New metal-free organic catalyst to produce hydrogen fuel using mechanical energy

New Delhi, May 5 (IANS) Researchers from the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR) Bengaluru (an autonomous institution under the Department of Science and Technology) develop a novel, cost-effective, metal-free porous organic catalyst for efficient production of Hydrogen (H2) by harvesting mechanical energy.

The team developed the metal-free donor-acceptor-based covalent-organic framework (COF) for piezocatalytic water splitting.

Piezocatalysis has emerged as a promising catalytic technology that harvests mechanical perturbations with a piezoelectric material to generate charge carriers that are utilised to catalyse water splitting.

The study, published in the journal Advanced Functional Materials, demonstrates a COF built from imide linkages between organic donor molecule tris(4-aminophenyl) amine (TAPA) and acceptor molecule pyromellitic dianhydride (PDA) acceptor exhibiting unique ferrielectric (FiE) ordering, which showed efficient piezocatalytic activity for water splitting to produce H2.

“The discovery breaks the traditional notion of solely employing heavy or transition metal-based ferroelectric (FE) materials as piezocatalysts for catalysing water splitting reactions,” said the team led by Professor Tapas K. Maji from the Chemistry and Physics of Materials Unit.

Conventional FE materials have limited charges confined at the surface only which usually leads to quick saturation of their piezocatalytic activity.

Using a simple donor molecule like TAPA and an acceptor molecule like PDA, Prof. Maji and his team built a COF system that has strong charge transfer properties, which creates dipoles (separation between positive and negative charges).

The TAPA units have a unique propeller-like shape, where their benzene rings twist and tilt to break the flat symmetry of the structure, helping it reach a more stable, lower-energy state.

Using theoretical analyses the team showed that COF has an unusual electronic structure with energy bands that couple and resonate with each other by dipolar ordering. This causes instability in the lattice structure, leading to FiE ordering. These FiE dipoles interact with flexible twisting molecular motion in the material, making them responsive to mechanical pressure.

The utilisation of a cost-effective, metal-free system with a high production rate of H2 by harvesting mechanical energy opens up a new route to green H2 based on porous heterogeneous catalysts, said the team.

--IANS

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