waste water

Hydrogen and drinking water created from dirty runoff using new material

A material mesh created using a mix of metal and polymer has been shown to generate hydrogen and fresh water from wastewater.

Researchers at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia believe the advanced material could address two problems simultaneously - producing clean water and renewable energy in the form of hydrogen.

Electrochemical membrane bioreactors recover clean water for reuse and energy from wastewater by integrating micro- or ultrafiltration membrane cathodes with a microbial electrochemical system.

This works by using a material full of pores small enough to block the passage of bacteria while allowing treated, clean water to pass through. The same material also acts as an electrode in an electrochemical circuit that recovers energy through the hydrogen-evolution reaction.

Previously, porous, flat electrodes have been used as both the cathode for the oxygen-reduction reaction and as the membrane to filter treated water. However, hollow fibres offer a greater surface-area-to-volume ratio, which improves the system’s performance.

The drawback of this geometry is that these more complicated structures can be difficult to create and to optimize. For example, materials made from polymers are cheap to produce and flexible, but in general, because they act as electric insulators, they are not used as electrodes.

The KAUST team addressed this problem by coating a non-conductive polymer with a very thin layer of platinum, allowing the coated fibre to act as a catalyst for the hydrogen-evolution reaction.

The application of a uniform layer of metal catalyst on three-dimensional, thin, porous, polymeric, hollow fibres is difficult using traditional deposition techniques.

To address this challenge, the team used atomic-layer deposition to expose hollow fluorinated polyoxadiazole polymer fibres to gas heated to 180C that contained platinum nanoparticles.

“We produced the polymer fibres by simply adapting the phase-inversion method, which is already used in the industry,” said Professor Suzana Nunes who worked on the project.

Despite significantly lower platinum loading, the researchers confirmed that the hydrogen-evolution reaction of their material was similar to that of a platinum-carbon cloth, a material combination typically used for this application.

Using atomic-layer deposition, the team could fine-tune the pore size of the hollow fibres, demonstrating effective reclamation of the treated effluent to yield high-quality water.

The team believes that the architecture of the three-dimensional porous, hollow fibres has broad applications. “These fibres can potentially be applied to directly convert carbon-dioxide waste from industrial sources to value-added products, such as methane and acetate, through microbial electrosynthesis,” said research scientist Krishna Katuri, the study’s lead author.

A team from the University of Edinburgh recently demonstrated a solar-powered water purification system designed for remote Indian villages. 

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