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The search for efficient ways to generate hydrogen (H₂) using sunlight has gained momentum over the past two decades due to growing concerns over the energy crisis and climate change. One promising method is photocatalytic water splitting, where sunlight is used to break down water molecules into hydrogen and oxygen. However, the efficiency of this process depends on two key reactions: the Hydrogen Evolution Reaction (HER) and the Oxygen Evolution Reaction (OER). A good photocatalyst must efficiently support both reactions.
Among various materials being explored, transition metal oxides (TMOs) have attracted significant attention. A particularly promising approach involves electrolytic doping (EDO), a technique that fine-tunes the properties of these materials. This method can be combined with suspension electrolytes to modify the electronic structure of composite photocatalysts, improving their ability to absorb light and generate hydrogen.
Today, the research community focuses on designing photocatalysts at the nanometer scale, particularly in the form of two-dimensional (2D) heterostructures. These materials have several advantages:
Their ultra-thin structure allows for more efficient interaction with light.
Their large surface area enhances the reactions required for water splitting.
Some 2D heterostructures follow a Z-scheme charge transfer mechanism, which helps to efficiently separate charge carriers, improving performance.
A promising type of 2D photocatalyst is based on perovskites, such as SrTiO₃ (strontium titanate) and Bi₄Ti₃O₁₂ (bismuth titanate). Researchers have explored combining these perovskites with graphitic carbon nitride (g-C₃N₄), a material with a narrow band gap (2.7 eV) and a highly negative conduction band (-1.13 eV). This combination enhances photocatalytic activity because:
g-C₃N₄ efficiently absorbs visible light.
The interaction between g-C₃N₄ and perovskites promotes better charge separation, reducing energy losses.
The g-C₃N₄/SrTiO₃ heterostructure has shown improved hydrogen production compared to its individual components.
Project H-GREEN addresses the important challenges in photocatalysis to achieve practical and efficient hydrogen generation:
Limited solar light absorption – Many photocatalysts do not absorb enough visible light, reducing efficiency.
Low charge carrier mobility – The movement of charge carriers (electrons and holes) within the material is often slow.
Fast recombination of charge carriers – Electrons and holes recombine too quickly, wasting energy.
Photo-corrosion – Some materials degrade when exposed to prolonged light exposure, reducing their lifespan.
Project H-GREEN aims to overcome these limitations by designing optimized 2D heterostructures that maximize light absorption, enhance charge transport, and improve photocatalytic efficiency. One example is the γ-MnO₂/TiO₂ photocatalyst, which has demonstrated improved performance in breaking down pollutants compared to its individual components. Similarly, better results are expected by refining the morphology of SrTiO₃ nanostructures, creating thin 2D nanoplatelets that can be effectively combined with g-C₃N₄ for enhanced hydrogen production
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