Think of a soft texture, elastic and porous, that shapes itself as easy as floating in water, while capturing solar light and making oxygen and hydrogen.
And think that this is exactly what Nature has engineered through billions of years of evolution, to fuel our aerobic life with renewable energy.
Solar water splitting by man-made devices is exceptionally difficult. More than 100 years ago, two Giants of all times were setting the bar extremely high: “Water will be the coal of the future” (Jules Verne, L’Ile Mystérieuse, 1874) “a quieter civilization based on the utilization of solar energy that will not be harmful to progress and to human happiness”, (Giacomo Ciamician, The Photochemistry of the Future, Science 1912).
Now we know that the goal of solar fuels is irrevocable and urgent, and our time-line cannot wait the slowness of evolutionary biology. A definite step forward is now traced by the work of an international team led by scientists at the Universities of Padova and Trieste, Italy and CICbiomaGUNE, San Sebastián, Spain.
Their results, published in the journal Nature Chemistry, identify the functional “Lego-blocks” that mimics the essentials of the Leaf-machinery. The idea is not to replicate “de-novo” the identical perfection of the biological systems and their fragile architecture. On the contrary, the real game-changer is likely to come from a divergent approach, by exploring artificial alternatives, designed with highly robust, versatile and tunable synthetic components, that are readily up-scalable to application size.
“Water splitting is a long-sought dream, which was one of my research themes long time ago”, Professor Jean-Pierre Sauvage of ISIS Strasbourg, Nobel Prize in Chemistry in 2016 says. “It is an extremely arduous process, with many research groups attempting to imitate Nature, but still out of reach. The work by Bonchio, Prato and collaborators opens new perspectives and new possibilities. The self-assembly of a robust sensitizer with an efficient catalyst generates an extremely fascinating and efficient system to oxidize water to oxygen, a fundamental step towards water splitting.”
The research combines bio-inspired catalysis with nanoscience. “In our first Nature Chemistry paper, in 2010, we promised to let the sunshine in” Maurizio Prato, Professor of Research at CICbiomaGUNE, San Sebastián, a world leader in the synthesis of carbon nanomaterials, tells about the major advancement of the team from the “dark” electrocatalysis to the new photo-electrodes. “In this work we have used a robust and versatile organic semiconductor to fabricate a photoactive framework around the catalytic center to transfer electrons and slow down recombination”.
“We went back at the very first principles of the problem, reading the earliest studies of Emerson and Arnold (1932) and Park and Biggins (1964), and we started our quest for the quantasome particles” says Marcella Bonchio, Professor at the University of Padova, “the quantasome is the minimal photosynthetic unit responsible for the “quantum” solar energy conversion. We made it by integrating a synthetic antenna to capture the solar radiation and a totally inorganic catalyst that can split water using visible light”
“Self-assembly of individual photosynthetic particles into ordered arrays forming a multi-lamellar architecture, is exciting as Nature uses the same strategy to enable solar energy conversion” says Nicola Armaroli, Research Director at the Italian CNR in Bologna and an internationally recognized expert on the photochemistry and photophysics of supramolecular arrays and materials and solar energy technologies.
The “Lego-block” model can be generalized and applied to alternative targets beyond the biological paradigm. A recent account by Markus Antonietti at Max Planck is critical on bio-inspired water splitting being an economical viable solution (Chem. Rec. 2018). Antonietti comments:
“I was one of the first to be aware of this research breakthrough, and I am looking forward to see new applications in the direction of valuable products, better targets than just oxygen. “The concept is there, the new step off, leaving the protein space out, is done. We shall see new progress soon”
The work stems from a valuable interdisciplinary effort, including scientists of CIC biomaGUNE, the University of Trieste, Ferrara, Messina, the ITM and ISOF CNR institutes, the Elettra-Sinchrotron in Trieste, the Graz University of Technology, and the University of Erlangen, Germany.