Seeing green: Computational chemistry leads to eco-friendly technology advances

// Chemical & Biological Engineering

Image of a platinum catalyst

Image of a platinum catalyst. Credit: Joel Hallberg.

Some of the most exciting advancements in modern chemistry don’t require test tubes, bioreactors or even lab coats. Computational chemistry is a branch of the science that uses computer simulations to determine the structure and properties of chemicals and materials. In two recent papers, University of Wisconsin-Madison chemical engineers used those tools to advance emerging green technologies.

Photo of Manos Mavrikakis
Manos Mavrikakis

In the first paper in the journal Nature Communications, Chemical and Biological Engineering Professor Manos Mavrikakis and postdoctoral researcher Roberto Schimmenti along with recent PhD graduate Ahmed Elnabawy collaborated with a multidisciplinary team of researchers, using their computational chemistry expertise in quantum mechanics to analyze a newly synthesized 2D material that may be important in carbon capture technology.

2D materials are monolayers only one atom thick—like the “wonder” material graphene, first synthesized in 2004. These materials have special electrical, chemical and magnetic properties.

In carbon capture, emissions from fossil fuel combustion or other carbon dioxide-emitting processes pass through a system in which catalysts trap and convert carbon dioxide into useful chemicals, before it is released. There are also designs for large-scale carbon dioxide scrubbers in which adsorbing materials pull excess carbon dioxide from the air directly in order to reduce its concentration in the atmosphere.

But current carbon capture technologies are inefficient and too costly to produce at scale. Over the last few decades, researchers have found that the element bismuth reacts with carbon dioxide and is one of the most promising catalysts. However, until now, no one had synthesized a form of bismuth that realized its full potential as a catalyst for converting carbon dioxide to chemicals.

In their paper, Mavrikakis, Schimmenti, Elnabawy and their co-authors report the first synthesis of freestanding bismuthene, a novel 2D material, which does live up to bismuth’s promise.

Researchers at the Changchun Institute of Applied Chemistry in China used a wet deposition method to produce the freestanding bismuthene.

Photo of Roberto Schimmenti
Roberto Schimmenti

Computational chemistry showed that the bismuthene monolayer acted as a superior electrocatalyst for converting carbon dioxide into formate, which has applications as a hydrogen carrier for energy-related technologies. “We compared the performance of 2D bismuthene with all the state-of-the-art catalysts and it showed the best performance, in terms of activity, selectivity, and stability” says Schimmenti.

Previously, bismuthene was synthesized as a nanosheet over substrates like silicon carbide. However, the nanosheets did not react with the carbon dioxide nearly as much as the freestanding bismuthene.

Using computational chemistry simulations, Schimmenti says he and Elnabawy with Mavrikakis were able to explain why the freestanding bismuthene performed so much better than the nanosheets, which may direct researchers in finding ways to scale up and bulk synthesize the catalyst.

“The best part of this was the collaboration between experimental and computational work,” says Schimmenti. “The properties at the atomic scale govern the macroscopic properties and computational chemistry can rationalize experimental findings. In addition, atomic-scale insights derived from quantum mechanics guide the materials synthesis community towards making materials with improved catalytic properties.”

The other paper, published in the journal Nature Materials on July 20, 2020, discusses electro-catalysts which are essential in the development of proton-exchange membrane fuel cells. Fuel cells produce chemical energy in a manner similar to batteries, but they keep working as long as they receive new fuel, often hydrogen. These type of fuel cells are already at the heart of non-battery-operated electric vehicles and are expected to replace batteries in other applications, including electronic devices such as laptops and cell phones.

Photo of Ahmed Elnabawy
Ahmed Elnabawy

One problem with the technology, however, is that the platinum cathodes performing the oxygen reduction reaction in the cells lose platinum over time through dissolution under operating conditions. Collaborators at Argonne National Laboratory in Illinois, led by senior scientist Vojislav Stamenkovic, were able to experimentally characterize dissolution rates in pure platinum and in alloys of platinum with other metals, whereas Mavrikakis and Schimmenti came up with atomic-scale models that could rationalize the diminished rate of platinum dissolution measured in platinum thin films deposited on gold.

The study was unique, says Schimmenti, because the team used computational chemistry to predict the stability of the electrocatalysts, an aspect as important as catalytic activity. Understanding the atomic-scale dissolution mechanism of electrocatalysts and proposing new theory-guided strategies to improve their stability is a critical step in making stable, efficient and affordable fuel cells.

“This increases electrode stability by about 30 times more than scientists have reported in other studies,” Schimmenti says. “It basically paves the way for practical and long-term utilization of platinum in fuel cells.”

Manos Mavrikakis is Paul A. Elfers Professor, James A. Dumesic Professor, and Vilas Distinguished Achievement Professor in chemical and biological engineering at UW-Madison. Other contributors to the Nature Communications paper include Fa Yang, Ping Song, Jiawei Wang, Zhangquan Peng, Shuang Yao, Ruiping Deng, Shuyan Song and Weilin Xu of the Changchun Institute of Applied Chemistry, Chinese Academy of Sciences and Yue Lin of the University of Science and Technology of China.

The work at UW-Madison was supported by the Paul A. Elfers Professorship and WARF Named Professorship funds.

Other contributors to the Nature Materials paper include Pietro P. Lopes, Dongguo Li, Haifeng Lv, Dusan Tripkovic, Yisi Zhu, Yijin Kang, Nigel Becknell, Dusan Strmcnik, and Nenad M. Markovic of Argonne National Laboratory, Karren More of Oak Ridge National Laboratory, Chao Wang of Johns Hopkins University, Hideo Daimon of Doshisha University, and Joshua Snyder of Drexel University.

Work at UW-Madison was supported by U.S. Department of Energy, Basic Energy Sciences, Division of Chemical Sciences grant DE-FG02-05ER15731.

Both studies were partially performed using supercomputer resources at the National Energy Research Scientific Computing Center, which is supported by the U.S. Department of Energy Office of Science, under contract no. DE-AC02-05CH11231.

Author: Jason Daley