This transmission electron microscope image shows details of carbon black particles after treatment with plasma. Defects in the carbon lattice caused by the oxygen plasma enhance the material's ability to catalyze the production of hydrogen peroxide. Image: Tour Group/Yakobson Research Group/Rice University.A team of researchers at Rice University have created a 'defective' catalyst that simplifies the generation of hydrogen peroxide from oxygen.
The team, led by Rice chemist James Tour and materials theorist Boris Yakobson, treated metal-free carbon black, an inexpensive, powdered product of petroleum production, with oxygen plasma. This introduced defects and oxygen-containing groups into the structure of the carbon particles, exposing more surface area for interactions.
When used as a catalyst, these defective particles, known as CB-Plasma, reduce oxygen to hydrogen peroxide with 100% Faradaic efficiency, a measure of charge transfer in electrochemical reactions. The process shows promise for replacing the complex anthraquinone-based method for producing hydrogen peroxide, which requires expensive catalysts and generates toxic organic by-products and large amounts of wastewater. The researchers report their work in a paper in ACS Catalysis.
Hydrogen peroxide is widely used as a disinfectant by the paper and pulp industries, as well as in wastewater treatment and for chemical oxidation. Tour expects the new process will influence the design of hydrogen peroxide catalysts going forward.
"The electrochemical process outlined here needs no metal catalysts, and this will lower the cost and make the entire process far simpler," Tour said. "Proper engineering of carbon structure could provide suitable active sites that reduce oxygen molecules while maintaining the oxygen-oxygen bond, so that hydrogen peroxide is the only product. Besides that, the metal-free design helps prevent the decomposition of hydrogen peroxide."
The researchers used plasma processing to create defects in carbon black particles that appear as five- or seven-member rings in the material's atomic lattice. The process sometimes removes enough atoms to create vacancies in the lattice.
The resulting CB-Plasma catalyst works by pulling two electrons from oxygen, allowing it to combine with two hydrogen electrons to create hydrogen peroxide. (Reducing oxygen by four electrons, a process used in fuel cells, produces water as a by-product.)
"The selectivity towards peroxide rather than water originates not from carbon black per se but, as [co-lead author and Rice graduate student] Qin-Kun Li's calculations show, from the specific defects created by plasma processing," Yakobson said. "These catalytic defect sites favor the bonding of key intermediates for peroxide formation, lowering the reaction barrier and accelerating the desirable outcome."
Tour's lab also tried treating carbon black with ultraviolet-ozone, as well as treating the CB-Plasma after oxygen reduction with argon to remove most of the oxygen-containing groups. CB-UV proved no better at catalysis than plain carbon black, but CB-Argon performed just as well as CB-Plasma with an even wider range of electrochemical potential.
Because the exposure of CB-Plasma to argon under high temperature removed most of the oxygen groups, the lab inferred that the carbon defects themselves were responsible for the catalytic reduction to hydrogen peroxide.
The simplicity of this process could allow more local generation of hydrogen peroxide, reducing the need to transport it from centralized plants. Tour noted CB-Plasma matches the efficiency of state-of-the-art materials now used to generate hydrogen peroxide.
"Scaling this process is much easier than present methods, and it is so simple that even small units could be used to generate hydrogen peroxide at the sites of need," Tour said.
The process is the second introduced by Rice University in recent months to make the manufacture of hydrogen peroxide more efficient. Rice chemical and biomolecular engineer Haotian Wang and his lab developed an oxidized carbon nanoparticle-based catalyst that produces the chemical from sunlight, air and water.
This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.