A team of researchers from Khalifa University has discovered an easy, low-cost and sustainable way to make catalysts that can split oxygen molecules from water, and in turn, produce hydrogen for energy storage and clean fuel applications.
The new catalyst, which is made of electrodeposited metallic elements cerium, nickel and iron, can split oxygen from water (called the Oxygen Evolution Reaction, or OER) at a rate that is two times more efficient than conventional catalysts, which are primarily made from noble metal oxides.
The collaborative team includes KU Post-Doctoral Researcher Dr. Ranjith Bose, KU Professor of Chemical Engineering Dr. Akram Alfantazi, Dr. Dhinesh Babu Velusamy from KAUST in Saudi Arabia, and Prof. Hyun-Seok Kim and Dr. K. Karuppasamy, both from Dongguk University in Seoul. The results of the team’s work was published in ACS sustainable Chemistry & Engineering in August 2019.
Traditional catalysts are made via a solution-based process, which can pose serious issues related to the catalyst efficacy. With a solution-based process, engineers cannot control the size of nanomaterials that are used, or control the growth of the crystals used to make the catalyst. The solution-based process is not recommended for industrial applications due to the complicated synthesis procedures, thus limiting the use of catalysts made this way to small-scale applications.
The researchers developed an alternative method to synthesizing catalysts using an electrodeposition technique. Electrodeposition is the process of coating an ultrathin layer of one metal on top of a different metal to modify its surface properties. It is a simple process that can be easily scaled up for industrial applications.
“Electrodeposition is low cost and offers high controllability, as well as compatibility with nano-scale features. Furthermore, it can be performed at room-temperature,” said Dr. Ranjith.
However, electrodeposition for synthesizing metallic catalysts also has limitations. Previous studies have reported that a flat substrate, such as the ultrathin metallic layer coating, results in limited available active sites – or places where the catalytic “action” happens. This is because only the outermost electrons of the catalyst substrate are in contact with the electrolyte – the electrically conducting solution that interfaces with the catalyst to complete the reaction. More robust reactivity depends on a larger surface area, and flat 2D structures don’t offer high surface area.
To overcome these obstacles, Prof. Akram’s team layered the ultrathin metallic composites on a 3D foam structure, giving their catalysts a larger surface area, which translated into more active sites and better catalytic performance.
“We developed a catalyst made of a 3D nickel foam core, coated with an ultrathin layer of cerium oxide and nickel-iron hydroxide. This unique design combines the features of cerium oxide and nickel-iron hydroxide, which have outstanding mass-transfer properties, enhanced active sites, and energetics for OER, with the mechanical robustness of the 3D nickel foam core,” Dr. Ranjith explained.
The cerium oxide and nickel-iron hydroxide was synthesized by a two-step process that started with the preparation of nickel-iron oxide by electrodeposition, followed by anodic electrolysis – a technique that uses an electric current – to introduce the cerium oxide into the nickel-iron coated film.
The resulting composite catalyst exhibited excellent OER activity with a lower overpotential – the difference between the applied and thermodynamic potentials of a given electrochemical reaction – and higher electrocatalytic activity.
The research is an important contribution to the selection, production and optimization of electrocatalytic materials that can be leveraged to improve the efficiency of hydrogen electrolytic production.
“The results achieved by our catalysts undoubtedly represent an important milestone toward the development of efficient catalysts that use electricity to break water into hydrogen and oxygen to further reduce the operational costs of hydrogen production,” Dr. Ranjith said.
The work being done through this project and others reflects KU’s commitment to supporting the UAE’s clean energy transformation.
3 November 2019