Green Hydrogen | HK University Researches Highly Efficient H2 Generation

The research team of the University of Hong Kong (HKU) introduces a new concept to promote efficient photocatalytic solar-to-H2 conversion. (Courtesy of HKU)

Hydrogen is a sustainable green energy, but most of it is “locked” in water molecules on earth. To extract hydrogen from water, electrolysis using electricity from solar energy is used to split water molecules into hydrogen and oxygen, but the efficiency is low and is not cost-effective.

However, a research team led by Professor Zheng Xiao Guo and Professor David Lee Phillips from the HKU-CAS Joint Laboratory on New Materials and the Department of Chemistry of The University of Hong Kong (HKU) has discovered a photocatalytic process for splitting water, leading to efficient hydrogen generation using visible solar light.

The research findings were recently published online in a top scientific journal, Energy & Environmental Science.

“The optimized photocatalyst shows an 800 percent increase in H₂ generation (6323 μmol h⁻¹ g⁻¹) and an about 5-fold increase in quantum efficiency (QE_{420 nm} = 5.08%).”

New Concept to Use Photocatalyst to Generate H2 Efficiently

In the past, the research on enhancing efficient hydrogen generation from water using visible solar light mainly started from several aspects, including the development of photocatalysts for solar-driven energy conversion with improved activity, efficiency, and durability, mostly by way of charge separation, transfer, and utilization. However, the complex multi-electron transfer, proton coupling, and intermediate dynamics can influence the photocatalytic pathway, kinetics, and efficiency, which have not been well understood.

The research team found a new fundamental process of a proton-mediated photocatalytic mechanism to enhance the photo-dynamics, charge separation, and hence the overall efficiency, of an interstitial phosphorus-doped carbon-nitride, g-C3N4.

The in-situ proton-mediated mechanism points to a new role of the water molecule, not just as a solvent or reactant but as an effective band-structure modifier of the catalyst in the overall design of effective photocatalytic processes.

Professor Guo said, “Spectroscopic investigations will cast more light on the mechanistic insights of science and technologies.”