the Future with Multi-element Alloys and Green Hydrogen

Researchers from the University of Science and Technology of China (USTC) have discovered a practical and scalable method to produce hydrogen oxidation catalysts for hydrogen fuel cells, overcoming present challenges in renewable fuel expansion and feasibility.

With the rising levels of pollution, various industries are encouraged to turn to renewable fuels as a more sustainable alternative to coal, gas and fossil fuels. Renewable fuels are primarily made from resources that are constantly replenished and offer a more sustainable alternative to power our electricity. The most common forms of renewable fuel utilise solar, wind, and hydro.

In recent years, scientists have taken one step further and developed hydrogen fuel cells to support sustainable green energy. Hydrogen fuel can be produced from renewable resources such as solar or wind power without cost to the environment. In addition, hydrogen energy is presently considered to be the cleanest energy derived from renewable sources, garnering significant attention in the pursuit of sustainability.

The production of hydrogen energy involves the use of a special type of fuel cell known as proton exchange membrane fuel cells (PEMFCs). In essence, these PEMFCs consume hydrogen and produce electricity. However, one particular challenge that has impeded the expansion of hydrogen fuels is the restricted commercialisation of traditional PEMFCs due to the use of expensive platinum-based catalysts in their cathodes.

One way to overcome this barrier of cost is to substitute the acidic electrolytes used in PEMFCs with alkaline ones. In doing so, inexpensive metal elements like cobalt, nickel, or manganese may be used to assemble the electrocatalyst of anion exchange membrane fuel cells (AEMFCs), presenting us a low-priced alternative. However, as it stands, there has yet to be a practical, scalable way to manufacture cheaper components for AEMFCs.

A group of researchers spearheaded by Professor Gao Minrui from the University of Science and Technology of China (USTC) developed a novel, inexpensive alloy made of nickel, tungsten, and copper, known as Ni5.2WCu2.2, which can be used as a cathode for AEMFCs. The team has found that their novel alloy can catalyse the oxidation of hydrogen much more efficiently as compared to platinum/carbon anodes and can sustain high performance for up to 20 hours.

The researchers first experimented on three-dimensional foam copper skeletons to construct copper hydroxide nanowires. They successfully developed these nanowires by anodic oxidation, which refers to the electrochemical method of producing an oxide film on a metal substrate by the removal of electrons. These nanowires were then submerged in a solution containing nickel and tungsten. After hydrothermal synthesis and annealing, the nickel-tungsten-copper alloy is obtained.

Through a series of trials, the team has found that the newly-developed Ni5.2WCu2.2 alloy exhibits a remarkable ability to catalyse hydrogen oxidation in an alkaline medium, increasing the efficiency of the process by 4.31 times as compared to the standard platinum/carbon anode.

Additionally, its oxidation potential was found to reach up to 0.3V, notably higher than the reversible hydrogen electrode. The oxidation potential is a measure of energy change needed to add or remove electrons from elements or compounds. The higher the oxidation potential, the better its ability to give up electrons and become oxidised, thus increasing its efficiency to catalyse the fuel cell process. Furthermore, the alloy can sustain high performance for up to 20 hours without notable decay.

Besides its remarkable catalytic power, the projected density of states of the Ni5.2WCu2.2 alloy is the lowest at Fermi level, suggesting that it possesses optimal hydrogen binding energy. The alloy also offers oxidation resistance and showed excellent resilience to carbon monoxide poisoning.

The findings of this study have undoubtedly shed light on the potential alloy-based catalysts hold to not only improve hydrogen fuel production but also make it affordable. [APBN]

Source: Qin et al. (2021). Ternary nickel–tungsten–copper alloy rivals platinum for catalyzing alkaline hydrogen oxidation. Nature Communications, 12(1), 1-10.