One of the biggest obstacles that humanity must overcome is how to switch to an energy economy that is sustainable and doesn’t produce carbon dioxide.

Hydrogen is seen as a possible replacement for fossil fuels. It can be created using electricity and water.

Hydrogen derived from renewable energy sources is referred to as green hydrogen.

However, it would be even more environmentally friendly if sunlight could be used to directly generate hydrogen.

In the natural world, plants use light to split water as they undergo photosynthesis. This is accomplished by plants using a sophisticated molecular component known as the photosystem II.

Mimicking its active center is a possible method for achieving sustainable hydrogen generation.

The Institute of Organic Chemistry and the Center for Nanosystems Chemistry at Julius-Maximilians-Universitat Würzburg (JMU), led by Professor Frank Würthner, are working on this.

Water splitting is not a simple task

H2O is made up of one atom of oxygen and two atoms of hydrogen. The initial stage of water splitting is difficult because two water molecules must have their oxygen removed in order to release the hydrogen.

Four protons and four electrons must first be taken out of each of the two water molecules in order to do this.

It is not a simple oxidative reaction. In order to catalyze this reaction, plants use a sophisticated structure that consists of a cluster of four manganese atoms that the electrons can move across.

The first breakthrough made by Würthner’s team, a “artificial enzyme” that can control the first stage of water splitting, was published in the journals Nature Chemistry and Energy & Environmental Science in 2016 and 2017.

This catalyst for the thermodynamically challenging process of water oxidation is made up of three Ruthenium centers interacting in a macrocyclic framework.

Success with an artificial pocket

Now, JMU chemists have been successful in getting the complex process to run smoothly on a single ruthenium center.

In the process, they have even attained catalytic activity that are as high as those found in the natural model, the photosynthetic system of plants.

“This success was made possible because our doctoral student Niklas Noll created an artificial pocket around the Ruthenium catalyst,” says Frank Würthner, adding, “Therein, the water molecules for the desired proton-coupled electron transfer are arranged in front of the ruthenium centre in a precisely defined arrangement, similar to what happens in enzymes.”

This principle, which was developed by the group consisting of Niklas Noll, Ana-Maria Krause, Florian Beuerle, and Frank Würthner, is, according to their opinion, also applicable to the enhancement of other catalytic processes.

The Würzburg group’s long-term objective is to include the water oxidation catalyst into an artificial device that, with the help of sunlight, splits water into oxygen and hydrogen.

This will take some time because the catalyst needs to be combined with other elements to create a working overall system. These other elements include so-called reduction catalysts and light-harvesting dyes.

Source: 10.1038/s41929-022-00843-x

Image Credit: Würthner group / University of Wuerzburg

You were reading: New Breakthrough: An “Artificial Enzyme” Can Split Water