Dr Nick Cox from the ANU Research School of Chemistry with his water-splitting technology. Photo: Lannon Harley
Fuel of the gods
Scientists have cracked a key step in nature’s water- splitting recipe, which powers all plant life on Earth and may be harnessed to make a limitless supply of cheap renewable fuel. Will Wright reports.
Around two and a half billion years ago, nature figured out how to use only solar energy to survive. Plants do this by storing solar energy in the form of energy-rich compounds called carbohydrates – a process called photosynthesis. Carbohydrates can be thought of as a solar fuel, whereby energy is stored in chemical bonds that keep carbohydrates together.
Plants can use this fuel whenever it is needed, which solves the problem of the Sun not always shining.
The first step in making carbohydrates is to split water into hydrogen and water. If we could do the same, in a cheap way, we could theoretically manufacture an endless supply of inexpensive hydrogen fuel for transportation, without carbon emissions that contribute to human-caused climate change.
ANU and the Max Planck Institute for Chemical Energy Conversion (MPI-CEC) in Germany led a study that, for the first time, identified an important photosynthetic process that enables plants to split water.
Lead researcher Dr Nick Cox, from the ANU Research School of Chemistry, says copying nature’s process of storing solar energy would lead to new and improved renewable energy storage technologies.
“Enough sunlight hits the Earth in a single hour to power all human activity for over a year,” he says.
“Humans have been able to split water to generate hydrogen fuel for a very long time. The problem is the way we do this on a commercial scale and use expensive materials – metals such as iridium.”
Cox says nature uses very cheap materials, the metals calcium and manganese, to split water.
“Our study provides new information on how the biological system works, which will allow new, cheaper catalysts to be developed in the future,” he says.
“This is a very competitive research area, with many people working on it.
That said, we’ve developed an innovative way of looking at this system.”
Cox says hydrogen is a clean fuel and burning it only generates water as a by-product.
“It is a green alternative to carbon-based fuels such as petrol and natural gas,” he says.
MPI-CEC researcher Dr Maria Chrysina says the study revealed how a key enzyme involved needed to ‘breathe’ to allow access to water.
“Half-way through its reaction cycle the enzyme develops the ability to stretch like a concertina, which enables the orderly uptake of water to begin the splitting process,” Chrysina says.
ANU co-researcher Dr Eiri Heyno says water splitting in nature could be hindered without the critical step identified by the team.
“Without the careful, sequential binding of water, more reactive oxygen molecules can potentially be released that could unravel the whole water-splitting process,” Heyno says.
The study, which also involved researchers from Sweden, is published in Proceedings of the National Academy of Sciences of the United States of America.
The research team used a technique called electron paramagnetic resonance (EPR) spectroscopy, which can be used to recreate a 3D image of the reactive site involved in the photosynthesis process.
Dr Cox is leading the establishment of a new state-of-the-art EPR facility at ANU, with support from the Australian Research Council (ARC), University of New South Wales, University of Queensland, University of Sydney and University of Wollongong.
“This new facility will operate at much higher magnetic fields than what’s possible today, allowing more detailed measurements to be taken for medical, biological, chemical and materials research, as well as industrial applications,” he says.
“The sky’s the limit in terms of the potential breakthroughs we can achieve with this technology.”