By Dr Himmat Singh
Japanese scientists have developed a new means of cracking water into hydrogen fuel using sunlight. Using a special photocatalyst, this new technology could help usher in cheaper, more abundant, and sustainable hydrogen fuel for various applications.
Currently, most free hydrogen is derived from natural gas feedstocks, meaning moving away from fossil fuels for this greener option is not an option. However, this easily manufactured sunlight-powered method could prove pivotal if hydrogen is to become an alternative in the future.
“Sunlight-driven water splitting using photocatalysts is an ideal technology for solar-to-chemical energy conversion and storage, and recent developments in photocatalytic materials and systems raise hopes for its realisation,” Prof Kazunari Domen of Shinshu University, senior author of the article in Frontiers in Science explained.
“However, many challenges remain,” he added.
The basic principle behind the new process is to split water into oxygen and hydrogen. While it sounds simple, this is energy-intensive and needs a catalyst, in this case, special ones called photocatalysts.
Hydrogen from water using light
When exposed to light, these catalysts facilitate chemical reactions that break down water into constituent parts. The concept is not new, but most existing, so-called “one-step” ones are inefficient and have a meager solar-to-hydrogen energy conversion rate.
Another more sophisticated two-step excitation system also exists, and it is more efficient. In these systems, one photocatalyst generates hydrogen from water, while another produces oxygen.
The Japanese team chose this second “two-step” water-cracking process. “Solar energy conversion technology cannot operate at night or in bad weather,” said Dr Takashi Hisatomi of Shinshu University, another study author.
“But by storing the energy of sunlight as the chemical energy of fuel materials, it is possible to use [it] anytime and anywhere,” he added.
Domen and Hisatomi’s team produced a successful proof of concept by operating a 1,076 ft2 (100 m2) reactor for three years. This reactor even performed better in real-world sunlight than in laboratory conditions.
“In our system, using an ultraviolet-responsive photocatalyst, the solar energy conversion efficiency was about one and a half times higher under natural sunlight,” said Hisatomi.
Not just theory
“Simulated standard sunlight uses a spectrum from a slightly high latitude region. Solar energy conversion efficiency could be higher in areas where natural sunlight has more short-wavelength components than simulated reference sunlight. However, currently, the efficiency under simulated standard sunlight is 1% at best, and it will not reach 5% efficiency under natural sunlight,” he added.
To move the technology forward and break that 5% barrier, the team says that more researchers need to develop more efficient photocatalysts and build larger experimental reactors.
“The most important aspect to develop is the efficiency of solar-to-chemical energy conversion by photocatalysts,” explained Domen.
“If it is improved to a practical level, many researchers will work seriously on developing mass production technology, gas separation processes, and large-scale plant construction. This will also change how many people, including policymakers, think about solar energy conversion and accelerate the development of infrastructure, laws, and regulations related to solar fuels,” he concluded.
(Dr Himmat Singh is ex-Scientist “G” CSIR- Indian Institute of Petroleum, and Advisor, R&D, BPCL, Mumbai)
