Discovering the next generation of catalysts

March 05, 2019

Energy The use of solar and wind energy must be doubled to meet the world's demand for clean energy over the next 30 years. Catalysts that can ensure the storage of solar and wind energy in fuels and chemicals will therefore play an increasingly important role. The catalysts that are used today are, however, often both expensive and ineffective. Now researchers at the University of Copenhagen and DTU have developed a method that makes it easier to find better and cheaper catalysts, with their results having recently been published in the journal "JOULE".

The world's energy needs will increase two to three times over the next 30 years - as the world's population goes from approx. 7.3 billion today to approx. 9.7 billion by 2050, according to UN figures.

It is not enough to expand the capacity of solar and wind energy as a substitute for fossil fuels. Both sources satisfy the need for environmental sustainability, but they are unstable due to their reliance on unpredictable weather conditions.

A result of this instability is that catalysts and electrolysis have become increasingly important, in the hope that they are able to ensure a stable energy supply. In addition to this, catalysts are used for many things in the chemical industry; from the conversion of harmful exhaust gases from cars to the conversion of nitrogen from the atmosphere for fertilizers.

BOX

Catalyst and Electrolysis: The role of a catalyst is to assist in the conversion of chemical substances in a chemical reaction, and an effective catalyst is able to provide a rapid, inexpensive and efficient pathway for the reaction. Electrolysis is a method of separating a substance by the use of electricity.

Still a long way to go

"There is still a long way to go in the development of catalysts that can be used for e.g. fuel cells, storage of solar and wind energy and new environmentally friendly fuels. The catalysts that exist today are not good enough to ensure a green transition," Professor Jan Rossmeisl at the Department of Chemistry for the University of Copenhagen, points out.

With the aid of two PhD students, Jack K. Pedersen and Thomas A.A. Batchelor, he is looking for "the famous needle in the haystack" among a new generation of catalysts.

But this is no easy task

"It is difficult to find the right alloy of metals for catalysts among infinitely many possibilities - despite today's supercomputers. Finding the best alloys would take a lifetime. We use the so-called high-entropy alloys, which are random mixtures of many different elements, as a starting point and we have developed computer models based on machine learning. In this way, it becomes easier to sort the myriad of combinations of alloys and find those that can solve the problem of converting and storing solar and wind energy efficiently," Professor Jan Rossmeisl emphasizes.

BOX-history

The next generation of catalysts

The chemical industry uses catalysts for processes to run efficiently while remaining environmentally friendly, from the transformation of exhaust gases from cars to the production of fertilizers using nitrogen from the atmosphere. Amongst these chemical processes there are some that do not yet have effective catalysts, and these will require solutions in the near future. For example the conversion of carbon dioxide into useful substances to mitigate climate change, and the reaction between oxygen and hydrogen to form water for use in fuel cells. The role of a catalyst is to aid the conversion of chemical substances in a chemical reaction, and an effective catalyst can do this quickly and with small energy loss. It is a great challenge to predict which material will act as a good catalyst for a chemical reaction, and it is exactly this problem that we propose a solution for with a new class of materials, the so-called high-entropy alloys.

High-entropy alloys are a composed of a mixture of five or more metals, having only recently been used as catalysts. We present the first theoretical study of how to systematically benefit from high-entropy alloys to provide the best alloy candidate that can catalyze a desired chemical reaction.

What makes the high-entropy alloys different from other catalysts is that they have a surface with countless local configurations of different atoms giving rise to as many local chemical environments. Imagine a Rubik's Cube: When it is solved, it consists of six faces each with its own color representing the pure metals. Mix the Rubik's Cube and each face is now composed of many colors. On each face, the six colors can be arranged many different ways. The nine squares represent a local combination of six different metals on the surface of a high-entropy alloy. Some combinations of atoms on the surface will bind the reacting chemical substances weakly, while with others they will bind strongly. For those combinations of atoms where the bond strength is perfect the catalytic activity will be greatest, and these combinations will govern the overall catalytic activity.

By calculating the bond strength of the chemical substances for all configurations of atoms, we can identify the best chemical environments and in what proportion the mixed metals are included at the atomic level. Here, however, we encounter the problem that it would take a lifetime to calculate the bond strengths for all the combinations even with modern quantum mechanical methods. We have solved this problem by calculating the bond strengths of a randomly selected subset of the possible combinations and then used machine learning to calculate the bond strengths for the entire span of combinations in just a few seconds.

When the bond strengths of all local combinations of atoms on the surface are known we are able to tune the ratio of the incorporated metals in order to promote the likelihood that the best bond strengths occur as frequently as possible. This optimal mixing ratio can be calculated and the outcomes are completely new, untested catalysts. The method thus gives us a systematic way of proposing catalysts which only depends on which metals we include. We have used the method to suggest catalysts for the reaction between oxygen and hydrogen forming water but the application is very broad so we are currently working on several other chemical reactions, as well as improving the approximations and assumptions of the method so that we can propose alloys that hopefully exceed the activity of present day catalysts.
-end-


Faculty of Science - University of Copenhagen

Related Fuel Cells Articles from Brightsurf:

Fuel cells for hydrogen vehicles are becoming longer lasting
An international research team led by the University of Bern has succeeded in developing an electrocatalyst for hydrogen fuel cells which, in contrast to the catalysts commonly used today, does not require a carbon carrier and is therefore much more stable.

Scientists develop new material for longer-lasting fuel cells
New research suggests that graphene -- made in a specific way -- could be used to make more durable hydrogen fuel cells for cars

AI could help improve performance of lithium-ion batteries and fuel cells
Imperial College London researchers have demonstrated how machine learning could help design lithium-ion batteries and fuel cells with better performance.

Engineers develop new fuel cells with twice the operating voltage as hydrogen
Engineers at the McKelvey School of Engineering at Washington University in St.

Iodide salts stabilise biocatalysts for fuel cells
Contrary to theoretical predictions, oxygen inactivates biocatalysts for energy conversion within a short time, even under a protective film.

Instant hydrogen production for powering fuel cells
Researchers from the Chinese Academy of Sciences, Beijing and Tsinghua University, Beijing investigate real-time, on-demand hydrogen generation for use in fuel cells, which are a quiet and clean form of energy.

Ammonia for fuel cells
Researchers at the University of Delaware have identified ammonia as a source for engineering fuel cells that can provide a cheap and powerful source for fueling cars, trucks and buses with a reduced carbon footprint.

Microorganisms build the best fuel efficient hydrogen cells
With billions of years of practice, nature has created the most energy efficient machines.

Atomically precise models improve understanding of fuel cells
Simulations from researchers in Japan provide new insights into the reactions occurring in solid-oxide fuel cells by using realistic atomic-scale models of the electrode active site based on microscope observations instead of the simplified and idealized atomic structures employed in previous studies.

New core-shell catalyst for ethanol fuel cells
Scientists at Brookhaven Lab and the University of Arkansas have developed a highly efficient catalyst for extracting electrical energy from ethanol, an easy-to-store liquid fuel that can be generated from renewable resources.

Read More: Fuel Cells News and Fuel Cells Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.