Breakthrough in solar photolysis of water for hydrogen production

The introduction of "carbon peaking" and "carbon neutral" strategies has led to a reduction in carbon emissions, with hydrogen being an attractive option as a clean fuel. On the other hand, hydrogen is also required for many chemical processes, such as the production of fertilisers. However, hydrogen is currently obtained mainly through the conversion of water and gas, a process that not only generates large carbon emissions but also consumes large amounts of thermal energy.

Natural photosynthesis (plants using sunlight to obtain hydrogen atoms from water) is well known, but is there an "artificial photosynthesis" technique to obtain hydrogen? Photocatalytic hydrogen production based on total hydrolysis is an environmentally friendly and sustainable technology that consumes only sunlight and water and does not produce any carbon emissions, which is why it is currently attracting a lot of attention. However, the low solar to hydrogen (STH) conversion efficiency of current photocatalytic THMs limits their practical application.

With this in mind, Professor Yonezawa's team at the University of Michigan has developed a strategy to achieve STH efficiencies of up to 9.2% using pure water, concentrated sunlight and an indium gallium nitride photocatalyst, which mimics the key steps in natural photosynthesis. Outdoor experiments show it represents a major leap forward for the technology, being nearly 10 times more efficient than comparable solar water splitting experiments. Specifically, the researchers have demonstrated that the photocatalytic total water disintegration on InGaN/GaN surfaces not only promotes the forward water decomposition reaction but also inhibits the reverse hydrogen-oxygen complexation reaction through the infrared thermal effect generated by high-intensity focused sunlight, enabling the InGaN nanowires to exhibit extremely high photocatalytic total water disintegration efficiency. The research results were published in the latest issue of Nature under the title "Solar-to-hydrogen efficiency of more than 9% in photocatalytic water splitting".

The researchers achieved a high STH efficiency of 9.2% using pure water, concentrated sunlight and an indium gallium nitride photocatalyst. The success of the strategy in this paper stems from the synergistic effect of promoting forward hydrogen-oxygen evolution and inhibiting reverse hydrogen-oxygen recombination, which can be achieved by operating at the optimum reaction temperature (~70 degrees Celsius), directly by harvesting previously wasted infrared light from sunlight. Furthermore, this temperature-dependent strategy also resulted in STH efficiencies of ~7% from widely available tap water and seawater, and 6.2% in a large photocatalytic water separation system with a natural solar light capacity of 25 7W. This research provides a practical approach to the efficient production of hydrogen fuel from natural sunlight and water, overcoming the efficiency bottleneck of solar hydrogen production.