Making hydrogen energy with the common nickel

A POSTECH research team led by Professor Jong Kyu Kim and Ph.D. candidate Jaerim Kim of the Department of Materials Science and Engineering and a team led by Professor Jeong Woo Han and Ph.D. candidate Hyeonjung Jung of the Department of Chemical Engineering have jointly developed a highly efficient nickel-based catalyst system doped with oxophilic transition metal atoms and have identified the correlation between catalytic adsorption properties and hydrogen evolution reaction (HER) kinetics in alkaline medium. Recognized for their significance, these research findings were featured as the front cover paper for the Journal of the American Chemical Society.

A fuel cell is an eco-friendly power generating device that produces electricity using a chemical reaction in which oxygen (O₂) and hydrogen (H₂) produce water (H₂O). During this process, water electrolysis reduction occurs as a counter-reaction, which dissociates water to generate hydrogen fuel. This is known to be the most environmentally-safe and sustainable way to produce high-purity hydrogen fuel in large quantities. However, it has a downside of being costly and inefficient since it requires the use of precious metals as electrodes. In order to reduce the unit cost of hydrogen fuel produced through water-electrolysis, it is paramount to develop highly active, stable, and inexpensive electrochemical catalyst, capable of maximizing the hydrogen production performance.

To this, the joint research team designed a highly effective catalyst by combining earth-abundant nickel with a series of oxophilic transition metal elements to optimize the adsorption abilities in alkaline HER. The team further demonstrated that the incorporation of oxophilic dopants can effectively control the adsorption properties of the surface of Ni-based catalysts.

In order to further enhance the HER activity of the Ni-based catalysts, the researchers introduced a unique 3-dimentional (3D) nanohelix (NH) array, easily fabricated by an oblique-angle codeposition method, for abundant surface active sites, efficient pathways for charge transfer, and open channels for mass transport. They had successfully fabricated highly active and stable Cr-incorporated Ni NHs catalyst showing an excellent hydrogen production efficiency with reduced overvoltage more than four times compared to the conventional nickel-based thin film catalysts.

"This research is significant in that it provides the scholarly foundation for high performance and commercialization of sustainable hydrogen energy conversion system," explained Professor Jong Kyu Kim, the corresponding author of the paper. "The core concepts of the design strategy and experimental methodology for efficient bimetallic electrocatalysts can be applied not only to water electrolysers, but also to fuel cells, carbon dioxide reduction, and photo-electrochemical system. It is anticipated that securing this original technology will have significant ripple effects and technological expansion in the environmental energy sector."

Professor Jeong Woo Han, the co-corresponding author of the paper, added, "Computational chemistry has dramatically accelerated the water electrolysis reaction by quickly finding bimetals that can control the catalyst adsorption strength to enable the fabrication of bimetallic electrocatalysts using only nonprecious materials."