30 November 2023
Seeking sustainable methods for splitting water
Published online 18 February 2022
Engineered cobalt-iron nanosheets provide an efficient and sustainable catalyst for water splitting with encouraging initial results.
Electrolysis is a promising option for separating water into its constituent parts – hydrogen and oxygen – to generate clean, sustainable hydrogen fuel. The electrodes in an electrolyser must include a suitable catalytic material, or ‘electrocatalyst’, to kickstart the separation process. Existing anode electrodes are often made from precious metals, and so scientists are keen to find sustainable, alternative electrocatalysts that maintain or improve the overall performance of the electrolyser.
Now, researchers at KAUST in Saudi Arabia and co-workers have demonstrated a novel design for an electrocatalyst made from cost-effective, abundant metals.
“We had already worked with cobalt-iron bimetallic electrodes, but limitations in performance meant they weren’t as good as precious metals for water splitting,” says Pravin Babar at KAUST’s Catalysis Center. “The deliberate design and manipulation of the surface structures on electrocatalysts can improve electronic activity, enhancing the rapid mass transfer of electrons, for example. Such interface engineering can also boost overall long-term stability of the electrocatalyst.”
To fabricate their novel electrocatalyst, the team used a simple wet chemical approach to coat a nickel foam substrate in a nanosheet of cobalt-iron hydroxide (CoFe-OH), before depositing iron oxyhydroxide (FeOOH) nanoparticles across its surface. The resulting composite material had a high density of electronically active sites and a robust mechanical structure.
To optimise the overall efficiency of the electrolyser, the team aimed to maximise the two reactions inherent in water splitting: the oxygen evolution reaction, which occurs at the anode, and the hydrogen evolution reaction at the cathode. They therefore coated the anode and cathode in their electrocatalyst.
“We’re delighted that our design showed enhanced oxygen evolution in particular, because this is difficult to get right and has limited some other electrocatalyst designs,” says Babar. “The high performance of the coated electrodes may be due to a seamless interface between the CoFe-OH and FeOOH, improving conductivity and intrinsic activity.”
“This method is easy to scale up, enabling the large-scale production of hydrogen,” adds Babar's supervisor and professor of chemical science, Cafer Yavuz. “However, first we need to fully understand the oxygen evolution reaction on our coated anode to make sure we mitigate any side losses. KAUST is supporting our quest to build a prototype sustainable electrolyser, and we are excited by our progress so far.”
“This study highlights the significance of tailoring the catalyst interface, because many subtle features of composition and structure play pivotal roles in the overall performance,” says Mohamed Alkordi, professor of chemistry and material science at Zewail City of Science and Technology, Egypt, who was not involved in the project. “The simplicity of the catalyst preparation is especially appealing.”
Babar, P. et al. Low-overpotential overall water splitting by a cooperative interface of cobalt-iron hydroxide and iron oxyhydroxide. Cell Reports Physical Science 3, 100762 (2022).