Illustration of the pomegranate-like Ni/NiO/C nanocatalyst for hydrogen evolution reaction (HER).
Illustration of the pomegranate-like Ni/NiO/C nanocatalyst for hydrogen evolution reaction (HER).

Researchers have created a pomegranate-like catalyst made up of tiny Ni nanoparticles and NiO nanoclusters that promises more efficient electrolysis of water [Jiang et al., Materials Today (2018),]. Water electrolysis produces hydrogen gas (along with oxygen as a harmless by-product) in an environmentally friendly and sustainable way, which could be crucial to developing hydrogen as a next-generation clean fuel.

Hydrogen generation via electrolysis currently requires Pt catalysts, a precious metal which is both expensive and limited in resource terms. Instead, interest is turning to highly efficient and cost-effective non-Pt alternatives. Although there has been some success to date, there is still a pressing need for non-Pt catalysts with sufficient activity to work effectively with alkaline water and seawater.

“Hydrogen evolution by water electrolysis is generally considered as a very promising way to realize large-scale hydrogen production, which is emerging as the next-generation energy carrier for both economic and environmental considerations,” explains Li Song of the University of Science and Technology of China in Hefei.

Along with colleagues from East China University of Science and Technology in Shanghai and the Norwegian University of Science and Technology, Song and his team have developed a new catalyst based on Ni and NiO clusters with a unique ternary interfacial structure. The structure resembles a pomegranate with very small Ni nanoparticles mounted on NiO clusters separated by ultrathin carbon layers. The ratio of Ni to NiO can be controlled easily by varying the temperature and conditions. The carbon layers, meanwhile, protect the Ni nanoparticles from excessive oxidation, creating a catalyst with stable activity.

“The Ni/NiO interface sites efficiently lower the energy barrier of the rate-determining step (RDS), contributing to fast reaction kinetics for the hydrogen evolution reaction (HER),” explains Song.

The carbon layers also facilitate fast charge transfer by providing a three-dimensional conduction network for electrons. Even with no precious metal content, the Ni/NiO catalyst still shows HER activity levels approaching those of commercial Pt/C catalysts.

“Compared with previously reported HER catalysts, we believe our catalyst represents the state-of-the-art for non-precious metal catalysts,” Song told Materials Today. “We are now exploring other applications in various fields, especially CO2 conversion.”

The only drawback is that the new catalyst is currently produced in the form of a nanopowder. For the material to be useful commercially, the Ni/NiO nano-catalyst must be formed into a practical electrode. The researchers believe it should be possible to load the nano-catalyst onto larger current collectors to get around this limitation.