Catalysts are substances that speed up chemical reactions by providing a more efficient route for a reaction to occur and making it easier to start and finish. Since catalysts are neither consumed nor altered in the reaction, they can be used repeatedly, and they are essential in a variety of industrial, environmental, and biochemical processes.

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The team, which included researchers from Hokkaido University, the University of Technology Sydney (UTS) and elsewhere, developed the catalyst, called NiOOH-Ni, by combining nickel (Ni) with nickel oxyhydroxide.

Ammonia can cause severe environmental problems, such as excessive algal growth in water bodies, which depletes oxygen and harms aquatic life. At high concentrations, ammonia can harm humans and wildlife. Effective management and conversion of ammonia are thus critical, but its corrosive nature makes it difficult to handle.

The researchers developed NiOOH-Ni using an electrochemical process. Nickel foam, a porous material, was treated with an electrical current while immersed in a chemical solution. This treatment resulted in the formation of nickel oxyhydroxide particles on the foam’s surface.

Despite their irregular and non-crystalline structure, these nickel-oxygen particles significantly enhance ammonia conversion efficiency. The catalyst’s design allows it to operate effectively at lower voltages and higher currents than traditional catalysts.

“NiOOH-Ni works better than Ni foam, and the reaction pathway depends on the amount of electricity (voltage) used,” explains Professor Zhenguo Huang from the University of Technology Sydney, who led the study.

“At lower voltages, NiOOH-Ni produces nitrite, while at higher voltages, it generates nitrate.”

This means the catalyst can be used in different ways depending on what is needed. For example, it can be used to clean wastewater by converting ammonia into less harmful substances. But in another process, it can also be used to produce hydrogen gas, a clean fuel. This flexibility makes NiOOH-Ni valuable for various applications.

“NiOOH-Ni is impressively durable and stable, and it works well even after being used multiple times,” says Associate Professor Andrey Lyalin from Hokkaido University, who was involved in the study.

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“This makes it a great alternative to traditional, more expensive catalysts like platinum, which aren’t as effective at converting ammonia.”

The catalyst’s long-term reliability makes it suitable for large-scale industrial use, potentially transforming how industries handle wastewater and produce clean energy.

The study has been published in Advanced Energy Materials.

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Having used fossil fuels for over a century for nearly everything, humanity has triggered a climate crisis. Now, the directive is to achieve net zero emissions or carbon neutrality by 2050.

A hydrogen economy is one way in which a carbon neutral world can thrive. At present, the simplest way to produce hydrogen fuel is electrochemical water splitting: running electricity through water in the presence of catalysts (reaction-enhancing substances) to yield hydrogen and oxygen.

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This reaction, however, is very slow, requires specialised conditions and noble-metal catalysts, and is overall expensive. Thus, achieving a high hydrogen yield in an energy-efficient manner at low cost is challenging. To date, hydrogen production from water splitting has not been successfully commercialised.

Now, a team of researchers from Pusan National University, South Korea, led by Professor Kandasamy Prabakar, have developed a method to design a novel electrocatalyst that can solve some of these problems. Their work was made available online on April 6, 2021, and will be published in print in the September 2021 issue of Volume 292 of Applied Catalysis B: Environmental.

Describing the study, Prof. Prabakar says, “Today, 90 per cent of hydrogen is produced from steam reforming processes that emit greenhouse gases into the atmosphere. In our laboratory, we have developed a non-noble metal based stable electrocatalyst on a polymer support which can effectively produce hydrogen and oxygen from water at a low-cost from transition metal phosphates.”

Prof. Prabakar’s team fabricated this electrolyzer by depositing cobalt and manganese ions, in varying proportions, on a Polyaniline (PANI) nanowire array using a simple hydrothermal process. By tuning the Co/Mn ratio, they have achieved an overall high surface area for the reactions to occur, and combined with the high electron conducting capacity of the PANI nanowire, faster charge and mass transfer was facilitated on this catalyst surface. The bimetallic phosphate also confers bifunctional electrocatalytic activity for the simultaneous production of oxygen and hydrogen.

In experiments to test the performance of this catalyst, they found that its morphology substantially decreases the reaction overpotential, thereby improving the voltage efficiency of the system. As a testament to durability, even after 40 hours of continuous hydrogen production at 100mA/cm², its performance remains consistent. And water splitting was possible at a low input voltage of merely 1.54V.

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In addition to these advantages, is the low cost of transition metals. Indeed, the system can be scaled and adapted for application to myriad settings.

Speaking of possible future applications, Prof. Prabakar explains, “Water-splitting devices that use this technology can be installed onsite where hydrogen fuel is required, and can function using a low energy input or a completely renewable source of energy. For instance, we can produce hydrogen at home for cooking and heating using a solar panel. This way, we can achieve carbon neutrality well before 2050.”

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