This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Over a century ago, the Haber-Bosch process, a two-step reaction for the synthesis of ammonia (NH₃), an irreplaceable chemical for the fertilizer industry, prevented the world from going into a serious food crisis. Today, however, the same method consumes about 1% of global energy and contributes more than 1% of annual anthropogenic CO₂ emissions.
In a recent study, researchers designed a new covalent organic framework that provided a promising solution to a long-standing problem in green ammonia synthesis. The team designed hydroxyl-functionalized copper phthalocyanine-based covalent organic frameworks as electrocatalysts for electrocatalytic nitrate reduction (NO₃RR). This process emerged as a viable, greener alternative to the industrial Haber-Bosch process, which is known to rely heavily on harsh high-temperature and high-pressure conditions.
Electrocatalytic nitrate reduction is kinder to the environment because it uses nitrate (NO₃⁻) from agricultural runoff and industrial sewage that pollute water systems to produce ammonia. The team developed three versions of the catalyst with 0, 2 or 4 hydroxyl (-OH) groups. The four-hydroxyl version (Cu-COF-4OH) performed the best, achieving a peak Faradaic efficiency of 98.95% (and 93.20% under standard testing conditions).
The catalyst directs nearly all the electrical charge toward ammonia production instead of unwanted byproducts. This was enabled by the addition of hydroxyl (-OH) groups around copper active centers, which cause the water molecules on the catalyst surface to reorganize into continuous hydrogen-bonded chains. The findings are published in Proceedings of the National Academy of Sciences.
Electrocatalytic ammonia production offers a potentially cleaner, less energy-intensive alternative to the Haber-Bosch process. Rather than using nitrogen gas, which is difficult to break apart because of its strong triple bond, this approach can use nitrate, which reacts more readily and dissolves easily in water. While turning nitrate into ammonia using electricity via NO₃RR is a cleaner alternative, the reaction requires nine protons per nitrate molecule.
This is a major bottleneck for practical application of this process because in standard catalysts, protons move sluggishly and randomly through water, leaving too few available at active sites and slowing the reaction. To overcome these issues, the team stitched together organic building blocks to create a porous, net-like material called a covalent organic framework (COF). They combined a copper-containing core molecule (CuPc) with an aldehyde building block containing hydroxyl groups.
Extract — continue reading at the source.
