Transition metal dichalcogenides (top) and graphitic carbon nitrides (bottom) are two promising graphene-inspired photocatalysts for converting carbon dioxide into fuels. Credit Cheng-May Fung
Transition metal dichalcogenides (top) and graphitic carbon nitrides (bottom) are two promising graphene-inspired photocatalysts for converting carbon dioxide into fuels. Credit Cheng-May Fung

Fuels made using sunlight could help mitigate climate change and develop a more sustainable energy cycle.

Making fuel from carbon dioxide (CO2) can be powered by sunlight, using ‘photocatalysts’ that are just one layer of bonded atoms thick. Researchers based at Monash University’s campus in Malaysia review the state of research aiming to fulfil the potential of these photocatalysts in the journal Materials Today Sustainability. Possibilities include using the CO2 to make the fuels methanol, methane and formic acid.

The study of so-called ‘2D’ materials was kick-started by the discovery of graphene, a material composed of a single layer of carbon atoms bonded in a hexagonal pattern. This 2D form of carbon has itself attracted great interest in exploiting its many unique chemical and physical properties. The possibilities are now being greatly expanded, however, by investigating a wide range of graphene-inspired materials in which other atoms are similarly bonded into 2D structures.

Some of the most promising modifications for building photocatalysts to convert CO2 into fuels are known as transition metal dichalcogenides (TMDs) and graphitic carbon nitrides (g-C3N4). TMDs are semiconductor materials with a layer of atoms from the transition metal elements held between two bonded layers of atoms from the chalcogen group elements. The g-C3N4-based semiconductor materials have nitrogen atoms in place of many of the carbon atoms of graphene, creating a somewhat similar hexagonal arrangement but with regularly spaced gaps.

“Utilizing 2D layered nanomaterials is fast becoming one of the hottest research themes worldwide, and interest in using them in photocatalysis is sky-rocketing,” says co-author Siang-Piao Chai.

Chai explains that the 2D nanomaterials covered in the review offer exceptional advantages over conventional photocatalysts. Their semiconducting properties are more readily tuned by design, offering superior light absorbance and efficiency, partly due to very high surface area to volume ratios. But more research and development work is needed to convert the potential into commercial reality.

The ongoing research efforts include exploring the effects of a wide range of structural modifications. Factors such as engineering the presence of defects in the materials’ crystal structures and ‘doping’ them with small quantities of different elements are being explored.

The work covered in this review is also just one part of a wider global research effort to turn atmospheric CO2 from an environmental problem into a resource. The review authors are themselves actively involved in research to develop and expand the possibilities.

Lead author Cheng-May Fung, says: “I am studying the design and development of phosphorus-based photocatalysts for converting CO2 into hydrocarbon fuels.” She explains that this metal-free route, using the abundant element phosphorus, may prove more affordable and sustainable than other more exotic catalysts.

“We have only 50 years left to seek fossil fuel alternatives before the current fuel reserves run dry,” says Chai. He finds it especially appealing that photocatalysts might “kill two birds with one stone” by making sustainable fuels while also combating climate change.

Article details:

Fung, C-M. et al.: “Recent progress in two-dimensional nanomaterials for photocatalytic carbon dioxide transformation into solar fuels,” Materials Today Sustainability (2020)