AsianScientist (Aug. 24, 2015) – AsianScientist (Aug. 24, 2015) – By tweaking the amount of nickel, researchers have developed a method to increase the efficiency of molybdenum disulphide (Mo2S) catalysts. Their results, published in Science Advances, could make hydrogen production cheaper and greener.
The rapid increase in the global consumption of fossil fuels has not only depleted our supply of the limited resource but also caused environmental damage. As a result, many areas of research are now focused on finding sources of clean, sustainable energy to replace fossil fuels.
“Artificial conversion of solar energy into chemical fuels—mimicking what Nature does—has attracted tremendous attention over the past few decades,” said study corresponding author Liu Bin, an assistant professor at Nanyang Technological University.
“Among the many systems that have been proposed, solar water splitting for hydrogen production is the most attractive one. Hydrogen evolution reaction, known as HER, is one of the important processes to realize practical solar water splitting,” Liu told Asian Scientist Magazine.
Although less effective than platinum as a HER catalyst, Mo2S is cheaper and more readily available. Several research groups have attempted to improve the catalytic ability of Mo2S, using it in various nanostructured forms. However, scaling-up existing lab-based methods to industrial processes has proven to be challenging.
To resolve these issues, a team led by Liu and co-corresponding author Zhang Hua synthesized Mo2S directly onto carbon fiber cloth, creating a HER catalyst that is flexible, strong and potentially suitable for large-scale manufacture.
“The hydrophobic surface of carbon fiber cloth made it challenging for us to grow uniform active materials on it from aqueous reaction solution. Furthermore, we found that layered Mo2S tended to form bulky aggregates, which severely affected the electrocatalytic performance,” Liu explained.
Interestingly, the researchers found that introducing nickel ions (Ni2+) into the precursor solution helped to tailor both the morphology and intrinsic properties of Mo2S on carbon fibers.
When nickel to molybdenum precursors were used in a 1:1 ratio, a uniform nanostructured film is formed over the carbon fiber scaffold. Three times thinner than the film grown without nickel, the Ni-Mo-S nanosheets were shown to assume interconnected, flake-like structures under high-resolution transmission electron microscopy.
The reduced aggregations in the Ni-Mo-S/C nanostructure prevented the accumulation of hydrogen bubbles during electrolysis, thereby improving the performance and stability of the catalyst.
“As HER reactions are typically performed in acidic environments, the most exciting part of our research is that we have successfully realized efficient hydrogen generation from neutral electrolyte using earth-abundant catalysts,” Liu added. “More interestingly, we have performed electrochemical hydrogen generation in natural seawater and have obtained positive results.”
Liu and Zhang are currently working on replacing nickel with other earth-abundant elements as well as developing effective electrocatalysts that can produce oxygen from water under varying pH conditions.
“Our ultimate goal is to design and promote an integrated device that can produce high-purity hydrogen and oxygen using sustainable energy at affordable cost, and eventually apply the mature set-up to interdisciplinary researches, such as waste water treatment, seawater desalination and artificial photosynthesis,” Liu said.
The article can be found at: Miao et al. (2015) Hierarchical Ni-Mo-S Nanosheets on Carbon Fiber Cloth: A Flexible Electrode for Efficient Hydrogen Generation in Neutral Electrolyte.
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Copyright: Asian Scientist Magazine; Photo: Liu Bin & Zhang Hua/NTU.
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